阅读说明：本技术 微粒检测传感器、灰尘传感器、空调设备 (Particle detection sensor, dust sensor, and air conditioning apparatus ) 是由 竹内昇 于 2020-01-21 设计创作，主要内容包括：一种对流体中包含的微粒的浓度进行检测的微粒检测传感器,所述微粒检测传感器包括发光元件、SPAD阵列受光部及信号处理部,所述信号处理部基于点亮期间内的第一脉冲计数值及熄灭期间内的第二脉冲计数值计算所述微粒的浓度。(A particle detection sensor for detecting the concentration of particles contained in a fluid, the particle detection sensor comprising a light-emitting element, a SPAD array light-receiving section, and a signal processing section for calculating the concentration of the particles based on a first pulse count value in a lighting period and a second pulse count value in a quenching period.)

1. A particle detection sensor that detects a concentration of particles contained in a fluid,

the particle detection sensor is characterized by comprising:

a light emitting element that projects light to the fine particles;

a SPAD array light receiving unit having a plurality of single photon avalanche diodes arranged in an array and operating in a geiger mode, the SPAD array light receiving unit receiving scattered light from the microparticles generated by light projected from the light emitting element and outputting a pulse signal; and

a signal processing unit that calculates a concentration of the fine particles based on a pulse count value obtained by counting the pulse signal,

the signal processing unit calculates the concentration of the fine particles based on a first pulse count value of the pulse signal in a lighting period in which the light emitting element projects the light and a second pulse count value of the pulse signal in a blanking period in which the light emitting element does not project the light.

2. The particle detection sensor according to claim 1,

the length of a period during which the first pulse count value is counted in the lighting period is the same as the length of a period during which the second pulse count value is counted in the blanking period.

3. The particle detection sensor according to claim 1,

the signal processing unit calculates a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value, and calculates the concentration of the particles based on the third pulse count value.

4. The particle detection sensor according to claim 1,

having a pulse counter for counting said pulse signals,

the pulse counter is constituted by an up/down counter,

the pulse signal in the lighting period is counted up, and the pulse signal in the blanking period is counted down.

5. The particle detection sensor of claim 1, comprising:

a temperature detection unit for measuring the ambient temperature of the SPAD array light receiving unit; and

a voltage setting unit that supplies a reverse bias voltage determined based on the measurement result of the ambient temperature to the SPAD array light receiving unit,

the measurement of the ambient temperature by the temperature detection unit is performed during a temperature detection period,

the reverse bias voltage is updated by the voltage setting unit based on the measurement result of the ambient temperature during a voltage setting period,

the temperature detection period and the voltage setting period are set in synchronization with a measurement period that is configured by a period during which the first pulse count value is counted in the lighting period and a period during which the second pulse count value is counted in the extinguishing period.

6. The particle detection sensor according to claim 5,

the signal processing unit calculates a second calculation coefficient by performing temperature correction using a preset temperature correction coefficient and a measurement result of the ambient temperature measured by the temperature detection unit, with respect to a preset first calculation coefficient for calculating the concentration of the fine particles,

calculating the concentration of the particles using the second operation coefficient and a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value.

7. The particle detection sensor according to claim 6,

the temperature correction coefficient is calculated based on measurement results of the concentrations of the fine particles at least two or more arbitrary temperatures in an inspection process at the time of manufacturing the fine particle detection sensor.

8. The particle detection sensor according to claim 5,

has a drive unit for driving the light emitting elements, the SPAD array light receiving unit, and a control unit for controlling the voltage setting unit,

the control unit has a function of outputting a first adjustment signal, a second adjustment signal, and a third adjustment signal for adjusting respective operating conditions of the drive unit, the SPAD array light receiving unit, and the voltage setting unit,

the driving section has a function of adjusting the amount of light emitted from the light emitting element in accordance with the first adjustment signal,

the SPAD array light receiving unit has a function of setting the activation and deactivation of each SPAD cell constituting the SPAD array light receiving unit according to the second adjustment signal,

the voltage setting section has a function of adjusting the reverse bias voltage in accordance with the third adjustment signal,

the first adjustment signal, the second adjustment signal, and the third adjustment signal are determined based on an inspection result in an inspection process at the time of manufacturing the fine particle detection sensor.

9. The particle detection sensor according to claim 1,

in an inspection step at the time of manufacturing the fine particle detection sensor, a fourth pulse count value is measured, the fourth pulse count value being a pulse count value of a stray light component in a state where the fine particle is not present,

when the signal processing unit calculates the concentration of the fine particles, the fourth pulse count value is subtracted from a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value.

10. The particle detection sensor of claim 9,

the fourth pulse count value is temperature-corrected based on a measurement result of a temperature detection unit that measures an ambient temperature of the SPAD array light receiving unit.

11. The particle detection sensor of claim 8,

the SPAD array light receiving unit has a function of dividing a SPAD array region, which is a region in which the SPADs are arranged in an array, into at least two or more reference regions, and selecting at least one of the reference regions as a measurement region,

the second adjustment signal is set so that the measurement region is selected so that a value obtained by dividing a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value by a fourth pulse count value, which is a pulse count value of the pulse signal in the lighting period in a state where the fine particles are not present in an inspection process at the time of manufacturing the fine particle detection sensor, becomes maximum.

12. The particle detection sensor according to claim 1,

the SPAD array light receiving unit has an optical band-pass filter that transmits only light in the vicinity of the emission wavelength of the light emitting element in the incident direction of the scattered light.

13. The particle detection sensor according to claim 1,

at least two or more of the components other than the light-emitting element are integrated on the same semiconductor substrate.

14. The particle detection sensor according to claim 1,

the lighting period, the blanking period, a first pulse count period which is a period during which the first pulse count value is counted in the lighting period, and a second pulse count period which is a period during which the second pulse count value is counted in the blanking period are controlled as a predetermined period,

the first pulse count period is controlled in synchronization with the lighting period,

the second pulse count period is controlled in synchronization with the blanking period,

the measurement of the lighting period and the extinguishing period is repeated at least once.

15. A dust sensor, characterized in that,

the particle detection sensor according to claim 1,

having a detection area for detecting dust particles suspended in the gas,

and detecting the concentration of the dust particles.

16. An air conditioning apparatus, characterized in that,

the dust sensor according to claim 15 is provided.

17. A method of controlling a particle detection sensor that detects a concentration of particles contained in a fluid,

the method for controlling the particle detection sensor is characterized by comprising the following steps:

projecting light to the fine particles by a light emitting element;

a step of receiving scattered light from the fine particles generated by light projected from the light emitting element by an SPAD array light receiving unit having a plurality of SPADs arranged in an array and operating in a geiger mode, and outputting a pulse signal; and

a step of calculating the concentration of the fine particles by a signal processing section based on a pulse count value which is a value obtained by counting the pulse signal,

in the calculating of the concentration of the fine particles, the concentration of the fine particles is calculated based on a first pulse count value of the pulse signal in a lighting period in which the light emitting element projects the light and a second pulse count value of the pulse signal in a blanking period in which the light emitting element does not project the light.

Technical Field

The present invention relates to a particle detection sensor for detecting a concentration of particles contained in a fluid, and a dust sensor and an air conditioner using the particle detection sensor.

Background

With the progress of science and technology, air pollution is becoming a problem. Along with this, for example, patent document 1 proposes a dust sensor that detects the concentration of fine particles such as coal dust, smoke particles, air pollutants, or indoor dust, and detects the pollution state of the air. In the following, particles such as coal dust suspended in the gas, smoke particles, air pollutants, and indoor dust will be collectively referred to as "dust".

In particular, in recent years, a particulate matter represented by PM2.5 (having a particle diameter of 2.5 μm or less) has been pointed out to be dangerous to health. Therefore, a fine particle detection sensor or a dust sensor capable of detecting the concentration of fine particles having a particle diameter of 2.5 μm or less with high accuracy is required.

Here, the concentration of the fine particles is a mass concentration, a number concentration, or the like of the fine particles contained in the fluid as a gas or a liquid. The mass concentration represents the total amount of the fine particles contained in a unit volume of the fluid, and the unit thereof is [ mu.g/m ]³]Etc. The number concentration represents the number of particles contained in a unit volume of fluid, and the unit is [1/m ]³]Etc. The fine particles to be treated in the present specification are those having a particle diameter in the range of about 0.1 μm to several tens μm.

Such a particle detection sensor and dust sensor are mounted on, for example, an air conditioner such as an air cleaner that operates automatically or an air conditioner with an air cleaning function, and detect air pollution by the sensor, and adjust the air volume and control the operation of the air conditioner according to the degree of the air pollution.

Fig. 17 shows an example of a circuit configuration of a conventional dust sensor 500. As shown in fig. 17, the dust sensor 500 includes a light emitting element 501 (e.g., an LED or the like) that projects light to a detection region 503, and a light receiving element 505 (e.g., a photodiode) that receives scattered light 504 scattered by dust particles present in the detection region 503. Further, the dust sensor 500 includes: a driver circuit 510 which drives the light emitting element 501; an IV conversion circuit 506 that converts the light-receiving current in the light-receiving element 505 into a voltage signal; a multistage amplification circuit 508 that amplifies the voltage signal; a high pass filter HPF507 composed of a resistor and a capacitor for removing low frequency noise; and a variable resistor R509 for adjusting the amplification factor of the amplification circuit.

Fig. 18 shows an example of an operation waveform of the dust sensor 500. The horizontal axis of fig. 18 represents time change. Fig. 18 (a) shows a drive signal waveform (pulse signal) of the light-emitting element 501, which indicates that the light-emitting element 501 is turned on at the H level and the light-emitting element 501 is turned off at the L level. Fig. 18 (b) shows the waveform of an output signal, and when the light-emitting element 501 is turned on, the scattered light 504 from dust particles enters the light-receiving element 505, and therefore the output signal obtains a pulse signal synchronized with the timing at which the light-emitting element 501 is turned on.

Since the intensity (light amount) of the scattered light 504 increases and decreases depending on the concentration of the dust particles, the amplitude of the pulse signal increases and decreases depending on the concentration of the dust particles. This state is shown in (b1), (b2), and (b3) in (b) of fig. 18. For example, since the amount of light received by scattered light increases as the density of dust particles increases, the amplitude of the pulse signal also increases as the density increases. Thereby, the dust particle concentration can be detected by measuring the peak voltage value of the pulse signal.

However, in the output signal shown in fig. 18 (b), in addition to the pulse signal generated by the scattered light 504, noise components such as shot noise and thermal noise generated by the light receiving element 505 and the amplifier circuit 508, and noise components based on external disturbance light noise and electromagnetic noise are superimposed. Therefore, the measured value of the peak voltage of the pulse signal contains the above noise component.

Fig. 19 shows the dependency of the measured value of the peak voltage of the pulse signal on the dust concentration. Since the measured peak voltage value changes depending on the dust concentration, the dust concentration can be detected from the measured value of the peak voltage. Here, the measurement value in the case where the dust particle concentration is zero (no dust) is determined by the noise component.

When the dust concentration is reduced, the amount of scattered light from the dust particles is reduced, and thus a signal component (peak voltage) by the scattered light 504 is reduced, and as a result, the scattered light component is also buried in the noise component. Therefore, as the dust particle concentration becomes low, the dust concentration measurement accuracy decreases, and a concentration range that cannot be measured in the low concentration region occurs. In addition, for example, when the noise component changes due to a change in the operating condition of the sensor such as a change in the ambient temperature, the accuracy of dust concentration measurement is also affected.

It is generally known that the intensity of scattered light from fine particles is proportional to the sixth power of the particle diameter, and the smaller the particle diameter of the dust particles, the lower the peak voltage measurement value measured by the dust sensor 500, and the lower the accuracy of the dust concentration measurement is because the peak voltage value of the scattered light component is buried in the noise component as in the measurement at the time of low concentration in fig. 19.

On the other hand, in the field of optical communication, distance measuring sensors, and the like, Avalanche Photodiodes (APDs) using an avalanche amplification (avalanche) effect of photodiodes have been used as light receiving elements for detecting weak light. The avalanche photodiode operates in a linear mode when a reverse bias voltage lower than a breakdown voltage (break reduction voltaga) is applied, and an output current changes so as to have a positive correlation with a light receiving amount. The avalanche photodiode operates in a geiger mode when a reverse bias voltage above a breakdown voltage is applied. The geiger-mode avalanche photodiode can obtain a large output current because avalanche multiplication (avalanche amplification) is caused by the incidence of even a single photon. Accordingly, the Geiger-mode Avalanche photodiode is known as a Single Photon Avalanche Diode (SPAD).

In addition, the light detection efficiency can be further improved by arranging a plurality of SPADs in array-like rows and columns. The photodetection efficiency of the SPAD array is defined by the product of the aperture ratio (the ratio of the photodetection region to the entire SPAD array photodetecting section), the quantum efficiency (the probability of photo-generated carriers entering the SPAD), and the avalanche multiplication ratio (the probability of avalanche multiplication by generated carriers).

In addition, by adding an active quenching resistor in series to the avalanche photodiode in the geiger mode, a pulse signal output (digital signal) synchronized with the photon incidence can be obtained. Fig. 20 (a) is a diagram showing an example of a circuit configuration in which an active quenching resistor is added in series to an avalanche photodiode in the geiger mode. The circuit shown in fig. 20 (a) includes an avalanche photodiode APD600, an active quenching resistor R600 (a resistance component of an NMOS transistor (n-type metal oxide film semiconductor field effect transistor)), and a buffer BUF 600.

The avalanche photodiode APD600 (hereinafter referred to as "APD 600") is a geiger-mode avalanche photodiode, and avalanche multiplication is generated for light incidence by applying a reverse bias voltage VHV600 equal to or higher than a breakdown voltage to generate a current. A current flows into an active quenching resistor R600 (hereinafter referred to as a resistor R600) connected in series with the APD600, and the inter-terminal voltage of the resistor R600 increases. Along with this, the reverse bias voltage VHV600 of the APD600 decreases, and avalanche multiplication stops.

When the current generated by the avalanche multiplication disappears, the voltage between the terminals of the resistor R600 decreases, and the APD600 returns to a state where the reverse bias voltage VHV600 equal to or higher than the breakdown voltage is applied again. The voltage change of the node a600 between the APD600 and the resistor R600 is output via the buffer BUF 600. Thereby, a digitized pulse signal synchronized with the photon injection is output from the buffer BUF 600. The pulse signal to be output may be a binary pulse signal. The operation waveform of the circuit in fig. 20 (a) is shown in fig. 20 (b). Patent document 2 discloses a diagram shown in fig. 20 (b).

Patent document 3 discloses a fine particle detection circuit in which an avalanche photodiode operating in the geiger mode is used as a light receiving element for detecting weak scattered light from fine particles. The fine particle detection circuit disclosed in patent document 3 includes two current-voltage conversion circuits, namely a current-voltage conversion circuit for measuring scattered light from fine particles and a current-voltage conversion circuit for measuring scattered light from particles having a large particle diameter. This can expand the input dynamic range for scattered light received by the avalanche photodiode, and can detect particles from fine particles to large particles using one light receiving circuit.

Disclosure of Invention

Technical problem to be solved by the invention

However, the above-described prior art has the following problems. That is, in the case of the circuit configuration disclosed in patent document 1, since the scattered light component and the noise component from the dust particles are mixed in the output signal as described above, the scattered light component and the noise component cannot be distinguished in the method of measuring the peak voltage value. Therefore, as the dust concentration becomes low or the dust particle diameter becomes small, the measurement accuracy is lowered, and the possibility of occurrence of an unmeasurable concentration range is increased.

In particular, as the ambient temperature increases, shot noise of the light receiving element and thermal noise of the circuit element increase, and a noise component appearing in the output signal increases. Therefore, when the ambient temperature is high, the dust concentration detection accuracy is greatly reduced, and the possibility that the dust concentration cannot be measured due to an increase in noise components is increased.

In the circuit configuration disclosed in patent document 1, since a plurality of amplifier circuits are used to form a high-gain amplifier in order to detect weak scattered light from dust particles, there is a possibility that the resistance against electromagnetic noise and external disturbance light noise may be deteriorated. This is because the metal wiring connected between the circuit elements serves as an antenna, electromagnetic noise is coupled to the wiring, noise is superimposed on the signal wiring, and the noise is amplified by the amplifier.

In particular, as a measure for deterioration of the tolerance due to electromagnetic noise, it is necessary to suppress the influence due to electromagnetic noise. As a countermeasure against this, there is a method of covering the entire dust sensor with a metallic shield case or using a conductive resin for the sensor housing case, and grounding the conductive resin to shield electromagnetic noise. Further, since a countermeasure such as noise removal by a high-pass filter is required for the circuit, there is a possibility that the sensor cost increases due to an increase in the number of components constituting the sensor including the plurality of amplifier circuits.

Further, the particle detection circuit disclosed in patent document 3 requires a plurality of power supply voltages and requires a bias voltage of 100V or more to be applied to the avalanche photodiode, and therefore is not suitable for installation in home air conditioning equipment such as an air cleaner. Further, since the operating voltages of the current-voltage conversion circuits are different, an isolation amplifier including a photocoupler or the like is required, and the number of components may increase, which may increase the cost.

Patent document 3 describes a method of increasing the S/N Ratio (Signal to Noise Ratio) by setting the value of the feedback resistance Rf of the IV conversion circuit to an optimal value to suppress Noise components such as thermal Noise, but does not mention a specific method of separating and removing scattered light components and Noise components. Therefore, measurement accuracy may be lowered in measurement of low concentration and measurement of fine particles.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a particulate detection sensor capable of detecting a particulate concentration with high accuracy, suppressing a decrease in measurement accuracy due to a change in ambient temperature, external disturbance optical noise, electromagnetic noise, manufacturing variation, and the like, and suppressing an increase in cost of the sensor by reducing the number of components constituting the sensor.

Means for solving the problems

In order to solve the above-mentioned problems, (1) one embodiment of the present invention is a particulate detection sensor that detects a concentration of particulates contained in a fluid, the particulate detection sensor including: a light emitting element that projects light to the fine particles; a SPAD array light receiving unit having a plurality of SPADs arranged in an array and operating in a geiger mode, the SPADs receiving scattered light from the microparticles generated by light projected from the light emitting elements and outputting pulse signals; and a signal processing unit that calculates a concentration of the fine particles based on a pulse count value obtained by counting the pulse signal, wherein the signal processing unit calculates the concentration of the fine particles based on a first pulse count value of the pulse signal in a lighting period in which the light emitting element projects the light and a second pulse count value of the pulse signal in a blanking period in which the light emitting element does not project the light.

(2) In addition, in the configuration of (1), a length of a period in which the first pulse count value is counted in the lighting period is the same as a length of a period in which the second pulse count value is counted in the extinguishing period.

(3) In the particle detection sensor according to an embodiment of the present invention, in addition to the configuration of (1) or (2), the signal processing unit calculates a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value, and calculates the concentration of the particles based on the third pulse count value.

(4) In addition to the configuration (1), (2), or (3), the particle detection sensor according to an embodiment of the present invention includes a pulse counter configured to count the pulse signal, the pulse counter being configured from an up/down counter configured to count up the pulse signal in the lighting period and count down the pulse signal in the blanking period.

(5) In addition, a particle detection sensor according to an embodiment of the present invention is configured as described in any one of (1) to (4), and includes: a temperature detection unit for measuring the ambient temperature of the SPAD array light receiving unit; and a voltage setting unit that supplies a reverse bias voltage determined based on a measurement result of the ambient temperature to the SPAD array light receiving unit, wherein the measurement of the ambient temperature by the temperature detection unit is performed during a temperature detection period, the reverse bias voltage is updated based on the measurement result of the ambient temperature by the voltage setting unit during a voltage setting period, and the temperature detection period and the voltage setting period are set in synchronization with a measurement period including a period in which the first pulse count value is counted during the lighting period and a period in which the second pulse count value is counted during the lighting-off period.

(6) In the fine particle detection sensor according to one embodiment of the present invention, in addition to the configuration of (5), the signal processing unit calculates a second calculation coefficient by performing temperature correction using a preset temperature correction coefficient and a measurement result of the ambient temperature measured by the temperature detection unit with respect to a preset first calculation coefficient for calculating the concentration of the fine particles, and calculates the concentration of the fine particles using the second calculation coefficient and a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value.

(7) In addition to the configuration of (6), the fine particle detection sensor according to an embodiment of the present invention is configured such that, in an inspection step at the time of manufacturing the fine particle detection sensor, the temperature correction coefficient is calculated based on measurement results of the concentrations of the fine particles at least two or more arbitrary temperatures.

(8) Further, in the particle detection sensor according to one embodiment of the present invention, in addition to the configuration of the above (5), the particle detection sensor includes a control unit that controls a driving unit that drives the light emitting element, the SPAD array light receiving unit, and the voltage setting unit, the control unit has a function of outputting a first adjustment signal, a second adjustment signal, and a third adjustment signal for adjusting respective operating conditions of the driving unit, the SPAD array light receiving unit, and the voltage setting unit, the driving unit has a function of adjusting the light emission amount of the light emitting element in accordance with the first adjustment signal, the SPAD array light receiving unit has a function of setting the activation and deactivation of each SPAD cell constituting the SPAD array light receiving unit in accordance with the second adjustment signal, and the voltage setting unit has a function of adjusting the reverse bias voltage in accordance with the third adjustment signal, the first adjustment signal, the second adjustment signal, and the third adjustment signal are determined based on an inspection result in an inspection process at the time of manufacturing the fine particle detection sensor.

(9) In addition to the configuration of any one of the above (1) to (8), the particle detection sensor according to an embodiment of the present invention measures a fourth pulse count value, which is a pulse count value of a stray light component in a state where the particle is not present, in an inspection process at the time of manufacturing the particle detection sensor, and subtracts the fourth pulse count value, which is a result of subtracting the second pulse count value from the first pulse count value, when the signal processing unit performs a concentration calculation of the particle.

(10) In the particle detection sensor according to an embodiment of the present invention, in addition to the configuration of (9) above, the fourth pulse count value is temperature-corrected based on a measurement result of the temperature detection unit that measures the ambient temperature of the SPAD array light receiving unit.

(11) In the particle detection sensor according to an embodiment of the present invention, in addition to the configuration of (8) above, the SPAD array light receiving unit has a function of dividing a SPAD array region, which is a region in which the plurality of SPADs are arranged in an array, into at least two or more reference regions, and selecting at least one or more of the reference regions as a measurement region, and the second adjustment signal is set so that the measurement region is selected so that a value obtained by dividing a third pulse count value obtained by subtracting the second pulse count value from the first pulse count value by a fourth pulse count value, which is a pulse count value of the pulse signal in the lighting period in a state in which the particle is not present in an inspection process at the time of manufacturing the particle detection sensor, becomes maximum.

(12) In the particle detection sensor according to an embodiment of the present invention, in addition to any one of the configurations (1) to (11), the SPAD array light receiving unit includes an optical band pass filter that transmits only light in the vicinity of the emission wavelength of the light emitting element in the incident direction of the scattered light.

(13) In addition, in the particle detection sensor according to an embodiment of the present invention, in addition to any one of the configurations (1) to (12), at least two or more of the components other than the light emitting element are integrated on the same semiconductor substrate.

(14) In addition, in the configuration of (1), the particulate detection sensor according to the embodiment of the present invention is configured such that the on period, the off period, a first pulse count period that is a period in which the first pulse count value is counted in the on period, and a second pulse count period that is a period in which the second pulse count value is counted in the off period are controlled as a predetermined period, the first pulse count period is controlled in synchronization with the on period, and the second pulse count period is controlled in synchronization with the off period, and measurement of the on period and the off period is repeated at least once.

(15) A dust sensor according to an embodiment of the present invention includes the particle detection sensor having any one of the configurations (1) to (12) above, and has a detection region for detecting dust particles suspended in a gas, and detects a concentration of the dust particles.

(16) An air conditioning apparatus according to an embodiment of the present invention is equipped with the dust sensor having the structure of (15) above.

(17) A method for controlling a particle detection sensor according to an embodiment of the present invention detects a concentration of particles included in a fluid, and includes: projecting light to the fine particles by a light emitting element; receiving scattered light from the fine particles generated by light projected from the light emitting element by an SPAD array light receiving unit having a plurality of SPADs arranged in an array and operating in a geiger mode, and outputting a pulse signal; and a step of calculating, by a signal processing unit, a concentration of the fine particles based on a pulse count value that is a value obtained by counting the pulse signal, wherein in the step of calculating the concentration of the fine particles, the concentration of the fine particles is calculated based on a first pulse count value and a second pulse count value, the first pulse count value being a pulse count value of the pulse signal in a lighting period in which the light emitting element projects the light, and the second pulse count value being a pulse count value of the pulse signal in a lighting-off period in which the light emitting element does not project the light.

Effects of the invention

According to an aspect of the present invention, it is possible to realize a particulate detection sensor capable of detecting a particle concentration with high accuracy, suppressing a decrease in measurement accuracy due to a change in ambient temperature, external disturbance optical noise, electromagnetic noise, manufacturing variation, and the like, and suppressing an increase in cost of the sensor by reducing the number of components constituting the sensor.

Drawings

Fig. 1 is a block diagram showing an example of a schematic configuration of a particulate detection sensor according to a first embodiment of the present invention.

Fig. 2 (a) is a diagram showing an example of a schematic circuit configuration of SPAD cells constituting the SPAD array light receiving section of the particle detection sensor. (b) An example of an operation waveform of the SPAD cell is shown. (c) The figure shows an example of the structure of the SPAD array light receiving unit. (d) The diagram explains the output of SPAD _ OUT.

Fig. 3 is a diagram showing an example of the structure of the SPAD array light receiving unit.

Fig. 4 is a diagram showing an example of an operation waveform of the particle detection sensor.

Fig. 5 (a) is a graph showing an example of the dependency of each pulse count value on the particle concentration. (b) A graph showing an example of the dependency of the third pulse count value on the particle concentration is shown. (c) A graph showing an example of a waveform of the particle concentration dependency of the third pulse count value.

Fig. 6 is a block diagram showing an example of a schematic configuration of a particulate detection sensor according to a second embodiment of the present invention.

Fig. 7 is a diagram showing an example of an operation waveform of the particle detection sensor.

Fig. 8 is a graph showing a setting example of the optimum reverse bias voltage with respect to the ambient temperature.

Fig. 9 (a) is a graph showing an example of the dependency of the first pulse count value on the particle concentration at an arbitrary temperature. (b) A graph showing an example of the temperature dependence of the third pulse count value on the particle concentration is shown.

Fig. 10 is a graph showing an example of the temperature dependence of the gradient α (T) of the third pulse count value.

Fig. 11 (a) is a graph showing an example of the dependence of the first pulse count value and the second pulse count value on the number of SPAD cells. (b) The graph shows an example of the dependency of the first pulse count value and the second pulse count value on the amount of emitted light. (c) The graph shows an example of the dependence of the first pulse count value and the second pulse count value on the reverse bias voltage.

Fig. 12 (a) is a graph showing an example of the dependency of the third pulse count value on the particle concentration when stray light enters the SPAD array light receiving unit. (b) The graph shows an example of the temperature dependence of the third pulse count value on the particle concentration when the temperature dependence of the stray light component is large. (c) A graph showing an example of the temperature dependence of the fourth pulse count value.

Fig. 13 is a diagram illustrating an example of a method for selecting a measurement region of the SPAD array light-receiving section of the particle detection sensor according to the third embodiment of the present invention.

Fig. 14 (a) is a diagram showing an example of the relationship between the first pulse count value and the particle concentration when the S/N ratio is large. (b) The graph shows an example of the relationship between the first pulse count value and the particle concentration when the S/N ratio is relatively small.

Fig. 15 is a schematic view showing an example of a schematic configuration of a dust sensor according to a fourth embodiment of the present invention. (a) The dust sensor is viewed from the top surface. (b) Is a cross-sectional view of A-A' of (a).

Fig. 16 is a schematic diagram showing an example of a schematic configuration of an air conditioner according to the present invention.

Fig. 17 is a diagram showing an example of a schematic circuit configuration of a conventional dust sensor.

Fig. 18 is a diagram showing an example of an operation waveform of the dust sensor. (a) A driving signal waveform (pulse signal) of the light emitting element is shown. (b) The output signal waveform is shown.

Fig. 19 is a graph showing the dependency of the peak voltage value of the above-described pulse signal on the dust concentration.

Fig. 20 (a) is a diagram showing an example of a circuit configuration in which an active quenching resistor is added in series to an avalanche photodiode in the geiger mode. (b) Is a diagram showing an operation waveform of the circuit of (a).

Detailed Description

The embodiments of the present invention will be described in detail below. For convenience of explanation, members having the same functions as those of the members shown in the embodiments are given the same reference numerals, and explanations thereof are appropriately omitted. The present invention also relates to a fine particle detection sensor for detecting a concentration of fine particles contained in a fluid such as a gas or a liquid, and the fine particles having a particle diameter of about 0.1 μm to several tens of μm are targets to be detected.

[ first embodiment ]

Fig. 1 is a block diagram showing an example of a schematic configuration of a particulate detection sensor 1 according to a first embodiment of the present invention. The particle detection sensor 1 includes a light emitting element 10, a driving unit 20, a SPAD array light receiving unit 30, a pulse counter 40, a signal processing unit 50, and a control unit 60.

The light emitting element 10 projects the projection light E1 toward the particles to be detected. The light emitting element 10 is assumed to be a Light Emitting Diode (LED), a Laser Diode (LD), or the like, but the present embodiment is not limited thereto. As the light Emitting element 10, an organic EL (organic electroluminescence) element, a VCSEL (Vertical Cavity Surface Emitting Laser), or the like may be used.

The driving section 20 drives the light emitting element 10. The SPAD array light receiving unit 30 is configured by an SPAD array in which a plurality of SPADs operating in the geiger mode are arranged in an array form for receiving scattered light E2 from the fine particles. The pulse counter 40 counts the digitized binary pulse signal output from the SPAD array light receiving section 30. The signal processing unit 50 stores and calculates data of a count value of pulse count (hereinafter referred to as a pulse count value). The control unit 60 controls the signal processing unit 50, the driving period of the light emitting element 10, and the pulse counting period of the pulse counter 40.

Fig. 2 shows an example of the configuration of the SPAD array light receiving unit 30 and an example of the operation waveform thereof. Fig. 2 (a) is a diagram showing an example of a schematic circuit configuration of the SPAD cell _1(SPAD cell) constituting the SPAD array light receiving section 30 of the particle detection sensor 1. The SPAD cell _1 has an active quenching resistor R1(NMOS, ON resistor) (hereinafter referred to as resistor R1) connected to the anode side (node a1 side) of an avalanche photodiode APD1 (hereinafter referred to as APD 1). The SPAD cell _1 outputs a digitized pulse signal to light incident on the APD1 via the AND circuit AND 1.

In the other input of the AND circuit AND1, the selection signal S _1 is input, AND the activation/deactivation of the SPAD cell _1 can be selected in accordance with the H/L level of the selection signal S _ 1. When the selection of the SPAD cell _1 is not necessary, the selection signal S _1 may be fixed to the H level in advance. Further, a reverse bias voltage VHV1 equal to or higher than the breakdown voltage of APD1 is applied to the negative electrode side of APD1, and APD1 operates in the geiger mode.

Fig. 2 (b) is a diagram showing an example of an operation waveform of the SPAD cell _ 1. As described in the above [ background art ], when incident light E1 is incident on the APD1 operating in the geiger mode, carriers generated by the incident light are multiplied by avalanche to generate a current, and the current flows into the resistor R1 connected in series to the APD 1. This increases the voltage between the terminals of the resistor R1, and the reverse bias voltage VHV1 of the APD1 decreases with the increase, thereby stopping avalanche multiplication.

When the current due to avalanche multiplication disappears, the voltage between the terminals of the resistor R1 drops, and the state returns to a state where the reverse bias voltage VHV1 equal to or higher than the breakdown voltage is applied to the APD1 again. The waveform indicating this state is the waveform of the node a1 shown in fig. 2 (b). When a large current is generated due to avalanche multiplication, the voltage value at the node a1 rapidly increases, and the voltage value gradually decreases after the avalanche multiplication stops. The time required for node a1 to rise to fall is referred to as the dead time. During this period, avalanche multiplication does not occur even if SPAD cell _1 is injected with new projection light E1.

The dead time (dead time) depends on circuit parameters and can be set to about 100ns or less. Further, the selection signal S _1 input to the AND circuit AND1 is set to H, AND the waveform of the node a1 is output via the AND circuit AND1, whereby a pulse signal shown in OUT1 in fig. 2 (b) can be obtained. Thus, an amplifier circuit, a high-pass filter, or other circuit is not required for signal processing, and an analog current pulse signal generated by APD1 can be converted into a digitized binary pulse signal by the incident light E1. As a result, no circuit such as an amplifier circuit or a high-pass filter is required for signal processing, the number of components is small, and a light receiving unit having a high light detection efficiency and S/N ratio can be formed.

Fig. 2 (c) is a diagram showing an example of the structure of the SPAD array light receiving unit 30. The SPAD array light receiving unit 30 is configured to connect the outputs of a plurality (N) of SPAD cell cells _1 to SPAD cell _ N to a logic OR circuit. The results of logical OR of the output signals OUT1 to OUTN, which are the output signals of the SPAD cell _1 to SPAD cell _ N, are output to the output signal SPAD _ OUT of the SPAD array light-receiving section 30. Fig. 2 (d) is a diagram illustrating the output of the output signal SPAD _ OUT. By configuring the SPAD array light receiving unit 30 to be a logical OR of the outputs of the plurality of SPAD cells cell _1 to SPAD cell _ N in this manner, the light detection efficiency can be further improved in the SPAD array in which the plurality of SPAD cells are arranged in an array form (matrix form) as compared with the case where the light receiving element is formed by one SPAD cell.

Fig. 3 is a diagram showing an example of the structure of the SPAD array light receiving unit 30. In fig. 3, each region denoted by a reference numeral represents SPAD cell _1 to SPAD cell _ N shown in fig. 2 (a), and a plurality of SPAD cells are arranged in an array. By arranging a plurality of SPAD cell cells in an array in this manner, the light receiving area of the light receiving element is enlarged as compared with a case where the light receiving element is formed by one SPAD cell, and as a result, the viewing angle of the light receiving element is enlarged, and therefore, the light detection efficiency is improved. In fig. 3, although the SPAD array is shown as a total of 100 cells of 10 cells × 10 cells, the SPAD array light receiving unit 30 to be handled in the present invention is not limited to the above number.

Since the output of the SPAD array light-receiving unit 30 is the logical OR of the outputs of the SPAD cell cells, for example, even when pulse signals are simultaneously output from two SPAD cell cells, only one pulse signal is output to the output of the SPAD array light-receiving unit 30.

When the number of SPAD cell cells is large or the amount of light received by the SPAD array light receiving unit 30 is large, the frequency at which each SPAD cell simultaneously outputs a pulse signal becomes high as described above. Therefore, the linearity of the output pulse number of the SPAD array light receiving unit 30 with respect to the incident light amount decreases as the number of SPAD cell cells increases or the light receiving amount of the SPAD array light receiving unit 30 increases. As described above, the light detection efficiency can be set high by increasing the number of SPAD cell cells, but the linearity of the number of output pulses with respect to the amount of light received by the SPAD array light receiving section 30 is reduced. Therefore, it is important that the SPAD array light receiving unit 30 is set to an optimum number of SPAD cell cells in accordance with the performance and the usage required for the particle detection sensor 1.

(operation of particle detecting sensor)

Fig. 4 is a diagram showing an example of an operation waveform of the particle detection sensor 1. The first control signal TS1 is a drive signal for controlling the drive of the light emitting element 10, and the first control signal TS1 is output from the controller 60 in fig. 1. Fig. 4 shows that the driving unit 20 turns on the light emitting element 10 when the first control signal TS1 is at the H level, and turns off the light emitting element 10 when the first control signal TS1 is at the L level. Fig. 4 shows, as an example, an operation waveform in a case where the light-emitting element 10 is repeatedly turned on and off at 50% of the measurement cycle (Duty ratio of 50%). The Duty ratio is not limited to 50%.

The second control signal TS2 is a signal for controlling the period during which the pulse counter 40 counts pulses. The second control signal TS2 indicates a period during which the output pulse signal of the SPAD array light-receiving unit 30 is pulse-counted, and is output from the control unit 60. The second control signal TS2 is set to be synchronized with the lighting period ONT and the turning-off period OFFT of the light emitting element 10, respectively. The pulse counter 40 counts the output signal SPAD _ OUT of the SPAD array light-receiving section 30 in pulses while the second control signal TS2 is at the H level.

Here, a pulse count period synchronized with the lighting period ONT is referred to as a first pulse count period PT1, and a pulse count period synchronized with the blanking period OFFT is referred to as a second pulse count period PT 2. The pulse count values counted in the first pulse count period PT1 and the second pulse count period PT2 are the first pulse count value PC1 and the second pulse count value PC2, respectively. As shown in fig. 4, the measurement period MT is set by adding the continuous lighting period ONT and the turning-OFF period OFFT (one measurement), and the measurement is continuously repeated (one set of the lighting period ONT and the turning-OFF period OFF).

In the operation waveform example of fig. 4, each pulse count period is shown as a period shorter than the driving period (lighting period ONT or turning-off period OFFT) of light emitting element 10, and each pulse count period may be set at exactly the same time as the driving period. Each pulse count period may be set to be shorter than the drive period. As the setting conditions of each pulse count period and each driving period, it is sufficient if "the driving period is equal to or longer than the pulse count period" is satisfied, and care should be taken to avoid setting the driving period < the pulse count period and avoiding setting the one pulse count period across the lighting period ONT and the lighting-off period OFFT.

The waveforms of the output signal SPAD _ OUT in fig. 4 (a) to 4 (c) show the waveforms (output waveforms) of the output signal SPAD _ OUT of the SPAD array light receiving unit 30 at different particle concentrations. Specifically, (a) of fig. 4 shows a waveform of the output signal SPAD _ OUT in the case where no fine particles are present, (b) of fig. 4 shows a waveform of the output signal SPAD _ OUT in the case where the density is low, and (c) of fig. 4 shows a waveform of the output signal SPAD _ OUT in the case where the density is high.

The solid-line pulse signal shown in the waveform of the output signal SPAD _ OUT represents a pulse signal of a scattered light component generated when the projection light E1 projected from the light-emitting element 10 is scattered by the fine particles and the scattered light E2 is received by the SPAD array light-receiving unit 30. Since the amount of light scattered by the microparticles (the amount of scattered light) changes depending on the concentration (or number) of the microparticles, the number of pulse signals of the scattered light component changes depending on the microparticle concentration as a result. In other words, when the particle concentration increases, the number of pulse signals of the scattered light component also increases.

The pulse signal of the broken line shown in the waveform of the output signal SPAD _ OUT represents a pulse signal of a noise component. The pulse signal as the noise component includes, for example, (1) and (2) described below. (1) The carriers thermally generated in the apd (spad) operating in the geiger mode cause avalanche multiplication to generate a pulse signal (referred to as a dark pulse). (2) Sunlight, fluorescent lamps, and the like, and pulse signals generated by the incident external disturbance light. The carrier described in (1) above represents an electron or a hole that is thermally generated even when light is not incident.

These noise components are generated in the same manner in both the lighting period ONT and the off period OFFT of the light emitting element 10, because they do not depend on the amount of received scattered light. Therefore, the first pulse count value PC1 in the lighting period ONT counts both the number of pulses of the scattered light component and the number of pulses of the noise component, and the second pulse count value PC2 in the off period OFFT counts the number of pulses of only the noise component.

(calculation of microparticle concentration)

Fig. 5 (a) is a graph showing an example of the dependency of each pulse count value on the particle concentration. In the solid-line waveform of fig. 5 (a), (5-1) shows the first pulse count value PC1 in the lighting period ONT, and (5-2) shows the second pulse count value PC2 in the blanking period OFFT. The second pulse count value PC2 of (5-2) is only a noise component and therefore takes a constant value without depending on the particle concentration. In contrast, since the first pulse count value PC1 of (5-1) includes both a scattered light component and a noise component, the scattered light component that changes depending on the particle concentration and the noise component that does not depend on the particle concentration are superimposed (and summed). In fig. 5 (a), the intercept is a pulse count value of the noise component.

Here, the solid line in fig. 5 (a) shows the case where the noise component is not changed, and the dashed line shows the change or fluctuation of the noise component. The change in the noise component indicated by the dashed line portion occurs, for example, when the ambient temperature T around the SPAD array light receiving unit 30 changes, the amount of incident light of external disturbance light noise changes, or the like. The noise component is not limited to the change in waveform shown by the broken line in fig. 5 (a). The dotted line portion in fig. 5 (a) shows that the count value of the noise component fluctuates when the measurement environment such as the ambient temperature T changes every time measurement is performed.

When the change in the noise component is relatively gradual and there is substantially no change in the measurement period MT (once lit + once extinguished), the value of the noise component contained in the first pulse count value PC1 in a certain measurement is substantially the same as the value of the noise component contained in the second pulse count value PC 2. In this case, only the pulse count value of the scattered light component is included in the third pulse count value PC3 obtained by subtracting the second pulse count value PC2 from the first pulse count value PC 1. Therefore, the third pulse count value PC3 having only the scattered light component, which is not affected by the change in the noise component, can be obtained by the subtraction processing.

Fig. 5 (b) is a graph showing an example of the dependency of the third pulse count value PC3 on the particle concentration. The third pulse count value PC3 of (5-3) has no influence of variations in noise components. Therefore, the signal processing unit 50 can detect the particle concentration by calculation using the third pulse count value PC3 measured at a certain particle concentration and a first calculation coefficient x1, which will be described later, set in advance for calculating the particle concentration.

Here, the first pulse count value PC1 is PC1, the second pulse count value PC2 is PC2, the third pulse count value PC3 is PC3, the particle concentration is D, the slope with respect to the particle concentration is α, and the count values of the noise components in the first pulse count value PC1 and the second pulse count value PC2 are N1 and N2, respectively. Since N1 is N2 as described above, the arithmetic processing can be expressed by the following equation. As shown in the following (equation 1-D), the particle concentration D can be calculated by dividing the first pulse count value PC1 and the second pulse count value PC2 or the third pulse count value PC3 by the gradient α. In this case, the first arithmetic coefficient x1 is the gradient α.

(1) PC1 ═ α × D + N1 (formula 1-a)

(2) PC2 ═ N2 (formula 1-b)

(3) PC3 ═ PC1-PC2 ═ α × D (formula 1-c)

D ═ PC1-PC2)/α ═ PC3/α (formula 1-D)

Strictly speaking, N1 is approximately equal to N2, and thus D is approximately equal to PC3/α, but in the above equation, it is assumed that N1 is equal to N2 for simplicity.

As described above, only when N1 — N2 is satisfied, the length of the first pulse count period PT1 is the same as the length of the second pulse count period PT 2. Therefore, when the first pulse count period PT1 is PT1 and the second pulse count period PT2 is PT2, the pulse count periods need to be set to the same length, i.e., PT1 is PT 2. For example, the first pulse count period PT1 and the second pulse count period PT2 are preferably generated using the same clock signal.

In addition, when PT1 ≠ PT2 is set for each pulse count period, since N1 ≠ N2, the arithmetic expression (expression 1-c) cannot be used as it is. However, the pulse count values N1 and N2 of the noise component of each pulse count value are proportional to the first pulse count period PT1 and the second pulse count period PT2, respectively. In this way, the same result as described above can be obtained by subtracting the second pulse count value PC2 after correcting it by the ratio of the first pulse count period PT1 to the second pulse count period PT2 at the time of subtraction processing. This case can be expressed by the following equation.

N2 ═ N1 × PT2/PT1 (formula 2-a)

(1) PC1 ═ α × D + N1 (formula 2-b)

(2) PC2 ═ N2 (formula 2-c)

(3) PC3 ═ PC1-PC2 × PT1/PT2 ═ α × D (formula 2-D)

D ═ D (PC1-PC2 xpt 1/PT2)/α (formula 2-e)

Here, PC3 ≠ PC 3'. The above expression shows that even when the time lengths of the first pulse count period PT1 and the second pulse count period PT2 are different, the particle concentration can be detected by calculation using PT1, PT2, and α and the measured first pulse count value PC1 and second pulse count value PC 2.

In this case, the first arithmetic coefficient x1 includes three first pulse count periods PT1, PT2 and a gradient α. For example, when each pulse count period is set so that PT1 > PT2, if the second pulse count period PT2 is set longer, the measurement time can be shortened without lowering the detection accuracy of the scattered light component. As a result, the response time of the particulate detection sensor 1 can be set to be fast. The second pulse count period PT2 can be set to 20ms or more, for example. Details will be described later.

(relationship between pulse count period and measurement accuracy)

The relationship between the pulse count period and the measurement accuracy (measurement error) will be described below.

Fig. 5 (c) is a graph showing an example of a waveform of the particle concentration dependency of the third pulse count value PC 3. Reference numeral (5-4) denotes a third pulse count value PC3 when each pulse count period is set to be long, and reference numeral (5-5) denotes a third pulse count value PC3 when each pulse count period is set to be short. Here, the solid line portion of the waveform indicates the average value of the subtracted third pulse count value PC3, and the width indicated by the broken line indicates the width of the measurement error of the third pulse count value PC 3. The value obtained by dividing the measurement error width at an arbitrary particle concentration by the average value of the particle concentrations detected by the particle detection sensor 1 corresponds to the "measurement accuracy" at that particle concentration. In the case of the waveform example of fig. 5 (c), the case (5-4) in which each pulse count period is set to be long is set to have a higher "measurement accuracy" than the case (5-5) in which each pulse count period is set to be short.

In addition, there is an upper limit to the pulse count value that can be normally measured by the pulse counter 40. In the measurement by the pulse counter 40, the pulse count value increases as the particulate concentration becomes high, and reaches the upper limit when the particulate concentration is equal to or higher than a certain particulate concentration, and therefore, the measurement at a high concentration equal to or higher than the upper limit cannot be performed. If the particulate matter concentration until the pulse count value reaches the upper limit is set as the "measurable range", the "measurable range" in which each pulse count period is set to be long in (5-4) is set to be narrow as a result. The "measurable range" in (5-5) in which each pulse count period is set to be short is set to be wide.

Under stable operating conditions in which the noise component is almost unchanged due to temperature fluctuations and the like, generally, by setting each pulse count period to be long, the measurement error can be suppressed, and the "measurement accuracy" of the particulate detection sensor can be set to be high. However, as described above, the longer each pulse count period is set, the narrower the "measurable range (dynamic range)" is set.

(setting of optimum pulse count period)

As factors of the occurrence of the measurement error, various factors such as (1) an intrinsic measurement error of the SPAD array, (2) a fluctuation in temperature, a fluctuation in external disturbance light noise, (3) an influence of a commercial power supply frequency (50Hz or the like), and (4) a variation in the existence probability of fine particles are considered. The optimal value of each pulse count period in which the measurement error of each pulse count value is minimum differs depending on the occurrence of the measurement error. Therefore, each pulse count period of the fine particle detection sensor 1 is preferably set so that the total measurement error becomes minimum in consideration of the optimal value (optimal range) of each occurrence factor. An example of setting the optimal value for each pulse count period is shown below.

First, when the measurement error factor is a change in noise components such as temperature fluctuation, fluctuation of external disturbance light, and commercial power supply frequency (50Hz or the like), only the pulse count value of the noise component affects each pulse count value. Here, when the noise component changes within one measurement period MT (once on + once off), the count value of each noise component is shifted between the first pulse count value PC1 in the on period ONT and the second pulse count value PC2 in the off period. As a result, the third pulse count value PC3 after subtraction varies with each measurement, and this variation becomes a measurement error.

In order to suppress the measurement error, it is desirable that the time of each pulse count period is set as short as possible. However, if each pulse count period is set shorter than the required period, the number of pulses of the scattered light component and the noise component that can be measured in one measurement period MT decreases, and as a result, the third pulse count value PC3 measured every time is shifted, and the measurement error increases.

Further, when the ambient temperature T changes with time, the influence of the change can be suppressed as the pulse count period is shorter, but if the pulse count period is made too short, a large number of pulse signals cannot be counted and the number of samples decreases, so the intrinsic measurement accuracy (sampling accuracy) decreases.

It is preferable that the pulse count period is set so that the measurement error based on the commercial power supply frequency is minimized. There are few situations where the ambient environment such as the ambient temperature T and the external disturbance light noise fluctuates at an extremely short cycle (1 μ s or less) all the time, and there are many cases where the fluctuation of the external disturbance light from the lighting devices such as the fluorescent lamp and the incandescent lamp fluctuates at the commercial power supply frequency (50Hz or the like). Here, in order to suppress a measurement error due to fluctuation caused by the commercial power supply frequency, it is preferable to set each pulse count period (or the driving period of the light emitting element 10) to about 20ms (50Hz) or to about an integral multiple of 20 ms. Thus, the fluctuations of the first pulse count value PC1 and the second pulse count value PC2 counted in the first pulse count period PT1 and the second pulse count period PT2, respectively, are averaged in time. As a result, the measurement error of the third pulse count value PC3 after subtraction caused by the commercial power supply frequency can be suppressed.

On the other hand, when the variation or fluctuation of the scattered light component due to the particle concentration or the like is considered as the error factor, it is desirable to set each pulse count period to be long. For example, when the concentration of microparticles is low (the number of microparticles is small), a case where the first pulse count period PT1 synchronized with the lighting period ONT is set to be short for a time period during which one microparticle passes through the detection region and is about 1/10 of the passage time (period) of one microparticle is considered. The frequency of receiving scattered light from the fine particles in the first pulse counting period PT1 in the 10-time pulse counting (measurement) is about 1 to 2 times, and the scattered light from the fine particles in the remaining 8 to 9 first pulse counting periods PT1 is completely unacceptable. Therefore, the measurement error per measurement becomes large. In order to suppress this measurement error, it is necessary to set the time of at least the first pulse count period PT1 to be longer than the time period during which one particle passes through the detection region.

When variations and fluctuations in scattered light components due to the particle concentration and the like are taken into consideration as factors of error, the optimum setting for each pulse count period changes in accordance with the target performance required for the particle detection sensor 1. For example, when the measurement accuracy of the particulate particle detection sensor 1 needs to be set high in the measurement when the particulate particle concentration is low, the first pulse count period PT1 needs to be set long in accordance with the measurement accuracy. This is because the lower the concentration of the target particles, the longer the time period for one particle to pass through the detection region. In contrast, when it is not necessary to set the measurement accuracy at low concentration to be high, the first pulse count period PT1 need not be set to be longer than the necessary period, and it is only necessary to set the measurement accuracy of each pulse count value to a level such as 20ms or the like, for example, so as not to extremely decrease.

As an example, as a target performance required for the fine particle detection sensor 1, it will be explained that the number density of fine particles is set to 0.01 particles/mm³The size of the detection region of the fine particles is set to a cubic region of 2mm × 2mm × 2mm, and the fine particles move at a speed of 1m/s in one direction, in the above case, the time period for one fine particle to pass through the detection region is about 25ms, and therefore, it is preferable to set the time period to be at least 25ms for each pulse count period, and further, in order to suppress the measurement error caused by the commercial power supply frequency (50Hz), it is preferable to set the time period to be an integral multiple of 20ms, and therefore, the greatest common divisor of both is taken, and each pulse count period is preferably set to about 100 ms.

The setting result of each pulse count period is merely an example, and each pulse count period is not limited to the setting. As described above, the optimum value of each pulse count period differs depending on the target performance (required specification) required for the particulate detection sensor 1, and therefore, it is preferable to set each pulse count period in accordance with the target performance such as the tolerance against the change in the operating conditions such as the measurement accuracy, the measurable range, and the ambient temperature T.

The waveform in fig. 5 (c) shows the third pulse count value PC3 in the one-time measurement period MT, and when it is necessary to further reduce (suppress) the measurement error, the averaging process of the third pulse count value PC3 that is measured a plurality of times and measured each time may be performed. For example, when the first pulse count period PT1 is the on period ONT and the second pulse count period PT2 is the off period OFFT, if each pulse count period is set to 100ms, the one-time measurement cycle is 200 ms. In this case, the particulate detection sensor 1 can output an average value of 5 measurement results at 1 second intervals.

In general, since the measurement error can be reduced by 1/√ N times by N times of averaging, the measurement error can be reduced by 1/√ 5 times by averaging in this case. When the measurement error needs to be further reduced, the measurement error can be reduced by further increasing the number of averaging times. However, when the number of averaging times is increased, the output rate (interval of output time) of the fine particle detection sensor 1 becomes longer and the response time is delayed, and therefore it is preferable that the number of averaging times is set to the optimum number of averaging times in accordance with the target performance (measurement accuracy, response time) required for the fine particle detection sensor 1.

Further, by performing a moving average process on the measurement result of any one measurement and setting the moving average value as the output value of the particulate detection sensor 1, it is possible to realize the particulate detection sensor 1 capable of further suppressing the measurement error and smoothing the measurement result.

The moving average processing is explained. For example, the M-time moving average processing is processing in which, after one measurement result (or output result) in any one measurement (or output), an average value including M-1 measurement results (or output results) in the latest (past) time is set as an output result in the measurement (or output). In the moving average processing, the processing of setting the average value as an output result is continuously repeated for each measurement (output).

By setting the output of the fine particle detection sensor 1 to a moving average value which is an average value based on the moving average processing, it is not necessary to set the output rate (output interval) to be long, and the number of averaging times can be increased. The moving average is smoothed by the latest measurement results (M-1). Therefore, for example, even when the measurement result has a large burst variation due to the incident of burst noise or instantaneous disturbance light noise, the influence of the burst measurement result variation is suppressed by performing the moving averaging process, as compared with the measurement result in the recent (past). As a result, malfunction of the device on which the particle detection sensor 1 is mounted can be suppressed.

However, since the moving average value output is smoothed by the latest measurement results (M-1 pieces), the response time of the particle detection sensor 1 becomes slow. It is preferable to select an optimal averaging process and output method according to the performance (measurement accuracy and response time) required for the fine particle detection sensor 1.

This will be specifically explained. For example, when the moving average processing is further performed 10 times for output values output at 1 second intervals (5 times of average value measurement), the processing is repeated at 1 second intervals with the average of any one output value and the output values of the last 9 times being the output result. Thus, the output was maintained at 1 second intervals, and 10 average values (average value of 50 measurements in total) were output. When the measured value increases from any time, the output value is smoothed by the past 9 times, and therefore the moving average output value does not change suddenly and changes gently. Thus, the influence (malfunction, etc.) on the instantaneous measurement value change due to noise, etc. is suppressed, but the response time to the measurement value change is slowed.

(Effect of the first embodiment)

As described above, in the first embodiment, the particle detection sensor 1 outputs the weak scattered light received by the SPAD array light receiving unit 30 as a pulse signal that is converted into a digital signal, and counts the pulses of the pulse signal. This makes it possible to realize a highly accurate particle detection sensor 1 that can receive weak scattered light without requiring a high-gain amplifier circuit.

Further, since the circuit configuration for amplifying the analog signal is not a high-gain amplification circuit, the particle detection sensor 1 having high electromagnetic noise resistance can be realized, and the number of components (materials) for electromagnetic noise countermeasure such as a shield case and a filter can be reduced. As a result, the cost of the particulate detection sensor 1 can be reduced.

Further, by subtracting the second pulse count value PC2 of the off period OFFT from the first pulse count value PC1 of the lighting period ONT of the light emitting element 10, it is possible to detect the particle concentration while suppressing the influence of the variation or fluctuation of the noise component.

Further, by setting each pulse count period (or drive period) to an optimum value, it is possible to realize the particulate detection sensor 1 that can cope with various target performances (required specifications) such as measurement accuracy, a measurable range, and a response time of the particulate detection sensor 1.

As one of the methods of the subtraction processing of each pulse count value in the first embodiment, a method implemented in the signal processing unit 50 of fig. 1 is considered. The signal processing unit 50 performs calculation of the particle concentration and averaging processing based on each pulse count value in addition to subtraction processing. Therefore, the operation method including the subtraction processing can be flexibly set without being limited to the above-described operation method, and therefore, reduction in circuit scale and improvement in response speed due to reduction in the number of operations and the like can be achieved.

Specifically, in addition to the method of performing subtraction of the pulse count value and the density calculation for each measurement, repeating the calculation a plurality of times, and finally averaging and outputting the result as in the first embodiment, for example, a method of averaging a plurality of measured values may be used. Specifically, the above method performs moving average processing and accumulation processing on the first pulse count value PC1 and the second pulse count value PC2, respectively, and updates each pulse count value (measurement result) for each measurement. Finally, the subtraction and density calculation of each averaged (integrated) pulse count value are performed only once, and the density detection result is output.

The former method requires data storage of a plurality of measurement values output for each measurement, and the corresponding data storage circuit such as SRAM requires the corresponding number of measurements. In contrast, with the latter method, since the averaged (or accumulated) pulse count value is updated only for each measurement, there is only one data storage circuit, and the number of circuits can be reduced.

(modification example)

A modification of the first embodiment will be described below. In the present modification, the pulse counter 40 of fig. 1 is configured by an up/down counter. That is, the down-count of the pulse count value is performed using an up/down counter.

In the present modification, the first pulse count period PT1 in the lighting period ONT is set to an up-count period (the count value is increased when the pulse signal is counted), and the second pulse count period PT2 in the off period OFFT is set to a down-count period (the count value is decreased when the pulse signal is counted). In other words, the up/down counter counts up the pulse signal in the lighting period ONT and counts down the pulse signal in the blanking period OFFT.

Thus, the pulse count value after one measurement is the same as the third pulse count value PC3 obtained by subtracting the second pulse count value PC2 from the first pulse count value PC1 described above. In this case, in contrast to the method of performing subtraction in the signal processing unit 50, the number of data output from the pulse counter 40 to the signal processing unit 50 can be reduced from two to one, and thus there is an effect that circuit elements such as a data storage circuit in the signal processing unit 50 can be reduced. However, the circuit scale of the pulse counter 40 increases in comparison with the first embodiment.

As described above, although there is no difference in the final result itself whether the subtraction method of the first embodiment or the subtraction method of the modification of the first embodiment is used, it is preferable to select the optimum subtraction method in consideration of the circuit scale, the response speed, the cost aspect, the size, and the like of the fine particle detection sensor 1.

[ second embodiment ]

In the second embodiment, a temperature correction method for ambient temperature change, a correction method for characteristic shift due to manufacturing variation, and a method for suppressing measurement error due to stray light components will be described.

Fig. 6 is a block diagram showing an example of a schematic configuration of a particulate detection sensor 1A according to a second embodiment of the present invention. In the second embodiment, the constituent elements of the particle detection sensor 1 shown in fig. 1 are provided with a temperature detection unit 70, a voltage setting unit 80, and a storage unit 90. The temperature detection unit 70 detects the ambient temperature T of the SPAD array light receiving unit 30. The voltage setting unit 80 sets the reverse bias voltage VHV to be supplied to the SPAD array.

The storage unit 90 stores initial setting values, calculation coefficients, and the like of the particulate detection sensors 1A. The storage unit 90 is a storage unit using a nonvolatile memory or the like, and as the nonvolatile memory, an EEPROM (registered trademark), fuse trimming (fuse trimming) or the like is considered, but the present embodiment is not limited to the above configuration. The basic concentration detection method of the particulate detection sensor 1A is the same as that of the first embodiment. Specifically, the particle detection sensor 1A calculates the particle concentration by subtracting the count value of each pulse counted in synchronization with the turning on and off of the light emitting element 10, similarly to the particle detection sensor 1.

(adjustment of reverse bias voltage due to ambient temperature variation)

First, a method of adjusting the reverse bias voltage VHV (see fig. 2 (a)) supplied to the SPAD array when the ambient temperature T changes will be described. When the ambient temperature T of the SPAD array changes, the breakdown voltage of the avalanche photodiode APD1(SPAD) (see fig. 2 a) constituting the SPAD array light receiving unit 30 changes depending on the ambient temperature T. Therefore, when the reverse bias voltage VHV supplied to the SPAD array is set to be constant, the avalanche multiplication factor of SPAD changes due to a change in the ambient temperature T, and as a result, the number of output pulses of the SPAD array light-receiving unit 30 changes greatly. In particular, when the ambient temperature T becomes high, the measured pulse count values may increase greatly, and thus the particle concentration may not be detected normally. Therefore, a mechanism for adjusting the reverse bias voltage VHV supplied to the SPAD array in accordance with a change in the ambient temperature T is required.

Here, the third control signal TS3 in fig. 6 is a signal for controlling the voltage setting period VT during which the voltage setting unit 80 sets the reverse bias voltage VHV. The third control signal TS3 indicates the voltage setting period VT described above. The fourth control signal TS4 is a signal for controlling the temperature detection period TT during which the temperature detector 70 detects the temperature. The fourth control signal TS4 indicates the above-described temperature detection period TT. As the configuration of the temperature detection unit 70 in fig. 6, for example, a configuration (a thermistor) for measuring a temperature change in a forward voltage value of a PN junction diode, a configuration for measuring a temperature change in a resistor such as a thermistor, and the like can be considered. The configuration and type of the temperature sensor are not limited.

The adjustment mechanism of the reverse bias voltage VHV in the second embodiment of fig. 6 will be explained. First, the ambient temperature T is detected at the timing of the fourth control signal TS4 (temperature detection period) in the temperature detection unit 70, and the optimum reverse bias voltage VHV set value is determined based on the detection result of the ambient temperature T in the signal processing unit 50. Then, at the timing of the third control signal TS3 (voltage setting period), the reverse bias voltage VHV is updated and set to the optimum value in the voltage setting unit 80, and the optimum reverse bias voltage VHV is supplied to the SPAD array light-receiving unit 30 by the voltage setting unit 80.

Further, by performing the following (1) and (2), the pulse count value in the one-time measurement period MT can be stably measured. (1) The temperature detection period TT controlled by the fourth control signal TS4 and the voltage setting period VT controlled by the third control signal TS3 are set in synchronization with the measurement period MT. (2) The voltage setting period VT update timing controlled by the third control signal TS3 is set to the first or last of the measurement period MT, and is not set in each pulse count period. This is because, with this, the reverse bias voltage VHV does not change abruptly during at least one measurement period MT.

Further, since there is a possibility that measurement errors of the measured temperature value may occur when the temperature detector 70 (a diode or the like) is irradiated with the projection light E1 from the light emitting element 10, the temperature detection period TT is preferably set at least within the light-off period OFFT of the light emitting element 10.

Fig. 7 is a diagram showing an example of an operation waveform of the particle detection sensor 1A. In fig. 7, the first control signal TS1 and the second control signal TS2 are set in the same manner as in fig. 4, and are repeatedly turned on and off at Duty 50%, and pulse count periods are set for the on time and the off time, respectively. The third control signal TS3 is set to H level immediately before the first pulse count period PT1 of the lighting period ONT starts. The optimum reverse bias voltage VHV is updated/set during the period in which the third control signal TS3 is at the H level.

The fourth control signal TS4 is set to H level after the second pulse count period PT2 of the blanking period OFFT ends. While the fourth control signal TS4 is at the H level, the ambient temperature T is detected by the temperature detection unit 70. As described above, the signal processing unit 50 determines the optimum reverse bias voltage VHV set value using the detection result of the ambient temperature T measured during the temperature detection period TT. In the next measurement, the setting of the reverse bias voltage VHV is updated in the voltage setting period VT in which the third control signal TS3 is at the H level.

Thus, the reverse bias voltage VHV does not change during one measurement period MT, and a constant value of the reverse bias voltage VHV is supplied to the SPAD array during the measurement period MT (during each pulse count period). Further, the reverse bias voltage VHV can be updated to an optimal value for each measurement period MT, and the particle detection sensor 1A that can operate in a wide temperature range can be realized.

Fig. 8 is a graph showing an example of setting the optimum reverse bias voltage VHV for the ambient temperature T. In the case of the setting example shown in fig. 8, a method of determining an optimum value of the reverse bias voltage VHV from a detection result of the ambient temperature T by determining a predetermined table in advance is employed. Specifically, when the ambient temperature T is in the range of T1 to T2, the voltage set value of the reverse bias voltage VHV is V1. Needless to say, the table shown in fig. 8 is not necessarily limited, and the table and the function for determining the optimum value of the reverse bias voltage VHV are preferably determined in accordance with the characteristics of the avalanche photodiodes APD constituting the SPAD array to be used.

(adjustment of third pulse count value based on ambient temperature variation)

Next, a method of correcting the gradient of the third pulse count value PC3 with respect to the particle concentration when the ambient temperature T changes will be described. Fig. 9 (a) is a graph showing an example of the dependency of the first pulse count value PC1 on the particle concentration at an arbitrary temperature. In fig. 5, the dependency of the first pulse count value PC1 on the particle concentration is shown as a linear characteristic (ratio). However, as described above, when the particle concentration is actually increased and the pulse count value is actually increased, the frequency of simultaneous avalanche multiplication of the SPAD cells constituting the SPAD array is increased, and therefore the linearity of the first pulse count value PC1 with respect to the particle concentration is decreased. Therefore, as shown in fig. 9 (a), the first pulse count value PC1 is saturated as the particle concentration increases. In other words, the first pulse count value PC1 has a disproportionate dependence on the particle concentration.

Even if the ambient temperature T varies, the reverse bias voltage VHV of the SPAD array is automatically adjusted according to (the detection result of) the ambient temperature T as described above, and the avalanche multiplication rate of the SPAD array is optimized. Therefore, the particle concentration dependency of the first pulse count value PC1 can be optimized to have the same characteristics as those in fig. 9 (a). However, as the ambient temperature T becomes high, the dependency (gradient) of the pulse count value on the particulate matter concentration changes as a result of the ambient temperature T. This is because the number of noise pulses (the number of dark pulses) caused by the increase of thermally generated carriers increases, and therefore the count value (intercept) when the particle concentration is zero, that is, the count value of the noise component increases.

This case will be equivalently described with reference to the circle and the solid/dashed line in fig. 9 (a). The leftmost circle represents a pulse count value of a noise component at a certain temperature, the right (middle) circle represents a pulse count value of a noise component at a temperature higher than the certain temperature, and the rightmost circle represents a pulse count value of a noise component at a higher temperature. The slope at each circle equivalently represents the gradient of the pulse count value versus the particle concentration at each temperature. It follows that the gradient decreases as the ambient temperature T increases.

Fig. 9 (b) is a graph showing an example of the temperature dependence of the third pulse count value PC3 with respect to the particle concentration. In fig. 9 (b), (9-1) shows the temperature dependence at a high temperature, (9-2) shows the temperature dependence at a normal temperature (e.g., 25 ℃), and (9-3) shows the temperature dependence at a low temperature. For the sake of simplicity of explanation, only the temperature dependence described above is shown in the lower concentration region, and the concentration dependence (slope) of the third pulse count value PC3 is shown as a linear characteristic.

The count value of the noise component is removed by subtracting the second pulse count value PC2 from the first pulse count value PC1, and thus the noise component (intercept) does not occur in the third pulse count value PC 3. However, as described above, the slope (see fig. 9 (a)) differs depending on the ambient temperature T. Therefore, when the ambient temperature T changes, the particle concentration calculated from the measured value of the third pulse count value PC3(PC in fig. 9 b) becomes different results (D1 to D3), and the difference in the detection results (D1 to D3) becomes a measurement error for the ambient temperature T. Therefore, in order to improve the accuracy of measuring the particulate concentration with respect to the change in the ambient temperature T, it is necessary to perform temperature correction with respect to the change in the ambient temperature T with respect to the measurement result. The method of correcting the temperature of the measurement result will be described below.

(temperature correction)

The particulate detection sensor 1A calculates a second calculation coefficient x2 by performing temperature correction using a preset temperature correction coefficient y1 and the measurement result of the ambient temperature T measured by the temperature detection unit 70 with respect to a preset first calculation coefficient x1 for calculating the concentration of the particulate, and calculates the concentration of the particulate using a third pulse count value PC3 obtained by subtracting the second pulse count value PC2 from the second calculation coefficient x2 and the first pulse count value PC 1.

Fig. 10 is a graph showing an example of the temperature dependence of the gradient α (T) of the third pulse count value PC 3. For simplicity of explanation, the gradient α (T) is set to a linear function (linear characteristic) of the temperature T. Here, assuming that the gradient α (T) with respect To the temperature T is a gradient β (constant) and the gradient at the reference temperature To is α (To), the relationship between the gradients α (T), T, and β can be expressed by the following equation.

α (T) ═ α (To) + (T-To) × β (formula 3-a)

Here, assuming that the particulate particle concentration D is D, the relationship between the particulate particle concentration D at the measured temperature T and the third pulse count value PC3(PC3(T)) is the following (expression 3-b), and substituting (expression 3-a) into (expression 3-b) results in the particulate particle concentration D being the following (expression 3-c).

PC3(T) ═ α (T) × D (formula 3-b)

D ═ PC3(T)/α (T) ═ PC3(T)/(α (To) + (T-To) × β) (formula 3-c)

According To this (expression 3-c), the temperature-corrected microparticle concentration D can be detected using the third pulse count value PC3(PC (T)) at the measured temperature T, the temperature detection result T (temperature T) measured by the temperature detection unit 70, the reference temperature To, the gradient α (To) at the reference temperature To, and the slope β of the gradient α (T). That is, the measured third pulse count value PC3 and the calculation coefficient (gradient α (T) (second calculation coefficient x2)) after the temperature correction can be used to detect the particle concentration D accurately without depending on the ambient temperature T.

Here, To, α (To), and β are temperature correction coefficients y1 for temperature-correcting the arithmetic coefficients used for the arithmetic operation, and are stored in the storage unit 90 shown in fig. 6, for example, and used as the temperature correction coefficients y1 in the arithmetic operation in the signal processing unit 50. Note that, in the above description, α (T) is assumed to be a linear function of T for the sake of simplicity, but the same correction can be realized even in the case of a higher-order function of a quadratic function or more.

When the temperature correction coefficient y1 differs for each fine particle detection sensor 1A due To variations in manufacturing or the like, the measurement is performed at ambient temperatures T (including the reference temperature To) of at least two points or more in the inspection step during manufacturing. Then, β is calculated from the measurement result of the gradient α (T) of the particulate concentration at each measurement temperature, and each measured coefficient is stored as an initial set value in the storage unit 90 for each particulate detection sensor 1A. This makes it possible to correct the deviation of the ambient temperature T dependency due to the manufacturing variation, and as a result, it is possible to further suppress the measurement error of the particulate concentration with respect to the change in the ambient temperature T.

However, although the measurement error with respect to the ambient temperature change can be suppressed by performing the correction with respect to the manufacturing variation, the inspection under the temperature condition of two or more points is required in the inspection process, and the manufacturing cost of the particulate detection sensor 1A may increase. Therefore, it is preferable to select whether or not to perform the manufacturing variation correction method according to the target (measurement accuracy, cost) required for the particulate detection sensor 1A. When the temperature correction coefficient y1 does not substantially change for each fine particle detection sensor 1A due to manufacturing variations or the like, the temperature correction coefficient may be added as a fixed value to the arithmetic expression of the signal processing unit 50, or may be stored in a memory such as a microcomputer when arithmetic processing is performed using a microcomputer or the like external to the fine particle detection sensor 1A.

As described above, in the configuration of the second embodiment, the particulate detection sensor 1A that operates in a wide temperature range and can measure an accurate particulate concentration with respect to a change in the ambient temperature T can be realized.

(adjustment for manufacturing variations)

Next, a method of correcting the manufacturing variations of the fine particle detection sensor 1A will be described. In general, the SPAD array light-receiving portion 30 is formed on a semiconductor substrate. Therefore, due to manufacturing variations such as crystal defects of semiconductors and variations in impurity concentration, the avalanche multiplication factor and noise components (dark pulses and the like) may vary for each SPAD that is configured, and the accuracy of measuring the particle concentration may be lowered.

In addition, the light-emitting element 10 may have variations in optical characteristics such as the amount of emitted light and directivity due to manufacturing variations, and similarly may have a reduced measurement accuracy. Further, since the breakdown voltage of the SPAD array light receiving unit 30 varies and the reverse bias voltage VHV is manufactured by the voltage setting unit 80, the reverse bias voltage VHV supplied to the SPAD array light receiving unit 30 is not optimized, and similarly, the measurement accuracy may be lowered and the measurement may not be possible.

Therefore, in order to improve the accuracy of measuring the particulate concentration, it is preferable to have a configuration in which the measurement error due to the manufacturing variation and the deviation of the operating condition can be adjusted at the time of manufacturing. An example of a method for realizing this configuration is described below.

(optimization of pulse count value)

A method of optimizing the pulse count value of the noise component will be described. Fig. 11 (a) is a graph showing an example of the dependence of the first pulse count value PC1 and the second pulse count value PC2 on the number of SPAD cells. In fig. 11 (a), (11-1) shows an example of the dependency of the first pulse count value PC1 on the number of SPAD cells in the lighting period, and (11-2) shows an example of the dependency of the second pulse count value PC2 on the number of SPAD cells in the blanking period. In fig. 11 (a), the particle concentration, the amount of emitted light, and each pulse count period are fixed to a certain value.

As shown in (11-2) of fig. 11 (a), the number of SPAD cell cells in which the pulse count value of the noise component is optimal is selected in the inspection step at the time of manufacturing, by increasing or decreasing the pulse count value of the noise component in accordance with the increase or decrease in the number of SPAD cell cells. The number of SPAD cells is selected by the second adjustment signal S2 output from the control unit 60 shown in fig. 6. The optimization result of the number of SPAD cells (second adjustment signal S2) is stored in the storage section 90 as an initial setting value.

The method of selecting the number of SPAD cell is not particularly limited, and may be a selection adjustment in which the number is increased or decreased uniformly from the entire SPAD array, or an adjustment method in which a predetermined area is selected to be valid or invalid. In other words, the second adjustment signal S2 is a signal for adjusting the operating conditions of the SPAD array light receiving unit 30, and the SPAD array light receiving unit 30 may have a function of setting the validity and invalidity of each SPAD cell constituting the SPAD array light receiving unit 30 based on the second adjustment signal S2. The noise component is corrected to an optimum value, as described above, in order to change the gradient α according to the magnitude of the count value of the noise component.

(optimization of gradient. alpha.)

A method of optimizing the gradient a of the pulse count value is explained. Fig. 11 (b) is a graph showing an example of the dependency of the first pulse count value PC1 and the second pulse count value PC2 on the amount of emitted light. In fig. 11 (b), (11-1) shows an example of the dependency of the first pulse count value PC1 on the amount of emitted light in the lighting period, and (11-2) shows an example of the dependency of the second pulse count value PC2 on the amount of emitted light in the blanking period.

In fig. 11 (b), the particle concentration and the pulse count period are fixed to certain values, and the number of SPAD cell cells is set to a value optimized in the above-described manner. Here, (11-1) the pulse count value increases for an increase in the amount of emitted light because the pulse count value contains a scattered light component from the fine particles, whereas (11-2) the pulse count value is a constant value because it is a pulse count value of only a noise component. By utilizing this dependency, in the inspection step at the time of manufacturing, the light emission amount is selected so that the gradient α of the pulse count value becomes an optimum value. The amount of emitted light is adjusted in the driving section 20 of the light emitting element 10 in accordance with the first adjustment signal S1 output from the control section 60 shown in fig. 6. In other words, the first adjustment signal S1 is a signal for adjusting the operating condition of the driving section 20, and the driving section 20 has a function of adjusting the light emission amount of the light emitting element 10 in accordance with the first adjustment signal S1. The first adjustment signal S1 is stored as an initial setting value in the storage section 90.

(optimization of reverse bias Voltage)

A method for optimizing the reverse bias voltage VHV supplied to the SPAD array light receiving unit 30 will be described. Fig. 11 (c) is a graph showing an example of the dependence of the first pulse count value PC1 and the second pulse count value PC2 on the reverse bias voltage. In fig. 11 (c), (11-1) shows an example of the dependency of the first pulse count value PC1 on the reverse bias voltage VHV in the lighting period, and (11-2) shows an example of the dependency of the second pulse count value PC2 on the reverse bias voltage VHV in the quenching period.

If the reverse bias voltage VHV is too large compared to the optimum range, the avalanche multiplication rate becomes too large, the count value of each pulse extremely increases, and normal measurement cannot be performed. If the reverse bias voltage VHV is too small compared to the optimum range, the reverse bias voltage VHV is lower than the breakdown voltage of the SPAD, and the operation is performed in the linear mode rather than the geiger mode. Therefore, the pulse count value is extremely reduced, and normal measurement cannot be performed.

The reason why the reverse bias voltage VHV is shifted from the optimum range is the manufacturing variation of the SPAD cell and the voltage setting unit 80 as described above, and the normal measurement can be realized by setting the reverse bias voltage VHV to the optimum range. As a specific method, in the inspection step during manufacturing, the dependence of the reverse bias voltage VHV of each pulse count value is measured, and the reverse bias voltage VHV at which each pulse count value becomes an optimum value is selected. For example, as shown in fig. 11 (c), in the inspection step, the normal operating range of the reverse bias voltage VHV may be roughly detected from the measurement result of each pulse count value, and the intermediate value may be selected as the reverse bias voltage VHV. Here, the reverse bias voltage VHV is set to avoid an extreme increase or decrease in the pulse count value, and therefore may be set roughly.

The adjustment of the reverse bias voltage VHV is performed as follows: the voltage setting unit 80 sets the reverse bias voltage VHV (initial value) in accordance with the third adjustment signal S3 output from the control unit 60 shown in fig. 6, and supplies the reverse bias voltage VHV to the SPAD array light receiving unit 30. In other words, the third adjustment signal S3 is a signal for adjusting the operating condition of the voltage setting unit 80, and the voltage setting unit 80 has a function of adjusting the reverse bias voltage VHV in accordance with the third adjustment signal S3. The third adjustment signal S3 determined at the time of the examination is stored as an initial setting value in the storage unit 90. The value of the reverse bias voltage VHV stored as the initial set value is the optimal reverse bias voltage VHV at the reference temperature To, and the table of the reverse bias voltage VHV with respect To the ambient temperature T described in fig. 8 is preferably adjusted in accordance with the result of the correction at the reference temperature To.

As described above, the set values of the number of SPAD cells, the light emission amount, and the reverse bias voltage VHV are adjusted according to the inspection result in the inspection step, and the first adjustment signal S1 to the third adjustment signal S3 for adjusting the set values are stored in the storage unit 90 as initial set values. This can suppress measurement errors due to manufacturing variations and measurement value shifts for each particulate detection sensor 1A, and can realize a particulate detection sensor 1A having high particulate concentration measurement accuracy.

(adjustment of manufacturing variations for temperature correction coefficient)

Next, an example of a specific procedure of measurement and adjustment when the manufacturing variation of the temperature correction coefficient with respect to the gradient of the ambient temperature T is adjusted in addition to the manufacturing variation adjustment will be described.

First, in the inspection step at the time of manufacture, the inspection temperature To (reference temperature To) and the dependence of the reverse bias voltage VHV of the second pulse count value PC2 when the particle-free state is extinguished are measured. Here, measurement in a state where fine particles are present may be performed. Based on the measurement result, the normal operating range of the reverse bias voltage VHV in which the second pulse count value PC2 has not increased or decreased extremely is detected, the intermediate value thereof is set as the set value VHVo of the reverse bias voltage, and the value thereof is stored in the storage unit 90 as the third adjustment signal S3.

Next, the dependency of the number of SPAD cells of the second pulse count value PC2 is measured at the inspection temperature To (reference temperature To), the reverse bias voltage VHVo, and the particulate-free state. Here, measurement in a state where fine particles are present may be performed. From the measurement result, the number Co of SPAD cell units in which the second pulse count value PC2 (noise component) becomes the optimum value is determined, and the value is stored as the second adjustment signal S2 in the storage unit 90.

Next, two measurements of a state without particles (particle concentration 0) and a state with particles (particle concentration Do as a reference) are performed at the inspection temperature To (reference temperature To), the reverse bias voltage VHVo, and the number of SPAD cells Co. From the two measurement values, the gradient α (To) of the first pulse count value PC1 or the third pulse count value PC3 is measured, and the dependency of the gradient α (To) on the amount of emitted light is measured. From the measurement result, the light emission amount Lo at which the gradient α (To) becomes the optimal value is determined, and the value is stored as the first adjustment signal S1 in the storage unit 90.

Next, the manufacturing variation of the temperature correction coefficient of the gradient α (T) is adjusted. Since the gradient α (To) in the reference temperature To is measured at the time of the gradient correction, the gradient α (T1) under the setting conditions (the reverse bias voltage VHVo (T1), the number of SPAD cells Co, and the light emission amount Lo) is measured at the other inspection temperature T1. Here, the reverse bias voltage VHVo (T1) is a value of the reverse bias voltage automatically adjusted for the reverse bias voltage VHVo that is an initial set value at the reference temperature To based on fig. 8 in the measurement at the inspection temperature T1. As shown in fig. 10, if the temperature dependency of α (T) is linear, the slope β of the gradient α (T) with respect To the temperature can be calculated from the measured values of the gradient α (To) and the gradient α (T1). The slope β, the reference temperature To, and the gradient α (To) of the reference temperature are stored in the storage unit 90 as a temperature correction coefficient of an arithmetic coefficient α (T) (third arithmetic coefficient x3) To be described later. With the above adjustment method, the measurement error due to the manufacturing variation can be suppressed in the inspection step at the time of manufacturing.

Here, the reference temperature To stored in the storage unit 90 is a temperature detection result To _1 at the inspection temperature To (reference temperature To). The reason why the temperature detection result To _1 at the inspection temperature To needs To be stored is as follows. That is, the measured value To (inspection temperature To) is merely the result of measurement by the temperature detection unit 70, and since there is a variation in the measured value To (inspection temperature To) for each fine particle detection sensor 1A, it is necessary To store the temperature detection result To _1 at the inspection temperature To for each fine particle detection sensor 1A in advance. In other words, no absolute temperature output needs to be calculated. According to such a method, correction including manufacturing variations of the temperature detection unit 70 can be realized.

(suppression of measurement error due to stray light component)

Next, the suppression of the measurement error due to the pulse count value of the stray light component occurring in the subtracted third pulse count value PC3 will be described. Here, the stray light represents unnecessary light which is incident on the SPAD array light-receiving unit 30 from light projected from the light-emitting element 10, unlike a scattered light component which is scattered by fine particles and incident on the SPAD array light-receiving unit 30. The stray light component is counted by, for example, (1) the projection light E1 from the light emitting element 10 being reflected by the housing, cover, or the like of the particle detection sensor 1A and entering the SPAD array light receiving unit 30 or (2) the light projected from the light emitting element 10 directly entering the SPAD array light receiving unit 30. Ideally, it is preferable that the SPAD array light receiving unit 30, the light emitting element 10, and the detection region are arranged so that such stray light components are 0 (zero) or as small as possible. However, since it is practically difficult to realize this, a mechanism for correcting or suppressing the measurement error due to the pulse count value of the stray light component is necessary.

Fig. 12 (a) is a graph showing an example of the dependency of the third pulse count value PC3 on the particle concentration when stray light enters the SPAD array light receiving unit 30. The stray light component takes a constant value with respect to the particle concentration regardless of the particle concentration, similarly to the pulse count value of the noise component described in fig. 5 and the like. As described above, the stray light component is generated by the reflected light from the housing or the sensor cover of the particle detection sensor 1A and the direct light from the light emitting element 10 entering the SPAD array light receiving unit 30. Therefore, the pulse count value of the stray light component may vary in each particle detection sensor 1A due to variations in the mounting position of the components during manufacturing, and the like.

As a method of suppressing the measurement error due to the pulse count of the stray light component, for example, in the inspection step at the time of manufacture, the fourth pulse count value PC4 having only the stray light component is measured by performing measurement in a particle-free state (at least one measurement). At the time of the particulate concentration measurement, the fourth pulse count value PC4 may be further subtracted from the measured third pulse count value PC3, and the particulate concentration may be calculated and detected in the signal processing unit 50. The particle concentration D can be expressed by the following equation, taking the gradient α of the third pulse count value PC3 as an arithmetic coefficient (third arithmetic coefficient x 3).

PC3 ═ α × D + PC4 (formula 4-a)

D ═ PC3-PC4)/α (formula 4-b)

The fourth pulse count value PC4 measured in the inspection step is stored as an initial setting value in the storage unit 90 in fig. 6, and is used as the fourth arithmetic coefficient x4 when the signal processing unit 50 calculates the fourth pulse count value PC 4. This method can suppress a measurement error due to the fourth pulse count value PC4 of the stray light component including manufacturing variations, and can suppress a reduction in measurement accuracy even in the structure of the particulate detection sensor 1A in which the stray light component cannot be completely removed.

The case where the above method is effective is limited to the case where the fourth pulse count value PC4 due to stray light components is small and does not change greatly due to the ambient temperature T. Fig. 12 (b) is a graph showing an example of the temperature dependence of the third pulse count value PC3 on the particle concentration when the temperature dependence of the stray light component is large. In fig. 12 (b), (12-1) shows the temperature dependence at a high temperature, (12-3) shows the temperature dependence at a low temperature, and (12-2) shows the temperature dependence at an intermediate temperature (e.g., room temperature) between (12-1) and (12-3).

The difference between the stray light component and the scattered light component is only whether or not it depends on the particle concentration. The scattered light component depends on the particle concentration, while the stray light component does not depend on the particle concentration. That is, the temperature dependence of the pulse count value of the stray light component is the same as the temperature dependence of the pulse count value of the scattered light component. Therefore, when the temperature dependence of the gradient α (T) is as shown in fig. 10, the temperature dependence of the third pulse count value PC3 with respect to the particle concentration when the temperature dependence of the stray light component is large is as shown in fig. 12 (b). In such a case, the measurement error due to stray light can be suppressed to some extent by the above-described method (the fourth pulse count value PC4 obtained by subtracting the stray light component at the time of inspection from the third pulse count value PC 3).

However, the above method alone is not sufficient when it is necessary to set the measurement accuracy of the particulate concentration to be high for all the ambient temperatures T. In such a case, as described below, a method of performing calculation processing of the particle concentration after temperature correction of the fourth pulse count value PC4 of the stray light component is preferable.

First, the third pulse count value PC3 at the measured temperature T is PC3(T), the fourth pulse count value PC4 of the stray light component is PC4(T), and the gradient of the third pulse count value PC3 is α (T). When PC3(T), PC4(T), and α (T) are used as arithmetic coefficients and the microparticle concentration is D, the relationship can be expressed by the following equation.

PC3(T) ═ α (T) × D + PC4(T) (formula 4-c)

Here, as shown in fig. 12 c, when the ambient temperature T is a linear function (linear characteristic), the ambient temperature dependency of the PC4(T) can be expressed by the following equation if the slope with respect To the temperature of the PC4(T) is γ, and the fourth pulse count value PC4 at the reference temperature To is PC4 (To).

PC4(T) ═ PC4(To) + (T-To) × γ (formula 4-d)

Here, the gradient α (T) of PC3(T) with respect to the microparticle concentration can be represented by the above (expression 3-a), and therefore, the microparticle concentration D can be calculated by the following equation from the (expression 3-a), (expression 4-c), and (expression 4-D).

D＝{PC3(T)-PC4(T)}/α(T)

(α (To) + (T-To) × β) (formula 4-e) { PC3(T) -PC4(To) - (T-To) × γ }/(α (To) + (T-To) × β)

In the above expression (expression 4-e), the gradient α (T) of PC3(T) is used as an arithmetic coefficient (third arithmetic coefficient x 3). In the above expression (expression 4-e), the calculation is performed using the temperature detection result T at the ambient temperature T, the PC3(T), which is the measurement result of the third pulse count value PC3 at the ambient temperature T, and the temperature correction coefficients (constants) of the PC4(To), the gradients α (To), To, β, and γ stored in the storage unit 90. According to the above expression (expression 4-e), even in the fine particle detection sensor 1A in which incidence of the stray light component is not negligible, temperature correction including the temperature dependency of the stray light component can be realized.

In addition, when the temperature correction coefficient differs (varies) for each of the fine particle detection sensors 1A due to variations in manufacturing or the like, it is possible to correct a variation in the ambient temperature T dependency caused by the manufacturing variations by performing the following processing. That is, in the inspection step at the time of manufacture, the ambient temperature T (including the reference temperature) is measured using at least two points or more. Then, the slope β and the slope γ are calculated from the gradient α at each measurement temperature and the measurement result of the fourth pulse count value PC4, and the measured constants are stored in the storage unit 90 for each fine particle detection sensor 1A. This makes it possible to correct a deviation in the ambient temperature T dependency due to manufacturing variations, and as a result, the accuracy of measuring the particulate concentration can be further improved.

However, although the measurement accuracy can be further improved by performing the correction for the manufacturing variation, the inspection under the temperature condition of two or more points is required in the inspection process, and the manufacturing cost of the sensor may increase. Therefore, it is preferable to select whether or not to implement the manufacturing variation correction method in accordance with target specifications (measurement accuracy, cost) required for the particulate detection sensor 1A.

[ third embodiment ]

In the second embodiment, a correction method in the case where stray light is incident on the SPAD array light receiving unit 30 is described. However, when the stray light component incident on the SPAD array light receiving unit 30 is extremely larger than the scattered light component, the pulse count value increases as a whole, and the linearity with respect to the particle concentration decreases. As a result, the measurement accuracy required for the particulate detection sensor 1A may not be obtained even by using the above-described suppression method. Accordingly, the SPAD array light receiving unit 30 of the particle detection sensor 1A is preferably configured to be able to be adjusted to avoid the incident of the stray light component or the influence of the stray light component as small as possible. As a third embodiment, an example for realizing such a configuration is described below.

As shown in fig. 6, the particle detection sensor 1B includes an SPAD array light receiving unit 30B instead of the SPAD array light receiving unit 30. The SPAD array light receiving unit 30B can be selected by being divided into at least two regions. The stray light component incident on the SPAD array light receiving unit 30B is rarely incident on the entire SPAD array at the same intensity, and the stray light component is strongly incident on a certain region and weakly incident on other regions in many cases. In addition, the distribution of the incident intensity of stray light in each SPAD array region often varies depending on the mounting position shift of each component element due to manufacturing variations. Thus, a specific region of the SPAD array in which the incidence of the stray light component is small and the incidence of the scattered light component is large is selected for each particle detection sensor 1B and measured, and the particle detection sensor 1B capable of reducing the influence of the stray light component as much as possible can be realized. Specifically, when the stray light component is N and the scattered light component is S, the region of the SPAD array having the highest S/N ratio is selected and measured, and thereby the particle detection sensor 1B capable of reducing the influence of the stray light component as much as possible can be realized.

The above method will be described with reference to fig. 13. Fig. 13 is a diagram illustrating an example of a method for selecting a measurement region of the SPAD array light-receiving section 30B of the particle detection sensor 1B according to the third embodiment of the present invention. The SPAD array shown in fig. 13 is composed of SPAD cell cells of 12 × 12(144 cells). The SPAD array light receiving unit 30B first divides the 3 × 3(9 cells) area into reference areas BA0 to BA15(16 areas). In the particle concentration measurement, the SPAD array light receiving unit 30B performs measurement using a6 × 6(36 cells) region in which a2 × 2 region (4 regions to be measured) of the reference region BA is selected, as indicated by a dotted line. The region in which this measurement is performed is set as a measurement region MA.

In the inspection step at the time of manufacture, measurement areas of 2 × 2 4 areas of the reference area BA are sequentially selected and measured. Specifically, first, the measurement area MA1 including the reference area BA0, the reference area BA1, the reference area BA4, and the reference area BA5 is measured. Next, measurement regions including the reference region BA1, the reference region BA2, the reference region BA5, and the reference region BA6 are measured, and the process is repeated. Finally, a measurement area MA2 including the reference area BA10, the reference area BA11, the reference area BA14, and the reference area BA15 is measured.

For measurement, as shown in fig. 14 (a) and 14 (b), in each measurement region MA, measurement is performed in the case where the particle concentration is 0 (zero) and measurement is performed in the case where the particle concentration is a certain reference concentration Do, the ratio of the scattered light component S to the stray light component N is calculated, and the measurement region MA where the S/N ratio is maximum is specified. Here, fig. 14 (a) is a diagram showing an example of the relationship between the first pulse count value PC1 and the particle concentration when the S/N ratio is relatively large. Fig. 14 (b) is a diagram showing an example of the relationship between the first pulse count value PC1 and the particle concentration when the S/N ratio is relatively small. The stray light component N is the measurement result itself with the particle concentration of 0 (zero), and the scattered light component S is a value obtained by subtracting the stray light component N from the measurement result at the reference concentration Do.

The measurement area MA of the SPAD array determined by the measurement is set based on the second adjustment signal S2 output from the control unit 60 shown in fig. 6. The second adjustment signal S2 is stored as an initial setting value in the storage section 90. This enables measurement of scattered light E2 in the SPAD region where the influence of the stray light component is minimal, and thus enables realization of the particulate detection sensor 1B that suppresses the influence of the stray light component as much as possible. Note that, when the third pulse count value PC3 is PC3(0) when the particle concentration is 0 (zero) and the pulse count value at the reference concentration Do is PC3(Do), the S/N ratio can be calculated easily by the following expression (expression 5-a). Since the above processing is intended to determine the magnitude of the S/N ratio, a more simplified (equation 5-b) may be used as the determination equation.

S/N ═ PC3(Do)/PC3(0) -1 (formula 5-a)

S/N ═ PC3(Do)/PC3(0) (formula 5-b)

In addition to the setting of the SPAD region, the adjustment in the inspection step including the adjustment of the manufacturing variation and the temperature correction described above is preferably performed in the order of (1) to (5) shown below. (1) Adjustment of the reverse bias voltage VHV, (2) selection of the measurement region MA of the SPAD array (stray light adjustment), (3) adjustment of the number of SPAD cells (noise count value adjustment), (4) adjustment of the light emission amount (slope adjustment), (5) temperature correction (adjustment of the temperature correction coefficient of the slope and the stray light, and storage of the stray light initial value). By performing such adjustment of the procedure, the characteristics of the particle detection sensor 1B can be uniquely specified, and therefore, the inspection time in the inspection process can be reduced as much as possible. For example, in the case of the last implementation (2), since the set values adjusted up to this point are shifted, it is necessary to perform the setting of (3) to (5) again, and therefore the inspection time becomes long, resulting in an increase in cost.

Although fig. 13 shows the SPAD array formed of 12 × 12 SPAD cell cells, it is needless to say that the SPAD array is not necessarily limited to the SPAD array setting described above. The measurement area MA is also a square area formed of 2 × 2 reference areas BA, but is not necessarily limited to such a selection method. For example, the measurement area MA may be an area including the reference areas BA0 to BA3 aligned in the vertical direction, or an area including the reference areas BA0, BA4, BA8, and BA12 aligned in the horizontal direction, or a circular area. The measurement area MA is set by an adjustment method suitable for each particle detection sensor 1B.

(optical Filter)

In the first and second embodiments, a method of removing the pulse count value of the noise component generated by the dark pulse generated by the hot carrier and the disturbance light by subtracting the second pulse count value PC2 in the turn-off period from the first pulse count value PC1 in the turn-on period has been described. As noise removal against the incidence of disturbance light, only the methods described in the first and second embodiments may be insufficient. The above method is effective when the external disturbance light incident on the SPAD array light receiving unit 30B is weak, but has a problem that the particle concentration cannot be accurately measured when the external disturbance light is strong. This is because, when the external disturbance light is strongly incident, the pulse count value of the noise component is large, and therefore, as described above, the gradient of the count value of the scattered light component with respect to the particle concentration changes (linearity decreases).

In order to avoid this problem, an optical filter (not shown) is preferably provided to suppress the incidence of external disturbance light in the direction of the upper surface of the SPAD array light receiving unit 30B (the direction in which scattered light is incident, the direction perpendicular to the light receiving surface). Specifically, it is preferable to provide an optical band-pass filter that transmits only light in the vicinity of the wavelength of the scattered light component (in the vicinity of the emission wavelength of the light-emitting element 10) and attenuates light of other wavelengths by an exponential function. As a method of installing the optical band pass filter, a commercially available (existing) optical glass filter may be installed in the light receiving surface direction (light incident direction) of the SPAD array light receiving unit 30B. Alternatively, the optical filter may be formed directly on the light-receiving surface of the SPAD array by vapor deposition or the like. By providing the optical band-pass filter in the direction of the upper surface of the SPAD array light receiving unit 30B in this manner, light other than the wavelength of the scattered light (i.e., external disturbance light noise) can be attenuated exponentially. As a result, it is possible to suppress a decrease in linearity due to an increase in the noise component count value caused by the incident of the disturbance light, and it is possible to realize the particulate detection sensor 1B having high accuracy in measuring the particulate concentration even in a situation where the disturbance light is strongly incident.

(integration of constituent elements)

In the first to third embodiments, the SPAD array light receiving unit 30B other than the light emitting element 10 and the respective components are preferably formed on the same semiconductor substrate in an integrated manner. This makes it possible to form wiring between the circuits short. This can suppress noise components generated by coupling of electromagnetic noise or the like to the wiring between the respective components, for example, and can further improve the accuracy of measuring the particulate concentration. Further, by integrating the above-described components on the same substrate, the number of components constituting the particle detection sensor 1B can be reduced, and the particle detection sensor can be downsized and reduced in cost.

[ fourth embodiment ]

In the fourth embodiment, a configuration example of the dust sensor 100 is shown for the purpose of detecting the concentration of dust particles suspended in the air (or in the gas) using the particle detection sensors 1 to 1B. Fig. 15 is a schematic diagram showing an example of a schematic configuration of a dust sensor 100 according to a fourth embodiment of the present invention. Fig. 15 (a) is a view of the dust sensor 100 as viewed from the top surface. Fig. 15 (b) is a sectional view of a-a' of fig. 15 (a).

The dust sensor 100 shown in fig. 15 has an integrated circuit IC mounted on a mounting substrate 160. The integrated circuit IC includes at least the SPAD array light receiving unit 30B, the pulse counter 40, the driving unit 20 of the light emitting element 10, the control unit 60, and circuit elements including the signal processing unit 50 (the configuration of the above embodiment). A sensor cover 150 (light shield) for suppressing the incidence of external disturbance light or stray light to the SPAD array light receiving unit 30B is mounted on the mounting substrate 160 so as to cover the integrated circuit IC. The light receiving window 130 (a portion, a hole, or the like through which the scattered light E2 is transmitted) for taking in the scattered light E2 from the dust particles SP into the SPAD array light receiving unit 30B is provided in the upper surface portion of the sensor cover 150 directly above the SPAD array 170.

An optical band-pass filter is provided in addition to the light receiving window 130, and external disturbance light is suppressed from entering the SPAD array light receiving unit 30B. A light emitting element module 110 for projecting a light beam 120 is mounted on the upper surface of the sensor cover 150. The light emitting element module 110 is composed of at least the light emitting element 10 and optical elements such as a lens 140. The light emitting element module 110 is electrically connected to (a driving portion of) the integrated circuit IC. The light beam 120 is projected parallel to the upper surface of the sensor cover 150 in a direction from the light emitting element module 110 toward the light receiving window 130(SPAD array light receiving section 30B). Here, a portion where the light beam 120 overlaps with the view angle of the SPAD array light receiving unit 30B is set as the detection region a of the dust sensor 100. The viewing angle of the SPAD array light receiving unit 30B is determined by the viewing angle of the SPAD array 170, the viewing angle of the optical band pass filter, the arrangement of the light receiving windows 130, and the like.

Further, an air blowing mechanism F for blowing air (gas) to the vicinity of the upper surface of the light receiving window 130 is provided on the side surface of the dust sensor 100, and the dust particles SP are sent to the detection area a at a constant speed by the flow of the air (gas) (arrow in fig. 15 (a)). When the dust particles SP fed by the air blowing mechanism F pass through the detection region a, the light beam 120 is scattered by the dust particles SP, and the scattered light E2 is incident on the SPAD array light receiving unit 30B. As described in the above embodiment, the pulse counter 40 counts the pulse signal corresponding to the light amount of the scattered light E2 and performs calculation using the calculation coefficient, thereby detecting the concentration of the dust particles SP. As the air blowing mechanism F, in addition to an air blower such as a fan, an air blowing mechanism using a temperature difference or a pressure difference generated by a heater or the like can be used.

In fig. 15, the positional shifts of the following (1) and (2) are considered. (1) Displacement of the mounting position when mounting the SPAD array 170(IC) on the mounting substrate 160. (2) The stray light component incident on the SPAD array light receiving unit 30 is deviated in incident position due to manufacturing variation such as deviation in the position of the light beam 120. Even when the above-described deviation occurs, the influence of the stray light component can be suppressed by setting the area of the light receiving window 130 to be wider than the detection region a (the emitted light beam diameter). This is because the measurement region MA of the SPAD array light receiving unit 30B can be adjusted (optimized) with the least influence of the stray light component as described in fig. 13 and 14.

With the configuration of fig. 15, the following dust sensor 100 can be realized: the particle concentration of dust particles floating in the air (in the gas) can be detected, the sensor is small in size, can withstand the incidence of external disturbance light noise, is high in the measurement accuracy of the dust particle concentration, is less affected by the ambient temperature change, and can suppress the influence of stray light components.

The structure of the dust sensor 100 is not limited to the structure shown in fig. 15. In fig. 15, the dust sensor 100 is mainly configured to receive scattered light E2 in the vicinity of the direction 90 ° with respect to the direction in which the luminous flux 120 is projected, that is, the luminous flux direction. However, by adjusting the arrangement of the SPAD array 170, the light receiving window 130, and the particle capture position (flow), the dust sensor 10 that mainly receives scattered light at 90 ° or more with respect to the emission light beam direction and scattered light at 90 ° or less with respect to the emission light beam direction can be realized. In addition, in the case where the detection device is used in an environment in which fine particles can be efficiently taken into the detection region a without providing the air blowing mechanism F, the air blowing mechanism F is not required. This can reduce the number of parts and suppress an increase in cost of the dust sensor 100.

Further, by mounting the dust sensor 100 on the air conditioner, the air conditioner 200 having the dust concentration detection unit capable of accurately detecting the concentration of particulate matter such as PM2.5 and having a small measurement error due to the incidence of disturbance light or a change in ambient temperature can be realized.

Fig. 16 is a schematic diagram showing an example of a schematic configuration of an air conditioner 200 according to the present invention. The air conditioning apparatus 200 can be implemented by an air cleaner, an air conditioner, a ventilator, or the like. The air conditioning apparatus 200 is composed of a power supply Unit 201, an air conditioning mechanism 202, an MPU (MicroProcessing Unit) 203, and a dust sensor 100. The power supply unit 201 supplies a power supply voltage to the air conditioning mechanism 202, the MPU203, and the dust sensor 100. The air conditioning mechanism 202 is a mechanism for performing air conditioning such as air conditioning control and ventilation. The MPU203 controls the operations of the air-conditioning apparatus 200 and the dust sensor 100, and has a function of controlling the air volume and the operation ON/OFF of the air-conditioning apparatus 200 based ON the dust concentration information output from the dust sensor 100. In the MPU203, calculation of the particle concentration, averaging processing of the particle concentration, and the like may be performed using the output result (pulse count value and the like) of the dust sensor 100 (the particle detection sensors 1/1a/1B in the dust sensor 100).

The dust sensor 100 shown in fig. 16 includes the particle detection sensor 1/1a/1B, the detection area a, the particle capturing mechanism 250, and the optical mechanism 260 described in the above embodiment. Here, the detection area a is an area for detecting suspended particles. The projected light E1 projected from the particle detection sensor 1/1a/1B is scattered by the particles SP suspended in the detection region a, and the scattered light E2 is received by the particle detection sensor 1/1a/1B, whereby the particle concentration is detected.

The fine particle taking-in mechanism 250 takes in fine particles SP (dust particles) from the outside of the dust sensor 100, sends the fine particles to the detection area a, discharges the fine particles SP from the detection area a, and further discharges the fine particles SP to the outside of the dust sensor 100. The mechanism 250 for taking in fine particles includes: an air blowing mechanism F for taking in and further discharging fine particles (air) from the outside of the dust sensor 100; a path for the fine particles SP for taking in and discharging the fine particles SP to the detection region a; an Inlet (Inlet) for taking in the particles SP from outside the dust sensor 100; and an Outlet (Outlet) for discharging the fine particles SP to the outside.

The optical mechanism 260 is constituted by the following items (1) to (5). (1) Optical components such as lenses for collecting the projection light E1 projected from the particle detection sensor 1/1a/1B to the detection region a, (2) the optical path of the projection light E1, (3) the optical path for receiving the scattered light E2 from the detection region a, (4) the light receiving window of the light receiving unit 210 for taking the scattered light E2 into the particle detection sensor 1/1a/1B, (5) the light shield (sensor cover) for suppressing the incidence of unnecessary light (stray light, external disturbance light) into the particle detection sensor 1/1a/1B, and (6) the optical trapping structure for suppressing the incidence of stray light into the particle detection sensor 1/1 a/1B.

[ software-based implementation example ]

The control block (particularly, the signal processing unit 50) of the particle detection sensor 1/1a/1B may be realized by a logic circuit (hardware) formed on an integrated circuit (IC chip) or the like, or may be realized by software.

In the latter case, the particle detection sensor 1/1a/1B has a computer that executes commands of a program that is software for realizing the respective functions. The computer has, for example, at least one processor (control device), and has at least one computer-readable recording medium storing the program. In the computer, the object of the present invention is achieved by the processor reading the program from the recording medium and executing the program. The processor may be, for example, a Central Processing Unit (CPU). As the recording medium, a "non-transitory tangible medium" may be used, and for example, a tape, a disk, a card, a semiconductor Memory, a programmable logic circuit, or the like may be used in addition to a ROM (Read Only Memory) or the like. In addition, a RAM (random Access Memory) for expanding the program may be further provided. The program may be supplied to the computer via an arbitrary transmission medium (a communication network, a broadcast wave, or the like) through which the program can be transmitted. It should be noted that an aspect of the present invention can also be realized by a method of electronically transmitting a data signal mounted on a carrier wave in which the program is realized.

[ conclusion ]

A particle detection sensor (1/1a/1B) according to a first aspect of the present invention is a particle detection sensor that detects a concentration of particles contained in a fluid, and includes: a light emitting element (10) for projecting light to the fine particles; a SPAD array light receiving unit (30/30B) that has a plurality of SPADs arranged in an array and operating in a Geiger mode, receives scattered light from the microparticles generated by light projected from the light emitting elements, and outputs a pulse signal; and a signal processing unit (50) that calculates the concentration of the microparticles on the basis of a pulse count value obtained by counting the pulse signal, wherein the signal processing unit calculates the concentration of the microparticles on the basis of a first pulse count value (PC1) and a second pulse count value (PC2), wherein the first pulse count value (PC1) is a pulse count value of the pulse signal in a lighting period (ONT) during which the light is projected by the light-emitting element, and the second pulse count value (PC2) is a pulse count value of the pulse signal in an extinguishing period (OFFT) during which the light is not projected by the light-emitting element.

According to the above configuration, the weak scattered light received by the SPAD array light receiving unit is output as a digitized pulse signal, and the pulse signal is pulse-counted, whereby a fine particle detection sensor that can receive the weak scattered light and has high measurement accuracy can be realized.

Further, since a configuration for amplifying an analog signal by a high-gain amplification circuit is not required, the resistance to electromagnetic noise is high, the number of components for electromagnetic noise countermeasure such as a shield case and a filter, which are indispensable for a conventional dust sensor, can be reduced, and the size and cost of the particle detection sensor can be reduced.

In the particulate detection sensor (1/1a/1B) according to the second aspect of the present invention, in addition to the first aspect, a length of a period (first pulse count period PT1) during which the first pulse count value (PC1) is counted in the lighting period (ONT) may be the same as a length of a period (second pulse count period PT2) during which the second pulse count value (PC2) is counted in the blanking period (OFFT).

According to the above configuration, by setting the pulse count period to the same time in the light-on period and the light-off period of the light-emitting element, the noise component can be removed with higher accuracy, and the particulate detection sensor having further improved resistance to the ambient temperature and the incidence of external disturbance light can be realized.

In the particulate detection sensor (1/1a/1B) according to the third aspect of the present invention, in addition to the first or second aspect, the signal processing unit (50) may calculate a third pulse count value (PC3) obtained by subtracting the second pulse count value (PC2) from the first pulse count value (PC1), and may calculate the concentration of the particulate based on the third pulse count value.

According to the above configuration, by subtracting the second pulse count value in the turn-off period from the first pulse count value in the turn-on period, it is possible to remove a noise component generated by heat and a noise component generated by the incident of disturbance light, and it is possible to realize a fine particle detection sensor having high tolerance against a change in ambient temperature and the incident of disturbance light.

In addition, the signal processing unit for calculating the particle concentration can flexibly set the calculation method of the particle concentration by performing the subtraction processing of the pulse count value in a lump, and there are effects that the response speed is improved by the reduction of the number of calculations, and the cost is reduced by the reduction of the circuit scale of the signal processing unit.

A particle detection sensor (1/1a/1B) according to a fourth aspect of the present invention may be configured such that, in addition to any one of the first to third aspects, the particle detection sensor includes a pulse counter (40) that counts the pulse signal, the pulse counter is configured by an up/down counter that counts up the pulse signal during the lighting period (ONT) and counts down the pulse signal during the blanking period (OFFT).

According to the above configuration, the pulse counter is an up/down counter, so that it is not necessary to perform a down process of the pulse count value in the signal processing unit, and there is an effect of further cost reduction due to reduction in the circuit scale of the signal processing unit.

A particle detection sensor (1A) according to a fifth aspect of the present invention may be any one of the first to fourth aspects, including: a temperature detection unit (70) that measures the ambient temperature of the SPAD array light receiving unit (30); and a voltage setting unit (80) that supplies a reverse bias voltage (VHV) determined based on a measurement result of the ambient temperature (T) to the SPAD array light receiving unit, wherein the measurement of the ambient temperature by the temperature detection unit is performed in a temperature detection period (TT), wherein the reverse bias voltage is updated by the voltage setting unit based on the measurement result of the ambient temperature in a voltage setting period (VT), and wherein the temperature detection period and the voltage setting period are set in synchronization with a measurement period (MT) that is configured from a period (first pulse count period PT1) during which the first pulse count value (PC1) is counted in the lighting period (ONT) and a period (second pulse count period PT2) during which the second pulse count value (PC2) is counted in the blanking period (OFFT).

According to the above configuration, the reverse bias voltage supplied to the SPAD array light receiving unit can be automatically adjusted to an optimum value in response to a change in the ambient temperature, and a particle detection sensor having a wide operable temperature range can be realized. Further, by setting the temperature measurement period of the temperature detection unit and the adjustment period of the reverse bias voltage in synchronization with the measurement period constituted by the lighting period and the lighting-off period of the light emitting element, it is possible to realize a configuration in which the reverse bias voltage does not change during the measurement period. As a result, more stable measurement can be realized.

In a particulate detection sensor (1A) according to a sixth aspect of the present invention, in addition to the fifth aspect, the signal processing unit (50) may calculate a second arithmetic coefficient (x2) by temperature-correcting a first arithmetic coefficient (x1) that is preset for calculating the concentration of the particulate using a preset temperature correction coefficient (y1) and the measurement result of the ambient temperature measured by the temperature detection unit, and may calculate the concentration of the particulate using the second arithmetic coefficient and a third pulse count value (PC3) obtained by subtracting the second pulse count value (PC2) from the first pulse count value (PC 1).

According to the above configuration, the calculation coefficient of the particulate concentration is temperature-corrected using the detection result of the ambient temperature, and thereby a particulate detection sensor capable of suppressing measurement errors of the particulate concentration due to changes in the ambient temperature can be realized.

A fine particle detection sensor (1A) according to a seventh aspect of the present invention may be the fine particle detection sensor (1A) according to the sixth aspect, wherein the temperature correction coefficient (y1) is calculated based on measurement results of the concentration of the fine particles at least two or more arbitrary temperatures in an inspection step at the time of manufacturing the fine particle detection sensor.

According to the above configuration, the temperature correction coefficient for performing the temperature correction is detected in the inspection step at the time of manufacturing, and stored in the storage unit as the initial set value, thereby realizing the particulate detection sensor that suppresses the influence of variations in temperature dependency relating to manufacturing variations.

A particle detection sensor (1A) according to an eighth aspect of the present invention may be the particle detection sensor (1A) according to the fifth aspect, further comprising a control unit (80) for controlling a drive unit (20) for driving the light emitting element (10), the SPAD array light receiving unit (30), and the voltage setting unit (80), wherein the control unit has a function of outputting a first adjustment signal (S1), a second adjustment signal (S2), and a third adjustment signal (S3), the first adjustment signal (S1), the second adjustment signal (S2), and the third adjustment signal (S3) are used to adjust respective operating conditions of the drive unit, the SPAD array light receiving unit, and the voltage setting unit, the drive unit has a function of adjusting the amount of light emitted from the light emitting element in accordance with the first adjustment signal, and the SPAD array light receiving unit has a function of setting the respective SPAD cells constituting the SPAD array light receiving unit in accordance with the second adjustment signal, the voltage setting unit has a function of adjusting the reverse bias voltage based on the third adjustment signal, and the first adjustment signal, the second adjustment signal, and the third adjustment signal are determined based on an inspection result in an inspection process at the time of manufacturing the particle detection sensor.

According to the above configuration, the optimum value of the reverse bias voltage, the pulse count value based on the noise component, and the deviation of the pulse count value with respect to the gradient of the particle concentration (correction of manufacturing variation) can be adjusted for each particle detection sensor. Further, it is possible to realize a particulate detection sensor that can suppress manufacturing variations in characteristics of each particulate detection sensor and satisfy target performance (measurement accuracy and the like) required for the particulate detection sensor.

A particle detection sensor (1A) according to a ninth aspect of the present invention may be the particle detection sensor (1A) according to any one of the first to eighth aspects, wherein a fourth pulse count value (PC4) is measured in an inspection process at the time of manufacturing the particle detection sensor, the fourth pulse count value (PC4) is a pulse count value of a stray light component in a state where the particle is not present, and when the signal processing unit (50) calculates the concentration of the particle, the fourth pulse count value is subtracted from a third pulse count value (PC3), and the third pulse value (PC3) is a value obtained by subtracting the second pulse count value (PC2) from the first pulse count value (PC 1).

According to the above configuration, a particulate detection sensor capable of suppressing a measurement error caused by the incidence of a stray light component can be realized.

In the particle detection sensor (1A) according to the tenth aspect of the present invention, in addition to the ninth aspect, the fourth pulse count value (PC4) may be temperature-corrected based on a measurement result of the temperature detection unit (70) that measures the ambient temperature of the SPAD array light receiving unit (30).

According to the above configuration, it is possible to correct a change in the influence of the stray light component with respect to the ambient temperature change, and to realize a particle detection sensor capable of suppressing a measurement error with respect to the ambient temperature change even in a sensor in which the incidence of the stray light component cannot be ignored.

In the particle detection sensor (1B) according to the eleventh aspect of the present invention, in addition to the eighth aspect, the SPAD array light receiving unit (30B) has a function of dividing a SPAD array region, which is a region in which the plurality of SPADs are arranged in an array, into at least two or more reference regions (BA) and selecting at least one of the reference regions as a measurement region (MA), and the second adjustment signal (S2) is set to, selecting the measurement region so that a value obtained by dividing a third pulse count value (PC3) obtained by subtracting the second pulse count value (PC2) from the first pulse count value (PC1) by a fourth pulse count value (PC4) becomes maximum, wherein the fourth pulse count value (PC4) is a pulse count value of the pulse signal in the lighting period (ONT) in a state where the particulate is not present in an inspection process at the time of manufacturing the particulate detection sensor.

According to the above configuration, the measurement region of the SPAD array region can be selected so that the ratio of the scattered light component incident on the SPAD array light receiving unit to the stray light component becomes maximum. Therefore, it is possible to realize a particle detection sensor capable of suppressing an influence caused by a shift of an incident position of a stray light component with respect to manufacturing variations. Further, by adopting the above configuration, it is possible to suppress the generation rate of defective products due to a large incident amount of the stray light component, and there is an effect of cost reduction due to an increase in yield of the fine particle detection sensor.

In the particle detection sensor (1/1a/1B) according to the twelfth aspect of the present invention, in addition to any one of the first to eleventh aspects, the SPAD array light receiving unit (30/30B) may include an optical band-pass filter that transmits only light in the vicinity of the emission wavelength of the light-emitting element (10) in the incident direction of the scattered light.

According to the above configuration, even when external disturbance light is strongly incident on the SPAD array light receiving unit, an increase in the pulse count value due to the external disturbance light component can be suppressed, and a particle detection sensor having high tolerance against the incident of external disturbance light noise can be realized.

In the particle detection sensor (1/1a/1B) according to the thirteenth aspect of the present invention, in addition to any one of the first to twelfth aspects, at least two or more of the constituent elements other than the light-emitting element may be integrated on the same semiconductor substrate.

According to the above configuration, by forming at least two or more circuit components other than the light-emitting element on the same semiconductor substrate, the number of components constituting the particle detection sensor can be reduced, and the particle detection sensor can be downsized and reduced in cost. Further, since the wiring between the components can be shortened by forming the components on the same substrate, noise caused by coupling of electromagnetic noise in the wiring can be reduced, and a fine particle detection sensor having high electromagnetic noise tolerance can be realized.

In the particulate detection sensor (1/1a/1B) according to the fourteenth aspect of the present invention, in addition to the first aspect, the on period (ONT), the off period (OFFT), a first pulse count period (PT1) which is a period in which the first pulse count value (PC1) is counted during the on period, and a second pulse count period (PT2) which is a period in which the second pulse count value (PC2) is counted during the off period (OFFT) may be controlled as predetermined periods, the first pulse count period being controlled in synchronization with the on period, the second pulse count period being controlled in synchronization with the off period, and measurement constituted by the on period and the off period being repeated at least once.

According to the above configuration, measurement is repeatedly performed, and the particle concentration is calculated and detected using the integrated pulse count value, whereby the measurement error can be reduced. Specifically, if the number of times of measurement is N, the measurement error can be reduced to 1/√ N times the measurement error in one measurement. Therefore, a particulate detection sensor with higher measurement accuracy can be realized.

A dust sensor (100) according to a fifteenth aspect of the present invention may be a dust sensor (100) that includes the particle detection sensor (1/1a/1B) according to any one of the first to fourteenth aspects, has a detection region (a) for detecting dust particles suspended in a gas, and detects a concentration of the dust particles.

According to the above configuration, the following dust sensor can be realized by taking dust particles in the air into a region (detection region) where the light beam overlaps with the viewing angle of the SPAD array light receiving unit. That is, it is possible to realize a dust sensor that has high measurement accuracy for detecting the concentration of dust particles floating in the air, has high tolerance against ambient temperature changes and external disturbance light incidence, and has a small measurement error due to manufacturing variations.

An air conditioning equipment (200) according to a sixteenth aspect of the present invention may be one having the dust sensor (100) according to the fifteenth aspect mounted thereon.

According to the above configuration, it is possible to realize an air conditioning apparatus having a dust concentration detection unit with high measurement accuracy, high resistance against ambient temperature changes and external disturbance light incidence, and less measurement errors due to manufacturing variations.

A method for controlling a particulate detection sensor (1/1a/1B) according to a seventeenth aspect of the present invention is a method for controlling a particulate detection sensor that detects a concentration of particulate contained in a fluid, the method including: projecting light to the fine particles by a light emitting element; a step of receiving scattered light from the fine particles generated by light projected from the light emitting element by an SPAD array light receiving unit having a plurality of SPADs arranged in an array and operating in a geiger mode, and outputting a pulse signal; and a step of calculating, by a signal processing unit, a concentration of the fine particles based on a pulse count value that is a value obtained by counting the pulse signal, wherein in the step of calculating the concentration of the fine particles, the concentration of the fine particles is calculated based on a first pulse count value and a second pulse count value, the first pulse count value being a pulse count value of the pulse signal in a lighting period in which the light emitting element projects the light, and the second pulse count value being a pulse count value of the pulse signal in a lighting-off period in which the light emitting element does not project the light. According to the above configuration, the same effects as those of the first aspect are obtained.

In this case, a control program for the fine particle detection sensor 1/1a/1B of the fine particle detection sensor 1/1a/1B and a computer-readable recording medium on which the program is recorded are also included in the scope of the present invention by operating a computer as each unit (software element) included in the fine particle detection sensor 1/1 a/1B.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention. In addition, new technical features can be formed by combining the technical methods disclosed in the respective embodiments.

Description of the reference numerals

1/1A/1B particle detection sensor

10 light emitting element

30/30B SPAD array light-receiving part

40 pulse counter

50 signal processing part

60 control part

70 temperature detecting part

80 voltage setting part

100 dust sensor

200 air conditioning equipment

APD/APD1 avalanche photodiode

BA/BA 1-BA 15 reference region

MA/MA1/MA2 measurement region

Period of MT measurement

ONT lighting period

OFF period

PC1-PC 4 first to fourth pulse count values

PT 1-PT 2 first pulse counting period-second pulse counting period

S1-S3 first to third adjustment signals

Temperature around T

TT temperature detection period

TS 1-TS 4 first to fourth control signals

VHV1/VHVo reverse bias voltage

VT voltage setting period

x 1-x 3 first to third operational coefficients

y1 temperature correction coefficient