阅读说明：本技术 热线型空气流量传感器用工作电路及其传感器 (Working circuit for hot wire type air flow sensor and sensor thereof ) 是由 台晓虹 申荣卫 刘学明 于 2019-08-29 设计创作，主要内容包括：本发明公开了一种热线型空气流量传感器用工作电路及其传感器,工作电路包括热丝电阻R_S用恒定温度掌控电路和输出信号调节电路,其中：热丝电阻R_S和精密电阻R2串联构成惠斯通电桥的热线臂,温度补偿电阻R_C和精密电阻R3串联构成惠斯通电桥的冷线臂；惠斯通电桥的负极通过电阻R1接地,惠斯通电桥的正极连接在第一运放器的输出端上,第一运放器的同向输入端通过电阻R5连接参考电压Uref；第一运放器的反向输入端连接在第四运放器的输出端上,第四运放器的输出端选择性的与控制电路电压U_(cr)和惠斯通电桥的负极相连接；热线臂和冷线臂上通过输出信号调节电路与输出电压U_0相连接,输出信号调节电路上连接与供电端Vcc。工作电路具有自清洁功能,提高灵敏度。(The invention discloses a working circuit for a hot wire type air flow sensor and the sensor thereof, wherein the working circuit comprises a hot wire resistor R S With constant temperature steering circuit and output signal conditioning circuit, wherein: resistance of hot wire R S A precision resistor R2 connected in series to form the hot wire arm of a Wheatstone bridge, a temperature compensation resistor R C The cold wire arm of the Wheatstone bridge is formed by connecting the precision resistor R3 in series; the negative electrode of the Wheatstone bridge is grounded through a resistor R1, the positive electrode of the Wheatstone bridge is connected to the output end of the first operational amplifier, and the equidirectional input end of the first operational amplifier is connected with a reference voltage Uref through a resistor R5; the reverse input end of the first operational amplifier is connected with the output end of the fourth operational amplifier, and the output end of the fourth operational amplifier is selectively connected with the control circuit voltage U cr The negative pole of the Wheatstone bridge is connected with the negative pole of the Wheatstone bridge; the hot wire arm and the cold wire arm are connected with an output voltage U through an output signal regulating circuit 0 Phase connection, output signal modulationThe power saving circuit is connected with a power supply terminal Vcc. The working circuit has a self-cleaning function and improves the sensitivity.)

1. The hot wire type air flow sensor operating circuit is characterized by comprising a hot wire resistor R_SWith constant temperature steering circuit and output signal conditioning circuit, wherein:

the constant temperature control circuit comprises a hot wire resistor R_STemperature compensation resistor R_CA Wheatstone bridge consisting of a precision resistor R2 and a precision resistor R3, wherein the hot wire resistor R_SAnd precision electricityA resistor R2 is connected in series to form the hot wire arm of the Wheatstone bridge, and the temperature compensation resistor R_CThe cold wire arm of the Wheatstone bridge is formed by connecting the precision resistor R3 in series;

one pole of the Wheatstone bridge is grounded through a resistor R1, the other pole of the Wheatstone bridge is connected to the output end of a first operational amplifier, and the homodromous input end of the first operational amplifier is connected with a reference voltage Uref through a resistor R5; the reverse input end of the first operational amplifier is connected to the output end of the fourth operational amplifier, and the output end of the fourth operational amplifier is selectively connected to the voltage U of the control circuit_crOr between the Wheatstone bridge and R1;

the hot wire arm and the cold wire arm are connected with an output voltage U through an output signal regulating circuit₀And the output signal regulating circuit is connected with a power supply terminal Vcc.

2. The hot-wire type air flow sensor operating circuit according to claim 1, wherein the hot wire resistance R is_SIs tungsten wire or platinum wire.

3. The hot-wire type air flow sensor operating circuit according to claim 1, wherein the hot wire resistance R is_SThe platinum wire is a platinum wire, and the diameter of the platinum wire is 1-10 micrometers.

4. The hot-wire type air flow sensor operating circuit according to claim 1, wherein the platinum wire has a length of 0.2 to 2 mm.

5. The hot-wire air flow sensor operating circuit of claim 1, wherein the ratio of current on the cold wire arm to current on the hot wire arm is 1: 4.

6. The hot-wire air flow sensor operating circuit of claim 1, wherein the output signal conditioning circuit comprises a second op amp and a third op amp.

7. The hot-wire type air flow sensor operating circuit according to claim 6, wherein said power supply terminal Vcc is connected to the output terminal of said second operational amplifier through a circuit in series with a resistor R6 and a resistor R7, and a circuit in series with a resistor R9 and a resistor R10, respectively, to ground, wherein a resistor R6 and a resistor R7 are connected to the output terminal of said second operational amplifier through a circuit in series with a resistor R8 and a resistor R13, and a resistor R9 and a resistor R10 are connected to the output terminal of said third operational amplifier through a circuit in series with a resistor R11 and a resistor R15;

the hot wire resistor R_SAnd the precision resistor R2 is connected with the homodromous input end of the third operational amplifier, and the output end of the third operational amplifier is connected with the output voltage U₀Connected, the temperature compensation resistor R_CAnd the precision resistor R3 is connected with the same-direction input end of the second operational amplifier, and the reverse input end of the second operational amplifier is connected with the output end of the third operational amplifier and the output voltage U through a resistor R12 and a capacitor C1 which are connected in series₀The output end of the second operational amplifier is connected with the reverse input end of the third operational amplifier through a resistor R14, one end of a series circuit formed by a capacitor C1 and a resistor R16 is connected with the reverse input end of the third operational amplifier, and the other end of the series circuit is connected with the output end of the third operational amplifier and an output voltage U₀On the connecting line between them.

8. A hot-wire type air flow sensor characterized by comprising a housing and the hot-wire type air flow sensor operation circuit according to any one of claims 1 to 7.

9. The hot-wire type air flow sensor according to claim 8, wherein the housing includes a passage through which gas flows, filter meshes fixed to openings at both ends of the passage, a connection flange fixed to an outer periphery of the passage, and a connection port connected to a side wall of the passage.

10. The hot-wire air flow sensor of claim 9, wherein heat in the operating circuitFilament resistance R_SFixed in a central position in said channel.

Technical Field

The invention relates to the technical field of automobile accessories, in particular to a working circuit for a hot wire type air flow sensor and a sensor thereof.

Background

The gas mass flowmeter is used as a core part of an electric control fuel injection system and is a core component of an automobile sensor, and the principle of the electric control fuel injection system is that an ECU calculates required fuel injection quantity through air inflow obtained by a gas mass flow sensor based on a theoretical air-fuel ratio.

The hot wire type gas flow sensor is the most commonly used gas flowmeter at present, the temperature of a hot wire is relatively high during operation, dust is accumulated on a hot wire filament when the hot wire type gas flow sensor is used for a long time, the accuracy of flow velocity measurement is interfered in the past, time and labor are wasted during manual cleaning, and the service life of the hot wire type gas flow sensor is influenced.

Disclosure of Invention

The invention aims to provide a working circuit for a hot-wire air flow sensor, aiming at solving the problems that dust is easy to accumulate on a hot wire filament of the hot-wire air flow sensor and is difficult to clean in the prior art, and self-cleaning is realized by a cleaning circuit.

It is another object of the present invention to provide a hot-wire type air flow sensor including the operating circuit.

The technical scheme adopted for realizing the purpose of the invention is as follows:

a working circuit of hot wire type air flow sensor comprises a hot wire resistor R_SWith constant temperature steering circuit and output signal conditioning circuit, wherein:

the constant temperature control circuit comprises a hot wire resistor R_STemperature compensation resistor R_CA Wheatstone bridge consisting of a precision resistor R2 and a precision resistor R3, wherein the hot wire resistor R_SA precision resistor R2 connected in series to form the hot wire arm of the Wheatstone bridge, and a temperature compensation resistor R_CThe cold wire arm of the Wheatstone bridge is formed by connecting the precision resistor R3 in series;

one pole of the Wheatstone bridge is grounded through a resistor R1, the other pole of the Wheatstone bridge is connected to the output end of a first operational amplifier, and the homodromous input end of the first operational amplifier is connected with a reference voltage Uref through a resistor R5; reversal of the first conveyorThe input end of the fourth operational amplifier is connected with the output end of the fourth operational amplifier, and the output end of the fourth operational amplifier is selectively connected with the voltage U of the control circuit_crOr between the Wheatstone bridge and R1;

the hot wire arm and the cold wire arm are connected with an output voltage U through an output signal regulating circuit₀And the output signal regulating circuit is connected with a power supply terminal Vcc.

In the above technical solution, the hot wire resistor R_SIs tungsten wire or platinum wire.

In the above technical solution, the hot wire resistor R_SThe platinum wire is a platinum wire, and the diameter of the platinum wire is 1-10 micrometers.

In the technical scheme, the length of the platinum wire is 0.2-2 mm.

In the above technical solution, the ratio of the current on the cold wire arm to the current on the hot wire arm is 1: 4.

In the above technical solution, the output signal adjusting circuit includes a second operational amplifier and a third operational amplifier.

In the above technical solution, the power supply terminal Vcc is connected to the ground through a circuit serially connected with a resistor R6 and a resistor R7, and a circuit serially connected with a resistor R9 and a resistor R10, wherein the resistor R6 and the resistor R7 are connected to the output terminal of the second operational amplifier through a circuit serially connected with a resistor R8 and a resistor R13, and the resistor R9 and the resistor R10 are connected to the output terminal of the third operational amplifier through a circuit serially connected with a resistor R11 and a resistor R15;

the hot wire resistor R_SAnd the precision resistor R2 is connected with the homodromous input end of the third operational amplifier, and the output end of the third operational amplifier is connected with the output voltage U₀Connected, the temperature compensation resistor R_CAnd the precision resistor R3 is connected with the same-direction input end of the second operational amplifier, and the reverse input end of the second operational amplifier is connected with the output end of the third operational amplifier and the output voltage U through a resistor R12 and a capacitor C1 which are connected in series₀The output end of the second operational amplifier is connected with the reverse input end of the third operational amplifier through a resistor R14, and the capacitor C1 is connected with the resistor R16 in seriesOne end of the circuit is connected with the reverse input end of the third operational amplifier, and the other end of the circuit is connected with the output end of the third operational amplifier and the output voltage U₀On the connecting line between them.

A hot wire type air flow sensor includes a housing and the operating circuit.

In the above technical scheme, the casing includes the passageway that supplies the gas circulation, fixes filter screen on the opening of passageway both ends, fix flange in the passageway periphery and connection are in connector on the passageway lateral wall.

In the above technical solution, the hot wire resistor R in the working circuit_SFixed in a central position in said channel.

Compared with the prior art, the invention has the beneficial effects that:

1. the sensor has no moving part, so the working profile is realized, the gas flow resistance is small, the influence of gas viscosity change is avoided, the measurement precision and sensitivity are higher than those of other sensors, the accuracy is good, the repeatability is excellent, and the response characteristic is excellent;

2. the anti-pollution capacity is very high, the anti-seismic strength is high, the stability is excellent, the power consumption is low, and the service time is long; the pollution is possibly small, and the cleaning is convenient; the occupied volume space is small, and the influence on a gas flow field is weak;

3. temperature compensation is arranged in the structure, so that high precision can be maintained in certain specific temperature range; the applicable range is wide, and the method can also be used for detecting most gases; the initial stabilization time is short.

Drawings

Fig. 1 is a schematic diagram showing an operation circuit of the hot wire type air flow sensor.

Fig. 2 is a schematic view of the structure of a housing of the hot wire type air flow sensor.

In the figure: 1-channel, 2-connecting flange, 3-filter screen, 4-connecting port and 5-opening.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

A working circuit of hot wire type air flow sensor comprises a hot wire resistor R_SWith constant temperature steering circuit and output signal conditioning circuit, wherein:

the constant temperature control circuit comprises a hot wire resistor R_STemperature compensation resistor R_CA Wheatstone bridge consisting of a precision resistor R2 and a precision resistor R3, wherein the hot wire resistor R_SA precision resistor R2 connected in series to form the hot wire arm of the Wheatstone bridge, and a temperature compensation resistor R_CThe cold wire arm of the Wheatstone bridge is formed by connecting the precision resistor R3 in series;

one pole of the Wheatstone bridge is grounded through a resistor R1, the other pole of the Wheatstone bridge is connected to the output end of a first operational amplifier, and the homodromous input end of the first operational amplifier is connected with a reference voltage Uref through a resistor R5; the reverse input end of the first operational amplifier is connected to the output end of the fourth operational amplifier, and the output end of the fourth operational amplifier is selectively connected to the voltage U of the control circuit_crOr between the Wheatstone bridge and R1;

the hot wire arm and the cold wire arm are connected with an output voltage U through an output signal regulating circuit₀And the output signal regulating circuit is connected with a power supply terminal Vcc.

The working principle is as follows: air velocity V fast and slow → heat change relative to flow dissipation → hot wire resistance temperature T_hDecrease → resistance R_SThe resistance value is reduced because the Wheatstone bridge supply current I is stable → the output voltage delta U₀Is raised so as to obtain an output voltage U₀As a function of the fluid flow rate.

The constant temperature control circuit mainly keeps the resistance R of the hot wire_SAt a constant operating temperature, a value (T) which is the subtraction of the temperature of the hot wire from the ambient temperature_h-T_f) Is a constant; the output signal regulating circuit focuses on filtering, direct current biasing and signal amplifying the detection signal of the gas flow sensor.

Example 2

This example will be described in further detail below with reference to example 1.

Preferably, the hot wire resistor R is_SThe tungsten wire or the platinum wire is high in mechanical strength compared with other materials, can withstand impact of dust particles, can be uneven outside the tungsten wire, is convenient to accumulate dust, and is easy to oxidize when the overheating proportion is more than 1.6; furthermore, the alignment characteristics of the tungsten filament are relatively susceptible to drift. The platinum wire has stable calibration characteristic, high use temperature and difficult oxidation, can be used as a sensitive material for a sensor with higher precision, has better process performance compared with other metals, is simpler to purify compared with other metals, can stably exist in a high-temperature medium and is not easy to be oxidized, and can be made into a very thin platinum wire or a very thin platinum foil, so the platinum wire is often used for precision measurement.

Preferably, the hot wire resistor R is_SThe platinum wire is a platinum wire, the diameter of the platinum wire is 1-10 micrometers, and the length of the platinum wire is 0.2-2 millimeters.

Preferably, the ratio of current on the cold arm to the hot arm is 1: 4.

In real work, the platinum fine wire R_SThe heating current I is constant between 50-120mA, depending on the air mass to be measured, and generally the heat wire is heated to 240 ℃ by the current. The other arm of the Wheatstone bridge is provided with a temperature compensation resistor R_CAnd bridge resistance R₃To reduce power consumption, the resistance is higher, the current through the cold leg is made smaller than the current through the hot leg, I is usually chosen_S：I_C＝4:1。

Preferably, the output signal conditioning circuit comprises a second op-amp and a third op-amp.

When fluid flows, the fluctuating air carries away heat from the hot wire (hot wire resistor) to make its resistance R_SDecrease of U_rhReduce and easily cause instability of the Wheatstone bridge circuit, thereby enabling the Wheatstone bridge to output the voltage U_ABA transition occurs, Δ U_ABAmplified by a second operational amplifier and a third operational amplifier, and finally output U by the third operational amplifier₀The speed of the fluid can be detected by the output voltage value.

Preferably, the power supply terminal Vcc is connected to the output terminal of the second operational amplifier through a circuit in series with a resistor R6 and a resistor R7, and a circuit in series with a resistor R9 and a resistor R10 is connected to ground, wherein the resistor R6 and the resistor R7 are connected to the output terminal of the second operational amplifier through a circuit in series with a resistor R8 and a resistor R13, and the resistor R9 and the resistor R10 are connected to the output terminal of the third operational amplifier through a circuit in series with a resistor R11 and a resistor R15;

the hot wire resistor R_SAnd the precision resistor R2 is connected with the homodromous input end of the third operational amplifier, and the output end of the third operational amplifier is connected with the output voltage U₀Connected, the temperature compensation resistor R_CAnd the precision resistor R3 is connected with the same-direction input end of the second operational amplifier, and the reverse input end of the second operational amplifier is connected with the output end of the third operational amplifier and the output voltage U through a resistor R12 and a capacitor C1 which are connected in series₀The output end of the second operational amplifier is connected with the reverse input end of the third operational amplifier through a resistor R14, one end of a series circuit formed by a capacitor C1 and a resistor R16 is connected with the reverse input end of the third operational amplifier, and the other end of the series circuit is connected with the output end of the third operational amplifier and an output voltage U₀On the connecting line between them.

The first operational amplifier is a Wheatstone bridge constant current source operational amplifier, wherein R₁For precision current measurement of the resistor, the current through the bridge is passed through R if it changes for some reason₁Voltage U across the resistor_R1Comparing with reference voltage Uref of first operational amplifier to control constant current flowing through Wheatstone bridge₂、IC₃Is a high-gain, low-drift operational amplifier, forms a pre-amplifier and is provided with an output end U of a third operational amplifier₀The hot wire heating current passes through the hot wire resistor R_SGiving an output signal, the magnitude of which is determined by the passing WheatstonePrecision resistor R in power-on bridge circuit₂A voltage drop.

Example 3

In another aspect of the present invention, there is also included a hot-wire type air flow sensor including a housing and an operating circuit as described in embodiment 1 or 2.

Preferably, the housing includes a channel 1 through which gas flows, a filter net 3 fixed to openings 5 at both ends of the channel 1, a connection flange 2 fixed to the outer periphery of the channel 1, and a connection port 4 connected to a side wall of the channel 1.

Preferably, the heater resistor R in the operating circuit_SIs fixed in a central position in the channel 1.

The filter screen 3 can filter solid particles in the air and prevent the solid particles from resisting the resistance R of the hot wire_SCausing an influence and prolonging the service life of the device. The connecting flange 2 is used for fixing the position of the shell, and the connecting port 4 is connected with a control circuit.

The hot-wire type air flow sensor can be applied to the following scenarios:

1. the automotive industry. The device can be used for measuring the amount of gas entering the engine and providing accurate fuel injection amount for the vehicle engine; therefore, the fuel injection quantity of the fuel injector is mastered, so that a relatively accurate fuel-air ratio is obtained, and the efficiency of the engine is brought into full play. Meanwhile, the pollution to the environment can be reduced, and the fuel can be saved.

2. The method comprises the steps of controlling the relative proportion of the air supply quantity and coal of a boiler in a power station, optimally controlling the gas quality and ventilation low-carbon environmental protection of an indoor air conditioner, and measuring the flow of part of combustible gases such as natural gas, liquefied gas, alkanes and the like in commercial and construction sites.

3. The respiratory function measuring instrument is used for measuring static and dynamic lung function parameters of a testee, such as the middle-stage respiratory flow rate, the peak respiratory flow rate, the tidal respiratory capacity, the forced vital capacity and the like, and provides a basis in the aspect of medical science for the diagnosis and treatment of respiratory diseases.

4. The device is used for experimental devices in the process industries of chemistry and chemical industry, petrochemical industry, food and the like. Such as the measurement of the liquid gas flow rate, the control flow rate during injection.

5. Measuring and controlling the mass flow of air for the combustion furnace and measuring and controlling the mass flow of hydrogen of the combustion turbine; gas mass flow measurement for instruments, measurement and control of food processing and carbonated beverage gas mass flow.

Spatially relative terms, such as "upper," "lower," "left," "right," and the like, may be used in the embodiments for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "lower" can encompass both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Moreover, relational terms such as "first" and "second," and the like, may be used solely to distinguish one element from another element having the same name, without necessarily requiring or implying any actual such relationship or order between such elements.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.