阅读说明：本技术 浓度测定方法 (Concentration measuring method ) 是由 永濑正明 石井秀和 西野功二 池田信一 于 2019-09-18 设计创作，主要内容包括：本发明提供一种浓度测定方法,其在浓度测定装置中执行,所述浓度测定装置具有：供被测定流体流动的测定单元；发出向测定单元的入射光的光源；检测来自测定单元的出射光的光检测器；基于光检测器的输出计算被测定流体的吸光度以及浓度的运算部；以及测定被测定流体的温度的温度传感器,所述浓度测定方法包括：使分子结构随温度而变化的气体作为被测定流体而在测定单元内流动的工序；使由被测定流体吸收的波长的光从光源向测定单元入射,并且通过光检测器测定从测定单元出射的光的强度的工序；以及基于由温度传感器测定的温度和光检测器的输出,计算被测定流体的浓度的工序。(The present invention provides a concentration measurement method executed in a concentration measurement apparatus having: a measuring unit through which a fluid to be measured flows; a light source that emits incident light to the measurement unit; a photodetector for detecting light emitted from the measurement unit; a calculation unit for calculating the absorbance and concentration of the fluid to be measured based on the output of the photodetector; and a temperature sensor for measuring a temperature of the fluid to be measured, the concentration measuring method including: a step of flowing a gas, the molecular structure of which changes with temperature, as a fluid to be measured in a measurement cell; a step of causing light having a wavelength absorbed by the fluid to be measured to enter the measurement unit from the light source and measuring the intensity of light emitted from the measurement unit by the photodetector; and calculating the concentration of the fluid to be measured based on the temperature measured by the temperature sensor and the output of the photodetector.)

1. A method for measuring a concentration of a substance,

the concentration measurement method is performed using an apparatus comprising:

a measurement unit having a flow path through which a fluid to be measured flows;

a light source that emits incident light to the measurement unit;

a photodetector that detects light emitted from the measurement unit;

a calculation unit that calculates the absorbance and concentration of the fluid to be measured based on the output of the photodetector; and

a temperature sensor that measures a temperature of the fluid to be measured in the measurement unit,

the calculation unit calculates the fluid concentration according to Lambert-beer law based on the detection signal of the photodetector,

the concentration determination method comprises the following steps:

a step of flowing a gas whose molecular structure changes with temperature as the fluid to be measured in the measurement cell;

a step of causing light having a wavelength absorbed by the fluid to be measured to enter the measurement unit from the light source and measuring the intensity of the light emitted from the measurement unit by the photodetector; and

and calculating the concentration of the fluid to be measured based on the temperature measured by the temperature sensor and the output of the photodetector.

2. The method according to claim 1, wherein the concentration of the analyte in the sample is measured,

the fluid to be measured is trimethylaluminum.

3. The method according to claim 2, wherein the concentration of the analyte in the sample is measured,

the wavelength of light incident on the measurement cell is a wavelength outside the range of 220nm to 240nm that is easily absorbed by the trimethylaluminum.

4. The method according to claim 3, wherein the concentration of the analyte in the sample is measured,

the wavelength of light incident on the measurement unit is 250nm to 300 nm.

5. The concentration determination method according to any one of claims 2 to 4,

the temperature of the gas containing trimethylaluminum in the measurement cell is not less than room temperature and not more than 150 ℃.

Technical Field

The present invention relates to a concentration measuring method, and more particularly to a method for measuring the concentration of a fluid by detecting the intensity of light in a measuring cell.

Background

Conventionally, there is known a concentration measuring apparatus (so-called inline concentration measuring apparatus) which is assembled to a gas supply line for supplying a source gas, which is a liquid material such as an organic Metal (MO) or a solid material, to a semiconductor manufacturing apparatus and which measures the concentration of a gas flowing through the gas supply line.

In such a concentration measuring apparatus, light having a predetermined wavelength is incident on a measuring cell through an entrance window from a light source to which a fluid flows, and transmitted light passing through the measuring cell is received by a light receiving element, whereby absorbance is measured. Further, the concentration of the fluid can be obtained from the measured absorbance according to the lambert-beer law (for example, patent documents 1 to 3).

In the present specification, various types of transmitted light detection structures used for detecting the concentration of a fluid introduced into the interior are broadly referred to as measurement units. The measurement unit includes not only a unit structure that is disposed separately from the gas supply line, but also an in-line transmission light detection structure provided in the middle of the gas supply line as shown in patent documents 1 to 3.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-219294

Patent document 2: international publication No. 2018/021311

Patent document 3: japanese patent laid-open No. 2018-25499

In order to measure the fluid concentration in the measurement cell based on the absorbance, light of a wavelength that can be absorbed by the incident fluid is required. However, according to the present inventors, it is found that the temperature in the measurement cell may change the light absorption characteristics even for the same gas type, and thus the accuracy of the concentration measurement may be lowered.

Disclosure of Invention

The present invention has been made in view of the above problems, and a main object thereof is to provide a concentration measuring method with further improved measurement accuracy.

A concentration measurement method according to an embodiment of the present invention is a concentration measurement method performed using an apparatus including: a measurement unit having a flow path through which a fluid to be measured flows; a light source that emits incident light to the measurement unit; a photodetector that detects light emitted from the measurement unit; a calculation unit that calculates the absorbance and concentration of the fluid to be measured based on the output of the photodetector; and a temperature sensor that measures a temperature of the fluid to be measured in the measurement unit, wherein the calculation unit obtains a fluid concentration according to lambert-beer's law based on a detection signal of the photodetector, and the concentration measurement method includes: a step of flowing a gas whose molecular structure changes with temperature as the fluid to be measured in the measurement cell; a step of causing light having a wavelength absorbed by the fluid to be measured to enter the measurement unit from the light source and measuring the intensity of the light emitted from the measurement unit by the photodetector; and calculating the concentration of the fluid to be measured based on the temperature measured by the temperature sensor and the output of the photodetector.

In one embodiment, the fluid to be measured is trimethylaluminum.

In one embodiment, the wavelength of light incident on the measurement cell is a wavelength outside a range of 220nm to 240nm that is easily absorbed by the trimethylaluminum.

In one embodiment, the wavelength of light incident on the measurement unit is 250nm to 300 nm.

In one embodiment, the temperature of the gas containing trimethylaluminum in the measurement cell is not lower than room temperature and not higher than 150 ℃.

Effects of the invention

According to the embodiments of the present invention, the concentration can be more accurately measured even when the temperature of the fluid changes.

Drawings

Fig. 1 is a schematic diagram showing the overall configuration of a concentration measuring apparatus according to an embodiment of the present invention.

Fig. 2 is a graph showing the difference in transmittance due to the temperature of TMAl.

Fig. 3 is a graph showing the difference in transmittance due to the temperature of TMAl.

FIG. 4 is a diagram for explaining dimer and monomer of TMAl.

Fig. 5 is a graph showing that the relationship between TMAl concentration and absorbance differs for each temperature.

Fig. 6 is a flowchart showing an exemplary flow of TMAl concentration measurement.

FIG. 7 is a schematic diagram showing a two-cartridge concentration measuring apparatus.

Description of the symbols

1 light source

3 Window part

4 measurement Unit

4a inflow port

4b outflow opening

4c flow path

5 reflective member

6 collimator

7 measuring photodetector

8 arithmetic unit

9 reference light detector

10a optical fiber

10b sensor cable

11 temperature sensor

20 pressure sensor

100 concentration measuring device

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

Fig. 1 is a schematic diagram showing the overall configuration of a concentration measuring apparatus 100 used in the embodiment of the present invention. The concentration measurement device 100 includes: a high-temperature gas unit 50 having the measurement unit 4 assembled to a gas supply line; and an electric unit 52 which is disposed separately from the high-temperature gas unit 50 and includes the light source 1, the arithmetic unit 8, and the like. The high-temperature gas unit 50 and the electric unit 52 are connected by the optical fiber 10a and the sensor cable 10 b.

The high-temperature gas unit 50 may be heated to, for example, about 100 to 150 ℃ depending on the kind of the fluid to be measured, but the electric unit 52 separated therefrom is typically maintained at room temperature (clean room atmosphere). The electrical unit 52 is connected to an external control device 54 that transmits an operation control signal to the concentration measurement device 100 or receives a measured concentration signal from the concentration measurement device 100. The "high-temperature gas unit" is not limited to being used at a high temperature, and may be used without heating when a gas that is fluid at or below room temperature (room temperature: e.g., 25 ℃) is used.

The high-temperature gas unit 50 is provided with a measurement unit 4 having an inlet 4a and an outlet 4b for a fluid to be measured, and a flow path 4c extending in the longitudinal direction therebetween. A translucent window portion (translucent plate) 3 is provided at one end of the measurement cell 4 so as to be in contact with the flow path 4 c. Further, a reflecting member 5 for reflecting incident light is provided at the other end of the measuring unit 4. In the present specification, light is not limited to visible light, and includes at least infrared rays and ultraviolet rays, and may include electromagnetic waves of any wavelength. The term "light-transmitting property" means that the internal transmittance of the light incident on the measurement cell 4 is sufficiently high to enable concentration measurement.

The window portion 3 of the measurement unit 4 is fixed to the unit body 40 by the window pressing member 30. The collimator 6 connected to the optical fiber 10a is attached to the window pressing member 30. The collimator 6 has a collimator lens 6a, and is capable of allowing light from the light source 1 to enter the measurement unit 4 as parallel light, and the collimator 6 is capable of receiving reflected light from the reflecting member 5 and transmitting the received light to the optical fiber cable 10 a. The collimator 6 is designed such that: the gas to be measured flowing through the measurement unit 4 is not broken even when the temperature is high, and the concentration can be measured with high accuracy.

In the present embodiment, the high-temperature gas unit 50 is provided with a pressure sensor 20 for detecting the pressure of the fluid to be measured flowing in the measurement unit 4. The measurement unit 4 is provided with a temperature sensor 11 (here, a temperature measuring resistor) for measuring the temperature of the fluid to be measured. The outputs of the pressure sensor 20 and the temperature sensor 11 are input to the electric unit 52 via the sensor cable 10 b. A plurality of temperature sensors 11 may also be provided. In addition to the temperature measuring resistor, a thermistor, a thermocouple, or the like can be used as the temperature sensor 11.

The electric unit 52 is provided with: a light source 1 that emits light incident into the measurement unit 4; a measurement photodetector 7 that receives light emitted from the measurement unit 4; a calculation unit 8 configured to calculate the concentration of the fluid to be measured based on a detection signal corresponding to the intensity of the received light, which is output from the measurement photodetector 7; and a reference photodetector 9 that receives the reference light from the light source 1.

In the present embodiment, the measurement photodetector 7 and the reference photodetector 9 are disposed to face each other with the beam splitter 12 interposed therebetween. The beam splitter 12 causes part of the light from the light source 1 to enter the reference photodetector 9, and causes the detection light from the measurement cell 4 to enter the measurement photodetector 7. As the light receiving elements constituting the measurement photodetector 7 and the reference photodetector 9, for example, photodiodes or phototransistors are preferably used.

The arithmetic section 8 is configured by, for example, a processor, a memory, and the like provided on a circuit board, includes a computer program for executing a predetermined arithmetic operation based on an input signal, and can be realized by a combination of hardware and software.

In the concentration measuring apparatus 100, the light source 1 and the measuring unit 4 are connected by an optical fiber 10a as a light guide member. Light from the light source 1 is guided to the window 3 of the measurement unit 4 through the optical fiber 10 a. The optical fiber 10a also has a function of guiding the light reflected by the reflecting member 5 to the measuring photodetector 7. The optical fiber 10a may include an optical fiber for incident light and an optical fiber for detecting light, and may be provided in the form of an optical fiber bundle. As described later, in another embodiment, an optical fiber for guiding incident light to the measurement unit 4 and an optical fiber for guiding light emitted from the measurement unit 4 may be separately provided.

In the present embodiment, the inflow port 4a and the outflow port 4b of the measurement unit 4 are disposed on both sides of the flow path 4c (on the right and left sides of the flow path 4c in the drawing), and when the measurement unit is assembled to the gas supply line, the concentration measurement device 100 is configured such that the gas flows in the horizontal direction as a whole. On the other hand, the flow path 4c extends in a direction orthogonal to the overall flow direction in the gas supply line. In this specification, such a configuration is referred to as a vertical measurement unit 4, and the use of the vertical measurement unit 4 has advantages of space saving and easy maintenance when it is assembled to a gas supply line. In the illustrated measurement unit 4, the inlet 4a is disposed in the vicinity of the reflecting member 5 and the outlet 4b is disposed in the vicinity of the window 3, but in another embodiment, the inlet 4a may be disposed in the vicinity of the window 3 and the outlet 4b may be disposed in the vicinity of the reflecting member 5, and the flow path 4c does not necessarily have to extend in a direction perpendicular to the overall flow direction.

As the window portion 3, sapphire having resistance to detection light used for concentration measurement of ultraviolet light or the like, high transmittance, and mechanical/chemical stability is suitably used, but other stable materials such as quartz glass can also be used. The cell main body 40 (flow path forming part) of the measurement cell 4 may be made of, for example, SUS 316L.

The reflecting member 5 disposed at the opposite end of the window portion 3 of the measurement unit is fixed to a support surface of a mounting recess provided on the lower surface of the unit body 40 via a spacer (not shown) by a pressing member 32. The reflecting surface of the reflecting member 5 is provided perpendicular to the traveling direction of the incident light or the central axis of the flow path, and the reflected light is reflected toward the window 3 through substantially the same optical path as the incident light.

The reflective member 5 has a structure in which an aluminum layer as a reflective layer is formed on the back surface of a sapphire plate by sputtering, for example. The reflecting member 5 may be a system in which a mirror is disposed on the back surface of a sapphire plate. The reflecting member 5 may include a dielectric multilayer film as a reflecting layer, and if the dielectric multilayer film is used, light in a specific wavelength region (for example, near ultraviolet rays) can be selectively reflected. The dielectric multilayer film is composed of a laminate of a plurality of optical films having different refractive indices (for example, a laminate of a high refractive index thin film and a low refractive index thin film), and can reflect or transmit light having a specific wavelength by appropriately selecting the thickness and refractive index of each layer.

Further, since the dielectric multilayer film can reflect light at an arbitrary ratio, for example, when incident light is reflected by the reflecting member 5, a part (for example, 10%) of the incident light is transmitted without reflecting 100%, and the transmitted light can be received by a photodetector provided at a lower portion (a surface opposite to a surface in contact with the flow path 4 c) of the reflecting member 5 or an optical device connected to the photodetector, and the transmitted light can be used as reference light instead of the reference photodetector 9.

In the measurement unit 4 described above, the optical path length of the reciprocating movement in the measurement unit 4 can be defined as twice the distance between the window 3 and the reflecting member 5. In the concentration measuring apparatus 100, the light incident on the measuring cell 4 and then reflected by the reflecting member 5 is absorbed by the gas passing through the flow path 4c existing in the measuring cell 4 in accordance with the concentration of the gas. The calculation unit can measure the absorbance a λ at the absorption wavelength λ by frequency analysis of the detection signal from the measurement photodetector 7, and can calculate the gas concentration C from the absorbance a according to the lambert-beer law shown in the following formula (1).

Aλ＝-log₁₀(I/I₀)＝αLC…(1)

In the above formula (1), I₀I is the intensity of light in the gas passing through the measurement cell, and α is the molar absorption coefficient (m)²L is the optical path length (m), C is the concentration (mol/m)³). The molar absorption coefficient α is a coefficient determined by a substance.

In addition, regarding the incident light intensity I in the above formula₀When there is no light-absorbing gas in the measurement cell 4 (for example, when a purge gas that does not absorb ultraviolet light is filled or when a vacuum is applied), the intensity of light detected by the measurement photodetector 7 may be regarded as the incident light intensity I₀。

As described above, since the optical path length L of the measurement unit 4 can be defined to be twice the distance between the window portion 3 and the reflecting member 5, the optical path length can be doubled as compared with a conventional density measurement device including a light entrance window and a light exit window at both ends of the measurement unit. This can improve the measurement accuracy even though the size is reduced. In the density measurement device 100, since light is incident and received through one window 3 provided on one side of the measurement unit 4 by using only one optical device, the number of components can be reduced.

Further, the concentration measuring apparatus 100 is provided with a pressure sensor 20, and can measure the pressure of the gas in the measuring unit 4. Therefore, the absorbance measured by the output of the photodetector can be corrected to the absorbance at a predetermined pressure (for example, 1 atm) based on the output from the pressure sensor 20. Then, based on the corrected absorbance, the concentration of the fluid to be measured can be calculated based on the lambert-beer law, as in the concentration measuring apparatus described in patent document 3. In this way, since the calculation unit 8 calculates the concentration of the fluid to be measured using the measurement photodetector 7 and the pressure sensor 20, the concentration can be measured with higher accuracy. Further, since the temperature sensor 11 for measuring the temperature of the gas flowing through the measurement unit 4 is further provided, the concentration detection including the correction based on the temperature can be performed.

A method for measuring the concentration of trimethylaluminum (TMAl) gas as a fluid to be measured using the concentration measuring apparatus 100 will be described below.

Fig. 2 is a graph showing the difference in transmittance due to the temperature of a gas containing about 1% TMAl in argon gas. The transmittance is determined by the incident light intensity I₀And the ratio of the transmitted light intensity I (I/I)₀) As can be seen from the above formula (1), the transmittance (I/I) can be used₀) The absorbance A.lamda.is defined. The transmittance of 100% means that no light is absorbed in the measurement unit 4, and the transmittance of 0% means that the light is completely absorbed in the measurement unit 4.

In FIG. 2, the temperature of the gas in the measurement cell (T1: room temperature, T2: 40.0 ℃, T3: 59.8 ℃, T4: 80.2 ℃, T5: 99.6 ℃, T6: 120.0 ℃, T7: 139.4 ℃) is shown as a relationship between the wavelength and the transmittance of the light incident on the measurement cell.

FIGS. 3(a) to (d) show TMAl mixed gas (concentration: about 1%) and TMAl non-mixed gas (specifically, 100% N) at 25 ℃, 50 ℃, 80 ℃ and 100 ℃ in the switched flow₂Gas) incident light intensity I₀The difference between the transmitted light intensity I (I)₀-I) a graph of the corresponding output.

As is clear from fig. 2 and 3, the transmittance characteristic of TMAl greatly varies with temperature. Specifically, the higher the temperature, the greater the degree of absorption, and the shift of the peak wavelength of absorption to the longer wavelength side.

This is considered to be because, as shown in fig. 4, TMAl exhibits a steady state at room temperature as a dimer d (dimer) based on 3-Center 2 Electron binding (Three-Center Two-Electron Bond), and the dimer decomposes with an increase in temperature, while the proportion of monomer m (monomer) increases. Since the proportion of the monomer TMAl contained in the gas increases at high temperatures, it is considered that the absorption of ultraviolet rays increases particularly in the wavelength region of 220 to 240 nm. In addition, the dimer of TMAl has the formula [ Al (CH)₃)₃]₂Expressed as molecular weight 144.18, monomeric formula and molecular weight Al (CH)₃)₃And 72.09.

Therefore, when the peak absorption wavelength region, i.e., 220-240nm is used, it is difficult to accurately determine the concentration by measuring the concentration from the absorbance without considering the temperature. Therefore, in the present embodiment, when the concentration of TMAl is measured, ultraviolet light in a wavelength region shifted from the peak absorption wavelength to the long wavelength side is incident, and the concentration is measured in a state where the temperature dependency is reduced.

More specifically, when the temperature of the TMAl gas is assumed to be about room temperature to 150 ℃, ultraviolet light of, for example, 250nm to 260nm, particularly, about 255nm is used instead of about 220nm to 240nm, which is the wavelength around the peak absorption wavelength. In this way, the light absorbing characteristic can be less susceptible to a change in the light absorbing characteristic due to the gas temperature. In addition, ultraviolet light having a longer wavelength of 260 to 300nm (e.g., 280nm or 300nm) may be used so as to be less susceptible to the temperature-dependent influence of the light absorption characteristics.

As described above, when ultraviolet light of 250nm to 260nm is used, it is understood from fig. 2 that even if TMAl gas is used at a concentration of about 1%, the transmittance is lower (i.e., the absorbance is higher) as the temperature is higher, and the transmittance is about 20% at room temperature and about 140 ℃. In addition, when ultraviolet rays of 260nm to 300nm are used, the degree is small, but a difference in transmittance due to temperature still occurs. Therefore, it is preferable to calculate the concentration by using the measurement temperature obtained from the temperature sensor 11, and correcting the transmittance or absorbance based on the temperature.

In order to perform the above correction, a correction coefficient of absorbance or absorption coefficient may be determined in advance for each temperature, and the absorbance obtained from the measurement of the detection light intensity may be corrected by using the correction coefficient determined based on the output of the temperature sensor 11 to obtain the corrected absorbance. The concentration can be obtained from the corrected absorbance according to the lambert-beer formula.

The correction coefficient described above may be given as a function of temperature, or the correction coefficient may be stored in a table for each temperature. For example, when the coefficient at 140 ℃ which is a typical concentration measurement temperature is 1, the correction coefficient is set to a value larger than 1 at a temperature lower than 140 ℃ and to a value smaller than 1 at a temperature higher than 140 ℃.

In addition, as shown in fig. 5, the TMAl concentration and the absorbance a λ are preliminarily made to be-log₁₀(I/I₀) The relationship (slope of the curve) of (a) is set as a function for each temperature or temperature, and concentration measurement corresponding to the temperature can be performed by performing multi-point correction according to the temperature. More specifically, the concentration C can be calculated based on the detected light intensity and the measured temperature from a line form in which the slope is corrected based on the measured temperature.

Fig. 6 is an exemplary flowchart showing a concentration measurement method according to the present embodiment.

First, as shown in step S1 of fig. 6, in a state where the gas containing TMAl is not flowing in the measurement cell 4 (for example, a state where 100% argon gas is flowing or a state where the inside of the measurement cell is evacuated), ultraviolet light having a wavelength of 250nm to 300nm is incident on the measurement cell from the light source 1, the intensity of light passing through the inside of the measurement cell is detected by the measurement photodetector 7, and the intensity is set as the incident light intensity I₀。

Next, as shown in step S2, a gas whose molecular structure changes with temperature, that is, a gas containing TMAl, flows through the measurement cell 4. Next, in a state where the gas is stably flowing, ultraviolet light having the same wavelength as described above is incident on the measurement cell 4 from the light source 1, and the intensity I of the light passing through the measurement cell 4 is detected by the measurement photodetector 7, as shown in step S3. In addition, the temperature T of the gas flowing through the measurement unit 4 is also measured using the temperature sensor 11 in a state where the gas is stably flowing.

Next, as shown in step S4, a λ is-log₁₀(I/I₀) The absorbance a λ is obtained, and the correction coefficient β (T) is determined based on the measurement temperature T.

Then, as shown in step S5, the concentration C is calculated based on the absorbance a λ obtained by the measurement and the correction coefficient β (T) by the corrected lambert-beer formula (a λ ═ α · β (T) · LC).

Although the concentration measuring apparatus according to the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, light in a wavelength region other than the ultraviolet region can be used as light used for measurement. In addition, although the correction of the absorbance in TMAl is shown in the present invention, it is assumed that the same tendency is observed in a material in which a dimer is decomposed to become a monomer (a material in which the molecular structure changes with temperature) as the temperature rises, and therefore, the absorbance can be determined by the same correction.

In addition, although the device for guiding incident light and outgoing light with one optical fiber 10a has been described above as shown in fig. 1, the device is also suitable for a two-core type concentration measuring device. Such a two-core concentration measuring apparatus is described in patent document 3 (fig. 8, etc.), for example.

As shown in fig. 7, in the two-core concentration measuring apparatus, the measuring unit 4 and the electric unit 52 are connected by the incident optical fiber 10c and the exit optical fiber 10d (here, the temperature sensor provided in the measuring unit 4, the sensor cable connected thereto, and the like are omitted). The light from the light emitting elements 13A and 13B is guided by the incident optical fiber 10c and enters the measurement unit 4 through the window 3. The measurement light reflected by the reflecting member 5 and emitted from the measurement unit 4 is guided through the emission optical fiber 10d and received by the measurement photodetector 7. Thus, by guiding the incident light and the outgoing light through different paths, the influence of stray light can be reduced. Further, as shown in fig. 7, the window surface normal direction of the window portion 3 is arranged to be inclined, for example, 1 to 5 ° from the optical axis direction of the collimator, whereby the occurrence of stray light can be reduced. The gas inlet and the gas outlet of the measurement unit 4 may be provided on the same side surface of the measurement unit 4, unlike the embodiment shown in fig. 1.

Although the reflection-type concentration measuring device using the reflection member has been described above, a transmission-type concentration measuring device configured as follows may be used: incident light is made incident from one end side of the measurement cell without using a reflection member, and measurement light is taken out from the other end side of the measurement cell.

Industrial applicability

The concentration measurement method according to the embodiment of the present invention is suitably used for measuring the concentration of a gas whose molecular structure changes with temperature.