JP6506124B2 - Gas concentration measuring device - Google Patents

Description

  The present invention relates to a gas concentration measuring apparatus, and more particularly to a gas concentration measuring apparatus using a calculation formula capable of highly accurate gas concentration measurement in a two-concentration test of a first concentration and a second concentration. .

  Conventionally, as a gas concentration measuring device for measuring the concentration of a gas to be measured in the atmosphere, the gas concentration is measured by detecting the amount of absorption utilizing the fact that the wavelength of infrared rays absorbed differs depending on the type of gas. Non-dispersive infrared gas concentration measuring devices are known. As a gas concentration measuring apparatus using this principle, for example, a combination of a filter (transmissive member) transmitting an infrared ray limited to a wavelength at which the gas to be measured has absorption characteristics and an infrared sensor, and measuring the amount of absorption of infrared rays There is one that is adapted to measure the concentration of gas.

  In addition, as a gas concentration measuring apparatus using an application of this principle, for example, the one described in Patent Document 1 is a reference filter that selectively transmits infrared light in a wavelength range in which absorption of infrared light by the gas to be measured does not occur. A plurality of infrared detection elements, each of which is provided with a measurement filter for selectively transmitting an infrared ray in a wavelength range in which absorption of infrared rays by the measurement target gas occurs, are measured based on output signals from the respective infrared detection elements These are a carbon dioxide gas concentration measuring device and a carbon dioxide gas detection method which perform detection and concentration measurement, and improve detection accuracy and stability of output.

  Hereinafter, including these, it is also referred to as a gas concentration measuring device and a gas concentration measuring method. The principle of operation is that the difference in the degree of absorption depending on the wavelength is applied to carbon dioxide gas detection. In the infrared rays emitted from the ceramic heater which is the light source, the infrared rays around a wavelength of 4.3 μm are absorbed by carbon dioxide gas in the gas container and the radiation intensity thereof is reduced. On the other hand, infrared rays with a wavelength of 3.9 μm are not absorbed by carbon dioxide gas, and their radiation intensity does not decrease.

  And, from infrared rays including different wavelengths that have passed through the gas container of the gas measuring device, two types of waves with a wavelength of 4.3 μm and a wavelength of 3.9 μm, two types of optical filters having passbands corresponding to the two types of waves. Filter and sort. The concentration of carbon dioxide gas in the gas container is calculated based on the radiation intensities of the infrared rays different in wavelength. The radiation intensity distribution of the ceramic heater is broad in the wavelength range of 2 μm to 50 μm including the infrared absorption spectrum of carbon dioxide gas, and has sufficient radiation intensity in the wavelength range near the infrared absorption spectrum of carbon dioxide gas. Therefore, the detection accuracy and the stability of the output of the gas measuring device using the ceramic heater as the light source are improved.

JP-A-9-33431

  In the non-dispersive infrared absorption type gas concentration measuring apparatus described above, the output characteristics of the measuring infrared detecting unit and the reference infrared detecting unit according to the following equation (1) obtained based on Lambert-Beer's law can be obtained.

In the equation, ε is the absorbance coefficient, l (L) is the optical path length, G is the gain ratio of the infrared detector for measurement and the infrared detector for reference, Vref is the output from the infrared detector for reference, Vout is for measurement It is an output from the infrared detection unit.
However, the optical path lengths from the light source to the measurement infrared detection unit and the measurement infrared detection unit, and the gain ratio of the measurement infrared detection unit and the reference infrared detection unit vary among individuals. Therefore, in the prior art, on the premise of the inspection of two concentrations, since the linear function having a difference from the actual characteristics is used as the concentration calculation formula, highly accurate gas concentration calculation can not be realized, and the calculation accuracy is improved. The only way to do this is to increase the number of concentration tests and to increase the order of the concentration calculation formula.

  The present invention has been made in view of such problems, and the object of the present invention is to calculate the gas concentration with high accuracy by the two concentration inspection of the first concentration and the second concentration. Providing a gas concentration measuring device using

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, the present inventors find out that the said subject can be solved by the following invention, and completed this invention.
According to a first aspect of the present invention, there is provided a light source, a measurement infrared detection unit for receiving light from the light source, a reference infrared detection unit disposed in the vicinity of the measurement infrared detection unit, and the measurement infrared light. A gas concentration measuring apparatus comprising: a detection unit and an operation unit to which an output from the reference infrared detection unit is input, wherein the operation unit is configured to have a first concentration and a first concentration different from the first concentration. The first measurement output output from the infrared detection unit for measurement when the light source is turned on in the measurement target gas having the concentration of 2 and the first concentration, and the measurement target gas of the first concentration The measurement infrared detection unit outputs the first reference output output from the reference infrared detection unit when the light source is turned on, and the measurement light source when the light source is turned on in the second concentration measurement target gas A second measurement output, and a measurement target gas of the second concentration A calculation formula including a coefficient obtained based on the second reference output output from the reference infrared detection unit when the light source is turned on, and the measurement for the output of the reference infrared detection unit at the time of measurement It is a gas concentration measuring device which computes concentration of measurement object gas based on a value which multiplied a value based on said 1st measurement output and said 1st reference output by ratio of an output of an infrared detection part.

  According to a second aspect of the present invention, there is provided a gas concentration measurement comprising: a light source; an infrared detection unit for measurement that receives light from the light source; and a calculation unit to which an output from the infrared detection unit for measurement is input. In the apparatus, the calculation unit may be configured to measure the first concentration, the second concentration different from the first concentration, and the measurement light source when the light source is turned on in the first concentration measurement gas. Obtained based on the first measurement output output from the infrared detection unit and the second measurement output output from the measurement infrared detection unit when the light source is turned on in the measurement target gas of the second concentration. Gas concentration measurement that calculates the concentration of the gas to be measured based on a calculation formula including the calculated coefficient, and a value obtained by multiplying the value based on the first measurement output by the output from the measurement infrared detection unit at the time of measurement It is an apparatus.

  According to the gas concentration measuring device of the present invention, it is possible to realize a gas concentration measuring device using a calculation formula capable of highly accurate gas concentration measurement.

It is a block diagram for demonstrating Embodiment 1 of the gas concentration measuring apparatus which concerns on this invention. It is a circuit block diagram of the calculating part shown in FIG. It is a block diagram for demonstrating Embodiment 2 of the gas concentration measuring apparatus which concerns on this invention. It is a circuit block diagram of the calculating part shown in FIG. It is a figure which shows the result which contrasted Example 1 and Comparative Example 1. FIG. It is a figure which shows the result which contrasted Example 2 and Comparative Example 2. FIG.

In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present invention. However, it will be apparent that other embodiments can be practiced without being limited to such specific specific configurations. In addition, the following embodiments do not limit the invention according to the claims, and include all combinations of characteristic configurations described in the embodiments.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1
FIG. 1 is a configuration diagram for explaining a first embodiment of a gas concentration measurement device according to the present invention. In the figure, reference numeral 10 is a gas cell, 11 is a gas inlet, 12 is a gas outlet, 20 is a light source, 31 is an infrared detection unit for measurement, 40 is an operation unit, 100 is a gas concentration measuring device, L is an optical path length of the shortest distance Is shown. Although the gas cell 10 is clearly shown here for reference, the gas cell is not an essential component in the present invention, and even in a form without a gas cell, the gas concentration measuring device is disposed in the test container etc. It is possible to carry out two concentration tests.
The gas concentration measurement apparatus 100 of the first embodiment includes a light source 20, a measurement infrared detection unit 31 that receives light from the light source 20, and a reference infrared detection unit 32 disposed in the vicinity of the measurement infrared detection unit 31. And a calculation unit 40 to which the outputs from the measurement infrared detection unit 31 and the reference infrared detection unit 32 are input.

  The calculation unit 40 operates the infrared detection unit for measurement when the light source 20 is turned on in the measurement target gas of the first concentration c1, the second concentration c2 different from the first concentration c1, and the first concentration c1. 31 and a first reference output Vref (c1) output by the reference infrared detector 32 when the light source 20 is turned on in the gas to be measured at a first concentration c1. And the second measurement output Vout (c2) output by the infrared detector 31 for measurement when the light source 20 is turned on in the measurement target gas of the second concentration c2, and the measurement target gas of the second concentration c2 A calculation equation including a coefficient ε obtained based on the second reference output Vref (c2) output by the reference infrared detection unit 32 when the light source 20 is turned on in the inside, and the reference infrared detection unit at the time of measurement Infrared for measurement with 32 outputs Vref A concentration c of the gas to be measured based on a value obtained by multiplying the ratio Vout / Vref of the output Vout of the output unit 31 by a value based on the first measurement output Vout (c1) and the first reference output Vref (c1) Calculate

  In the gas concentration measuring apparatus according to the first embodiment, the infrared ray for measurement when the light source is turned on in the gas to be measured of the first concentration, the second concentration different from the first concentration, and the first concentration A first measurement output output from the detection unit, a first reference output output from the reference infrared detection unit when the light source is turned on in the first concentration measurement target gas, and a second concentration measurement target The second measurement output output by the measuring infrared detection unit when the light source is turned on in the gas, and the second measurement output when the light source is turned on in the second concentration measurement target gas by the reference infrared detection unit The first measurement output and the first reference output are calculated based on the calculation formula including the coefficient obtained based on the reference output and the ratio of the output of the infrared detection unit for measurement to the output of the infrared detection unit for reference at the time of measurement. Calculate the concentration of the gas to be measured based on the value obtained by It brings about an effect that only by previously acquired the output of the output and the reference infrared detector of the measuring infrared detector at two different known concentrations, allowing accurate gas concentration measurement than the conventional.

  The coefficient ε is the ratio Vref of the first reference output Vref (c1) to the first concentration c1 and the second concentration c2 different from the first concentration c1 and the first measurement output Vout (c1) Obtained based on (c1) / Vout (c1) = Rc1 and the ratio Vref (c2) / Vout (c2) = Rc2 of the second reference output Vref (c2) to the second measurement output Vout (c2). It may be possible to

In addition, the calculation unit 40 calculates the first reference output Vref using a calculation formula including the coefficient ε and the ratio Vout / Vref of the output Vout of the measurement infrared detection unit 31 to the output Vref of the reference infrared detection unit 32 at the time of measurement. The concentration c of the gas to be measured may be calculated based on a value obtained by multiplying the ratio Vout (c1) / Vref (c1) = Rc1 of the first measurement output Vout (c1) with respect to (c1).
Further, the calculation unit 40 calculates the concentration c of the gas to be measured based on the following equation (2). That is, as an example of a specific calculation formula in the gas concentration measuring device of the first embodiment, the following formula (2) can be mentioned.

  In the equation, c1 is a first concentration, c2 is a second concentration, Rc1 is an output ratio of the reference infrared detection unit 32 to the output of the measurement infrared detection unit 31 at the first concentration c1, Rc2 is a second The output ratio of the reference infrared detection unit 32 to the output of the measurement infrared detection unit 31 at the concentration c 2, Vout is the output of the measurement infrared detection unit 31 at the time of measurement, and Vref is the output of the reference infrared detection unit 32 at the time of measurement It is.

  From the above equation (2), the calculation equation is the first gas concentration c1 and the second gas concentration c2, and the output ratios Rc1 and Rc2 of the reference infrared detection unit to the output of the measurement infrared detection unit at each gas concentration It is understood that the concentration calculation can be performed by substituting the output Vout of the measurement infrared detection unit at the time of measurement and the output Vref of the reference infrared detection unit at the time of measurement. Since the above equation (2) does not include the optical path length l (L) or the gain ratio G of the infrared detector for measurement and the infrared detector for reference, it is not necessary to derive them quantitatively or qualitatively in advance. It is understood that, since the calculation formula is compensated for individual variation, it is possible to measure the gas concentration with high accuracy.

<Derivation of Equation (2)>
Hereinafter, the derivation process of the above equation (2) will be described.
The outputs of the measuring infrared detection unit 31 and the reference infrared detection unit 32 are respectively signal amplified before the arithmetic processing in the arithmetic unit 40. The gain ratio at this time is G.
First, the gas concentration is calculated by the following equation (3) from Lambert-Beer's law.

In the equation, ε is the absorbance coefficient, l (L) is the actual optical path length, G is the gain ratio of the infrared detector for measurement 31 and the infrared detector for reference 32, and Vref is the output of the infrared detector for reference 32 , Vout are the outputs of the measurement infrared detector 31.
The output ratio between the output from the measuring infrared detection unit 31 and the output from the reference infrared detection unit 32 obtained when the light source 20 is turned on in the measurement target gas of any known first concentration c1 is Rc1. Then, the first concentration c1 is represented by the following formula (4).

  The following equation (5) is obtained from the above equations (3) and (4).

  The output ratio between the output from the measuring infrared detection unit 31 and the output from the reference infrared detection unit 32 obtained when the light source 20 is turned on in the measurement target gas of any known second concentration c2 is Rc2 By substituting the above equation (5), the following equation (6) is obtained.

  By substituting the above equation (6) into the above equation (5), the equation (2) can be obtained.

  From the above, the output of the measuring infrared detection unit obtained when the light source is turned on in the first concentration measurement target gas, the output of the reference infrared detection unit, and the light source in the second concentration measurement target gas Using the calculation formula obtained based on the output of the measurement infrared detection unit obtained when the light is turned on and the output of the reference infrared detection unit, the output and reference of the measurement infrared detection unit at two different known concentrations By obtaining the output of the infrared detector for this purpose only in advance, it is possible to derive a calculation formula that does not include the gain ratio G, the absorbance coefficient ε, and the optical path length l (El), and gas concentration measurement with higher accuracy than before is possible It will be understood that

Moreover, in the gas concentration measuring device according to the first embodiment, an offset may be added to each parameter of the equation (2). This makes it possible to further improve the accuracy of the gas concentration to be measured.
FIG. 2 is a circuit diagram of the operation unit shown in FIG.
The calculation unit 40 includes a coefficient calculation unit 41, a ratio calculation unit 42, a multiplication unit 43, and a density calculation unit 44.

The coefficient calculation unit 41 calculates a calculation formula including the coefficient ε. Further, the ratio calculation unit 42 calculates the ratio Vout / Vref of the output Vout of the measurement infrared detection unit 31 to the output Vref of the reference infrared detection unit 32 at the time of measurement.
Further, the multiplying unit 43 sets the ratio Vout (c1) / Vref (c1) of the first measurement output Vout (c1) to the first reference output Vref (c1) to the ratio Vout / Vref calculated by the ratio calculating unit 42. ) = Rc1 is multiplied.
Further, the concentration calculation unit 44 calculates the concentration c of the measurement target gas based on the calculation formula calculated by the coefficient calculation unit 41 and the value of the multiplication unit 43.

Second Embodiment
FIG. 3 is a configuration diagram for explaining a second embodiment of the gas concentration measurement device according to the present invention. The components having the same functions as those in FIG. 1 are denoted by the same reference numerals. That is, the configuration is such that the reference infrared detection unit 32 in FIG. 1 is removed. Although the gas cell 10 is clearly shown here for reference, the gas cell is not an essential component in the present invention, and even in a form without a gas cell, the gas concentration measuring device is disposed in the test container etc. It is possible to carry out two concentration tests.

The gas concentration measurement apparatus according to the second embodiment includes a light source 20, a measurement infrared detection unit 31 for receiving light from the light source 20, and an operation unit 40 to which an output from the measurement infrared detection unit 31 is input. It is a gas concentration measuring device provided.
The calculation unit 40 operates the infrared detection unit for measurement when the light source 20 is turned on in the measurement target gas of the first concentration c1, the second concentration c2 different from the first concentration c1, and the first concentration c1. The first measurement output Vout (c1) 31 and the second measurement output Vout (c2) output from the measurement infrared detector 31 when the light source 20 is turned on in the measurement target gas at the second concentration c2 And a value obtained by multiplying the value Vout based on the first measurement output Vout (c1) by the calculation equation including the coefficient ε obtained based on the output Vout from the measurement infrared detector 31 at the time of measurement Based on the calculated concentration c of the gas to be measured.

  The gas concentration measurement apparatus according to the second embodiment detects the infrared ray for measurement when the light source is turned on in the measurement target gas of the first concentration, the second concentration different from the first concentration, and the first concentration. Including a coefficient obtained on the basis of the first measurement output output by the unit and the second measurement output output by the infrared detection unit for measurement when the light source is turned on in the measurement target gas of the second concentration. Two different known concentrations are calculated by calculating the concentration of the gas to be measured based on the calculation formula and the value obtained by multiplying the value based on the first measurement output by the output from the measurement infrared detection unit at the time of measurement By acquiring the output of the measurement infrared detection unit in advance in advance, it is possible to perform gas concentration measurement with higher accuracy than in the prior art without using the reference infrared detection unit. In addition, since it is not necessary to use the reference infrared detection unit, it is possible to realize a more compact and low-cost gas concentration measuring apparatus.

Further, the coefficient ε is the ratio Vout of the first measurement c1 and the second concentration c2 different from the first concentration c1, and the second measurement output Vout (c2) to the first measurement output Vout (c1). It may be obtained based on (c2) / Vout (c1).
In addition, the calculation unit 40 is based on a calculation expression including the coefficient ε and a ratio Vout (c1) / Vout of the first measurement output Vout (c1) to the output Vout of the measurement infrared detection unit 31 at the time of measurement. The concentration c of the gas to be measured may be calculated.
Further, the calculation unit 40 calculates the concentration c of the gas to be measured based on the following equation (7). That is, as an example of a specific calculation formula in the gas concentration measurement device of the second embodiment, the following formula (7) may be mentioned.

In the equation, c1 is a first concentration, c2 is a second concentration, Vout (c1) is an output of the measuring infrared detection unit 31 at the first concentration c1, and Vout (c2) is at the second concentration c2. The output of the measurement infrared detection unit 31 and Vout are the output of the measurement infrared detection unit 31 at the time of measurement.
From the above equation (7), the calculation equation uses the output Vout (c1) of the infrared detection unit for measurement at each of the first gas concentration c1 and the second gas concentration c2 as a constant, and the measurement at the time of measurement It is understood that concentration calculation is possible by substituting the output Vout of the infrared detection unit. Since the above equation (7) does not include the optical path length l (L), it is not necessary to derive it quantitatively or qualitatively in advance, so it is a calculation equation in which the variation among individuals is compensated. It is understood that accurate gas concentration measurement is possible.

<Derivation of Equation (7)>
Hereinafter, the derivation process of the above equation (7) will be described.
The output of the measurement infrared detection unit 31 is signal amplified before the arithmetic processing in the arithmetic unit 40. The gain at this time is G.
First, from Lambert-Beil's law, the gas concentration in the case where the reference infrared detector is not used is derived by the following equation (8).

In the equation, ε is the absorbance coefficient, l (L) is the actual optical path length, Vout (0) is the virtual output of the infrared detection unit for measurement when there is no absorption by the gas to be measured, and Vout is the gas to be measured It is an output of the infrared detector for measurement when there is absorption.
Assuming that the output from the infrared detection unit for measurement obtained when the light source 20 is turned on in the measurement target gas of any known first concentration c1 is Vout (c1), the first concentration c1 has the following formula ( 9).

  By modifying the equations (8) and (9) to obtain the following equation (10).

  The output from the infrared detector for measurement obtained when the light source 20 is turned on in the measurement target gas of any known second concentration c2 is Vout (c2), and is substituted for the above equation (10). Then, the following equation (11) is obtained.

  By substituting the equation (11) into the equation (10), the equation (7) can be obtained.

From the above, the output of the measuring infrared detection unit obtained when the light source is turned on in the first concentration measurement target gas, and the measurement obtained when the light source is turned on in the second concentration measurement target gas By using the calculation formula obtained based on the output of the infrared detection unit, the output of the measurement infrared detection unit at two different known concentrations can be obtained in advance only by using Vout (0), the absorbance coefficient ε, and the optical path. It is understood that a calculation formula which does not include the length l (l) can be derived, and gas concentration measurement with higher precision than before can be performed.
However, it is assumed that Vout (0) is the same at calibration and measurement.
Moreover, in the gas concentration measuring device according to the second embodiment, an offset may be added to each parameter of the equation (7). This makes it possible to further improve the accuracy of the gas concentration to be measured.

FIG. 4 is a circuit diagram of the operation unit shown in FIG.
Components having the same functions as those in FIG. 2 are denoted by the same reference numerals. That is, the configuration is such that the multiplication unit 43 in FIG. 2 is removed.
The calculation unit 40 includes a coefficient calculation unit 41, a ratio calculation unit 42, and a density calculation unit 44.
The coefficient calculation unit 41 calculates a calculation formula including the coefficient ε. Further, the ratio calculation unit 42 calculates a ratio Vout (c1) / Vout of the first measurement output Vout (c1) to the output Vout of the measurement infrared detection unit 31 at the time of measurement.

Further, the concentration calculating unit 44 calculates the concentration c of the gas to be measured based on the calculation equation calculated by the coefficient calculating unit 41 and the ratio Vout (c1) / Vout calculated by the ratio calculating unit 42.
Hereinafter, each component of the gas concentration measuring apparatus of the present embodiment will be described. Specific examples and technical features of each component can be applied singly or in combination without departing from the technical concept of the present invention.

(Infrared detector)
The measuring infrared detection unit 31 and the reference infrared detection unit 32 have sensitivity to the infrared light output from the light source 20, and output a signal corresponding to the incident infrared light. The measurement infrared detection unit 31 is not particularly limited as long as the ratio of the sensitivity of the gas to be measured to the infrared absorption band to the sensitivity of the band other than the infrared absorption band is larger than that of the reference infrared detection unit 32. The infrared detection unit 31 for measurement and the infrared detection unit 32 for reference include a thermal infrared sensor such as a pyroelectric sensor (Pyroelectric sensor), a thermopile (Thermopile), a bolometer (Bolometer), a quantum infrared sensor, etc. It is suitable.

  The measurement infrared detection unit 31 and the reference infrared detection unit 32 may further include an optical filter having desired optical characteristics in addition to the measurement target gas. For example, when the gas to be measured is carbon dioxide gas, the measurement infrared detection unit 31 is equipped with a band pass filter capable of filtering out infrared rays in a wavelength range (typically around 4.3 μm) where much infrared absorption by carbon dioxide occurs. The form which mounts the band pass filter which can filter the infrared rays of the wavelength range (typically around 3.9 micrometers) which infrared absorption by carbon dioxide does not produce in the reference infrared detection part 32 is illustrated.

(light source)
The light source 20 is not particularly limited as long as the measurement infrared detection unit 31 and the reference infrared detection unit 32 can output an infrared band having sensitivity. For example, an incandescent lamp, a ceramic heater, a MEMS (Micro Electro Mechanical Systems) heater, an LED, or the like can be used.

(Operation unit)
The calculation unit 40 is not particularly limited as long as calculation in gas concentration calculation is possible, and for example, an analog IC, a digital IC, a CPU (Central Processing Unit), and the like are preferable. The calculation unit 40 may include a function for controlling the light source.

(Gas cell)
The gas concentration measuring apparatus of the present embodiment can introduce the gas to be measured inside, and can arrange the gas cell 10 in which the light source 20, the infrared detection unit for measurement 31, the infrared detection unit for reference 32, and the calculation unit 40 can be disposed. You may provide further. By further including the gas cell 10, the SNR of the signals output from the measurement infrared detection unit 31 and the reference infrared detection unit 32 can be increased, and a more accurate gas concentration measurement device is realized. It is preferable that the inside of the gas cell be formed of a material that reflects infrared light from the viewpoint of the efficiency of the infrared light incident on the infrared detection unit. Specifically, metal materials such as aluminum and copper can be mentioned.
Next, the gas concentration measuring device of the present embodiment will be described based on examples.

  Quantum type infrared sensor “IR1011” as an infrared detector 31 for measurement equipped with an optical filter for selectively filtering out a wavelength band of 4.2 μm to 4.4 μm having infrared absorption by CO 2 and tungsten light source Quantum type infrared sensor “IR1011” (Asahi Kasei Electronics Co., Ltd.) as an infrared detection unit 32 for reference equipped with an optical filter for selectively filtering out a 3.7 μm to 3.9 μm wavelength band without infrared absorption by CO 2 A carbon dioxide gas concentration measuring device was prepared in which an IC having a storage unit and a processing unit as an operation unit 40 was disposed on a printed circuit board.

  Next, the carbon dioxide concentration measuring apparatus is placed in a test container, and when the carbon dioxide gas having a concentration of 967 ppm is filled, the outputs from the measuring infrared detection unit 31 and the reference infrared detection unit 32 amplified by the amplifier, respectively. The gas concentration measuring apparatus according to the first embodiment described above from the outputs from the infrared detector for measurement 31 and the infrared detector for reference 32 amplified by the amplifier when carbon dioxide gas having a concentration of 2953 ppm is filled in the test container. An arithmetic expression corresponding to the following expression (12) in which the output offset of the measuring infrared detection unit 31 is added to the expression (7) in the above is derived.

In the equation, a1 represents the offset of the measurement infrared detection unit 31, and R1 (c1) represents the value obtained by subtracting the offset from the output value of the measurement infrared detection unit 31 at the first gas concentration. The ratio of output values, R1 (c2), is the ratio of the output value of the reference infrared detection unit 32 to the value obtained by subtracting the offset from the output value of the measurement infrared detection unit 31 at the second gas concentration.
Since an offset may occur also to parameters other than the output of the measurement infrared detection unit 31, the offset is added to each parameter as necessary as shown in the following equation (13).

In the equation, a2 is the offset of the reference infrared detection unit, R2 (c1) is the output of the reference infrared detection unit 32 for the value obtained by subtracting the offset from the output value of the measurement infrared detection unit 31 at the first gas concentration. The ratio of the value obtained by subtracting the offset from the value, R2 (c2) is the offset from the output of the reference infrared detector 32 for the value obtained by subtracting the offset from the output of the measurement infrared detector 31 at the second gas concentration It is the ratio of the value minus the minutes.
The offsets such as a1 and a2 are obtained by measuring the sensitivity spectra of the infrared detector 31 for measurement and the infrared detector 32 for reference obtained from representative samples, the optical offset obtained from the emission spectrum of the light source 20, and It is a representative value obtained by adding the offsets.

Comparative Example 1
When the test container is filled with carbon dioxide at a concentration of 967 ppm, when the outputs from the infrared detection unit for measurement and the infrared detection unit for reference amplified by the amplifier are filled with carbon dioxide at a concentration of 2953 ppm. Primary from the output from the measuring infrared detection unit and the reference infrared detection unit amplified by the amplifier, the correlation between the carbon dioxide concentration and the output ratio of the reference infrared detection unit to the output of the measuring infrared detection unit I derived the function.

Quantum type infrared sensor “IR1011” as an infrared detector 31 for measurement equipped with an optical filter for selectively filtering out a wavelength band of 4.2 μm to 4.4 μm having infrared absorption by CO 2 and tungsten light source A carbon dioxide gas concentration measuring device provided with an IC having a storage unit and a processing unit as a calculation unit 40 was prepared.
Next, the carbon dioxide concentration measuring apparatus is installed in the test container, and when the carbon dioxide gas having a concentration of 967 ppm is filled in the test container, the output from the infrared detector 31 for measurement amplified by the amplifier and the concentration of 2953 ppm From the output from the measuring infrared detection unit 31 amplified by the amplifier when carbon dioxide gas is filled in the test container, the above-mentioned equation (7) in the gas concentration measuring apparatus of Embodiment 2 described above is subjected to the measurement infrared detection unit An operational expression corresponding to the following expression (14) in which the output offset of the above is added is derived.

  The offsets such as a1 and a2 are obtained by measuring the sensitivity spectra of the infrared detector 31 for measurement and the infrared detector 32 for reference obtained from representative samples, the optical offset obtained from the emission spectrum of the light source 20, and It is a representative value obtained by adding the offsets.

Comparative Example 2
The output of the infrared detection unit for measurement amplified by the amplifier when carbon dioxide gas having a concentration of 967 ppm is filled in the test container, and the measurement amplified by the amplifier when the carbon dioxide gas having a concentration of 2953 ppm is filled in the test container From the output of the infrared detecting unit, a linear function representing the correlation between the carbon dioxide concentration and the output of the infrared detecting unit was derived.
FIG. 5 is a diagram showing the result of comparison between Example 1 and Comparative Example 1 described above.
From the results of FIG. 5, according to the operation equation of Example 1, the error was only 25 ppm at -12 ppm at 396 ppm, 0 ppm at 967 ppm, 38 ppm at 1919 ppm, 0 ppm at 2953 ppm and 4914 ppm.

On the other hand, according to the calculation formula of Comparative Example 1, an error of -154 ppm at 396 ppm, 0 ppm at 967 ppm, 77 ppm at 1919 ppm, 0 ppm at 2953 ppm, and -375 ppm at 4914 ppm occurred.
From the above results, it is understood that according to the gas concentration calculation device of the first embodiment, highly accurate concentration calculation is possible in a wider range than the conventional concentration calculation formula.

FIG. 6 is a diagram showing the result of comparison between Example 2 and Comparative Example 2 described above.
From the results of FIG. 6, according to the calculation formula of Example 2, the error remained at -8 ppm at 396 ppm, 0 ppm at 967 ppm, 41 ppm at 1919 ppm, 0 ppm at 2953 ppm, and 19 ppm in the high concentration region of 4914 ppm.
On the other hand, according to the calculation formula of Comparative Example 2, an error of -130 ppm at 396 ppm, 0 ppm at 967 ppm, 115 ppm at 1919 ppm, 0 ppm at 2953 ppm, and -496 ppm occurred at 4914 ppm.

From the above results, it is understood that according to the gas concentration calculation device of the second embodiment, even when the reference infrared detection unit is not used, highly accurate concentration calculation can be performed in a wider range than the conventional concentration calculation formula. Ru.
As mentioned above, although embodiment of this invention was described, the technical scope of this invention is not limited to the technical scope as described in embodiment mentioned above. It is also possible to add various changes or improvements to the embodiment described above, and it is possible from the description of the claims that forms obtained by adding such changes or improvements can be included in the technical scope of the present invention. it is obvious.

  The present invention is suitable as a gas concentration measuring device for a gas that produces infrared absorption represented by carbon dioxide gas and the like.

Reference Signs List 10 gas cell 11 gas inlet 12 gas outlet 20 light source 31 infrared detection unit for measurement 32 infrared detection unit for reference 40 operation unit 41 coefficient calculation unit 42 ratio operation unit 43 multiplication unit 44 concentration operation unit

Claims (12)

Light source,
An infrared detector for measurement that receives light from the light source;
A reference infrared detection unit disposed in the vicinity of the measurement infrared detection unit;
A calculation unit to which outputs from the measurement infrared detection unit and the reference infrared detection unit are input;
A gas concentration measuring device comprising
The arithmetic unit is
The first concentration,
A second concentration different from the first concentration;
A first measurement output that the infrared detection unit for measurement outputs when the light source is turned on in the gas to be measured of the first concentration;
A first reference output that the reference infrared detector outputs when the light source is turned on in the first concentration measurement target gas;
A second measurement output that is output by the infrared detection unit for measurement when the light source is turned on in the measurement target gas of the second concentration;
A second reference output that the reference infrared detection unit outputs when the light source is turned on in the measurement target gas of the second concentration;
A calculation formula including a coefficient obtained based on
Measurement based on a value obtained by multiplying the ratio of the output of the infrared measuring unit for measurement to the output of the infrared detecting unit for reference at the time of measurement by the value based on the first measurement output and the first reference output A gas concentration measuring device that calculates the concentration of the target gas. The factor is
The first concentration,
A second concentration different from the first concentration;
A ratio of the first reference output to the first measured output;
The gas concentration measurement device according to claim 1, obtained based on a ratio of the second reference output to the second measurement output. The arithmetic unit is
A formula including the coefficient,
Measurement target based on a value obtained by multiplying the ratio of the first measurement output to the first reference output by the ratio of the output of the measurement infrared detection unit to the output of the reference infrared detection unit at the time of measurement The gas concentration measuring device according to claim 1 or 2 which calculates concentration of gas. The gas concentration measuring device according to any one of claims 1 to 3, wherein the calculation unit calculates the concentration of the gas to be measured based on the following equation (1).

(Wherein, c1 is the first concentration, c2 is the second concentration, Rc1 is the output ratio of the reference infrared detection unit to the output of the measurement infrared detection unit at the first concentration, and Rc2 is the measurement at the second concentration The output ratio of the reference infrared detection unit to the output of the reference infrared detection unit, Vout is the output of the measurement infrared detection unit at the time of measurement, and Vref is the output of the reference infrared detection unit at the time of measurement.)   The gas concentration measuring device according to claim 4, wherein an offset is added to each parameter of the equation (1). The arithmetic unit is
A coefficient calculation unit that calculates a calculation formula including the coefficient;
A ratio calculation unit that calculates a ratio of an output of the infrared detection unit for measurement to an output of the infrared detection unit for reference at the time of measurement;
A multiplication unit that multiplies the ratio calculated by the ratio calculation unit by the ratio of the first measurement output to the first reference output;
A concentration calculation unit that calculates the concentration of the gas to be measured based on the calculation formula calculated by the coefficient calculation unit and the value of the multiplication unit;
The gas concentration measuring device according to any one of claims 1 to 5, comprising: Light source,
An infrared detector for measurement that receives light from the light source;
An operation unit to which an output from the measurement infrared detection unit is input;
A gas concentration measuring device comprising
The arithmetic unit is
The first concentration,
A second concentration different from the first concentration;
A first measurement output output from the measurement infrared detection unit when the light source is turned on in the first concentration measurement target gas;
A second measurement output that the infrared detection unit for measurement outputs when the light source is turned on in the measurement target gas of the second concentration;
A calculation formula including a coefficient obtained based on
A gas concentration measuring device that calculates the concentration of a gas to be measured based on a value obtained by multiplying an output from an infrared detection unit for measurement at the time of measurement by a value based on the first measurement output. The factor is
The first concentration,
A second concentration different from the first concentration;
The gas concentration measuring device according to claim 7, obtained based on the ratio of the second measurement output to the first measurement output. The arithmetic unit is
A formula including the coefficient,
9. The gas concentration measuring apparatus according to claim 7, wherein the concentration of the gas to be measured is calculated based on the ratio of the first measurement output to the output of the measurement infrared detection unit at the time of measurement. The gas concentration measuring device according to any one of claims 7 to 9, wherein the calculation unit calculates the concentration of the gas to be measured based on the following equation (2).

(Wherein, c1 is the first concentration, c2 is the second concentration, Vout (c1) is the output of the infrared detector for measurement at the first concentration, and Vout (c2) is the infrared detection for measurement at the second concentration The output of the unit, Vout is the output of the measuring infrared detection unit at the time of measurement.)   The gas concentration measuring apparatus according to claim 10, wherein an offset is added to each parameter of the equation (2). The arithmetic unit is
A coefficient calculation unit that calculates a calculation formula including the coefficient;
A ratio calculation unit that calculates a ratio of the first measurement output to an output of the measurement infrared detection unit at the time of measurement;
A concentration calculation unit that calculates the concentration of the gas to be measured based on the calculation formula calculated by the coefficient calculation unit and the ratio calculated by the ratio calculation unit;
The gas concentration measuring device according to any one of claims 7 to 11, comprising:

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