JP2017015678A - Gas concentration measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow two concentration inspections to measure gas concentration with high accuracy.SOLUTION: A computation unit 40 in a gas concentration measurement device of the present invention is configured to: standardize a measurement output upon measurement by a first measurement output; substitute the standardized measurement output into a concentration calculation expression including a coefficient to be obtained from a first measurement output to be output by a measurement infrared detection unit 31 when lighting a light source 20 in measurement object gas of first concentration, a second measurement output to be output by the measurement infrared detection unit 31 when lighting the light source 20 in measurement object gas of second concentration different from the first concentration, a first solution serving a value of a variable when concentration to be obtained from a reference concentration calculation expression is the first concentration, and a second solution serving a value of a variable when concentration to be obtained from the reference concentration calculation expression is the second concentration, an expression having the reference concentration calculation corrected by the first solution and the first concentration, and the first concentration; and thereby compute concentration of the measurement object gas.SELECTED DRAWING: Figure 1

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.

  Conventionally, as a gas concentration measurement device that measures the concentration of the gas to be measured in the atmosphere, the gas concentration is measured by detecting the amount of absorption using the fact that the wavelength of infrared rays that are absorbed depends on the type of gas Non-dispersive Infrared gas concentration measuring devices are known. As a gas concentration measurement device using this principle, for example, by combining a filter (transmission member) that transmits infrared light limited to a wavelength with which the measurement target gas has absorption characteristics and an infrared sensor, the amount of infrared absorption is measured. The gas concentration can be measured.

In addition, as a gas concentration measuring device using the 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 infrared absorption by the measurement target gas does not occur. , A plurality of infrared detection elements each having a measurement filter that selectively transmits infrared light in a wavelength range in which infrared absorption by the measurement target gas occurs, and the measurement target gas based on an output signal from each infrared detection element Are a carbon dioxide concentration measuring device and a carbon dioxide detection method that improve detection accuracy and output stability.
In the following, these are 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 as the light source, the infrared rays having a wavelength of about 4.3 μm are absorbed by the carbon dioxide gas in the gas container, and the radiation intensity is reduced. On the other hand, infrared rays having a wavelength of 3.9 μm are not absorbed by carbon dioxide gas, and their radiation intensity does not decrease.

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

JP-A-9-33431

  In the non-dispersive infrared absorption type gas concentration measuring device, the output of the infrared detecting unit for measurement is ideally obtained according to the following equation (1) obtained based on Lambert-Beer's law (Lambert-Beer_law).

(Where c is the gas concentration, ε is the absorbance coefficient, l (el) is the actual optical path length, V _out (0) is the virtual output of the infrared detector for measurement when there is no absorption by the gas to be measured, V _out is the output of the measurement infrared detector when there is absorption by the gas to be measured.)
However, the actual output characteristics deviate from the Log function as shown in Equation (1) due to the influence of circuit and optical offset included in the output of the measurement infrared detection unit. The circuit-like offset here is caused by, for example, an amplifier circuit included in the measurement infrared detector. The optical offset is caused by, for example, incidence of light having a wavelength that is not absorbed by the measurement target gas into the measurement infrared detection unit.

Further, the optical path length from the light source to the measurement infrared detection unit and the virtual output of the measurement infrared detection unit when there is no absorption by the measurement target gas vary from individual to individual.
Therefore, when calculating the concentration value of the measurement target gas on the premise of the two-concentration test, conventionally, for example, a quadratic function that outputs the concentration of the measurement target gas with the output of the measurement infrared detector as a variable is defined. A function for density calculation is determined by determining one of the three coefficients included in the next function as a fixed value and obtaining the remaining two coefficients from the two-density test. However, this calculation method cannot completely compensate for the effects of circuit and optical offsets, the effects of many optical paths, the optical output length of the measurement infrared detector when there is no absorption by the optical path length and the gas to be measured, and so on. The calculation accuracy was low.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a gas concentration measuring apparatus capable of measuring a gas concentration with high accuracy by a two-concentration test.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by the following invention, and have completed the present invention.
According to an aspect of the present invention, a gas including a light source, a measurement infrared detection unit that receives light from the light source and outputs a measurement output that is a signal corresponding to the light, and a calculation unit to which the measurement output is input. In the concentration measurement device, the calculation unit outputs a first measurement output that is output from the measurement infrared detection unit when the light source is turned on in the measurement target gas having the first concentration, and a second that is different from the first concentration. Is the second measurement output output from the measurement infrared detection unit when the light source is turned on in the measurement target gas having the concentration, and the value of the variable when the concentration obtained from the reference concentration calculation formula is the first concentration. The coefficient obtained from the first solution and the second solution which is the value of the variable when the concentration obtained from the reference concentration calculation formula is the second concentration, and the reference concentration calculation formula are expressed as the first solution and the first solution. The measurement output at the time of measurement is added to the density calculation formula including the formula corrected with the density of 1 and the first density. A gas concentration measuring apparatus which calculates a concentration of the measurement target gas by substituting normalized by the first measurement output.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to implement | achieve the gas concentration measuring apparatus using the calculation which can measure a gas concentration with high precision.

It is a figure for demonstrating embodiment of the gas concentration measuring apparatus which concerns on this invention. It is a figure for demonstrating the structure which added the infrared rays detection part for a reference in embodiment of the gas concentration measuring apparatus which concerns on this invention. It is a figure which shows the result which contrasted the Example and comparative example which were mentioned above.

In the following detailed description, numerous specific specific configurations are described to provide a thorough understanding of embodiments of the invention. However, it will be apparent that other embodiments may be practiced without limitation to such specific specific configurations. Further, the following embodiments do not limit the invention according to the claims, but 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]
FIG. 1 is a diagram for explaining an embodiment of a gas concentration measuring apparatus according to the present invention. In the figure, reference numeral 1 is a gas concentration measuring device, 10 is a gas cell, 11 is a gas inlet, 12 is a gas outlet, 20 is a light source, 31 is an infrared detector for measurement, 40 is a calculator, and L is the optical path length of the shortest distance. Is shown. In addition, although the gas cell 10 is clearly shown here for reference, the gas cell is not an essential configuration in the present invention, and even in a form without the gas cell, a gas concentration measuring device is arranged in a test container or the like, and the same as described below. A two-concentration test can be performed.

The gas concentration measuring apparatus 1 of the present embodiment receives a light source 20, a measurement infrared detector 31 that receives light from the light source 20 and outputs a measurement output that is a signal corresponding to the light, and a measurement output. A gas concentration measuring device including a calculation unit 40.
The calculation unit 40 measures the first measurement output output from the measurement infrared detection unit 31 when the light source 20 is turned on in the measurement gas having the first concentration, and the measurement of the second concentration different from the first concentration. The second measurement output that is output from the measurement infrared detector 31 when the light source 20 is turned on in the target gas, and the first value that is a variable value when the concentration obtained from the reference concentration calculation formula is the first concentration. And the second solution which is the value of the variable when the concentration obtained from the reference concentration calculation formula is the second concentration, the coefficient obtained from the first solution and the first solution The concentration of the measurement target gas is calculated by normalizing and substituting the measurement output at the time of measurement with the first measurement output into the concentration calculation equation including the equation corrected by the concentration and the first concentration. As a result, it is possible to provide a gas concentration measuring apparatus capable of measuring the gas concentration with high accuracy by the two concentration inspection.

In the gas concentration measuring apparatus 1 of the present embodiment, the coefficient is obtained from the ratio between the second measurement output and the first measurement output, and the ratio between the second solution and the first solution. May be. As a result, there is an effect that density calculation with higher accuracy becomes possible.
In the gas concentration measuring apparatus 1 of the present embodiment, the reference concentration calculation formula is an nth order polynomial, and the concentration calculation formula corrects the first to nth order coefficients of the reference concentration calculation formula with the first solution. Alternatively, the equation obtained by correcting the zeroth-order coefficient with the first density may be multiplied by the coefficient, and then the first density may be added. As a result, there is an effect that density calculation with higher accuracy becomes possible.
Further, when the reference concentration calculation formula in the gas concentration measuring apparatus 1 of the present embodiment is an nth order polynomial (formula (2)), the following formula (3) is given as an example of a specific gas concentration calculation method. It is done.

(Wherein, _{a n} is the n-th order _{coefficient, V std} is a variable reference density calculation formula.)

(Where c is the gas concentration, c ₁ is the first concentration, c ₂ is the second concentration, V _out (c ₁ ) is the measurement output at the first concentration, and V _out (c ₂ ) is the second concentration. , V _std (c ₁ ) is a variable when the output of the reference concentration calculation formula is the first concentration, and V _std (c ₂ ) is the output of the reference concentration calculation formula is the second concentration. ( _Vout is a measurement output at the time of measurement.)
Equation (3) is obtained by calculating the measured outputs V _out (c ₁ ) and V _out (c ₂ ) at the respective concentrations of the first concentration and the second concentration, and the variable V _std of the reference concentration calculation formula at each concentration. _{(c 1),} and _V std _{(c 2),} and the n-th coefficient _{a n} constants reference density calculating equation, only substituting the measured output _{V out} at the time of measurement, it is possible density arithmetic Is understood.

Here, looking at the equation (3), the equation (2) of the reference concentration calculation equation is corrected to an arithmetic equation in accordance with the concentration characteristic of the gas concentration measuring device of the present embodiment, whereby the light source The gas path can be calculated with higher accuracy by reducing the influence of individual variations in the optical path length from the measurement infrared detector to the measurement infrared detector and the virtual output of the measurement infrared detector when there is no absorption by the measurement target gas. It turns out that it becomes.
Further, when the reference concentration calculation formula in the gas concentration measuring apparatus 1 of the present embodiment is a logarithmic function (Formula (4)), Formula (5) is given as an example of a specific calculation method of the gas concentration.

(In the formula, d _{1 to 4} are coefficients of the reference concentration calculation formula.)

The above equation (5) is obtained by measuring the output V _out (c ₁ ) and V _out (c ₂ ) at the respective concentrations of the first concentration and the second concentration, and the variable V of the reference concentration calculation formula at each concentration. _Std (c ₁ ), V _std (c ₂ ) and coefficients d ₁ to ₄ of the reference concentration calculation formula are constants, and concentration calculation is possible only by substituting measurement output V _out at the time of measurement. Is understood.
Here, looking at the equation (5), the equation (4) of the reference concentration calculation equation is corrected as an arithmetic equation in accordance with the concentration characteristic of the gas concentration measuring apparatus of the present embodiment, whereby the light source The gas path can be calculated with higher accuracy by reducing the influence of individual variations in the optical path length from the measurement infrared detector to the measurement infrared detector and the virtual output of the measurement infrared detector when there is no absorption by the measurement target gas. It turns out that it becomes.

Further, from the equations (5) and (3), in the gas concentration measurement apparatus of the embodiment, the first measurement output from the measurement infrared detection unit when the light source is turned on in the measurement target gas having the first concentration. The output, the second measurement output output from the measurement infrared detection unit when the light source is turned on in the measurement target gas having the second concentration different from the first concentration, and the concentration obtained from the concentration calculation formula are the first A coefficient obtained from a first solution that is a value of a variable when it is a concentration, a second solution that is a value of a variable when the concentration obtained from the reference concentration calculation formula is a second concentration, and a reference The measurement output at the time of measurement is normalized with the first measurement output and substituted into the concentration calculation expression including the first solution, the expression obtained by correcting the concentration calculation expression with the first solution, the first concentration, and the first concentration. Thus, it is understood that highly accurate concentration calculation is possible.
Further, from the equations (5) and (3), in the gas concentration measurement apparatus of the present embodiment, the coefficient is the ratio between the second measurement output and the first measurement output, the second solution, and the first solution. It is understood that the density calculation can be performed with high accuracy by obtaining from the above ratio.

<Derivation of Formula (3)>
Hereinafter, the derivation process of Formula (3) will be described.
From the Lambert-Beer law (Lambert-Beer_law), the gas concentration measurement device of this embodiment should be able to calculate the concentration of the measurement target gas based on the equation (6).

(Where c is the gas concentration, ε is the absorbance coefficient, l is the actual optical path length, V _out (0) is the virtual measurement output when there is no absorption by the gas to be measured, and V _out is the measurement. (Measurement output at the time.)
However, equation (6) includes the actual optical path length l that varies from individual to individual and the virtual measurement output V _out (0) when there is no absorption by the measurement target gas. Therefore, a mathematical expression that does not include these variation factors is derived from the measurement output at any known first density and second density.
Assuming that the first measurement output V _out (c ₁ ) output from the measurement infrared detection unit when the light source is turned on in the measurement target gas having any known first concentration, the first concentration c ₁ is It is represented by Formula (7).

  From the above formulas (6) and (7), the following formula (8) is obtained.

When the measurement output obtained when the light source is turned on in any measurement gas having a known second concentration c ₂ is V _out (c2) and is substituted into the above equation (8) and transformed, the equation ( 9) is obtained.

  By substituting equation (9) into equation (8), equation (10) can be obtained.

However, due to the influence of circuit and optical offset included in the output of the measurement infrared detection unit, the actual characteristics deviate from the Log function such as the above equation (10). The circuit-like offset is generated in, for example, an amplifier circuit included in the measurement infrared detection unit. The optical offset is caused by, for example, incidence of light having a wavelength that is not absorbed by the measurement target gas into the measurement infrared detection unit.
Therefore, a reference concentration calculation formula such as equation (2) is defined, and the concentration calculation formula is derived therefrom. The reference concentration calculation formula here is an approximate expression of a gas concentration characteristic in a separate gas concentration measurement apparatus showing a gas concentration characteristic close to that of the gas concentration measurement apparatus of the present embodiment, that is, a concentration calculation expression.

(Wherein, _{a n} is the n-th order _{coefficient, V std} is a variable reference density calculation formula.)
Expression (10) is transformed into Expression (11).

(In the formula, V _std (c ₁ ) is a variable of the reference concentration calculation formula when the value obtained from the reference concentration calculation formula is the first concentration.)
Further, when the Log function of Expression (10) is replaced with a polynomial, Expression (12) is obtained.

(Where b _n is an n-th order coefficient.)
Replacing V _out in equation (12) with V _std , V _out (c ₁ ) with V _std (c ₁ ), and V _out (c ₂ ) with V _std (c ₂ ) yields equation (13). .

(In the formula, V _std (c ₂ ) is a variable of the reference concentration calculation formula when the value obtained from the reference concentration calculation formula is the second concentration.)
Assuming that Expression (11) is equal to Expression (13) and obtaining coefficients such as b _n , Expression (14-0) to Expression (14-n) are obtained.

  When Expression (14-0) to Expression (14-n) are substituted into Expression (12), Expression (3) can be obtained.

<Derivation of Formula (5)>
Hereinafter, the derivation process of Formula (3) will be described.
As described above, since the formula (10) has a deviation from the actual characteristics, a reference density calculation formula like the formula (4) is defined, and the density calculation formula is derived therefrom. The reference concentration calculation formula here is an approximate expression of a gas concentration characteristic in a separate gas concentration measurement apparatus showing a gas concentration characteristic close to that of the gas concentration measurement apparatus of the present embodiment, that is, a concentration calculation expression.

( _Where d _{1 to 4} are constants, and V _std is a variable of the reference concentration calculation formula.)
Equation (4) is transformed into Equation (5).

(In the formula, V _std (c ₁ ) is a variable of the reference concentration calculation formula when the value obtained from the reference concentration calculation formula is the first concentration.)
Further, when an offset or the like is added to the Log function of Expression (10), Expression (16) is obtained.

( _Wherein e _{1 to 4} are constants)
When V _out in equation (16) is replaced with V _std , V _out (c ₁ ) is replaced with V _std (c ₁ ), and V _out (c ₂ ) is replaced with V _std (c ₂ ), equation (17) is obtained. .

(In the formula, V _std (c ₂ ) is a variable of the reference concentration calculation formula when the value obtained from the reference concentration calculation formula is the second concentration.)
Assuming that the formula (15) and the formula (17) are equal, e ₁ to ₄ are obtained, thereby obtaining the formula (18-1) to the formula (18-4).

  By substituting Equations (18-1) to (18-4) into Equation (17), Equation (5) can be obtained.

  Further, in the gas concentration measurement device according to the present embodiment, the gas concentration measurement device further includes a reference infrared detection unit that receives light from the light source and outputs a reference output that is a signal corresponding to the light, and an arithmetic unit May correct the measurement output with the reference output.

FIG. 2 is a diagram for explaining a configuration in which a reference infrared detecting unit is added in the embodiment of the gas concentration measuring apparatus according to the present invention. Reference numeral 32 in the figure denotes a reference infrared detection unit. In addition, the same code | symbol is attached | subjected to the component which has the same function as the component described in FIG. In addition, although the gas cell 10 is clearly shown here for reference, the gas cell is not an essential configuration in the present invention, and even in a form without the gas cell, a gas concentration measuring device is arranged in a test container or the like, and the same as described below. A two-concentration test can be performed.
Even if V _out (0) in Equation (1) (the output of the infrared detecting unit for measurement when there is no absorption by the measurement target gas) changes over time by correcting the measurement output based on the reference output Since the amount of change can be corrected, the gas concentration can be measured with higher accuracy than before.
A specific example of the correction is equation (19).

(In the formula, V _std ′ is a measurement output corrected with a reference output.)
Also, the denominator and numerator on the right side of Equation (19) may be reversed.
Further, in the gas concentration measurement apparatus according to the present embodiment, the calculation unit converts at least one of the measurement output and the reference output when the light source is turned on into at least one of the measurement output and the reference output when the light source is turned off. Corrections may be made based on this.
As a specific example of the correction, the difference between the measurement output and the reference output when the light source is turned on and the measurement output and the reference output when the light source is turned off is obtained as in Expression (20) and Expression (21). and so on.

(In the formula, D _OUT is a value obtained by correcting the measurement output when the light source is turned on with the measurement output when the light source is turned off, and D _ref is the reference output when the light source is turned on when the light source is turned off. those of the corrected reference _{output, V out_on} measurement output when is lit light _{source, V out_off} measurement output when turns off the light _{source, V ref_on} reference output when is lit light _{source, V ref_off} is This is a reference output when the light source is turned off.
Here, the state in which the light source is turned on refers to a state in which the light source emits more infrared rays than the amount of infrared rays emitted from the surrounding environment.
Moreover, the state where the light source is turned off may not be a state where the light source is completely turned off.
Regardless of whether or not power is supplied to the light source, even if the light source emits infrared rays, if the amount of infrared rays emitted is less than or equal to the amount of infrared rays emitted when the light source is turned on, or infrared rays emitted from the surrounding environment When the amount is equal to or less than the amount, the light source is considered to be in a light-off state because it is in a state of substantially not emitting infrared rays.

Based on the measurement output and reference output when the light source is turned off, the circuit offset included in the measurement output and reference output can be corrected by correcting the measurement output and reference output when turning on the light source. There is an effect that the gas concentration can be measured with higher accuracy than before.
Here, the circuit-like offset is, for example, an output offset of an amplifier circuit incorporated in a measurement infrared detection or reference infrared detection unit.
Hereinafter, each component in the gas concentration measuring apparatus of this embodiment is demonstrated. Specific examples and technical features of each constituent element can be applied alone or in combination without departing from the technical idea of the present invention.

(Infrared detector for measurement and infrared detector for reference)
The infrared detecting unit for measurement and the infrared detecting unit for reference have sensitivity to the infrared rays output from the light source, and output signals corresponding to the incident infrared rays. The measurement infrared detection unit is not particularly limited as long as the ratio of the sensitivity to the infrared absorption band by the measurement target gas to the sensitivity to the band other than the infrared absorption band is larger than that of the reference infrared detection unit. Thermal infrared sensors such as pyroelectric sensors, thermopiles, bolometers, quantum infrared sensors, and the like are suitable for the measurement infrared detection unit and the reference infrared detection unit. is there.
The measurement infrared detection unit and the reference infrared detection unit may further include an optical filter having desired optical characteristics in addition to the measurement target gas. For example, when the measurement target gas is carbon dioxide, the measurement infrared detector is equipped with a bandpass filter capable of filtering infrared light in a wavelength band (typically around 4.3 μm) where infrared absorption by carbon dioxide occurs a lot. Examples of the reference infrared detection unit include a band-pass filter capable of filtering infrared light in a wavelength band (typically around 3.9 μm) in which infrared absorption by carbon dioxide gas does not occur.

(light source)
The light source is not particularly limited as long as the measurement infrared detection unit and the reference infrared detection unit can output a sensitive infrared band. For example, an incandescent bulb, a ceramic heater, a MEMS (Micro Electro Mechanical Systems) heater, an LED, or the like can be used.
(Calculation unit)
The calculation unit is not particularly limited as long as it can perform calculation in gas concentration calculation. For example, an analog IC, a digital IC, and a CPU (Central Processing Unit) are suitable. The calculation unit may include a function for controlling the light source.

(Gas cell)
The gas concentration measurement apparatus of the present embodiment may further include a gas cell capable of flowing a measurement target gas therein and in which a light source, a measurement infrared detection unit, a reference infrared detection unit, a calculation unit, and the like can be disposed. good. Here, “inflowable” means that the infrared light output from the light source can reach the measurement infrared detection section through the space where the measurement target gas exists. By further providing a gas cell, the signal-to-noise ratio of signals output from the measurement infrared detection unit and the reference infrared detection unit can be increased, and a more accurate gas concentration measurement device is realized. From the viewpoint of increasing the efficiency of infrared rays incident on the infrared detection unit, the gas cell is preferably formed of a material that reflects infrared rays. Specifically, metal materials, such as aluminum and copper, are mentioned.
Next, examples of the gas concentration measuring apparatus according to this embodiment will be described.

Quantum infrared sensor “IR1011” (Asahi Kasei Electronics) as an infrared detector 31 for measurement equipped with a tungsten light source, an optical filter that selectively filters a wavelength band of 4.2 μm to 4.4 μm where infrared absorption by CO ₂ is absorbed Co., Ltd.), IR type infrared sensor “IR1011” (Asahi Kasei Co., Ltd.) as a reference infrared detector equipped with an optical filter that selectively filters the wavelength band of 3.7 μm to 3.9 μm without infrared absorption by CO ₂ Electronics Co., Ltd.), a carbon dioxide concentration measuring device was prepared in which an IC having a storage unit and a processing unit as a calculation unit was placed in a gas cell in which phosphor bronze was gold-plated.

Next, when the light source is turned on and off when carbon dioxide with a concentration of 0 ppm is filled in the gas cell, the output from the measurement infrared detection unit and the reference infrared detection unit amplified by the amplifier, and the concentration Using the output from the measurement infrared detector and the reference infrared detector amplified by the amplifier when the light source is turned on and off when 986 m of carbon dioxide gas is filled in the gas cell, The concentration calculation of the embodiment was performed.
The specific calculation is as follows.
Hereinafter, the measurement output described in this embodiment is the difference between the measurement output when the light source is turned on and the measurement output when the light source is turned off, and the reference output is the light source turned on. The difference between the reference output at the time and the reference output when the light source is turned off.

First, the ratio of the reference output to the measurement output at the time of measurement (D _out '), the ratio of the reference output to the measurement output at the carbon dioxide concentration of 0 ppm (D _out (c ₁ )'), and the measurement at the carbon dioxide concentration of 986 ppm The ratio of the reference output to the output (D _out (c ₂ ) ′), the value of the variable of the reference concentration calculation formula when the value obtained from the reference concentration calculation formula is 0 (V _std (c ₁ )), the reference concentration calculation formula The value (V _std (c ₂ )) of the reference concentration calculation equation when the value obtained from 986 is 986 was calculated. Next, V _out (c ₁ ) = D _out (c ₁ ) ′ and V _out (c ₂ ) = D _out (c ₂ ) ′ are set, and a necessary value is substituted into equation (3) to calculate the carbon dioxide concentration. did.

  The reference concentration calculation formula is the ratio of the carbon dioxide concentration and the reference output to the measured output of a separate gas concentration measuring device (standard gas concentration measuring device) that exhibits gas concentration characteristics close to those of the gas concentration measuring device used here. Is a mathematical expression that directly or approximately represents the relationship. Here, the reference concentration calculation formula like Formula (22) was derived | led-out from the density | concentration test result in 0-5000 ppm of the reference gas concentration measuring apparatus.

Here, f (V _std ) is a variable for the reference concentration calculation formula, and V _std is a variable for the reference concentration calculation formula.

[Comparative example]
Hereinafter, the measurement output described in this comparative example is the difference between the measurement output when the light source is turned on and the measurement output when the light source 20 is turned on, and the reference output is the light source turned on. The difference between the reference output at the time and the reference output when the light source is turned off.
First, a concentration calculation formula was prepared, in which the second-order coefficient is fixed and the first-order coefficient (b ₁ ) and the zero-order coefficient (b ₀ ) are undetermined, such as Expression (23).

Here, g (D _out ′) is the concentration calculation formula in the comparative example, D _out ′ is the output of the reference infrared detection unit relative to the output of the measurement infrared detection unit at the time of measurement, and f ₁ is the primary of the concentration calculation formula. coefficient, f ₀ is the zero-order coefficient of the density calculating equation.
The second-order coefficient of the concentration calculation formula (formula (23)) is the measurement output for the carbon dioxide concentration and the reference output of a separate gas concentration measurement device that exhibits a gas concentration characteristic close to that of the gas concentration measurement device used here. Is a secondary coefficient of a quadratic approximate expression that represents the relationship with the ratio of. Here, a quadratic approximate expression representing the relationship between the carbon dioxide concentration and the ratio of the measured output to the reference output is obtained from the concentration test results at 5 points of 0 to 5000 ppm of the standard gas concentration measuring apparatus used in the example ( Formula (22)) and the quadratic coefficient of the quadratic function were used as the secondary coefficient in the concentration calculation formula (formula (23)).

  Next, the first-order coefficient and the zero-order coefficient of the equation (22) are obtained by using the output of the reference infrared detection unit relative to the output of the measurement infrared detection unit 31 when the carbon dioxide concentration is 0 ppm, and the reference infrared detection when the carbon dioxide concentration is 987 ppm. This was obtained from the ratio of the output of the measurement infrared detecting unit 31 to the output of the unit to obtain the equation (24).

Next, the ratio of the measured output to the reference output at the time of measurement was substituted into Equation (12), and the carbon dioxide concentration was calculated.
FIG. 3 is a diagram showing a result of comparing the above-described example and comparative example.
From the results of FIG. 3, the maximum error was −14 ppm according to the calculation of the example, but the maximum +273 ppm error was generated according to the calculation of the comparative example 1.
From the above results, it is understood that the gas concentration calculation device of this embodiment can perform concentration calculation with higher accuracy than the conventional concentration calculation formula.

  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 possible to add various changes or improvements to the above-described embodiments, and it is possible to add such changes or improvements to the technical scope of the present invention. it is obvious.

  The present invention is suitable as a gas concentration measuring device for gases that generate infrared absorption typified by carbon dioxide.

DESCRIPTION OF SYMBOLS 10 Gas cell 11 Gas inlet 12 Gas outlet 20 Light source 31 Measurement infrared detection part 32 Reference infrared detection part 40 Calculation part

Claims (6)

A light source;
An infrared detector for measurement that receives light from the light source and outputs a measurement output that is a signal corresponding to the light;
A calculation unit to which the measurement output is input;
A gas concentration measuring device comprising:
The computing unit is
A first measurement output that is output from the measurement infrared detection unit when the light source is turned on in a measurement gas having a first concentration;
A second measurement output output by the measurement infrared detection unit when the light source is turned on in a measurement target gas having a second concentration different from the first concentration;
A first solution which is a value of a variable when the concentration obtained from a reference concentration calculation formula is the first concentration;
A coefficient obtained from a second solution that is a value of a variable when the concentration obtained from the reference concentration calculation formula is the second concentration;
An equation in which the reference density calculation formula is corrected with the first solution and the first density;
The first concentration;
A gas concentration measuring device that calculates the concentration of the gas to be measured by substituting the measurement output at the time of measurement with the first measurement output into a concentration calculation formula including The coefficient is
A ratio of the second measurement output to the first measurement output;
The ratio of the second solution to the first solution;
The gas concentration measuring device according to claim 1 obtained from the above. The reference concentration calculation formula is an nth order polynomial,
The concentration calculation formula is:
The first to nth order coefficients of the reference density calculation formula are corrected with the first solution, the zeroth order coefficient is corrected with the first density, the coefficient is multiplied, and the first The gas concentration measuring device according to claim 1 or 2, wherein the concentration is a formula obtained by adding the concentrations. The computing unit is
The gas concentration measuring apparatus according to any one of claims 1 to 3, wherein the concentration of the measurement target gas is calculated based on the following equation (1).

(Where c is the gas concentration, c ₁ is the first concentration, c ₂ is the second concentration, V _out (c ₁ ) is the measurement output at the first concentration, and V _out (c ₂ ) is the second concentration. , V _std (c ₁ ) is a variable when the output of the reference concentration calculation formula is the first concentration, and V _std (c ₂ ) is the output of the reference concentration calculation formula is the second concentration. variable when, a _n is the n-th order coefficient of the reference density calculation formula is V _out measurement output of the measurement.) The gas concentration measuring device includes:
It further includes a reference infrared detection unit that receives light from the light source and outputs a reference output that is a signal corresponding to the light,
The gas concentration measuring device according to any one of claims 1 to 4, wherein the calculation unit corrects the measurement output with the reference output. The computing unit is
At least one of the measurement output and the reference output when the light source is turned on,
The gas concentration measurement apparatus according to claim 1, wherein correction is performed based on at least one of the measurement output and the reference output when the light source is turned off.

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