JP6530669B2 - 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. Since the radiation intensity distribution of the ceramic heater includes the infrared absorption spectrum of carbon dioxide gas and is broad in the wavelength range of 2 μm to 50 μm, it 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, for example, the output of the infrared detection unit for measurement according to the following equation (1) can be obtained based on the Lambert-Beer_law law.

In equation (1), V is the output of the infrared detector for measurement, G is the gain when the infrared detector for measurement converts an optical signal into an electrical signal, and I ₀ is for measurement when there is no absorption by the gas to be measured Is an absorbance coefficient, l (L) is an optical path length, c is a concentration of a gas to be measured, and α is an output offset of an infrared detection unit for measurement. The output offset α is generated, for example, by the incidence of light of a wavelength not absorbed by the gas to be measured to the infrared detection unit for measurement.

However, the output offset α, the gain G, and the output I ₀ when there is no absorption vary among individuals, and it is extremely difficult to quantify them. Therefore, when calculating the concentration value of the gas to be measured on the premise of the two concentration inspection, conventionally, for example, one of the three coefficients is fixed, and the remaining coefficient is determined from the two concentration inspection. The output of the unit was used as a variable to define a quadratic function that outputs the concentration of the gas to be measured, and the concentration operation was performed using the quadratic function. In this calculation method, the calculation accuracy is low because the influence of variations in gain and output offset can not be completely eliminated.
The present invention has been made in view of such problems, and an object of the present invention is to provide a gas concentration which can measure gas concentration with high accuracy in a two-concentration test of a first concentration and a second concentration. It is in providing a measuring device.

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 an aspect of the present invention, there are provided a light source, an infrared detection unit for measurement which outputs a measurement output which is a signal corresponding to light from the light source, and an operation unit to which an output from the infrared detection unit for measurement is input. It is a gas concentration measurement device provided, wherein the calculation unit is configured to be different from a first measurement output outputted by the infrared detection unit for measurement in a gas to be measured of a first concentration, and the first concentration. A second measurement output outputted by the infrared detection unit for measurement in the gas whose concentration is to be measured, and a first obtained from the difference between the second measurement output and the first measurement output The ratio of the second correction value obtained from the difference between the measurement output at the time of measurement and the first measurement output with respect to the correction value of is substituted into the variable value of the reference concentration calculation formula having a quadratic or higher order term. It is a gas concentration measuring device which calculates the concentration of the gas to be measured.

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

It is a block diagram for describing the embodiment of the gas concentration measuring device concerning the present invention. It is a figure which shows the result of having compared an Example and a comparative example.

  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]
FIG. 1 is a configuration diagram for explaining an 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.

In the gas concentration measurement apparatus 100 of the present embodiment, the light source 20, the measurement infrared detection unit 31 that outputs a measurement output that is a signal according to the light from the light source 20, and the output from the measurement infrared detection unit 31 are input. And a calculation unit 40, and a gas concentration measurement device.
The calculation unit 40 performs light measurement in a measurement target gas having a second concentration different from the first measurement output from the measurement infrared detection unit 31 in the first concentration measurement target gas and the first concentration. Measurement output at the time of measurement with respect to a first correction value obtained from the difference between the second measurement output and the first measurement output, having a second measurement output output from the infrared detection unit 31 This is a gas concentration measuring device that calculates the concentration of the gas to be measured based on the ratio of the second correction value obtained from the difference with the measurement output of 1.

An example of the effect by this embodiment is demonstrated using Formula (1).
First, the first correction value is the difference between the second measurement output and the first measurement output, and the second correction value is the difference between the output of the measurement infrared detector 31 at the time of measurement and the first measurement output. Assuming the difference, the following equation is obtained.

Here, A ₁ is a first correction value, A ₂ is a second correction value, V _m is an output of the measurement infrared detection unit 31 at the time of measurement, and V ₁ is a case where the gas to be measured has a first concentration. Of the measurement infrared detector 31, V ₂ is the output of the measurement infrared detector 31 when the constant target gas has the second concentration, c ₁ is the first concentration of the measurement target gas, and c ₂ is the measurement The second concentration of the target gas, _cm, is the concentration of the measurement target gas at the time of measurement.

が得られる。
ここで、Ｒは第１の補正値に対する第２の補正値の比である。 From equations (2) and (3), it is understood that the first correction value and the second correction value do not include the offset component α which is a variation component.
Further, when the ratio of the second correction value to the first correction value is taken,

Is obtained.
Here, R is the ratio of the second correction value to the first correction value.

From equation (4), it can be seen that G and I ₀ which are variation components are eliminated by taking the ratio of the second correction value to the first correction value.
As described above, in the gas concentration measurement apparatus 100 according to the present embodiment, the first measurement output output from the measurement infrared detection unit 31 in the first concentration measurement target gas is different from the first concentration. A second measurement output output from the measurement infrared detection unit 31 in the concentration measurement target gas, and a first obtained from the difference between the second measurement output and the first measurement output at the time of measurement Measurement output at two different known concentrations by calculating the concentration of the gas to be measured based on the ratio of the second correction value obtained from the difference between the measurement output at measurement and the first measurement output to the correction value It is understood that the gas concentration can be measured with higher accuracy than in the prior art only by acquiring.

  Here, various formulas can be used as a concentration calculation formula for calculating the concentration of the gas to be measured. As an example, an equation such as equation (5) may be used.

Here, c is the concentration of the gas to be measured, a ₂ the secondary coefficient of the density calculating equation, a ₁ is the first-order coefficient of the density calculating equation, a ₀ is the zero-order coefficient of the density calculating equation. The coefficient of the concentration calculation equation such as a ₂ is a coefficient of the quadratic approximation equation representing the relationship between R and c in a separate gas concentration measurement device that exhibits gas concentration characteristics close to those of the gas concentration measurement device 100 of this embodiment. It is.

Even when any concentration conversion equation is used, various variation components are eliminated by calculating the concentration of the gas to be measured based on the ratio of the second correction value to the first correction value as described above. It is obvious that highly accurate concentration calculation is possible.
Further, in the gas concentration measurement apparatus 100 according to the present embodiment, the gas concentration measurement apparatus 100 is disposed in the vicinity of the measurement infrared detection unit 31 and outputs a reference output that is a signal corresponding to the light from the light source. An infrared detection unit (not shown) may be further provided, and the calculation unit may correct the measurement output based on the reference output.

By correcting the measurement output based on the reference output, even if I ₀ in equation (1) changes over time, the change can be corrected, so gas concentration measurement with higher accuracy than before is possible. The effect is
Formula (6) etc. are given as a specific example of the correction.

Here, V ′ is the measured output corrected at the reference output, and V _ref is the reference output.
In the gas concentration measurement apparatus 100 according to the present embodiment, the calculation unit may correct the measurement output based on the measurement output when the light source 20 is turned off. Further, in the gas concentration measurement apparatus 100 according to the present embodiment, the calculation unit may correct the reference output based on the reference output when the light source 20 is turned off.
As a specific example of the correction, a difference between the measurement output and the reference output when the light source 20 is turned on and the measurement output and the reference output when the light source 20 is turned off as shown in the equations (7) and (8) Etc.

Here, D is the measurement output corrected by the measurement output when the light source 20 is turned off, D _ref is the reference output corrected by the reference output when the light source 20 is turned off, V _on is the light source 20 Measured output when lit, _Voff : measured output when light source 20 is turned off, _{Vref_on} : reference output when light source 20 is turned on, _{Vref_off} : reference output when light source 20 is turned off, It is.

Here, the state in which the light source 20 is turned on refers to a state in which the light source 20 emits more infrared light than the amount of infrared light emitted from the surrounding environment.
Further, the state in which the light source 20 is turned off may not be the state in which the light source 20 is completely turned off.
Even when power is supplied to the light source 20 and the light source 20 emits infrared light, if the amount of infrared light emitted is less than the amount of infrared light emitted when the light source 20 is lit, or the amount of infrared light emitted from the surrounding environment In the following cases, the light source 20 is considered to be in the unlit state because it is in a state not to emit substantially infrared light.

Since the circuit offset included in the measurement output or the reference output can be corrected by correcting the measurement output or the reference output based on the measurement output or the reference output when the light source 20 is turned off, the accuracy is higher than that in the related art. The effect of enabling gas concentration measurement is achieved.
Here, the circuit offset is, for example, an output offset of an operational amplifier built in the infrared detection unit for measurement or the infrared detection unit for reference.
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 for measurement and infrared detector for reference)
The measuring infrared detection unit 31 and the reference infrared detection unit (not shown) 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 band other than the infrared absorption band is larger than that of the reference infrared detection unit. For the infrared detection unit 31 for measurement and the infrared detection unit for reference, a thermal infrared sensor such as a pyroelectric sensor (Pyroelectric sensor), a thermopile (Thermopile), a bolometer (Bolometer), a quantum infrared sensor, etc. are suitable It is.

  The measurement infrared detection unit 31 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 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 a reference infrared detection part 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 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 20.

(Gas cell)
The gas concentration measuring apparatus 100 according to the present embodiment is capable of introducing the gas to be measured inside, and capable of disposing the light source 20, the infrared detector for measurement 31, the infrared detector for reference, the arithmetic unit 40, etc. You may provide further. Here, “inflowable” indicates that the infrared light output from the light source 20 can reach the infrared detection unit 31 for measurement through the space where the gas to be measured is present. By further including a gas cell, the SN ratio of the signals output from the measuring infrared detection unit 31 and the reference infrared detection unit can be increased, and a more accurate gas concentration measuring 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, an example of the gas concentration measuring apparatus of the present embodiment will be described.

Quantum type infrared sensor “IR1011” as an infrared detection unit 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 Corporation) as an infrared detector for reference equipped with an optical filter that selectively filters out the 3.7 μm to 3.9 μm wavelength band without infrared absorption by CO ₂ CO ₂ A carbon dioxide gas concentration measuring device was prepared in which an IC provided with a storage unit and a processing unit as an operation unit 40 was placed in a gold-plated gas cell of phosphor bronze as an operation unit 40.

  Next, when the gas cell is filled with carbon dioxide gas having a concentration of 0 ppm, and when the light source 20 is turned on and off, the outputs from the measuring infrared detection unit 31 and the reference infrared detection unit amplified by the amplifier are When the light cell 20 is turned on and off when carbon dioxide gas having a concentration of 986 m is filled in the gas cell, the outputs from the measuring infrared detection unit 31 and the reference infrared detection unit amplified by the amplifier are respectively The density calculation of the above-described embodiment was performed using this.

The specific operation is as follows.
Hereinafter, the measurement output described in the present embodiment is the difference between the measurement output when the light source 20 is on and the measurement output when the light source 20 is off, and the reference output is the light source 20 This is the difference between the reference output when the light source 20 is turned off and the reference output when the light source 20 is turned off.
First, 'the ratio of the measurement output for the reference output during the carbon dioxide concentration 0 ppm (D ₁ ratio of the measured output to the reference output during the measurement (D _m)' was calculates the difference). Further, the difference between the ratio (D ₂ ′) of the measured output to the reference output at the carbon dioxide concentration of 986 ppm and the ratio (D ₁ ′) of the measured output to the reference output at the carbon dioxide concentration of 0 ppm was calculated. Next, the ratio of these two differences was taken, and this was substituted into the reference concentration calculation formula to calculate the carbon dioxide concentration.

  The reference concentration calculation formula is the ratio of the above two differences and the carbon dioxide gas concentration of the gas concentration measurement device (reference gas concentration measurement device) of a separate body that exhibits gas concentration characteristics close to the gas concentration measurement device used here Is a mathematical expression that directly or approximately expresses the relationship of Here, the reference concentration calculation formula like Formula (9) was derived | led-out from the density | concentration test result in 5 points | pieces of 0-5000 ppm of a reference | standard gas concentration measuring apparatus.

ここで、ｆ（ｘ）は基準濃度算出式、ｘは基準濃度算出式の変数である。
上述した２つの差分の比は、ゲインと出力オフセットを含まない値のため、これを基準算出式に代入することで、精度良く炭酸ガス濃度を演算できることが理解される。
本実施例の演算を表す数式を式（１０）に示す。

Here, f (x) is a reference concentration calculation formula, and x is a variable of the reference concentration calculation formula.
It is understood that since the ratio of the two differences described above does not include the gain and the output offset, it is possible to calculate the carbon dioxide gas concentration with high accuracy by substituting this in the reference calculation formula.
An equation representing the operation of the present embodiment is shown in equation (10).

ここで、Ｄ_ｍ’は測定時の参照出力に対する測定出力の比、Ｄ_１’は炭酸ガス濃度０ｐｐｍである場合の参照出力に対する測定出力の比、Ｄ_２’は炭酸ガス濃度９８６ｐｐｍである場合の参照出力に対する測定出力の比である。

Here, D _m 'is the ratio of the measured output to the reference output at the time of measurement, D ₁ ' is the ratio of the measured output to the reference output when the carbon dioxide concentration is 0 ppm, and D ₂ 'is the case where the carbon dioxide concentration is 986 ppm. It is the ratio of the measured output to the reference output.

[Comparative example]
Hereinafter, the measurement output described in this comparative example is the difference between the measurement output when the light source 20 is on and the measurement output when the light source 20 is off, and the reference output is the light source 20 This is the difference between the reference output when the light source 20 is turned off and the reference output when the light source 20 is turned off.
First, a concentration calculation equation such as equation (11) 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 undecided.

ここで、ｇ（Ｄ_ｍ’）は比較例における濃度算出式、Ｄ_ｍ’は測定時の参照出力に対する測定出力、ｂ_１は濃度算出式の１次の係数、ｂ_０は濃度算出式の０次の係数である。

Here, g (D _m ') is the concentration calculation formula in the comparative example, D _m ' is the measurement output with respect to the reference output at the time of measurement, b ₁ is the linear coefficient of the concentration calculation formula, and b ₀ is ₀ in the concentration calculation formula It is the next coefficient.

  The second-order coefficient of the concentration calculation equation (Equation (11)) is the measurement output with respect to the carbon dioxide gas concentration and the reference output of a separate gas concentration measuring device showing a gas concentration characteristic close to that of the gas concentration measuring device used here It is a second-order coefficient of a second-order approximation expression that represents the relationship with the ratio of. Here, from the concentration test results at five points of 0 to 5000 ppm of the reference gas concentration measuring apparatus used in the example, a quadratic approximation formula representing the relationship between the carbon dioxide concentration and the ratio of the measurement output to the reference output is determined The second-order coefficient of the second-order function is taken as the second-order coefficient in the concentration calculation equation (Equation (11)).

次いで、式（１２）に測定時の参照出力に対する測定出力の比を代入し、炭酸ガス濃度を演算した。 Next, the output of the reference infrared detection unit with respect to the output of the infrared detection unit 31 for measurement when the carbon dioxide concentration is 0 ppm, and the infrared detection for reference when the carbon dioxide concentration is 987 ppm Formula (12) is obtained from the ratio of the output of the measurement infrared detection unit 31 to the output of the unit.

Next, the ratio of the measurement output to the reference output at the time of measurement was substituted into equation (12) to calculate the carbon dioxide concentration.

FIG. 2 is a diagram showing the result of comparison between the above-described embodiment and the comparative example.
According to the results of FIG. 2, according to the calculation of the embodiment, the error was at most 40 ppm, but according to the calculation of the comparative example 1, a difference of 326 ppm was generated at the maximum.
From the above results, it is understood that according to the gas concentration calculation device of the present embodiment, concentration calculation with higher accuracy than the conventional concentration calculation formula is possible.

  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 40 for measurement calculation unit 100 gas concentration measuring device

Claims (4)

Light source,
An infrared detection unit for measurement that outputs a measurement output that is a signal corresponding to the 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
A first measurement output that the infrared detection unit for measurement outputs in a gas whose first concentration is to be measured;
A second measurement output that the infrared detection unit for measurement outputs in a measurement target gas of a second concentration different from the first concentration;
Have
A second correction value obtained from the difference between the measurement output at the time of measurement and the first measurement output with respect to a first correction value obtained from the difference between the second measurement output and the first measurement output The gas concentration measuring device which calculates the concentration of the gas to be measured by substituting the ratio of the two into the variable value of the reference concentration calculation formula having a second or higher term . It further comprises a reference infrared detection unit disposed in the vicinity of the measurement infrared detection unit and outputting a reference output that is a signal according to the light from the light source,
The arithmetic unit is
The gas concentration measuring device according to claim 1 which amends said measurement output based on said reference output. The arithmetic unit is
The gas concentration measuring apparatus according to claim 1 or 2, wherein the measurement output is corrected based on the measurement output when the light source is turned off. The arithmetic unit is
The gas concentration according to claim 2, wherein at least one of the measurement output and the reference output is corrected based on at least one of the measurement output when the light source is turned off and the reference output when the light source is turned off. measuring device.

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