JP2001159608A - Gas concentration measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration measuring apparatus, which dispenses with calibration of phase synchronism and capable of using an inexpensive low speed DSP and the like. SOLUTION: After demodulation by a fundamental wave orthogonal demodulation part 1 and a duplicate wave orthogonal demodulation part 2, higher harmonic components are removed by higher harmonic component removing parts 3, 4 and the amplitude values of a fundamental wave, and a duplicate wave are calculated by a measure operation part and the ratios of the calculated values are taken so as to obtain the measure of the concentration of gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration measuring device used in a gas detector for measuring the concentration of a gas such as methane gas or carbon dioxide gas with high accuracy by utilizing an absorption spectrum peculiar to each gas. The present invention relates to a processing apparatus, and particularly to a gas concentration measurement processing apparatus using a frequency modulation method.

[0002]

2. Description of the Related Art Each gas has an absorption spectrum peculiar to gas molecules, and an attempt to measure the concentration of a gas by oscillating a laser at a frequency where this absorption spectrum exists was made in 1965 by Moore (CBMoore). It was done for the first time.

[0003] This principle is briefly described below. The absorption spectrum of a gas has local minima at various frequencies according to the vibrational energy of the gas molecule.
When one is taken out, a characteristic generally called a Lorentz type is obtained as shown in FIG. The horizontal axis in FIG. 5 is frequency, and the vertical axis is transmittance. The frequency f of the minimum value of the absorption spectrum is shown.
The transmittance at c decreases as the gas concentration increases. Therefore, when the gas is irradiated with a laser beam having an oscillation frequency of fc, the transmitted signal is received by a photodetector and converted into an electric signal, and the change in transmittance is calculated. Since the gas concentration is proportional to the gas concentration, the gas concentration can be measured by multiplying this measure by a coefficient obtained by measuring a gas whose concentration is known in advance.

Focusing on this principle and developing it, 2
There are a wavelength difference method and a frequency modulation method, and these two methods are currently the mainstream of gas concentration measurement using a laser. For a detailed description of the two-wavelength difference method and the experimental results, see K. Uehara: Appl. Phys. B, Vol. 38, No. 1, pp. 37--4.
0, 1985.Hideo Tai, Kazunari Yamamoto, Ken Abe, Takashi Ueki, Hiroaki Tanaka, Kiyoji Uehara: Transactions of the Society of Instrument and Control Engineers 24, pp.452--458, 19
88. ・ Hideo Tai, Hiroaki Tanaka, Kiyoji Uehara: Optics, Vol.19, No.
4, pp. 238-244, 1990.

[0005] Further, a detailed description of the frequency modulation method and experimental results are given in: DTCassidy: Appl. Opt., Vol. 27, No. 3, pp. 610--6.
14, 1988. Hideo Tai, Masayuki Matsuura, Hiroaki Tanaka, Kiyoji Uehara: Optics, Vol.19, No.9, pp.616--619, 1990.

First, the two-wavelength difference method will be described.
After that, the frequency modulation method according to the present invention will be described. FIG. 10 shows a block diagram of a gas detector using the two-wavelength difference method. In FIG. 10, the frequency switch 40 is a laser
The oscillation frequency of 10 is used to switch between the frequency fc at which the transmittance is minimal in the gas absorption spectrum of the gas cell 20 and the frequency fn at which no gas absorption spectrum exists. The signal converted into an electric signal by the photodetector 30 is a laser
By switching the ten oscillation frequencies fc and fn, the transmittance changes as shown in FIG. 5, so that the amplitude value changes, and the difference between the amplitudes becomes the transmittance variation, which is a measure of the gas concentration.

Here, as a general application, it is convenient to make the optical path length from the laser 10 to the photodetector 30 variable.
For example, the longer the optical path length of the laser light passing through the gas, the greater the change in transmittance and the more accurately the gas concentration can be measured.
This is because a small gas cell may be selected for ease of carrying. When the optical path length becomes longer, the laser light diverges or the laser light is attenuated due to the influence of surrounding dust and the like, so that the amplitude of the input signal to the gas concentration measurement processing device 80 becomes smaller. As a result, a difference in amplitude representing a change in transmittance becomes smaller, and a problem arises in that the value of gas concentration converted from the output value of the gas concentration measurement processing device 80 decreases. In order to prevent the above-mentioned problem from occurring, a method is used in which the difference between the amplitudes is divided by the amplitude at a frequency having no gas absorption spectrum. In addition, since the difference in the amplitude is proportional to the optical path length of the laser light passing through the gas, when converting into the concentration, the division is performed by the optical path length. By multiplying the measure of the gas concentration thus obtained by an appropriate proportional constant, the gas concentration can be obtained without depending on the optical path length.

In the two-wavelength difference method, since the signal which is converted into an electric signal by the photodetector 30 and which is input to the gas concentration measurement processing device 80 is a DC signal, the DC offset generated due to the drift of the operational amplifier or the like. Since components cannot be removed, there is a disadvantage that gas concentration cannot be detected with high accuracy. There is also a disadvantage that the concentration of gas cannot be detected with high accuracy due to interference of extraneous light. The frequency modulation method described below has been devised to improve this disadvantage.
In this method, the gas concentration can be measured only by the AC component signal so that the presence of a DC offset component or extraneous light does not adversely affect the gas concentration measurement.

FIG. 6 shows the principle of the frequency modulation method. The laser is frequency-modulated at the modulation frequency fm with the center frequency being fc, and the laser is irradiated to the gas to be measured. Since the gas absorption spectrum shows a characteristic called Lorentz type and is almost quadratic function with respect to the detuning frequency, the signal converted into an electric signal by the photodetector includes a signal having a frequency twice as high as the modulation frequency. (Hereinafter, this signal is referred to as a second harmonic signal). The amplitude value of this signal increases as the gas concentration increases because the transmittance decreases and becomes a measure of the gas concentration, and can be converted into a gas concentration by multiplying by an appropriate proportional constant.

In the following, a method of canceling the influence of the optical path length by the frequency modulation method will be described in the same manner as described in the description of the two-wavelength difference method. In order to frequency-modulate the laser, current control must be performed. When this current control is performed and frequency modulation is performed at the frequency fm, amplitude modulation is also automatically performed at the frequency fm. For this reason, the signal converted into an electric signal by the photodetector includes a signal having a frequency of fm generated by amplitude modulation (hereinafter, this signal is referred to as a fundamental signal). Using this fundamental wave,
Dividing the amplitude value of the second harmonic by the amplitude value of the fundamental wave cancels out the effect of laser light divergence or surrounding dust caused by an increase in the optical path length, and this value is determined by the gas concentration. Measure. As a method for estimating the amplitude of the fundamental wave and the second harmonic of the frequency modulation method for measuring the gas concentration, phase-sensitive phase-sensitive detection is used.

FIG. 11 shows a conventional gas detector using a frequency modulation method. In this method, the reference signal from the frequency modulator 50 of the laser 10 is connected to the fundamental wave phase sensitive detector 91 and the second harmonic phase sensitive detector 92 of the gas concentration measuring device 90, and the amplitude values A and 2 The phase is manually shifted little by little so that the amplitude value B of the harmonic wave becomes the maximum, and the phase is synchronized. The amplitude value A obtained by this calibration is divided by the amplitude value B to obtain a measure of the gas concentration. By multiplying it by an appropriate proportional constant, it can be converted to the gas concentration.

[0012]

In the phase sensitive detection conventionally used in the frequency modulation method, a signal of a reference from a frequency modulator 50 of a laser 10 is processed by a gas concentration measurement processing apparatus.
90 fundamental wave phase sensitive detector 91 and 2nd harmonic phase sensitive detector 92
A problem arises that the user must connect to As an example, when measuring the concentration of methane gas generated in a paddy field, it is necessary to separate the laser 10 from the gas concentration measurement processing device 90 by several tens of meters, and it is very difficult to prepare such a long-distance cable.

In the phase sensitive detection method, the phase is manually shifted little by little so as to maximize the amplitude of the fundamental wave and the second harmonic before estimating the gas concentration in order to perform phase synchronization. Has to be found, which takes several minutes.

Further, the phase sensitive detection is performed by a DSP (Digital Si
Since the processing cannot be performed in time with the processing speed of a gnal processor) or a CPU (Central Processing Unit), it cannot be digitized and cannot be reduced in size and cost. An object of the present invention is to maintain the accuracy of a conventional gas concentration measurement processing device using phase-sensitive detection, and eliminate the need to connect a reference synchronized signal from the laser frequency modulator to the gas concentration measurement processing device. In addition, there is no need to manually shift the phase a little at a time for calibration to find the maximum point of the amplitude level.In addition, a gas concentration measurement processing device that can use DSPs and CPUs to reduce the size of the circuit and reduce costs To provide.

[0015]

In order to solve the above-mentioned problems, an asynchronous envelope detection is adopted.
According to the invention, a high-frequency component removing unit is further provided. In the second invention, a multiple sum processing unit is provided. The reason why the high-frequency component removing unit is provided and the reason why the multiple sum processing unit is provided will be described in detail in the section of operation.

[Operation] Since the asynchronous envelope detection is employed, there is no need to connect a reference-synchronized signal to the gas concentration measurement processor, and the amplitude level is manually shifted slightly for calibration. There is no need to find the maximum point, and processing using a DSP or CPU is possible. The high frequency component is removed by the high frequency component removing unit or the multiplex sum processing unit. As described above, the parameters necessary for measuring the gas concentration by the frequency modulation method include the fundamental wave signal of the signal converted into the electric signal by the photodetector and the absorption spectrum of the gas to be measured. This is the amplitude value of the harmonic signal. Dividing the amplitude value of the second harmonic signal by the amplitude value of the fundamental wave signal provides a measure of gas concentration, which can be converted to gas concentration by multiplying by an appropriate constant.

However, when the ratio of the amplitude of the fundamental wave signal to the amplitude of the second harmonic signal is calculated using the asynchronous envelope detection, this ratio is obtained every time the power is turned on again, even though the gas concentration does not change. A phenomenon such as a change in the amplitude ratio occurs. When the power is turned on, the ratio of this amplitude is constant, and when the power is turned on again, the ratio of this amplitude becomes constant at a value different from the previous value. It cannot be prevented.

The above phenomenon will be described in detail. To process the signal converted by the photodetector into an electric signal by DSP
When harmonic components are removed by LPF (Low Pass Filter), the signal sampled by AD converter becomes

[0019]

(Equation 1)

It can be expressed as Here, the first term is a fundamental wave component, the second term is a second harmonic component, the third term is a white noise component, fm is a fundamental wave frequency, fs is a sampling rate, and θ and φ are initial phases. Here, in order to simply represent Equation 1,

[0021]

(Equation 2)

## EQU2 ##

[0023]

(Equation 3)

Can be rewritten. The amplitude A of the fundamental wave and the amplitude B of the second harmonic are required to measure the gas concentration. First, in order to obtain the amplitude A of the fundamental wave, a frequency transition is performed using the local frequency as the frequency of the fundamental wave, and harmonic components are removed by LPF.

[0025]

(Equation 4)

Therefore, when the norm of Equation 4 is obtained,

[0027]

(Equation 5)

The amplitude A of the fundamental wave is obtained. It seems that the amplitude B of the second harmonic may be obtained by using the same operation as described above. However, when measuring a gas having a low concentration, a problem occurs with the second harmonic. The reason for this is that when measuring a gas having a low concentration, the amplitude value A of the fundamental wave component is much larger than the amplitude value B of the second harmonic component, so that the frequency transition at the second harmonic frequency 2fm is performed. LP after going
This is because the fundamental wave component that has been shifted in frequency and becomes a higher harmonic component cannot be sufficiently attenuated at F. Even if the fundamental component is attenuated using HPF (High Pass Filter) as a pre-process to change the frequency, the fundamental component is lower than the second harmonic component for lower concentration gas. Also has a large value and cannot be sufficiently attenuated by the LPF, which eventually affects the second harmonic component. With the local frequency as the frequency of the second harmonic, the frequency shift is performed to extract the second harmonic component.

[0029]

(Equation 6)

As a result, the signal of only the DC component for estimating the amplitude of the second harmonic is not obtained, and the second and third harmonic components generated by shifting the frequency of the fundamental wave component are generated. I will. FIG. 7 shows Equation 6 as a vector. Also,
Amplitude values X0 and Y0 of two second harmonic signals having different initial phases
Is represented by a vector as shown in FIG. That is, if the initial phase changes according to the timing of turning on the power, the amplitude value of the second harmonic also changes.

On the other hand, in the phase-sensitive phase-sensitive detection of the phase synchronization system, such a problem does not occur because the phase is manually adjusted before measuring the gas concentration so that the amplitude value becomes maximum. In the present invention, a harmonic component removal unit or a multiplex sum processing unit is provided in the envelope detection of the phase asynchronous system, and the harmonic component is removed in the measurement of the amplitude of the second harmonic, whereby the amplitude value of the second harmonic is removed. No fluctuations occurred. 6 of the above
The harmonic components of the term and the third term are line spectra at the frequency fm and the frequency 3fm, respectively. The signals of this harmonic component are

[0032]

(Equation 7)

By adding N times given by
(Where M is any integer and GCM (fs, fm) is f
greatest common divisor of s and fm)

[0034]

(Equation 8)

[0035]

[0036]

(Equation 9)

Thus, harmonic components can be removed.
Therefore, the impulse response

[0038]

(Equation 10)

The harmonic component can be completely removed by passing the signal given by Equation 6 through a comb filter having the following. This will be described below on the frequency axis. The frequency response of the filter given by Equation 10 is

[0040]

[Equation 11]

## EQU1 ## As an example, M = 1, fs = 8f
m, N = 8 and the response given by equation 11 is
As shown in FIG. 9, the frequency fm and the frequency 3fm
The components in the region are completely removed. Therefore, by passing the signal given by equation (6) through the filter given by equation (10), the in-phase / quadrature component B of the second harmonic from which the harmonic component has been removed
× (e raised to the power of −jφ) is obtained, and the amplitude value B of the second harmonic can be obtained by performing the same norm operation as in Equation 5. Since the amplitude value B of the second harmonic does not include a harmonic component, the amplitude value does not change every time the power is turned on, and the gas concentration can be measured with high accuracy.

When measuring a gas having a low concentration, the amplitude value A of the fundamental wave is much larger than the amplitude value B of the second harmonic. Although the filter given by 10 is inserted, when measuring a gas with a high concentration, it is necessary to insert the filter given by Expression 10 on the opposite fundamental wave side. By dividing the amplitude value B of the second harmonic obtained in this way by the amplitude value A of the fundamental wave, a measure of the gas concentration can be obtained with the same accuracy as that of the phase sensitive detection, and multiplied by an appropriate proportional constant. Can be converted to gas concentration.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the gas to be measured is methane gas will be described below. The center frequency of the laser is set at a wavelength of 1.6538 μm where the transmittance is minimum in the absorption spectrum of methane gas, and the modulation frequency fm of the frequency modulation is set to 3
The frequency was set to 2.5 kHz, the maximum frequency shift was set so that frequency modulation was performed at the full width at half maximum, and the sampling rate fs was set to 260 kHz, eight times the modulation frequency fm. In addition, in Equation 7, M = 1 and the filter of Equation 10 is realized with N = 8. Texas Instruments TMS320C25 was used as a DSP for performing arithmetic processing.

The respective embodiments of the first and second inventions will be described below. FIG. 2 shows a gas concentration measurement processing apparatus according to the first embodiment (first invention). In the fundamental wave quadrature demodulation unit 1 shown in FIG. 2, an input signal s (n) is received, and the input signal is applied to a local signal 13 [2 cos (2πfm n / f) by a multiplier 11.
s)], filtered by a low-pass filter (LPF) 12, and the result is output. The input signal s (n) is multiplied by a local signal 16 [2 sin (2πfm n / fs)] orthogonal to the local signal 13 by a multiplier 14,
Filtered by LPF15 and the result is output.

The harmonic component removing unit 3 receives the output of the LPF 12 and removes the harmonic components by a comb filter 31 having an impulse response of h (n) of Formula 10, and removes the in-phase component of the input signal s (n). Is output. Further, the output of the LPF 15 is received, the harmonic component is removed by a comb filter 32 having an impulse response of h (n), and the quadrature component of the input signal s (n) is output.

In the measure calculation section 5, the in-phase component output from the comb filter 31 is squared by a multiplier 51, and the quadrature component output from the comb filter 32 is squared by a multiplier 52. The squared values are added by an adder 53, a square root operation is performed by a square root device 54, an amplitude value A of the fundamental wave is calculated, and this value is input to a divider 59 as a denominator. The second-harmonic quadrature demodulation unit 2 receives an input signal s (n), and the input signal is multiplied by a multiplier 21 into a local signal 23 [2 cos (4πfm n /
fs)], filtered by the LPF 22 and the result is output. Also, the input signal s (n) is
And a local signal 26 [2 si
n (2πfm n / fs)], filtered by the LPF 25, and the result is output.

The harmonic component removing unit 4 receives the output of the LPF 22 and removes the harmonic components by a comb filter 41 having an impulse response of h (n) of Formula 10, thereby removing the in-phase component of the input signal s (n). Is output. Further, the output of the LPF 25 is received, the harmonic component is removed by a comb filter 42 having an impulse response of h (n), and the quadrature component of the input signal s (n) is output. In the measure calculation unit 5, the in-phase component output from the comb filter 41 is squared by a multiplier 55, and the quadrature component output from the comb filter 42 is squared by a multiplier 56.
These squared values are added by the adder 57, and the square root
A square root operation is performed at 58 to calculate the amplitude value B of the second harmonic, and this value is input as a numerator into the divider 59, and a value obtained by dividing the amplitude value B of the second harmonic by the amplitude value A of the fundamental wave Is output as a measure of gas concentration.

The gas concentration is determined by multiplying the output value by a predetermined coefficient. In the first embodiment, the harmonic component removing sections are provided on the fundamental wave side and the second harmonic side, respectively. However, depending on the concentration of the gas to be measured, it may be provided on only one side as described in the section of the operation. Embodiment 2 (second invention)
Reduces the computational complexity of the first embodiment,
The gas concentration measurement process can be performed with U. In order to reduce the amount of calculation, the sampling rate for sampling the input signal to the gas concentration measurement processor is fixed to eight times the frequency of the fundamental wave (fs = 8fm). When the sampling rate is determined in this way, the values of the local signals of the fundamental wave are as shown in Table 1.

[0049]

[Table 1]

When n is 8 or more, the values of the local signals shown in Table 1 are repeated again. The values of the local signal cos (2πfm n / fs) in Table 1 are ± 1 and ± 1 / √.
In the case of (2), the operation registers are a and b, respectively, and the value of the local signal sin (2πfm n / fs) is ± 1 and ± 1 /
レ ジ ス タ The operation registers at the time of (2) are c and d, respectively.
The register for operation when the value of cos (4πfm n / fs) is ± 1 is e, and the register for operation when the value of sin (4πfm n / fs) is ± 1 is f. Assuming that the input signal to the gas concentration measurement processing device is s (n), the fundamental wave quadrature demodulation unit 1 of the first embodiment
The in-phase and quadrature components of the second-harmonic quadrature demodulation unit 2 are calculated by using the registers defined above to calculate n =
K (where K is a multiple of 8)

[0051]

[Table 2]

After that

[0053]

(Equation 12)

Can be obtained by calculating. However, n mod8 in Table 2 means the remainder when n is divided by 8, AI and AQ in Equation 12 are the in-phase and quadrature components of the fundamental wave, and BI and BQ are the in-phase components of the second harmonic, respectively. It is an orthogonal component. . In the above calculation, since the sum calculation is performed, the fundamental wave quadrature demodulation units 1 and 2 of the first embodiment are used.
This means that the quadrature demodulation of the harmonic quadrature demodulation unit 2 and the filter processing of the LPF have been performed, and the number of repetitions of this sum is a multiple of the period of the fundamental wave.
Is also performed. Also, since the amplitude value B of the second harmonic is divided by the amplitude value A of the fundamental wave by the divider 59 of the first embodiment, the division by the repetition number K of Expression 12 is not necessary.

FIG. 3 shows an embodiment using the multiple sum processing described above. FIG. 4 shows details of the multiplex sum processing unit 6. In the figure, a to f are the registers a to f. The multiplex sum processing unit 6 receives the input signal s (n) and performs the above-described arithmetic processing to perform the in-phase component AI of the fundamental wave, the quadrature component AQ of the fundamental wave, the in-phase component BI of the second harmonic, and the in-phase component BI of the second harmonic. An orthogonal component BQ is output. In the measure calculation unit 7, upon receiving the four signals output from the multiplex sum processing unit 6, the in-phase component AI of the fundamental wave is squared by the multiplier 71, and the quadrature component AQ of the fundamental wave is squared by the multiplier 72. Then, the squared values are added by the adder 73 and the sum is input to the divider 77 as a denominator. The in-phase component BI of the second harmonic wave is squared by the multiplier 74, the quadrature component BQ of the second harmonic wave is squared by the multiplier 75, and the squared values thereof are added by the adder 76. As a molecule. The divider 77 performs the division and outputs the value, and the square root device 78 performs the square root operation and outputs a measure of the gas concentration.
By multiplying the output value by a predetermined coefficient, the gas concentration is obtained.

According to the first or second aspect of the present invention, by performing gas concentration measurement processing using a DSP or a general-purpose CPU as in the first and second embodiments, the circuit can be reduced in size and cost. In addition, since the signal to be handled has a lower frequency than that of the phase sensitive detection used in the conventional apparatus, it is possible to perform stable measurement with little dependence on the ambient temperature and the secular change of the component characteristics.

[0057]

The gas concentration measurement processing apparatus of the present invention employs asynchronous envelope detection and has means for removing a harmonic component of a signal obtained by transmitting a gas to be measured. Therefore, there is no need to connect a reference-synchronized signal from the laser frequency modulation unit to the gas concentration measurement processing device, and manually shift the phase a little at a time for calibration to find the maximum point of the amplitude level. No action is required. In addition, the gas concentration can be measured with the same accuracy as the phase sensitive detection employed in the conventional gas concentration measurement processing device. In addition, since the gas concentration measurement process can be performed using a DSP or a general-purpose CPU, the circuit can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a block diagram of a gas concentration measurement processing device according to a first invention.

FIG. 2 is a block diagram of a gas concentration measurement processing apparatus according to the first embodiment.

FIG. 3 is a block diagram of a gas concentration measurement processing apparatus according to a second embodiment.

FIG. 4 is a block diagram illustrating details of a multiple sum processing unit of the gas concentration measurement processing apparatus according to the second embodiment.

FIG. 5 shows an absorption spectrum of a gas.

FIG. 6 is a principle diagram of a frequency modulation method.

FIG. 7 is a vector diagram after quadrature demodulation of a second harmonic.

FIG. 8 is a vector diagram after two-wave quadrature demodulation of two signals having different initial phases.

FIG. 9 is a diagram showing a frequency response of a comb filter.

FIG. 10 is a block diagram of a gas detector using a two-wavelength difference method.

FIG. 11 is a block diagram of a gas detector using a conventional frequency modulation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quadrature demodulator for fundamental wave 2 Quadrature demodulator for 2nd harmonic 3, 4 Harmonic component elimination unit 5, 7 Measure calculation unit 6 Multiple sum processing unit

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[Procedure amendment]

[Submission date] November 30, 2000 (200.11.
30)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (1)

[Claims] 1. A fundamental wave signal (frequency) of an optical signal having an absorption characteristic of a gas to be measured, obtained by irradiating light having undergone amplitude modulation and frequency modulation at a predetermined frequency (fm) to the gas to be measured. fm) and a second harmonic signal (frequency 2fm), a gas concentration measurement processing device for receiving an input signal obtained by converting the optical signal into an electric signal, and converting an in-phase component and a quadrature component of a fundamental signal. A quadrature demodulation unit (1) for obtaining and outputting, a quadrature quadrature demodulation unit (2) for receiving the input signal and obtaining and outputting an in-phase component and a quadrature component of the second harmonic signal, and the fundamental wave demodulation A fundamental harmonic component elimination unit (3) for receiving in-phase and quadrature component signals output from the unit and removing harmonic components included in the components, and an output from the second harmonic demodulation unit. Receiving the in-phase component and quadrature component signals Double wave harmonic component removing unit for removing a harmonic component contained in the component (4)
And a measure calculation for receiving signals of the in-phase component and the quadrature component output from the fundamental harmonic component remover and the second harmonic component remover, and obtaining and outputting a gas concentration measure proportional to the gas concentration. A gas concentration measurement processing device comprising a signal processing unit comprising a unit (5).