JPH0545279A - Gas sensing device - Google Patents

Abstract

PURPOSE:To calculates gas concentration by mixing two types of gas emitting laser beam modulated with a specific frequency, allowing the mixture to pass through two types of cells, sending signals from these cells to phase sensitive wave-detectors, and feeding the output therefrom to a calculator. CONSTITUTION:A control system 40 includes a fiber coupler 44 which mixes one laser beam L1 modulated with a specific frequency f0, having a wavelength corresponding to the absorptive wavelength of methane, with another laser beam L2 modulated with a frequency f0 with different phase by PHI and having a wavelength corresponding to the apsorptive wavelength of acetylene. The resultant mixture is allowed to pass through a reference cell 45 and passed to a photo-receiver 46 to undergo conversion into an electric signal. The oscillative wavelength of each gas is stabilized under temp. control made by laser elements 42, 43 on the basis of 1st order differentiated signals about these laser beams L1, L2. In the measuring system 41, on the other hand, the mixture laser beam is passed through a measuring cell 48 and fed to another photo-receiver 49 to undergo conversion into an electric signal, which is passed to phase sensitive wave-detectors 50, 51, and 2nd order differentiated signals about L1, L2 are fed to calculators 52, 53, which calculate the concentrations d2, d3 of methane and acethylene, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector using a semiconductor laser device.

[0002]

2. Description of the Related Art It is known that the presence or absence of gas can be detected by utilizing the fact that a laser beam of a specific wavelength is easily absorbed by a certain type of gas. Sensing technology applying this principle is used in industrial measurement, pollution monitoring, etc. Widely used in. As an example, it is possible to detect the presence or absence of methane with high sensitivity by utilizing the fact that the 3.3922-μm oscillation line of the laser light generated by the He-Ne laser is strongly absorbed by methane. Since methane is the main component of city gas, the leakage of city gas can be detected by detecting methane gas. However, when gas detection is performed using a semiconductor laser, the oscillation wavelength of the semiconductor laser element greatly changes depending on the temperature, and therefore it is necessary to stabilize the oscillation wavelength of the laser light in accordance with the central wavelength of the absorption line of the gas.

Therefore, the applicant of the present application has filed an application on July 24, 1991 for a gas detection device capable of accurately controlling the oscillation wavelength of a semiconductor laser element to detect two kinds of gases. FIG. 4 is a block diagram of the gas detection device.

In the figure, the gas detection device comprises a control system 1 and a measurement system 2. The control system 1 modulates the two laser oscillators 3 and 4 and the laser oscillator 3 at a frequency f1 and determines the oscillation wavelength. The measuring system 2 includes a stabilizing modulator / controller 5 and a modulator / controller 6 which modulates the laser oscillator 4 at a frequency f2 and stabilizes the oscillation wavelength. A fiber coupler 7 for mixing the laser beam of 1., a measuring cell 8 in which a gas having an unknown concentration is filled, a light receiver 9 for converting the laser light passing through the measuring cell 8 into an electric signal, and receiving light The output signal from the detector 9 is subjected to phase sensitive detection at the frequency f ₁ and outputs the primary phase sensitive detection signal (first derivative signal) I _f1. phase-sensitive detection and in f ₁ A phase sensitive detector 11 which outputs a second-order phase-sensitive detection signal (second-order differential signal) I _2f, likewise phase-sensitive detection to primary phase-sensitive detection of the output signal from the light receiver 9 at the frequency f ₂ The phase sensitive detector 12 that outputs the signal I _f2 and the output signal from the light receiver 9 are output at the frequency f ₂ of 2
A phase-sensitive detector 13 that outputs a second-order phase-sensitive detection signal I _2f2 after phase-sensitive detection with a harmonic wave, a first-order phase-sensitive detection signal I _f1,2 and a second-order phase-sensitive detection signal I _2f1,2 It has calculators 14 and 15 for respectively calculating the gas concentration from the ratio and a recorder 16 for recording the calculation result.

FIG. 5 is a schematic configuration diagram of the laser oscillator 3 and the modulator / controller 5 shown in FIG.

The laser oscillator 3 includes a semiconductor laser element 17 which emits a laser beam back and forth, a Peltier element 18 which heats or absorbs heat depending on the direction of current, a reference cell 19 in which a gas of known concentration is sealed, and Light receiver 20 that receives the laser light that has passed through the reference cell 19 and converts it into an electrical signal
And a collimator lens 21 that collects the laser light emitted from the semiconductor laser element 17, and the modulator / controller 5 includes an oscillator 22 that oscillates a signal of frequency f, a phase-sensitive detector 23, and Integrator 24, current source 25, constant current source 26, current mixer 27, bias current generator 2
8 and.

The semiconductor laser element 17 excited by the current of the constant current source 26 is modulated by the current mixer 27 with a high frequency of the frequency f from the oscillator 22, and oscillates a laser beam in the front-back direction. The laser light that has passed through the reference cell 19 is converted into an electric signal by the photodetector 20, and the phase-sensitive detector 23 detects the phase-sensitive signal to detect the primary phase-sensitive detected signal.
Output to 4. The integrator 24 is biased by the current from the bias current generator 28 to control the output current of the constant current source 26 to control the temperature of the Peltier device 18 and the temperature of the semiconductor laser device 17, that is, the oscillation wavelength. ..

Returning to FIG. 4, for example, when a laser beam corresponding to the absorption wavelength of methane is emitted from the laser oscillator 3 and a laser beam corresponding to the absorption wavelength of acetylene is emitted from the laser oscillator 4, both laser beams are transmitted to the fiber. It is mixed by the coupler 7, passes through the measuring cell 8 via the optical fiber 29, and is converted into an electric signal by the light receiver 9 via the optical fiber 30. The converted electrical signal is a phase sensitive detector 10-1.
3, the phase-sensitive detector 10 outputs a primary phase-sensitive detection signal corresponding to the absorption wavelength of methane, and the phase-sensitive detector 11 outputs a secondary phase-sensitive detection signal corresponding to the absorption wavelength of methane. Output. Since the primary phase-sensitive detection signal is proportional to the light quantity and the secondary phase-sensitive detection signal is proportional to the light quantity and the gas concentration, the divider 14 detects the primary phase-sensitive detection signal with the secondary phase-sensitive detection signal. When the signal is divided, the concentration of methane is calculated and recorded in the recorder 16. Similarly, the concentration of acetylene is calculated by the phase sensitive detectors 12 and 13 and the divider 15.

The laser oscillator 4 and the modulator / controller 6 have the same structure and operation.

[0010]

Therefore, in the above-described gas detector for detecting two kinds of gas by the applicant of the present application, two oscillators having different frequencies and two reference cells are used to stabilize the wavelength. Two light receivers, two phase sensitive detectors are required, and in order to obtain the gas concentration, 4
Since a single phase sensitive detector is required, the system becomes bulky and the cost becomes high.

The present invention has been made in view of the above points, and an object thereof is to detect two kinds of gas with a simple device and a small device.

[0012]

According to the present invention, the above-mentioned object is as follows: (a) a first laser which oscillates a laser beam having a wavelength corresponding to an absorption line of a first gas and is modulated by a signal of a predetermined frequency. Of the first semiconductor laser that emits the laser light of (1) and (b) the laser light of the wavelength corresponding to the absorption line of the second gas are oscillated, and the phase of the signal of the predetermined frequency is Φ (Φ ≠ nπ /
2, n = 0, ± 1, ± 2 ...), and a second semiconductor laser that emits a second laser beam modulated by signals different from each other,
(C) a mixer that mixes the first laser light and the second laser light, and (d) a reference cell that is output from the mixer and is filled with the first gas and the second gas of known concentrations. A first light-receiver for receiving the passed laser light and converting it into an electric signal;
(E) s of the primary phase sensitive detection signal that receives the output of the photodetector
A first phase sensitive detector that outputs an in component and a cos component, and (f) stabilizes the wavelength of the first laser light by obtaining a primary phase sensitive detection signal related to the first laser light from the sin component. Stabilize the wavelength of the second laser light by subtracting the product of the sin component and cotΦ from the (g) cos component by the first wavelength stabilizer to obtain a first-order phase-sensitive detection signal for the second laser light. And a second wavelength stabilizer for receiving the laser light that has passed through the measurement cell in which the first gas and the second gas of unknown concentration are sealed from the mixer (h) and converts the laser light into an electric signal. And (i) a second phase-sensitive detector that receives the output of the second light-receiver and a signal of a predetermined frequency and outputs a sin component and a cos component of the primary phase-sensitive detection signal, ) The output of the second photoreceiver and the signal of the specified frequency sin of only a second-order phase-sensitive detection signal
A third phase-sensitive detector that outputs a component and a cos component, and (k) a value obtained by subtracting the product of the sin component and cotΦ from the cos component of the first-order phase-sensitive detection signal related to the first laser light. The value obtained by subtracting the product of the sin component of the secondary phase-sensitive detection signal of the first laser light and the product of cot2Φ from the cos component of the secondary phase-sensitive detection signal of the laser light of First to seek
And (l) the sin component of the secondary phase sensitive detection signal for the second laser light is
And a second arithmetic unit for obtaining the concentration of the second gas by dividing by the sin component of the next phase sensitive detection signal.

[0013]

The gas detecting device of the present invention has a phase of Φ (Φ ≠ nπ / 2, n = 0, with the first laser light having a wavelength corresponding to the absorption line of the first gas which is modulated at a predetermined frequency. ± 1, ± 2
...) mixed with a second laser beam having a wavelength corresponding to the absorption line of the second gas, which is modulated at a predetermined frequency different from each other, and passes through the reference cell and the measurement cell. The laser light that has passed through the reference cell is converted into an electric signal by the first light receiver, and is input to the first phase sensitive detector. Sin of the first-order phase sensitive signal obtained from the first phase sensitive detector
The wavelength of the first laser light is stabilized based on the component,
From the cos component of the next phase sensitive signal to the sin component and cot
The wavelength of the second laser light is stabilized based on the value obtained by subtracting the product of Φ.

On the other hand, the laser beam that has passed through the measuring cell is converted into an electric signal by the photodetector and then input to the second and third phase sensitive detectors. The second phase-sensitive detector detects the sin and cos components of the first-order phase-sensitive detection signal as the first component.
And a second arithmetic unit, the third phase sensitive detector outputs the sin component and the cos component of the secondary phase sensitive detection signal to the first and second arithmetic units, and the first arithmetic unit outputs Cos of the first-order phase sensitive detection signal regarding the first laser light
The value obtained by subtracting the product of the sin component and cotΦ from the component is the co of the secondary phase-sensitive detection signal for the first laser light.
The value obtained by subtracting the product of the sin component of the second-order phase sensitive detection signal relating to the first laser light and cot2Φ from the s component is divided to obtain the concentration of the first gas, and the second computing unit uses the second Sin of the second-order phase-sensitive detection signal related to laser light
The component is divided by the sin component of the first-order phase sensitive detection signal regarding the second laser light to obtain the concentration of the second gas.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of a gas detection device according to the present invention, and is illustrated as a device for detecting the concentration d _{m of} methane gas and the concentration d _{a of} acetylene gas.

As shown in the figure, the gas detection device includes a control system 4
0 and measuring system 41.

The control system 40 includes two semiconductor laser elements 42 and 43 each having a Peltier element attached thereto, and a laser beam L ₁ emitted from the semiconductor laser elements 42 and 43.
A fiber coupler 44 that mixes L ₂ through the optical fibers F ₁ and F _2, and a mixed gas of known concentration (methane CH ₄
And a reference cell 45 in which acetylene C ₂ H ₂ ) is enclosed,
A light receiver 46 that receives the laser light that has passed through the reference cell 45 and converts it into an electrical signal, and a modulator / controller 47 that stabilizes the oscillation wavelengths of the semiconductor laser elements 42 and 43 based on the electrical signal from the light receiver 46. And have.

On the other hand, the measuring system 41 is a measuring cell 48 in which a mixed gas of methane and acetylene of unknown concentration is enclosed.
And a photodetector 49 that receives the laser light that has passed through the measuring cell 48 and converts it into an electric signal, and an electric signal from the photodetector 49 is phase-sensitively detected by an electric signal of frequency f from the modulator / controller 47. A phase-sensitive detector 50 that outputs a first-order phase-sensitive detection signal I _f, and a phase-sensitive detector 51 that outputs a second-order phase-sensitive detection signal I _2f by phase-sensitive detection of the same signal;
Next phase sensitive detection signal I _f and second phase sensitive detection signal I _2f
And a calculator 53 for calculating the concentration d _m of methane as the first gas and a calculator 53 for similarly calculating the concentration d _a of acetylene as the second gas.

FIG. 2 is a schematic configuration diagram of the control system for explaining the control system 40 shown in FIG. 1 in more detail.

The control system 40 comprises semiconductor laser elements 42, 4
3, fiber coupler 44, reference cell 45, light receiver 4
In addition to 6, two cosine wave signals cos (2πf _o t) and cos (2πf _o t + Φ) whose phases are different from each other by Φ
And an oscillator 54 for generating the s of the primary phase sensitive detection signal.
Provided in the semiconductor laser device 42, a phase sensitive detector 55 that outputs the in component and the cos component at the same time, a calculator 56, integrators 57 and 58 that integrate the primary phase sensitive detection signal of the phase sensitive detector 55. A current source 59 for applying a current to the Peltier device, a bias current generator 60 for applying a bias current to the current source 59, and a semiconductor laser device 43.
Current source 61 for applying current to the Peltier device provided in the
And a bias current generator 62 that applies a bias current to the current source 61. However, Φ is a phase angle that satisfies Expression 1.

[0022]

Φ ≠ nπ / 2, n = 0, ± 1, ± 2 (radian) Laser light L emitted from the semiconductor laser elements 42 and 43
_1, L ₂ isolator I ₁ for preventing reflection of the laser beam, respectively, I ₂ and the fiber coupler 4 through the optical fiber F _1, F ₂ laser light through a lens L _e1, L _e2 for condensing Be led to.

The semiconductor laser devices 42 and 43 have such characteristics that the oscillation wavelength becomes longer as the temperature of the device itself becomes higher and the oscillation wavelength becomes shorter as the temperature lowers. Peltier devices are attached to the semiconductor laser devices 42 and 43, and these Peltier devices are devices utilizing the Peltier effect. The Peltier effect is a phenomenon in which, when N-type semiconductors and P-type semiconductors are alternately joined and a current is passed, Joule heat is generated and, in addition, heat is generated or heat is absorbed at the junction. In this phenomenon, heat generation and heat absorption are reversed when the direction of current flow is reversed, so the oscillation wavelength of the semiconductor laser device can be controlled by controlling the voltage or current applied to the Peltier device.

The oscillator 54 has a cos (2πf _o t), c
Oscillates two cosine wave signals represented by os (2πf _o t + Φ) (phase difference is Φ). Here f _o is the frequency, t represents the time. The constant current source 63 generates a constant current for causing the semiconductor laser element 42 to oscillate at a wavelength corresponding to the absorption line of methane, and the constant current source 64 causes the semiconductor laser element 43 to have a wavelength corresponding to the absorption line of acetylene. Generates a constant current required to oscillate. Therefore, the laser light emitted from the semiconductor laser element 42 is frequency-modulated with a signal of frequency f, and the laser light emitted from the semiconductor laser element 43 is frequency-modulated with a signal having the same frequency f and a phase difference of Φ.

The fiber coupler 44 mixes the laser light L ₁ emitted from the semiconductor laser element 42 and the laser light L ₂ emitted from the semiconductor laser element 43, and the mixed laser light passes through the optical fiber F ₃ . Reference cell 4 via
5, and enters the measuring cell 48 through the optical fiber F ₄ and the lens L _e3 (see FIG. 1).

The light receiver 46 is an element for converting the laser light passing through the reference cell 45 into an electric signal, and for example, a photodiode is used, but not limited to this, a phototransistor may be used. (Fig. 1) Phase sensitive detector 55
Extracts only a component (first-order differential signal) having a specific frequency and a specific phase from the electric signal output from the light receiver 46 and demodulates it. As a result, it is possible to detect a minute signal with a high S / N ratio.

Generally, when laser light modulated at a specific frequency passes through a gas absorbing a light of a specific wavelength and is received by a sensor, the output signal of this sensor has the same DC frequency as the modulation frequency. It consists of a fundamental wave component having a frequency and its harmonic components. When the fundamental wave component and the second harmonic component are phase-sensitive detected by the phase-sensitive detector, a signal corresponding to the first derivative or the second derivative with respect to the wavelength can be obtained, and the sin component and cos of the first derivative signal can be obtained. , And the sin component of the second derivative signal and c
The os component and the os component can be output at the same time.

FIG. 3 shows a vector (a) representing the frequency-modulated laser light, the laser light being detected by a phase-sensitive detector.
Vector diagrams of the signal (b) that is secondarily differentiated and the signal (c) that is secondarily differentiated by the phase sensitive detector of the laser light are shown.

The phase sensitive detector 55 first-order differentiates the transmitted light intensities of acetylene and methane, and further decomposes the first-order differentiated signal into sin and cos components as shown in FIG. ^f _sin (= I ^f _a sinΦ) and I ^f _cos
Output as (= I ^f _m + I ^f _a cosΦ). The magnitude of the oscillation frequency ω _a of the frequency-modulated laser light L ₂ emitted from the semiconductor laser element 43 is expressed by the equation 2, and the magnitude of the frequency-modulated laser light L ₁ emitted from the semiconductor laser element 42 is The magnitude of the oscillation frequency ω _m is expressed by Equation 3.

[0030]

[ _Formula 2] ω _a = ω _0a + ω _1a cos (2πf _o t + Φ)

[0031]

Ω _m = ω _0m + ω _1m cos (2πf _o t) where ω _0a is the angular frequency of the laser beam L _{2 having} a wavelength corresponding to the absorption wavelength of acetylene, ω _1a is the angular frequency of the modulation amplitude, and ω
_0m represents the angular frequency of the laser beam L _{1 having} a wavelength corresponding to the absorption wavelength of methane, and ω _1m represents the angular frequency of the modulation amplitude.

As shown in the figure, two vectors ω _1m and ω _1a
It can be seen that there is a phase difference of Φ. These laser light L
₁ and L ₂ are mixed and passed through the reference cell 45 to receive the light receiver 4
Into an electric signal when the input to the phase sensitive detector 55 at 6, first derivative signal I _f is obtained, the vector I ^f _m as shown in FIG. 3 (b), I ^f _a is obtained.

As shown in FIG. 3B, the first-order differential signal I _f
Is output in a state in which the phase difference is Φ, the phase is different, so that ^if _a sin Φ (=
I ^f _sin ), but I ^f _a cos as the cos component
Φ + I ^f _m (= I ^f _sin ) is output and 1 for acetylene
Resulting in output while containing the first derivative signal I ^f _a for the next differential signal I ^f _a and methane.

However, in order to control the oscillation wavelength of the semiconductor laser device 42, the first-order differential signal I of the acetylene transmitted light is used.
^f _a 1 of methane transmitted light-order differential signal I ^f _m the arithmetic unit 56 so as thereby to control the wavelength accidentally be separated the I ^f
performing the calculation of _cos -I ^f _{sin cotΦ.}

The integrator 57 is a primary differential signal corresponding to the laser beam L ₁ frequency-modulated by the sine wave signal of frequency f,
That is, I ^f _sin is integrated, and the integrator 58 has a first-order differential signal corresponding to the laser light L ₂ frequency-modulated with a sine wave signal whose phase is different by Φ at frequency ^f , that is, I ^f _cos −I ^f
Integrate _sin cotΦ.

The integrator 57 is _a sin of the first derivative signal I ^f _a .
The component produces the signal necessary to drive the current source 59, which supplies the current corresponding to the output of the integrator 57 to the Peltier element, which in turn supplies the current magnitude of the current source 59 and Depending on the direction, it will absorb heat or generate heat.

On the other hand, the integrator 58, a signal required to drive the current source 61 from the sin component of the first derivative signal I ^f _m occurs, the current source 61, current corresponding to the output of the integrator 58 Is supplied to the Peltier element, and the Peltier element is a current source 61
Heat is absorbed or generated depending on the magnitude and direction of the current.

The bias current generator 60 can apply a bias current to the current source 59. This is because the semiconductor laser element 42, the light receiver 46, the phase sensitive detector 55, the integrator 57, the current source 59, and the Peltier element form a loop in which the wavelength is stabilized when the first-order differential signal becomes zero. This is because the wavelength of the semiconductor laser element 42 is adjusted to a predetermined value when it is desired to change to another wavelength. Similarly, the semiconductor laser element 43 and the light receiver 4
6, the phase sensitive detector 55, the calculator 56, the integrator 58, the current source 61, and the Peltier element also form a loop such that the first-order differential signal becomes zero. Therefore, the bias current generator 62 is used to bias the bias current. The oscillation wavelength can be changed by applying a current.

Returning to FIG. 1 again, the measurement system 41 will be described.
In, the measurement cell 48 is connected to the methane gas cylinder 65, the nitrogen gas cylinder 66, and the acetylene gas cylinder 67, and the component ratio in the measurement cell 48 can be changed by opening and closing the cocks 68, 69, and 70.
Nitrogen N ₂ is used for adjusting the concentration d _m of methane and the concentration d _a of acetylene, but other gas may be used as long as it does not cause a chemical reaction with methane and acetylene. The laser light from the fiber coupler 44 is incident on the measuring cell 48, and the lens L _e4 ,
The light enters the light receiver 49 via L _e5 and the optical fiber F ₅ . The light receiver 49 converts the mixed laser light into an electric signal, and the converted signal is input to the phase sensitive detectors 50 and 51.

The phase-sensitive detector 50 uses the electrical signal from the photodetector 49 and the oscillation frequency f from the modulator / controller 47 to determine the s of the primary differential signal for the laser beams L ₁ and L _2.
Outputs in component and cos component, and phase sensitive detector 5
1 is the si of the second derivative signal with respect to the laser beams L ₁ and L _2.
Output the n and cos components.

The arithmetic unit 52 as the first arithmetic unit is a value obtained by subtracting the value of the product I ^f _sin cotΦ of the sin component and cotΦ from the value of the cos component I ^f _cos of the first-order differential signal relating to the laser beam L _1. (I ^f _cos −I ^f _sin cotΦ) laser light L
2 from the value of cos component I ^2f _{cos 1} about second-order differential signal
Value of product of sin component of second derivative signal and cot2Φ I ^2f _sin
A value obtained by subtracting cot2Φ (I ^2f _cos −I ^2f _sin cot2
By dividing the [Phi) to calculate the concentration d _m of methane, calculator 53 as the second computing unit, first derivative to a laser beam L ₁ values I ^2f _sin of the laser beam L ₂ relating to the secondary differential signal The acetylene concentration d _a is calculated by dividing by the signal value I ^f _sin .

FIG. 3C is a vector diagram showing the secondary differential signal.

As shown in the figure, since the secondary differential signal I ^2f _m is a horizontal vector and the secondary differential signal I ^2f _a is a vertical vector, the cos component is I ^2f _m + I ^2f _a cos 2Φ
Since the sin component is I ^2f _a sin 2Φ, the methane concentration d _m is (I ^2f _cos −I ^2f _sin cot 2Φ) (I ^f _cos −
Divide by I ^f _sin cotΦ) to obtain the concentration of acetylene d
_a can be obtained by dividing I ^2f _sin by I ^f _sin .

Next, the operation of the gas detector will be described with reference to FIGS.
Will be described.

In FIG. 2, two signals cos (2πf _o t) and cos (2π) from the oscillator 54 having different phases Φ.
(f _o t + Φ) is superimposed on the current generated by the constant current sources 63 and 64, whereby the semiconductor laser elements 42 and 43 are frequency-modulated. The laser beams L ₁ and L ₂ emitted from the semiconductor laser elements 42 and 43 are mixed by a fiber coupler 44, and one of the mixed laser beams is a reference cell 45.
And the other laser beam is incident on the measuring cell 48. The laser light that has passed through the reference cell 45 is received by the light receiver 46.
Then, it is converted into an electric signal and sent to the phase sensitive detector 55. The sin component of the primary differential signal is sent from the phase sensitive detector 55 to one input of the integrator 57 and the subtractor 56, and the cos component of the primary differential signal is sent to the other input of the arithmetic unit 56. The integrator 57 integrates the sin component, that is, the first-order differential signal of the methane signal as it is to integrate the current source 5
9, a predetermined current is applied to the Peltier element, the temperature of the Peltier element is controlled, and the laser light L ₁ emitted from the semiconductor laser element 42 is stabilized at a wavelength corresponding to the absorption wavelength of methane. The calculator 56 has a cos component I ^f _cos
By subtracting the product of the sin component and cotΦ from I ^f _sin cotΦ, only the first-order differential signal of the acetylene signal is extracted and integrated to drive the current source 61, and a predetermined current is applied to the Peltier element. The semiconductor laser device 43
The laser beam L ₂ emitted from is stabilized at a wavelength corresponding to the absorption wavelength of acetylene.

As shown in FIG. 1, the laser light passing through the measuring cell 48 is converted into an electric signal by the light receiver 49 and sent to the phase sensitive detectors 50 and 51, which are also sent to the phase sensitive detectors 50 and 51. the signal f _o of the oscillator 54 of the modulator / controller 47 is input. The phase-sensitive detector 50 outputs the cos component I ^f _cos of the first-order differential signal to the calculator 52 and outputs 1
The sin component I ^f _sin of the secondary differential signal is output to the calculator 53. The phase sensitive detector 51 has a cos component I of the second derivative signal.
^2f _cos is output to the calculator 52, and the sin component I ^2f _sin is output to the calculator 53. The calculator 52 calculates the concentration of methane d _m, and the calculator 53 calculates the concentration of acetylene d _a .

As described above, according to this embodiment, the control system 40
In the laser oscillation wavelength corresponding to the absorption wavelength of a predetermined laser beam L ₁ of an oscillation wavelength corresponding to the absorption wavelength of the modulated methane frequency f _o, it is modulated by Φ only phase different predetermined frequencies f _o acetylene The light L ₂ is mixed with the fiber coupler 44, passed through the reference cell 45, converted into an electric signal by the light receiver 46, and the semiconductor is generated based on the first-order differential signal related to the laser light L ₁ corresponding to the absorption wavelength of methane. By controlling the temperature of the laser element 42, the oscillation wavelength corresponding to the absorption wavelength of methane is stabilized, and the temperature of the semiconductor laser element 43 is adjusted based on the first-order differential signal relating to the laser beam L ₂ corresponding to the absorption wavelength of acetylene. By controlling, the oscillation wavelength corresponding to the absorption wavelength of acetylene is stabilized.

On the other hand, in the measuring system 41, the laser light mixed by the fiber coupler 44 passes through the measuring cell 48 and is then converted into an electric signal by the light receiver 49, and the laser light L ₁ , L ₂ is converted by the phase sensitive detector 50. The first-order differential signal relating to the laser beams L ₁ and L ₂ is input to the calculator 52 by the phase-sensitive detector 51, and the methane concentration d _{m is} calculated by the calculator 52. Is calculated, and the calculator 53 calculates the acetylene concentration d _a .

Therefore, conventionally, two reference cells, three light receivers, and six phase sensitive detectors were required to obtain the concentrations d _m and d _a of the mixed gas of methane and acetylene. In the present embodiment, one reference cell and 2
The methane concentration d _m and the acetylene concentration d _a can be obtained with one light receiver and three phase sensitive detectors, and the device can be downsized, the cost can be reduced, and the operability can be improved.

Although the phase difference is Φ in this embodiment,
When Φ is π / 4, cotΦ becomes 1 and cot2Φ becomes 0, so that the processing in the computing units 52 and 56 is simplified. That is, the calculation of the methane concentration d _{m in} the calculator 52 is simplified from Equation 4 to Equation 5,

[0051]

## EQU00004 ## d _m = (I ^2f _cos −I ^2f _sin cot2Φ) / (I ^f _cos −I ^f _sin cotΦ)

[0052]

D _m = I ^2f _cos / (I ^f _cos −I ^f _sin ) The calculation in the calculator 56 is simplified from the formula 6 to the formula 7.

[0053]

[Equation 6] I ^f _a = I ^f _cos −I ^f _sin cotΦ

[0054]

Equation 7] ^{_{I f a = I f cos -I}} f sin Furthermore, the computing unit 52 in the present embodiment, the value of I ^2f _cos a value obtained by subtracting the value of I ^f _sin cotΦ from the value of I ^f _cos in the figure I ^2f
_Although the value obtained by subtracting _sin cot2Φ is divided, a subtractor and a divider may be used instead of the calculator 52. Further, the gas filled in the reference cell 44 and the measurement cell 48 is not limited to methane and acetylene. Further, two laser lights are mixed by the fiber coupler 44, but a beam splitter may be used.

[0055]

As described above, according to the present invention, the first laser beam having the wavelength corresponding to the absorption line of the first gas and the absorption line of the second gas which are modulated by the signal of the predetermined frequency. The laser light of the wavelength corresponding to is mixed with a second laser light which is modulated with a signal having the same frequency as the predetermined frequency but a phase different from Φ, and the mixed laser light is passed through the reference cell. Convert it into an electrical signal with the first light receiver,
The wavelength of the first laser light is stabilized based on the sin component of the first-order phase-sensitive detection signal relating to the first laser light of the phase-sensitive detector of The wavelength of the second laser light is stabilized based on the value obtained by subtracting the sin component from the cos component.

On the other hand, the laser signal mixed by the mixer is passed through the measuring cell and the electric signal obtained by the second photodetector and the signal of a predetermined frequency are detected by the second phase sensitive detector and the third phase detector.
Is received by the second phase-sensitive detector and the sin and cos components of the first-order phase-sensitive detection signal are output from the second phase-sensitive detector and the second-order phase-sensitive detection signal is output from the third phase-sensitive detector. The sin component and the cos component are output, and the first arithmetic unit relates to the first laser light with a value obtained by subtracting the product of the sin component and cotΦ from the cos component of the first-order phase sensitive detection signal relating to the first laser light. The value obtained by subtracting the product of the sin component of the secondary phase-sensitive detection signal relating to the first laser beam and cot2Φ from the cos component of the secondary phase-sensitive detection signal is divided to obtain the concentration of the first gas. The second computing unit outputs the sin component of the second-order phase-sensitive detection signal regarding the second laser beam to the first component regarding the second laser beam.
Since the concentration of the second gas is obtained by dividing by the sin component of the next phase sensitive detection signal, it is possible to detect the concentrations of two types of gas with a simple configuration and a small device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a gas detection device according to the present invention.

FIG. 2 is a schematic configuration diagram for explaining the control system shown in FIG. 1 in more detail.

FIG. 3 is a vector (a) representing the frequency-modulated laser light, a signal (b) obtained by first-order differentiation of the laser light by a phase-sensitive detector, and a signal (c) second-order differentiated by the phase-sensitive detector of the laser light. ) Vector diagrams are shown.

FIG. 4 is a block diagram of a gas detection device by the applicant of the present application.

5 is a schematic configuration diagram of a laser oscillator and a modulator / controller of the gas detection device shown in FIG.

[Explanation of symbols]

 40 Control System 41 Measurement System 42, 43 Semiconductor Laser Element 44 Fiber Coupler 45 Reference Cell 46, 49 Light Receiver 48 Measurement Cell 50, 51, 55 Phase Sensitive Detector 52, 53 Operator 54 Oscillator 56 Operator

Claims (3)

[Claims] (A) A first semiconductor laser which oscillates a laser beam having a wavelength corresponding to an absorption line of a first gas and emits a first laser beam modulated by a signal having a predetermined frequency; b) A laser beam having a wavelength corresponding to the absorption line of the second gas is oscillated, and the phase is Φ (Φ ≠ nπ / 2, n = 0, ± 1, ± 2 at the same frequency as the signal of the predetermined frequency. A second semiconductor laser that emits a second laser light modulated by signals that are different from each other; (c) a mixer that mixes the first laser light and the second laser light; A first light receiver that receives the laser light that has been output from the mixer and has passed through a reference cell in which the first gas and the second gas of known concentrations are sealed and that converts the laser light into an electric signal; ) A first unit for receiving the output of the photodetector and outputting the sin and cos components of the primary phase sensitive detection signal A phase sensitive detector, for the first laser beam from the (f) the sin component 1
A first wavelength stabilizer for stabilizing the wavelength of the first laser light by obtaining the next phase-sensitive detection signal; and (g) subtracting the product of the sin component and cotΦ from the cos component, Second phase stabilizer for stabilizing the wavelength of the second laser light by obtaining a first-order phase-sensitive detection signal relating to the laser light of (1), (h) the first gas of unknown concentration from the mixer, and A second photoreceiver for receiving the laser light that has passed through the measurement cell in which the second gas is sealed and converting it into an electric signal; and (i) the output of the second photoreceiver and the predetermined frequency. A second phase-sensitive detector that receives the signal and outputs a sin component and a cos component of the primary phase-sensitive detection signal; and (j) a secondary phase-sensitive detector that receives the output of the second photodetector and the signal of the predetermined frequency. And cos components of the phase sensitive detection signal of A third phase-sensitive detector that outputs (k) a value obtained by subtracting the product of sin component and cotΦ from the cos component of the first-order phase-sensitive detection signal relating to the first laser light, The value obtained by subtracting the product of the sin component of the secondary phase-sensitive detection signal of the first laser beam and cot2Φ from the cos component of the secondary phase-sensitive detection signal of A first computing unit to be obtained, and (l) the sin component of the secondary phase-sensitive detection signal regarding the second laser light is divided by the sin component of the primary phase-sensitive detection signal regarding the second laser light. A second computing unit for obtaining the concentration of the second gas. 2. The gas detection device according to claim 1, wherein the Φ is π / 4. 3. The gas detection device according to claim 1, wherein the first gas is methane gas and the second gas is acetylene gas.