JPH0715439B2 - Gas remote sensing device using diffraction grating - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention changes the concentration or pressure of a gas by modulating a diffraction grating having an optical characteristic of a narrow band filter according to the absorption spectrum of the gas whose concentration (pressure) is detected. The present invention relates to a gas remote sensing device for detecting.

[0002]

2. Description of the Related Art Conventionally, as a means for detecting the concentration (pressure) of methane gas or the like, there has been a circuit configuration as shown in FIG. This is because after passing a part of the light transmitted through the gas cell in which methane gas is enclosed by the half mirror 101 and reflecting a part of the light, and photoelectrically converting the reflected light as the reference light by the photodiode 102,
The photoelectrically converted DC signal is amplified by the amplifier 103, and the amplified DC signal is applied to one input terminal of the differential amplifier 104, while the light transmitted through the half mirror 101 has a center wavelength that matches the absorption spectrum of methane gas. After passing through the interference filter 105, the light passing through the interference filter 105 is photoelectrically exchanged by the photodiode 106 as measurement light, and then the photoelectrically exchanged DC signal is amplified by the amplifier 107.
By applying the amplified DC signal to the other input terminal of the differential amplifier 104, the differential amplifier 104 amplifies the difference between the DC signal corresponding to the reference light and the DC signal corresponding to the measurement light, and the differential amplifier The concentration of methane gas is detected based on the signal output from 104.

[0003]

In the conventional gas concentration (pressure) detecting means, the optical path is divided into the reference light and the measuring light by the half mirror 101, and the respective electric circuits are made independent. When the electric characteristics of the differential amplifiers 103 and 107 and the differential amplifier 104 fluctuate due to changes in ambient temperature, the amplification factors of the respective amplifiers slightly fluctuate, and the DC signal corresponding to the reference light and the DC signal corresponding to the measurement light change in temperature. However, there is a problem in that it is not possible to accurately detect the concentration because it varies. Therefore, conventionally, it was necessary to put the electric circuit in a constant temperature bath to stabilize the circuit characteristics with respect to temperature. Then, in order to increase the concentration (pressure) detection accuracy, it was necessary to increase the temperature control accuracy of the constant temperature bath. However, there is a technical limitation in increasing the temperature control accuracy of the constant temperature bath, and there is a problem that the constant temperature bath having high temperature control precision is expensive.

Further, there is a problem in that it is difficult to remove noise due to the DC signal amplification method, and it is extremely difficult to remove it even if a drift current is superimposed. Therefore, in the present invention, in order to solve the above problem, the light transmitted through the gas cell is passed through a single optical path without being branched into two optical paths of a reference light and a measurement light, and a diffraction grating provided in the middle of this single optical path. Is controlled to slightly modulate the wavelength around the absorption wavelength of the gas whose concentration (pressure) is detected, and the center of modulation of the wavelength of the diffraction grating is automatically adjusted to It is a technical issue to be solved to detect the gas concentration (pressure) with high accuracy by performing feedback control so as to match the absorption wavelength of.

[0005]

The technical means for solving the above-mentioned problems is an absorptivity of a gas remote sensing device using a diffraction grating when a gas whose concentration or pressure is detected is transmitted through the gas remote sensing device. Is a light emitting means that emits light in a wavelength band including the largest wavelength, a forward light path that guides the light emitted from the light emitting means to a gas cell in which the gas is sealed, and an incident light path that passes through the gas cell. A light returning path for guiding light, a diffraction grating provided on the forward light path or the light returning path, and a first light having a wavelength that is largely absorbed by the gas by modulating the diffraction grating at a predetermined timing. And diffraction grating modulation control means for generating second light of a wavelength that is not absorbed by the gas,
A light receiving unit that is provided at a terminal portion of the returning path and receives the first light and the second light and outputs a first electric signal and a second electric signal corresponding to the light amounts of the respective lights. And a modulation for correcting the modulation of the diffraction grating by the diffraction grating modulation control means based on the total light quantity of the first light and the second light corresponding to the added value of the respective electric signals from the light receiving means. Control correction means, and an operation of calculating an absorption rate of the first light by the gas based on the first electric signal and the second electric signal, and calculating a concentration or pressure of the gas from the absorption rate. And a means provided with the means.

[0006]

According to the gas remote sensing device using the diffraction grating having the above structure, when the diffraction grating is provided in the return path, the light emitted from the light emitting means is guided to the return path and enters the gas cell. And transmitted. The light transmitted through the gas cell is guided by the returning path and is incident on the diffraction grating.
The diffraction grating is modulated and controlled by the diffraction grating modulation control means, and by this modulation, the diffraction grating generates first light having a wavelength that is largely absorbed by gas and second light having a wavelength that is not absorbed by the gas. Each light is transmitted to the light receiving means. When the light receiving means receives the first light and the second light, it converts the respective light into a first electric signal and a second electric signal and outputs the first electric signal and the second electric signal. When the first electric signal and the second electric signal are input to the modulation control correction means, the modulation control correction means outputs the first light and the second light corresponding to the added value of the respective electric signals. The modulation of the diffraction grating by the diffraction grating modulation control means is corrected based on the total light amount. Then, the calculating means calculates the absorption rate of the first light by the gas based on the first electric signal and the second electric signal, and calculates the concentration or pressure of the gas from the absorption rate.

When the diffraction grating is provided in the middle of the outgoing light path, the light emitted from the light emitting means is divided into the first light and the second light by the diffraction grating in front of the gas cell. It is transmitted through the gas cell, then guided by the return path, received by the light receiving means, and converted into a first electric signal and a second electric signal. The subsequent action is that the diffraction grating is in the middle of the return path. It is similar to the case of being provided in.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of the gas remote sensing device of the present invention.

In FIG. 1, light having a wavelength of, for example, 1.3 micrometer band is emitted from the super luminescent diode (SLD) 3 by the constant current supplied from the constant current circuit 2 provided in the main case 1. Then, this light is transmitted to the optical instrument bracket 6 via the optical connector 4 and the multimode optical fiber 5. The optical bracket 6 has a density (pressure) whose density (pressure) is detected.
A gas cell 7 in which, for example, methane gas as a detection gas is uniformly enclosed is provided. The light transmitted to the optical instrument bracket 6 is incident on the lens 8, and the light ray L1 condensed by the lens 8 in a beam shape passes through the gas cell 7. The light ray L1 transmitted through the gas cell 7 is condensed by the lens 9, and the multimode optical fiber 10 and the optical connector 11 are connected.
Is returned to the sub-case 12 provided in the main case 1 via.

The light L2 incident on the sub case 12 is incident on the reflection type diffraction grating 21. A piezo element 22 is attached to the diffraction grating 21, and the piezo element 22 expands and contracts in the longitudinal direction according to the voltage applied to the piezo element 22, so that the diffraction grating 21 has a small angle about the axis 21A. That is, it is rotationally displaced to the positions shown by the solid line and the broken line. When the diffraction grating 21 is rotationally displaced by the piezo element 22, the light L2 is the first light (λ0) having a wavelength corresponding to the absorption spectrum of methane gas, that is, a wavelength of 1.3312 micrometers, and The wavelength is shifted from the wavelength of 3312 micrometers by 6 nm (nanometer).
It is modulated with a second light (λ1) having a wavelength that is not absorbed by methane gas of 3372 micrometers. (See Figures 2 and 3)

1.331 generated by the above modulation control
A first light having a wavelength of 2 micrometers and the 1.
1.32 slightly deviated from the wavelength of 3312 micrometers
After the second light having a wavelength of 372 micrometers and the second light alternately pass through the slit 14 as reflected light, those lights are incident on the bidirectional spectroscope 24 through the optical connector 13 and the multimode optical fiber 15, and The bidirectional spectroscope 24 splits the split light into L3 and L4. In the branched light L3, the gas having the same component as the methane gas as the concentration (pressure) detection gas is 1
After passing through the reference cell 16 filled with a concentration of 00%, photoelectric conversion is performed in the photodiode PD1.
In the process of the branched light L3 passing through the reference cell 16, the first light having a wavelength of 1.3312 μm is absorbed and attenuated by the methane gas in the reference cell 16, while 1.3372 μm.
The second light of wavelength m is transmitted with little attenuation. Therefore, the amount of light received by the photodiode PD1 is
The intensity changes alternately in synchronization with the modulation cycle. Photoelectric exchange is performed in the photodiode PD1, and the photodiode P
The DC signal D1 output from D1 is input to the synchronization control circuit 28.

On the other hand, the branched light L4 is generated by the photodiode PD.
Photoelectrically exchanged at 2. The DC signal D2 photoelectrically exchanged in the photodiode PD2 and output from the photodiode PD2 is gain-adjusted by the programmable gain amplifier 33 capable of gain adjustment, and its output signal D3.
Is input to the synchronization control circuit 34.

The microcomputer 18 is also the center of the gas remote sensing device. The oscillation circuit 36 connected to the microcomputer 18 oscillates and outputs a signal of a predetermined frequency in synchronization with the clock signal from the microcomputer 18, and the oscillation signal S1 is output to the adder 37. The adder 37 outputs an addition signal S4 obtained by adding an oscillation signal S1 and a modulation control correction signal S3 described later to the piezo driver 23 that drives the piezo element 22.

On the other hand, the phase control circuit 38 connected to the microcomputer 18 inputs the clock S2 from the microcomputer 18 and outputs rectangular wave pulse signals S5 and S6 of a predetermined cycle. The pulse signal S5 is input to the synchronization control circuit 28, and the other pulse signal S6 is input to the synchronization control circuit 34.

The synchronization control circuit 28 uses the pulse signal S5.
And the DC signal D1 from the photodiode PD1 are input, the signal D1 is converted into an AC signal in synchronization with the pulse signal S5, and then synchronous detection is performed. The output signal S7 synchronously detected by the synchronous control circuit 28 is input to the PI circuit (proportional integrator circuit) 40. When the diffraction grating 21 is finely rotationally displaced by the piezo element 22, the synchronously detected output signal S7 changes its displacement width from a predetermined value for some reason, and has a wavelength of 1.3312 micrometers. Light and the second light having a wavelength of 1.3372 micrometers slightly deviated from the wavelength of 1.3312 micrometers are corrected so that the displacement width is returned to a predetermined value so as not to be obtained. This signal S7 is applied to the adder 37 as a more precise modulation control correction signal S3 through the PI circuit (proportional integration circuit) 40. Therefore, the signal S4 output from the adder 37 to the piezo driver 23 is a signal obtained by adding the oscillation signal S1 and the modulation control correction signal S3 as a kind of feedback signal for correcting the displacement width.

The synchronization control circuit 34 receives the pulse signal S6 and the output signal D3, converts the signal D3 into an AC signal, and synchronously detects the AC signal in synchronization with the pulse signal S6. The output signal S8 synchronously detected in the synchronous control circuit 34 is input to the microcomputer 18 after being converted into a digital signal S9 by the AD converter 17.

When the microcomputer 18 receives the digital signal S9 corresponding to the output signal S8 output from the synchronization control circuit 34, the microcomputer 18 receives the digital signal S9 and then outputs the digital signal S9.
A signal corresponding to the amount of the first light having a wavelength of 2 micrometers and the above-mentioned 1.3 that is not absorbed by methane gas.
The difference from the signal corresponding to the light amount of the second light having the wavelength of 372 micrometers is calculated, and the concentration (pressure) of the methane gas in the gas cell 7 is calculated and detected based on the difference. Then, the calculated concentration (pressure) of methane gas is displayed on the LED display 42 by the setting operation of the keyboard 41.

As described above, the wavelength corresponding to the absorption spectrum of the first light absorbed by the concentration (pressure) detection gas,
Means for detecting the gas concentration (pressure) with high accuracy by controlling the diffraction grating 21 that modulates to the non-absorption wavelength of the second light slightly deviated from the absorption spectrum corresponding wavelength is the methane gas disclosed in this embodiment. Not just the concentration of any gas (pressure)
It is also useful when detecting and displaying.

The arrangement position of the diffraction grating 21 may be before the gas cell 7 instead of after the gas cell 7 as in the embodiment.

Next, an application example of the present invention will be described. Figure 5
Shows a first application example. When methane gas is flowing through a long pipe 51, the concentration of methane gas in each of a plurality of gas cells 52, 53, 54 provided in the middle of the pipe 51 is concentrated. This is a means for detecting leakage of methane gas from the long pipe 51 by performing a physical measurement. In the case of this application example, two cores of a multi-core optical fiber 56 are connected to the gas cells 52, 53, 54 respectively from the main body 55 accommodating the super luminescent diode 3, the microcomputer 18, the diffraction grating 21 and the like. The gas concentration of each of the gas cells 52, 53, 54 is calculated by switching and receiving the light returning from each of the gas cells 52, 53, 54, or by time-divisionally controlling the photoelectrically converted electric signal. Leakage of methane gas from the long pipe 51 in the vicinity of each of 52, 53, 54 can be detected.

FIG. 6 shows a second application example, L
In a system for carrying out natural gas from the NG ship 61 using the loading arm 62 or carrying natural gas into the LNG ship 61, a plurality of gas cells 63, 64, 65 are provided at intermediate positions of the loading arm 62 and the loading arm 62 is provided. 6 shows a system for detecting leakage of natural gas from 62. In this system, the method of calculating the gas concentrations of the gas cells 63, 64, 65 and detecting the leakage of natural gas from the loading arm 62 is the same as in the first application example.

FIG. 7 shows a third application example, and shows a system for detecting that the gas in the inner diameter portion of the loading arm 62 or a general pipeline is sufficiently purged. This system is second
Taking the loading arm 62 shown in the application example as an example, the loading arm 62 is generally filled with nitrogen gas when the loading arm 62 is in a rest state, and the nitrogen gas that is previously filled when passing the natural gas through the loading arm 62. Need to be thoroughly purged. As the procedure, methane gas was sent to the loading arm 62 to discharge nitrogen gas, and then the concentration of methane gas in the gas cell 71 communicated with the loading arm 62 was detected to confirm that nitrogen gas was sufficiently discharged. after,
The operation of flowing the liquefied natural gas is started, and after the operation is finished, the concentration of methane gas in the loading arm 62 is detected again, and nitrogen gas is sealed when the concentration is sufficiently low.

[0024]

As described above, according to the present invention, beam-shaped light is transmitted through a gas cell in which an arbitrary gas whose concentration (pressure) is detected is sealed, and the first wavelength of the wavelength absorbed by the gas is transmitted. When the gas concentration is calculated and detected according to the light absorption degree of the first light, the first light as the measurement light is modulated by modulating the diffraction grating provided in the light path after the gas cell or in the light path before the gas cell. And a second light as a reference light having a wavelength that is not absorbed by the gas are generated at a predetermined timing, the total light quantity of the first light and the second light is monitored, and the diffraction grating of the diffraction grating is adjusted according to the total light quantity. Feedback control is performed so that the center of modulation is automatically adjusted to the absorption wavelength of the light of the concentration (pressure) detection gas, and the first light and the second light are controlled.
The absorption rate of the first light by the concentration (pressure) detection gas is calculated on the basis of the first electric signal and the second electric signal obtained by photoelectrically converting the above-mentioned light, and the concentration (pressure) is calculated from the absorption rate. Since the concentration (pressure) of the detection gas can be calculated, there is an effect that the concentration (pressure) of the gas can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a system diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is an absorption spectrum characteristic diagram of methane gas.

FIG. 3 is an explanatory diagram of modulation characteristics by a diffraction grating.

FIG. 4 is a configuration system diagram of a conventional gas concentration (pressure) detection device.

FIG. 5 is an explanatory diagram showing a first application example.

FIG. 6 is an explanatory diagram showing a second application example.

FIG. 7 is an explanatory diagram showing a third application example.

[Explanation of symbols]

 3 Super Luminescent Diode 7 Gas Cell 18 Microcomputer 21 Diffraction Grating 22 Piezo Element 23 Piezo Driver 24 Spectroscope 28 Synchronous Control Circuit PD1, PD2 Photodiode 34 Synchronous Control Circuit 36 Oscillation Circuit 37 Adder 38 Phase Control Circuit

Front Page Continuation (72) Inventor Seiji Aji 122, Kamishima, Aichi Prefecture, Osamu 122, Suntech Co., Ltd. Documents JP-A-1-145547 (JP, A) JP-A-54-71685 (JP, A) JP-A-62-257044 (JP, A) JP-A-63-167244 (JP, A)

Claims (1)

[Claims] 1. A light emitting means for emitting light in a wavelength band including a wavelength having a maximum absorptance by the gas when the light is transmitted through the gas whose concentration or pressure is detected, and the light emitting means. A forward light path for guiding the light to the gas cell in which the gas is sealed and entering the light, a backward light path for guiding the light transmitted through the gas cell, a diffraction grating provided in the forward light path or the backward light path, and its diffraction Diffractive grating modulation control means for generating first light having a wavelength that is largely absorbed by the gas and second light having a wavelength that is not absorbed by the gas by modulating a grating at a predetermined timing; A light receiving means which is provided at a terminal portion of the return path, receives the first light and the second light, and outputs a first electric signal and a second electric signal corresponding to the light quantities of the respective lights. , Its light receiving means Modulation control correction means for correcting the modulation of the diffraction grating by the diffraction grating modulation control means based on the total light amount of the first light and the second light corresponding to the added value of the respective electric signals. The first gas by the gas based on the first electrical signal and the second electrical signal.
A gas remote sensing device using a diffraction grating, comprising: a light-absorption rate of light, and a calculation means for calculating the concentration or pressure of the gas from the light absorption rate.