JPH0510879A - Gas detecting network - Google Patents

Abstract

PURPOSE:To obtain a gas detector reduced in its scale by realizing gas detection parts arranged at a plurality of places using an optical system simple in constitution. CONSTITUTION:The light from a light source 1 synchronized to the absorption wavelength of gas is made to enter an optical fiber 3 and a plurality of gas detection parts arranged so as to propagate light through the gap provided between the optical fiber 3 and an optical fiber 7. A mirror 14 is arranged at the end surface of a final optical fiber and, further a judging circuit 12 operating the ratio of the monitor intensity of the light source and the intensity of the emitted light from the optical fiber is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to gas detection utilizing the phenomenon of absorption of light by gas, and more particularly to a gas detection network for remote multipoint measurement using optical fibers.

[0002]

2. Description of the Related Art Conventionally, as a device for remotely detecting a gas by using an optical fiber, there is a gas detection device for one measuring point. For example, FIG. 8 shows JP-A-60-9833.
It is a block diagram of the conventional gas detection apparatus shown by the 4th publication, 71 is a light emission source, 72 is an optical coupler, 73 is an optical fiber, 74 is a measurement cell, 74a, 74b is attached to the measurement cell. Optical coupler, 75 is an optical fiber, 76 is an optical coupler, 77 is a beam splitter, 7
Reference numerals 8, 80, 82 and 83 denote light beams branched at respective points, 81 denotes a beam splitter, 79, 84 and 85 denote narrow band wavelength filters, 86, 87 and 88 denote photodetectors, and 8
9, 90 and 91 are amplifiers, 92 is a signal processing circuit, and 93 is a display circuit.

Next, the operation will be described. The light emitted from the light source 71 passes through the optical coupler 72, is transmitted by the optical fiber 73, and is sent to the measurement cell 74. The light sent into the measurement cell passes through the optical coupler 74a, is transmitted in the cell space, and then is transmitted by the optical transmission line 75 via the optical coupler 74b. At this time, if the target gas is present in the cell, the propagated light is absorbed and the intensity is reduced. The light transmitted through the optical coupler 76 is split into two by the beam splitter 7. One of the branched light beams 78 passes through a narrow band wavelength filter 79 containing the absorption wavelength of gas and is received by the photodetector 16. On the other hand, the luminous flux 80 transmitted through the beam splitter 77
Is further split into two light beams by the beam splitter 81. One branched light beam 82 is transmitted through a narrow band wavelength filter 84 whose transmission center wavelength is the absorption wavelength of the same gas having a wavelength different from that of the narrow band wavelength filter 79, and is received by the photodetector 87. Beam splitter 8
The light flux 83 that has passed through 1 has two narrow band filters 79,
Unlike 84, the light passes through a narrow band filter 85 having a transmission center wavelength that is not affected by the absorption of light by a gas, and is received by a photodetector 88. Photodetectors 76, 77,
The output signals from 78 are amplifiers 89, 90 and 91, respectively.
Is amplified by and input to the signal processing circuit 92. In the signal processing circuit 92, the ratio of the output signals from the two photodetectors 76 and 78 and the calculation from the two photodetectors 77 and 78 are calculated, and the presence or absence of the gas to be detected is determined from the respective ratio values. The result is displayed on the display circuit 93.

As a means for expanding the measurement points of this type of gas detection apparatus from one point to multiple points, one gas detection apparatus is installed at each measurement point and the output from each detection apparatus is centrally controlled. The scheme is considered to be the easiest to configure.

Further, a semiconductor gas sensor is used as a sensor as another gas detecting means for a plurality of measurement points,
A gas detection system has been developed as a plant inspection system in which a sensor is installed at each measurement point and these outputs are centrally monitored.

[0006]

Since the conventional multipoint gas detection device is constructed as described above, the number of measurement points is increased and the number of optical fibers and signal lines for transmitting the output signal from the sensor is increased. There has been a problem that the system becomes huge and the scale of the system becomes large, and the controller for collecting the output signals from the sensors is required to have high functionality, and the device cost increases. Further, the semiconductor sensor has a poor gas selectivity and reacts with a gas other than the gas to be detected, which causes a problem of frequent malfunction.

The present invention has been made to solve the above problems, and an object thereof is to obtain a gas detection network which can realize gas detection at a plurality of measurement points with a single optical fiber and has a simple apparatus configuration. To do.

[0008]

In the gas detection network according to the first aspect of the present invention, a light projection means for making light tuned to the absorption wavelength of gas incident on an optical fiber, and a light beam is transmitted through a gap between the fibers at a measurement point. It comprises a gas detector configured as described above, an optical transmission means in which each detector is connected by an optical fiber, and a signal processing means for detecting a change in intensity of light emitted from the optical fiber.

A second aspect of the present invention is provided with an optical means in which the end surface of the optical fiber network on the final emission side is processed so that light can be reflected, and the incident end surface side can project and receive light.

In a third aspect of the present invention, in the above optical fiber network, a light projecting means for injecting frequency-modulated light for gas detection into the optical fiber and another gas sensor such as a semiconductor sensor are installed at a measuring point, and an output signal thereof is provided. It is provided with a sensor signal input means for converting a frequency-modulated optical signal corresponding to a measurement location to be incident on the optical fiber, and a light receiving means for separating and detecting the modulation frequency and intensity of the optical signal on the emission side.

In a fourth aspect of the present invention, in the above optical fiber network, light projecting means for making monochromatic light tuned to the absorption wavelength of gas into the optical fiber as an optical pulse, and reflected light from the fiber end face of each measurement point on the optical fiber incident side. It is provided with a light receiving means for receiving light and a signal processing means for detecting the intensity of the received light pulse train.

In a fifth aspect of the present invention, in the above optical fiber network, a plurality of monochromatic lights having different wavelengths are modulated at a frequency corresponding to each wavelength, and then the respective lights are superposed and incident on the fiber. It is provided with a light receiving means for receiving the emitted light, and a signal processing means for separating the output signal from the light receiving means for each modulation frequency and detecting the intensity change of each wavelength.

In a sixth aspect of the present invention, in the above optical fiber network, a light projecting means for causing white light having a continuous wavelength to enter the fiber, and light emitted from the fiber are separated and received for each wavelength component by using a wavelength separating element. The light receiving means and the signal processing means for detecting a change in the output signal obtained from the light receiving means are provided.

[0014]

According to the first aspect of the invention, when the gas to be detected is present at the measurement point, the light is absorbed in the detection section and the intensity of the light transmitted through the optical fiber is reduced.

In the second aspect of the invention, the incident light is reflected by the final emitting end face of the optical fiber, passes through the same path as the incident optical path, and is emitted from the incident end face of the optical fiber.
At this time, if the detection target gas is present in any of the detection units, the intensity of the emitted light is reduced.

In the third aspect of the invention, when gas is generated in any one of the detection sections, only the intensity of the light signal modulated for gas detection in the light transmitted through the fiber decreases in accordance with the gas concentration, and A modulated signal with a frequency corresponding to the position of the measurement point is detected.

According to the fourth aspect of the invention, when a single optical pulse is incident on the optical fiber, a part of the optical pulse is reflected by the end face of the optical fiber of the detecting section, and an optical pulse train having an interval corresponding to the distance between the detecting sections is incident on the optical fiber. It is emitted from the edge.
When gas is generated in the detection unit, the pulse intensity after the light pulse corresponding to the generation position decreases corresponding to the gas concentration.

In the fifth aspect of the invention, when gas is generated, the intensity of the light transmitted through the optical fiber is reduced only at the wavelength corresponding to the gas.

In the sixth invention, when gas is generated, the intensity of the wavelength component corresponding to the gas in the light transmitted through the optical fiber is reduced.

[0020]

【Example】

Example 1. An embodiment of the first invention will be described with reference to the drawings. FIG. 1 shows an apparatus configuration of an embodiment of the present invention. In the figure, 1 is a light source, 2 is a lens, 3 is an optical fiber, 4 is a collimating lens, 5 is a condenser lens,
Reference numeral 6 is a case for fixing the detection location, 7 and 8 are optical fibers, 9 is a condenser lens, 10 is a photodetector, 11 is an amplifier, 12 is a determination circuit for detecting a change in the received light level and determining the presence or absence of gas, 100 Is a half mirror, 101 is a photodetector, and 102 is an amplifier.

Next, the operation will be described. The light emitted from the monochromatic light source 1 tuned to the absorption wavelength of the gas is narrowed down to the incident end face of the optical fiber 3 using the lens 2, and is partially branched by the half mirror 100 and monitored by the photodetector 101. The light incident on the optical fiber propagates through the optical fiber 3 and is sent to the detection unit. Optical fiber 3
The light emitted from the exit end of the light is converted into a parallel beam by the collimator lens 4 and propagates through the gap of the detection unit, and then is converged by the condenser lens 5 onto the incident end surface of the optical fiber 7. After that, the same operation is repeated in a plurality of detectors installed on the network, and the light is emitted from the emission end of the optical fiber 8 at the final end. The emitted light is condensed on the photodetector 10 by the condenser lens 9. The amplifier 11 amplifies the received light intensity signal photoelectrically converted by the photodetector and inputs it to the determination circuit 12. The intensity of the transmitted light from the optical fiber maintains a constant level when no gas is generated, but when the gas is generated in the detector, the intensity of the received light decreases according to the concentration of the gas. The monitor intensity signal received by the photodetector 101 is amplified by the amplifier 102 and input to the determination circuit 12. The determination circuit 12 calculates the ratio between the transmitted light intensity of the optical fiber and the monitor intensity, detects the change in the calculation result due to the generation of gas, and determines the presence or absence of gas generation.

Example 2. An embodiment of the second invention will be described with reference to the drawings. FIG. 2 is a device configuration diagram of an embodiment of the present invention. In the figure, 1 is a light source, 2 is a lens, 3 is an optical fiber, 4 is a collimating lens, 5 is a converging lens, and 6 is a case for fixing the detection position. , 7 and 8 are optical fibers, 9 is a condenser lens, 10 is a photodetector, and 11
Is an amplifier, 12 is a determination circuit for determining the presence or absence of gas by detecting a change in received light level, 13 is a half mirror, 14 is a mirror, 100 is a half mirror, 101 is a photodetector, 102
Indicates an amplifier.

Next, the operation will be described. The light emitted from the monochromatic light source 1 tuned to the absorption wavelength of the gas is narrowed down to the incident end face of the optical fiber 3 by using the lens 2, and is partially branched by the half mirror 100 and monitored by the photodetector 101. The incident light propagates through the optical fiber 3 and is sent to the detector. The light emitted from the emission end of the optical fiber 3 is converted into a parallel beam by the collimator lens 4, propagates through the gap of the detection section, and is focused on the incident end face of the optical fiber 7 by the condenser lens 5. After that, the same operation is repeated in each detection unit installed on the network, and propagates through the final optical fiber 8 to reach the emission end.
A mirror 14 is installed at the emitting end, and the propagating light is reflected here and propagates toward the incident side through the same optical fiber. The light emitted from the incident side of the optical fiber 3 is branched by the half mirror 13, and the photodetector 1
It is focused on 0. The amplifier 11 amplifies the received light intensity signal photoelectrically converted by the photodetector and inputs it to the determination circuit 12. In addition, the monitor intensity signal received by the photodetector 101 is amplified by the amplifier 102, and the determination circuit 1
Entered in 2. The intensity of the transmitted light from the optical fiber maintains a constant level when no gas is generated, but when the gas is generated in the detector, the intensity of the received light decreases according to the concentration of the gas. The determination circuit 12 calculates the ratio between the transmitted light intensity of the optical fiber and the monitor intensity, detects the change in the calculation result due to the generation of gas, and determines the presence or absence of gas generation.

Example 3. An embodiment of the third invention will be described with reference to the drawings. FIG. 3 is a device configuration diagram of an embodiment of the present invention. In the figure, 1 is a light source, 2 is a lens, and 3 is a lens.
Is an optical fiber, 4 is a collimating lens, 5 is a condenser lens, 6 is a case for fixing the detection position, 7 and 8 are optical fibers, 9 is a condenser lens, 10 is a photodetector, 11 is an amplifier, and 12 is a light receiving level. A determination circuit that detects a change and determines the presence or absence of gas, 15 is a modulation circuit that frequency-modulates the light source 1,
Reference numeral 16 is a semiconductor gas sensor, 17 is a drive circuit that modulates an output signal from the gas sensor 16 at a frequency corresponding to the position of a measurement point and drives a light source with the output signal, 18 is a light emitting element, 19 is a detection circuit, 20, 21, 22 and 23 are output level detection circuits for detecting the level of a signal detected at a set frequency, 100 is a half mirror, 101 is a photodetector, and 102 is an amplifier.

Next, the operation will be described. The modulation circuit frequency-modulates the light emitted from the light source 1 at the frequency f1. The light emitted from the light source is narrowed down by the lens 2 onto the incident end face of the optical fiber 3, and is partially branched by the half mirror 100 and monitored by the photodetector 101. The light incident on the optical fiber propagates through the optical fiber 3 and is sent to the detection unit. The light emitted from the emitting end of the optical fiber 3 is converted into a parallel beam by the collimator lens 4, propagates through the gap of the detecting portion, and is converged by the condenser lens 5 into the optical fiber 7.
Is focused on the incident end face of. After that, the same operation is repeated in each detection unit installed on the network, and propagates through the final optical fiber 8 to reach the emission end. A gas sensor such as a semiconductor gas sensor is installed side by side in the detection unit. When gas is generated, the semiconductor gas sensor 16
Generates a signal. This output signal is driven by the drive circuit 17
Drives the light emitting element 18 by modulating at a preset frequency f2. The light emitted from the light emitting element is incident on the incident end surface of the fiber in the detection unit and is superimposed on the gas detection light propagating in the optical fiber. The same semiconductor gas sensor is installed in each detection unit, and modulation is performed at different frequencies (f3, ..., Fn) corresponding to the position of the detection unit. The light emitted from the optical fiber is focused on the photodetector 10 by the lens 9. The output signal from the photodetector 10 is amplified by the amplifier 11, and the detector 19
Entered in. The detector 19 detects the input signal at a preset frequency (f1, f2, ..., Fn), and detects the obtained frequency components from the corresponding level detection circuits 20 and 2.
It outputs to 1, 22, 23. A level detection circuit that detects a frequency component for gas detection calculates the ratio between the obtained signal level and monitor intensity, and determines the presence or absence of gas from the change. On the other hand, in the level detection circuit that detects the modulation frequency component of the output signal of the semiconductor gas sensor, the presence or absence of the signal of each frequency component is detected, and the output frequency is identified, thereby detecting the gas generation position.

Example 4. Next, one embodiment of the fourth invention will be described with reference to the drawings. FIG. 4 is a device configuration diagram of an embodiment of the present invention, and FIG. 5 is a diagram showing optical waveforms of incident light to an optical fiber and reflected light from the fiber. In the figure, 1 is a light source, 2 is a lens, 3 is an optical fiber, and 4
Is a collimator lens, 5 is a condenser lens, 6 is a case for fixing the detection position, 7 and 8 are optical fibers, 10 is a photodetector, 11 is an amplifier, 13 is a half mirror, and 24 is a drive circuit for driving a light source. , 25 are non-reflective coating parts applied to the output end face of the optical fiber in the detection part, 2
6 is a reflection coating part applied to the optical fiber incident end face in the detection part, 27 is the intensity waveform of the light emitted from the light source, 28 is the intensity waveform of the light emitted from the incident end face of the optical fiber when no gas is generated, Reference numeral 29 is an intensity waveform of light emitted from the incident end face of the optical fiber when gas is generated, 30 is a pulse separation circuit for separating the pulse signals of the reflected light pulses in time series, 3
1 is a clock oscillation circuit, 32, 33 and 34 are peak hold circuits for holding the peak values of the separated pulse signals,
Reference numerals 35, 36, and 37 are A / D circuits that convert the peak-held values into digital signals, and 38 is a determination that determines the presence or absence of gas generation and the gas generation location based on the output signals from the respective A / D circuits. Circuit, 100 is a half mirror, 10
Reference numeral 1 is a photodetector, 102 is an amplifier, and 104 is an A / D circuit for digitizing the peak value of an optical pulse.

Next, the operation will be described. Drive circuit 24
Drives the light source 1 so that the emitted light is pulsed like 27. The light emitted from the light source 1 is narrowed down by the lens 2 onto the incident end face of the optical fiber 3, and
The photodetector 101 is partially branched by the half mirror 100.
Be monitored at. The light incident on the optical fiber propagates in the optical fiber 3. The light that has propagated through the optical fiber 3 is emitted from the optical fiber 3 in the detection unit, converted into a parallel beam by the collimator lens 4, propagated in the space of the detection unit, and then focused by the condenser lens 5 onto the incident end face of the optical fiber 7. . At this time, the exit end face 25 of the optical fiber 3 is non-reflection coated so that light is not reflected, while the entrance end face 26 of the optical fiber 7 is coated so as to have a slight reflectance. As a result,
Part of the light that has passed through the detection unit is reflected to the incident side by the emission end face 25, emitted from the incident end face of the optical fiber 3, and incident on the photodetector 10 via the half mirror 13. This operation is repeated in each detection unit, a part of the incident light is reflected from each detection unit with respect to one incident light pulse 27, and the light returning from the optical fiber is observed as a pulse train as shown by 28. . At this time, each pulse is generated with an interval corresponding to the distance between the detectors, and in the absence of gas, the peak value of each pulse is reflected from the end face of the optical fiber and is attenuated by propagation in the optical fiber from the incident end face of the optical fiber. As the reflected light from the distant detection portion becomes regular, it attenuates as shown by the waveform 28. On the other hand, when gas is generated in any of the detection units, the light is absorbed by the gas, so the peak value of the light pulse reflected from the measurement point where gas was generated decreases.
The light pulses from this point and beyond are also reduced. Amplifier 1
1 amplifies the pulse train signal from the photodetector and inputs it to the pulse separation circuit 30. The clock oscillation circuit 31 generates a clock synchronized with the light emission pulse of the light source, and the pulse separator 3
0, and input to the peak hold circuits 32, 33, 34.
The pulse separation circuit separates the input pulse train in time series, and inputs the respective pulses to the peak hold circuits 32, 33, 34 in order. The peak hold circuit holds the peak value of each pulse, and the A / D circuit 3
It is input to 5, 36 and 37, converted into a digital signal, and then output to the determination circuit 38. The monitoring result of the peak intensity of the incident light pulse is also input to the determination circuit 38. The determination circuit 38 corrects the peak value of each pulse based on the monitoring result, compares this correction value with the peak value obtained in advance when no gas is generated, and determines the peak values of both pulses for each pulse. Always observe if there is a difference. When a difference occurs in the peak value, the generation position is specified by the order of the generated pulses, and the generated gas concentration is calculated from the difference value.

Example 5. Next, one embodiment of the fifth invention will be described with reference to the drawings. FIG. 6 is a device configuration diagram of an embodiment of the present invention. In the figure, 1, 42 and 44 are light sources, 3 are optical fibers, 4 is a collimating lens, 5 is a converging lens, and 6 is a case for fixing the detection location. , 7, 8 are optical fibers, 9 is a condenser lens, 10, 52, 56 are photodetectors, 11, 53, 57 are amplifiers, 12, 54, 58.
Is a determination circuit for detecting a change in the received light level and determining the presence or absence of gas, 39, 43 and 45 are collimating lenses, and 40 and 41.
Is a half mirror, 46 is a condenser lens, 47 is a collimating lens, 48 and 49 are dichroic mirrors, and 50 and 5
1, 55 is a condenser lens, 100 is a half mirror, 101
Is a photodetector, 102 is an amplifier, 104 and 107 are half mirrors, 105 and 108 are photodetectors, 106 and 109 are amplifiers, 110 is a detection circuit, and 111, 112 and 113 are level detectors.

Next, the operation will be described. Light source 1,4
The wavelengths 2, 44 are tuned to the absorption wavelengths λ1, λ2, λ3 of the different target gases, and are modulated at different frequencies (f1, f2, f3) corresponding to the respective wavelengths. The light emitted from each light source is collimated by a collimator lens 39,
After being converted into parallel beams by 43 and 45, they are superimposed on one beam through the half mirrors 40 and 41, narrowed down on the incident end face of the optical fiber 3 by the condensing lens 46, and each wavelength λ1, λ2. The light beams are partially branched by the half mirrors 100, 104, and 108 for each λ3, amplified by the photodetectors, 102, 106, and 109, and input to the determination circuits 12, 58, and 54. The incident light propagates through the optical fiber 3 and is sent to the detector. The light emitted from the optical fiber 8 is focused on the photodetector 10 by the lens 9. The output signal from the photodetector 10 is amplified by the amplifier 11 and input to the detector 110. The detector 110 detects the input signal at a preset frequency (f1, f2, f3), and detects each frequency component obtained by the corresponding level detection circuit 111, 112,
Output to 113. In the level detection circuit, the ratio between the signal level obtained for each wavelength corresponding to the modulation frequency and the monitor intensity is calculated, and the presence or absence of gas is determined from the change.
The intensity of the transmitted light from the optical fiber maintains a constant level when no gas is generated, but when the gas is generated in the detector, the intensity of the received light decreases according to the concentration of the gas.

Example 6. Next, one embodiment of the sixth invention will be described with reference to the drawings. FIG. 7 is a device configuration diagram of an embodiment of the present invention. In the figure, 1 is a light source, 2 is a lens, 3 is an optical fiber, 4 is a collimating lens, 5 is a condenser lens, and 6 is a detection position. Case, 7, 8 are optical fibers, 9 is a condenser lens, 59 is a slit, 60
Is a diffraction grating, 61 is a line sensor, 62 is a line sensor drive circuit, 63 is an A / D circuit, and 64 is a waveform comparison circuit.

Next, the operation will be described. The light emitted from the light source 1 having a continuous wavelength is narrowed down to the incident end face of the optical fiber 3 using the lens 2. The incident light propagates through the optical fiber 3, and the light emitted from the emitting end of the optical fiber 3 in the detecting portion is converted into a parallel beam by the collimating lens 4 and propagates through the gap of the detecting portion and the incident end surface of the optical fiber 7 by the condensing lens 5. Narrowed down. After that, the same operation is repeated in each detection unit installed on the network, and the light is emitted from the emission end of the last optical fiber 8. The emitted light is slit 59 by the lens 9.
The diffraction grating 60 is narrowed down and is irradiated. The incident light is dispersed by the diffraction grating 60 and imaged in the order of the wavelength of the light on the line sensor 61 installed on the focal plane of the diffraction grating. The output signal from the line sensor reflects the wavelength distribution of the transmitted light intensity of the fiber and is input to the waveform comparison circuit 64. The waveform comparison circuit 64 compares the wavelength distribution of the input transmitted light intensity with the previously determined wavelength distribution in the case of no gas, and the gas generated by the value of the wavelength at which there is a difference in intensity between them. The type of
The concentration of each gas is detected by the value of the intensity difference.

[0032]

According to the first aspect of the present invention, gas absorption is utilized to detect a gas by connecting a plurality of measurement points with one optical fiber and detecting the change in transmitted light intensity of the final optical fiber. Since it is configured so that it can be performed, gas detection at a plurality of points can be realized with a simple configuration.

In the second aspect of the invention, in the above-mentioned gas detection network, since the light is reflected on the final end of the optical fiber, it is possible to project and receive light on the incident side of the optical fiber, thus realizing the miniaturization of the device.

According to the third aspect of the invention, since a semiconductor gas sensor is provided at the measurement location and the output signal of the semiconductor gas sensor can be incident on the fiber as an optical signal, the presence or absence of gas and the generation location can be detected simultaneously.

According to a fourth aspect of the present invention, an optical system is configured so that an optical pulse is incident on an optical fiber and the reflected light from the fiber end face at a measurement point can be received, and the peak value of each pulse of the received optical pulse train can be detected. Since the signal processing system is configured, it is possible to simultaneously detect the presence or absence of gas and the generation location with a simple configuration that does not require the installation of other gas sensors.

In a fifth aspect of the invention, a plurality of lights tuned to the absorption wavelengths of a plurality of different kinds of gases are made incident on the optical fiber, and the light emitted from the optical fiber is separated into each of the above wavelengths to transmit the transmitted light of each wavelength. Since it is configured to detect the intensity, it is possible to detect multiple gases in real time.

In the sixth aspect of the invention, light having a continuous emission spectrum is made incident on the optical fiber, and is separated into wavelength components on the output side so that the transmitted light intensity of each wavelength can be detected. Now it is possible to detect multiple gases.

[Brief description of drawings]

FIG. 1 is a device configuration diagram of an embodiment relating to a first invention.

FIG. 2 is a device configuration diagram of an embodiment relating to a second invention.

FIG. 3 is a device configuration diagram of an embodiment relating to a third invention.

FIG. 4 is a device configuration diagram of an embodiment relating to a fourth invention.

FIG. 5 is a characteristic diagram showing a relationship between an incident light pulse and a reflected light pulse train.

FIG. 6 is a device configuration diagram of an embodiment relating to a fifth invention.

FIG. 7 is a device configuration diagram of an embodiment relating to a sixth invention.

FIG. 8 is a device configuration diagram of a conventional device.

[Explanation of symbols]

1 light source 3,7,8 optical fiber 10 Photodetector 11 amplifier 12 Judgment circuit 13 Half mirror 14 mirror 15 Modulation circuit 16 Semiconductor gas sensor 17 Drive circuit 18 Light emitting element 19 Detection circuit 20, 21, 22, 23, output level detection circuit 24 Light source drive circuit 30 pulse separation circuit 32, 33, 34 Peak hold circuit 38 Judgment circuit 42,44 light source 110 detection circuit 111, 112, 113 level detection circuit 40, 41, 104, 107 Half mirror 105 photo detector 108 Photodetector 60 diffraction grating 61 line sensor 62 line sensor drive circuit 64 waveform comparison circuit

Claims (6)

[Claims] 1. A light projecting means for allowing light tuned to the absorption wavelength of gas to enter an optical fiber and splitting a part of the light to monitor the intensity, and a gap is provided between the fibers at a measurement point so that the light beam is transmitted between them. A plurality of gas detecting units, an optical transmission unit in which each detecting unit is connected by an optical fiber, and a signal processing unit for detecting a change in the ratio of the intensity of the light emitted from the optical fiber to the monitor intensity. network. 2. A light projecting means for allowing light tuned to the absorption wavelength of gas to enter an optical fiber and splitting a part of the light to monitor the intensity, and a gap is provided between the fibers at a measurement point so that the light beam is transmitted between them. A plurality of gas detection units, an optical transmission unit that connects each detection unit with an optical fiber, a reflection unit that reflects light at the final end face of the optical fiber, a signal that detects a change in the ratio of the intensity of light emitted from the optical fiber and the monitor intensity. A gas detection network comprising a processing means. 3. A light projecting means for irradiating an optical fiber with frequency-modulated light for gas detection, which is tuned to the absorption wavelength of the gas, and for branching a part of the light for monitoring the intensity, and providing a gap between the fibers at a measuring point. A plurality of gas detectors configured to transmit a light beam between them, an optical transmission means connecting each detector with an optical fiber, and another gas sensor such as a semiconductor sensor at the measurement location are installed, and the output signal corresponds to the measurement location. Sensor signal input means for converting into an optical signal modulated at
Signal processing that separates the output signal detected at the output side for each modulation frequency and detects the intensity of each signal, and also calculates the ratio of the transmitted light intensity of the fiber and the monitor intensity for each modulation frequency and detects the change A gas detection network comprising means. 4. A light projecting means for allowing monochromatic light tuned to the absorption wavelength of gas to enter an optical fiber as an optical pulse, and branching a part of the light to monitor the intensity, and a gap between the fibers at a measurement point to provide a light beam between them. A plurality of gas detectors configured to pass through, an optical transmitter that connects the detectors with an optical fiber, a light receiver that receives the reflected light from the fiber end face of each measurement point on the optical fiber entrance side, and a received optical pulse train. Signal processing that separates each pulse, detects the peak intensity, corrects the obtained peak intensity with the monitor intensity, and specifies the concentration and position of the generated gas from the time-series occurrence of the peak intensity of each pulse. A gas detection network comprising means. 5. The emission intensity of each wavelength is monitored by tuning the absorption wavelengths of a plurality of gases, superposing a plurality of monochromatic lights modulated at frequencies corresponding to the respective wavelengths, and making them incident on a fiber, and branching them partially. A plurality of gas detection units configured to form a gap between the fibers at the measurement point so that the light beam is transmitted between them, an optical transmission unit in which each detection unit is connected by an optical fiber, and light emitted from the fiber is received. A gas comprising a light receiving means, a signal processing means for separating an output signal from the light receiving means for each modulation frequency, detecting the intensity of each wavelength, calculating a ratio with the monitor intensity, and detecting the change. Detection network. 6. A light projecting means for injecting light having continuous wavelengths into the fiber, a plurality of gas detection portions configured so that a light beam is transmitted between the fibers at measurement points with a gap between the fibers, and each detection portion is an optical fiber. The optical transmission means connected, the light receiving means for separating the light emitted from the optical fiber into each wavelength component by using the wavelength separating element and receiving the light, and the signal processing means for detecting the change of the output signal obtained from the light receiving means are provided. Gas detection network characterized by.