JP2005140738A - Method and device for multi-point gas concentration detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for multi-point gas concentration detection in which a light is introduced to multi point gas detecting part without shortening the life of an optical switch. <P>SOLUTION: In the optical gas concentration detection method which irradiates a light from a light source to a plurality of gas detecting parts 8 where gas atmosphere to be measured exists and receives a transmitted light to detect each gas concentrations from the received signals, the light form the light source is sequentially introduced to one of a plurality of branching light paths 4 by a first stage optical switch 5, lights from each branching light paths 4 are sequentially introduced to one of a plurality of individual branching paths 6 by a next stage or later optical switch 7, and then lights from individual branching paths 6 are introduced to each of the gas detecting parts 8. Therefore, the number of switching the optical switches 5 and 7 can be reduced comparing with the number of the gas detecting parts 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to gas concentration detection using light absorption by gas, and relates to a multipoint gas concentration detection method and apparatus capable of guiding light to a multipoint gas detection unit without shortening the life of an optical switch.

  Semiconductor-type electrical sensors are used as sensors to detect gas, but power supply equipment is required near the sensor and periodic calibration is required. However, there are problems in terms of maintainability and economy.

  On the other hand, there is a sensor using light. Since there is a phenomenon in which gas molecules absorb light of a specific wavelength, for example, laser light, the presence or concentration of gas can be detected using this phenomenon. This type of sensor is widely used for industrial measurement and pollution monitoring. At this time, remote monitoring is also possible by transmitting laser light through an optical fiber. Therefore, the present applicant has developed a remote gas monitoring apparatus using an optical fiber as a transmission path as disclosed in Patent Document 1. In this apparatus, the drive current of the semiconductor laser is modulated at a high frequency around a predetermined current value, and laser light having a modulated wavelength and intensity is oscillated. Further, by controlling the current and temperature, the laser beam emitted to the rear of the semiconductor laser is used for the monitor so that the center wavelength of oscillation becomes the center of the gas absorption line, and the laser beam emitted forward is stabilized. Then, laser light that is stably emitted forward is introduced into a gas cell filled with a gas of unknown concentration through an optical fiber, transmitted through the gas atmosphere, and the transmitted light is introduced into another optical fiber that faces it. The transmitted light is guided to the light receiving unit by this optical fiber, and the gas concentration is detected with a higher S / N ratio than the double wave detection signal or the fundamental wave signal of the received signal.

JP-A-5-256769

  In the optical sensor described above, when gas is detected at a plurality of points, that is, at multiple points, the gas detectors composed of gas cells are measured one by one, and therefore light source light is sequentially guided to different gas detectors using an optical switch. It will be. However, the optical switch has a durable switching number for which the operation is guaranteed, and the lifetime is determined by the durable switching number, which causes a problem that the lifetime of the entire apparatus is defined.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and provide a multipoint gas concentration detection method and apparatus capable of guiding light to a multipoint gas detection unit without shortening the optical switch life. .

  In order to achieve the above object, according to the method of the present invention, the light source light is sequentially passed through a plurality of gas detection units having a gas atmosphere to be measured, and the transmitted light is received, and each gas concentration is detected from the received light signal. In the optical gas concentration detection method, the light source light is sequentially guided to one of a plurality of branch optical paths by an optical switch in the first stage, and the light emitted from each branch optical path is The light is sequentially guided to guide the light from each individual branch optical path to each gas detector.

  In addition, the apparatus of the present invention includes a plurality of gas detection units filled with a gas atmosphere to be measured, a light source unit that generates light transmitted through the gas detection unit, and transmission through the gas detection unit. In an optical gas concentration detection device having a signal processing unit that receives light and detects a gas concentration from a light reception signal, an optical switch in the first stage for sequentially guiding the light source light to any one of a plurality of branch optical paths, and each branch optical path And a subsequent optical switch that sequentially guides light emitted from each of the plurality of individual branch optical paths to each individual branch optical path, and an individual gas detector is connected to each individual branch optical path.

  The present invention exhibits the following excellent effects.

  (1) Since the number of switching times of the optical switch is smaller than the number of gas detectors, the life can be extended.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the gas concentration detection apparatus according to the present invention mainly includes a light source unit 1, an optical system 2, and a signal processing unit 3.

  The light source unit 1 includes a distributed feedback semiconductor laser (DFB-LD) 11 that oscillates laser light having a single wavelength, a Peltier element 12 that includes the DFB-LD 11 and controls temperature, and supplies power to the Peltier element 12. A power supply unit 13 that supplies a frequency signal f, an oscillator 14 that outputs a sine wave signal X having a frequency f, a frequency multiplier 15 that creates a second harmonic signal XX having a frequency 2f from the signal having the frequency f, and a DBF-LD 11. A bias current source 16 for adding a bias current, a triangular wave sweeper 17 for determining how to sweep the bias current source 16, a capacitor C for supplying a sine wave signal from the oscillator 14 to the DFB-LD 11, and a bias It comprises an inductor L for supplying a bias current from the current source 16 to the DFB-LD 11.

  The optical system 2 includes a first-stage optical switch 5 that sequentially guides light source light from the light source unit 1 to any one of a plurality of branch light paths 4a, 4b, and 4c, and a plurality of individual light beams emitted from the branch light paths 4a, 4b, and 4c. A second-stage optical switch 7 (7a, 7b, 7c) that sequentially guides one of the branched optical paths 6 (6a1, 6a2, 6a3, 6a4, 6b1, 6b2, 6b3, 6b4, 6c1, 6c2, 6c3, 6c4) Provided, and individual gas detectors 8 (8-1 to 8-9) are connected to the individual branch optical paths. Each of the optical switches 5 and 7 can switch between two optical paths in conjunction with each other. In the second-stage optical switch 7, the individual branch optical path 6 that is the incident optical path of each gas detection unit and the corresponding output optical path (not indicated) are linked to each other, and the branch optical paths 4 a, 4 b, 4 c and the return branch optical path ( In the first stage optical switch 5, the branch optical paths 4 a, 4 b, 4 c to the second stage optical switches 7 a, 7 b, 7 c and the corresponding return branch optical paths are interlocked to each other in the light source section. The light source optical path from 1 and the light receiving optical path to the signal processing unit 3 are selectively switched. In the second-stage optical switches 7a, 7b, and 7c, the individual branch optical paths 6a1, 6b1, and 6c1 are returned to the return system without using the gas detection unit, and are used as reference optical paths.

  In this embodiment, the optical switch has a two-stage configuration. The first stage optical switch 5 has one optical path pair to three optical paths (this is referred to as a 1 × 3 configuration), and has a 2 × 6 configuration for two systems. Each second-stage optical switch 7 has a 1 × 4 configuration for one system and a 2 × 8 configuration for two systems.

  As shown in FIG. 2, the gas detection unit 8 includes a container (gas cell) 21 filled with various gases (methane or the like) having an unknown concentration to be measured, and can be easily installed at an arbitrary place. It has become. Opposite optical connectors 22, 23 are provided at both ends of the container 21, and an optical path for incidence 24 including an individual branch optical path 6 is connected to the optical connector 22 so that light can be introduced into the container. An output optical path 23 is connected to 23 so that light can be led out from the container.

  Returning to FIG. 1, the signal processing unit 3 includes a light detector 31 and a phase detector 32 that performs phase-sensitive detection of the output of the light receiver 31 in synchronization with the frequency f of the sine wave signal X from the oscillator 14 of the light source unit 1. And a phase detector 33 that performs phase-sensitive detection of the output of the light receiver 31 in synchronization with the frequency 2f of the sine wave signal XX from the frequency multiplier 15, and optical path switching in each of the optical switches 5, 7a, 7b, and 7c. It comprises a computer 34 that controls and individually identifies the gas detector 8 and records and calculates the output ratio of both phase detectors 32 and 33 to determine the gas concentration.

  The gas concentration detection method according to the present invention will be described below.

  By controlling the power supply from the power supply unit 13, the temperature of the Peltier element 12 is controlled to keep the temperature of the DFB-LD 11 constant, and the bias current source 16 and the triangular wave sweeper 17 are used to change the bias current into a triangular waveform. Sweep so that the direction of increase / decrease is one direction. At the same time, a sinusoidal alternating current (modulated current) is superposed from the oscillator 14. Accordingly, the light source unit 1 emits laser light having a modulated wavelength and intensity.

  At this time, the computer 34 controls the optical switches 5 and 7 so that the light source light is sequentially guided to the individual branch optical paths 6 including the reference optical path. For example, if the first-stage optical switch 5 first selects the A1 channel connected to the branch optical path 4a and the second-stage optical switch 7a selects the B01 channel connected to the individual branch optical path 6a1, then the second-stage optical switch 5a selects the second stage optical switch 5a. The optical switch 7a is switched so as to select the B02 channel connected to the individual branch optical path 6a2. Thereafter, the second-stage optical switch 7a sequentially switches so as to select the B03 and B04 channels. Next, the first-stage optical switch 5 selects the A2 channel connected to the branch optical path 4b, and the second-stage optical switch 7b is the individual branch optical path. Switch to select the B02 channel connected to 6b1. When the switching of the second stage optical switch 7b to all the channels is completed, the first stage optical switch 5 is switched so as to select the A3 channel. When the optical switches 5 and 7 are sequentially switched in this way, the light source light from the light source unit 1 is sequentially guided to the individual branch optical paths 6 including the reference optical path. Since similar switching occurs in the systems linked in the optical switches 5 and 7, the light from each individual branch optical path 6 including the reference optical path always returns to the signal processing unit 3. That is, the light transmitted through the reference optical path or the gas detection unit 8 is returned to the signal processing unit 3.

  The computer 34 repeats the above sequential switching operation. Thereby, the transmitted light that has passed through the gas atmosphere of each gas detector 8 is sequentially received by the light receiver 31. The computer 34 calculates the gas concentration of each gas detection unit based on the received light signal.

  The gas concentration is calculated as follows.

A signal synchronized with the frequency f of the sine wave signal X from the oscillator 14 among the light reception signals of the light receiver 31 is detected by the phase detector 32 and a signal synchronized with the frequency 2f of the sine wave signal XX from the frequency multiplier 15. Is detected by the phase detector 33. The output ratio F (f, 2f) of the signals extracted by both phase detectors 32 and 33 is transmitted to the computer 34. In the computer 34, the output ratio F ₀ (f, 2f; referred to as a reference signal) obtained by passing the light source light through the individual branch optical paths 6a1, 6b1, 6c1, which are the respective reference optical paths, is stored as a reference value. A difference value ΔF (F ₀ , F _G ) between this reference value and the output ratio (F _G (f, 2f); referred to as gas signal) obtained by sequentially passing the light source light through the gas detector 8 is calculated.

In FIG. 3, the horizontal axis represents the wavelength, and the vertical axis represents the magnitude of the gas signal F _G (f, 2f) and the reference signal F ₀ (f, 2f). As shown, both the reference value 101 and the gas signal 102 are wavelength dependent. In FIG. 4, the horizontal axis represents the wavelength, and the vertical axis represents the difference value ΔF (F ₀ , F _G ). As shown in the figure, the difference value between them has a peak at a certain wavelength. This peak is an enlargement of the one located in the middle abdominal part 103 in FIG. From the peak value of this peak, the gas concentration is determined from the relationship between the peak value determined in advance and the reference gas concentration. By using the output ratio of the received light signal by the light passing through the reference optical path for the difference processing, the wavelength dependency of the light source unit 1, the optical switches 5 and 7, and the signal processing unit 3 can be removed, and an accurate gas concentration can be obtained. Can be obtained.

  Here, the background art and the present invention are compared.

  Assume that only one optical switch is provided to sequentially guide light from one light source unit 1 to a plurality of gas detection units 8. In the case where there are nine gas detectors 8, this optical switch requires 10 channels in consideration of the reference optical path. That is, the optical switch has a 1 × 10 configuration (2 × 2 configuration with 2 systems). If the gas detection unit 8 or the reference optical path is switched every 10 seconds at this time, the channel of the optical switch is switched once every 10 seconds. On the other hand, it is assumed that the number of endurance switching of the optical switch is 10 million. In this case, the lifetime is 10 million × 10 seconds ÷ (3600 seconds × 24 hours × 365 days) = about 3.17 years.

  In contrast, in the above embodiment, if the gas detection unit 8 or the reference optical path is switched every 10 seconds, the channel of the first-stage optical switch 5 is switched once every 40 seconds. Further, the channel of the second stage optical switch 7 is switched four times in 120 seconds, and once in 30 seconds on average. The lifetime of the first-stage optical switch 5 is 10 million × 40 seconds ÷ (3600 seconds × 24 hours × 365 days) = about 12.7 years. Since the lifetime of the second stage optical switch 7 is similarly increased, the lifetime of the entire apparatus is also increased.

  As described above, in the present invention, the light source light is sequentially guided to one of the plurality of branch optical paths 4 by the first-stage optical switch 5, and the light emitted from each branch optical path 4 is respectively transmitted to the plurality of optical switches 7 by the subsequent stages. Since the light is sequentially guided to one of the individual branch optical paths 6 and the light is guided from each individual branch optical path 6 to each gas detection unit 8, the number of switching times of the optical switches 5 and 7 is larger than the number of gas detection units 8. Therefore, the lifetime can be extended.

  In the above embodiment, the optical switch has a two-stage configuration. However, by configuring three or more stages, more gas detectors 8 can be connected and the life can be extended.

It is a block diagram of the gas concentration detection apparatus which shows one Embodiment of this invention. It is a block diagram of the gas detection part used for this invention. It is a characteristic view of the magnitude | size of the received light signal with respect to the wavelength of a laser beam. It is a characteristic view of the magnitude | size of the difference value with respect to the wavelength of a laser beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source part 2 Optical system 3 Signal processing part 4 Branch optical path 5 First stage optical switch 6 Individual branch optical path 7 Second stage optical switch 8 Gas detection part

Claims (2)

  In an optical gas concentration detection method that sequentially passes through a plurality of gas detectors having a gas atmosphere whose measurement target is a light source light and receives transmitted light, and detects each gas concentration from the received light signal, the light source light is the first stage The optical switch sequentially guides to one of a plurality of branch optical paths, and the light emitted from each branch optical path is sequentially guided to one of a plurality of individual branch optical paths by the optical switches of the next and subsequent stages. A multi-point gas concentration detection method characterized in that light is guided to a detection unit. A plurality of gas detection units filled with a gas atmosphere to be measured, a light source unit that generates light source light that is transmitted through the gas detection unit, and a light reception signal that receives the transmitted light through the gas detection unit An optical gas concentration detection device having a signal processing unit for detecting a gas concentration from a first stage optical switch that sequentially guides the light source light to one of a plurality of branch optical paths, and a plurality of individual light beams from each branch optical path A multi-point gas concentration detection device comprising: an optical switch for the next stage and the subsequent stages sequentially guided to any one of the branch optical paths; and an individual gas detector connected to each individual branch optical path.

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