CN220305144U - Variable-range gas concentration detection system - Google Patents
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- CN220305144U CN220305144U CN202321269131.0U CN202321269131U CN220305144U CN 220305144 U CN220305144 U CN 220305144U CN 202321269131 U CN202321269131 U CN 202321269131U CN 220305144 U CN220305144 U CN 220305144U
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- 238000001514 detection method Methods 0.000 title claims abstract description 51
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 10
- 238000000034 method Methods 0.000 description 8
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 6
- 238000003199 nucleic acid amplification method Methods 0.000 description 6
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- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
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- 229910052760 oxygen Inorganic materials 0.000 description 3
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- 238000004458 analytical method Methods 0.000 description 2
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
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Abstract
The utility model discloses a gas concentration detection system with variable measuring range, comprising: the laser is used for generating laser beams required for detecting the gas concentration, and the output end of the laser is connected with the first input end of the lock-in amplifier; a multi-pass absorption tank is arranged in the light emergent direction of the laser, a light incidence window for enabling laser beams to enter the multi-pass absorption tank is arranged on the multi-pass absorption tank, and a photoelectric detector is arranged at a preset distance from the light emergence window of the multi-pass absorption tank and used for converting incident light signals into original electric signals containing gas absorption information; the output end of the photoelectric detector is connected with the input end of the preamplifier; one path of output signal of the pre-amplifier enters a first input end of the data acquisition card, the other path of output signal enters a second input end of the phase-locked amplifier, an output end of the phase-locked amplifier is connected with the second input end of the data acquisition card, and an output end of the data acquisition card is connected with signal processing equipment.
Description
Technical Field
The present disclosure relates to the field of gas detection technologies, and in particular, to a variable range gas concentration detection system.
Background
Gas detection concentration detection is an important aspect of environmental protection, and conventional gas detection methods include fluorescence detection, electrochemical detection, spectroscopic detection, and the like. The spectrum detection method is far higher than other detection methods in terms of detection precision and detection speed. The spectrum detection method is also classified into a laser spectrum method, a non-dispersive infrared method, an ultraviolet spectrum method and the like. Further, laser spectroscopy can be further classified into direct absorption spectroscopy and tunable diode laser spectroscopy. The method is also different according to the type and concentration of the gas to be measured, and under the general condition that the gas emission concentration is high, the method for measuring the gas emission concentration is high, but under the condition that the gas emission concentration is low, the tunable diode laser spectrometry is generally selected in the related technology.
When the concentration span range of the gas to be detected is large, for example, the detection concentration requirement of the carbon dioxide to be detected is 0-30%, and the measurement accuracy is required for both the gas to be detected with low concentration (for example, when the concentration is less than 1%) and the gas to be detected with high concentration, two sets of equipment are generally required to be designed for measuring the gas to be detected with high concentration and low concentration respectively at present, namely, one set of equipment is used for measuring the gas to be detected with high concentration, and the other set of equipment is used for measuring the gas to be detected with low concentration, which increases the cost of the gas concentration detection equipment in the production, use and maintenance processes.
Therefore, it is necessary to provide a gas concentration detection system with a variable range, so as to improve the integration level of the system and ensure the concentration detection precision, so that the system can measure the gas to be detected with higher concentration and the gas to be detected with lower concentration.
Disclosure of Invention
In order to solve the above technical problems, the embodiments of the present specification are implemented as follows: the utility model provides a variable-range gas concentration detection system, which comprises:
a laser for generating a laser beam required to detect the gas concentration;
the output end of the laser is connected with the first input end of the phase-locked amplifier and is used for generating a reference signal required by the phase-locked amplifier during operation;
a multi-pass absorption tank is arranged in the light emergent direction of the laser, a light incidence window for enabling the laser beam to enter the multi-pass absorption tank is arranged on the multi-pass absorption tank, a photoelectric detector is arranged at a preset distance from the light emergent window of the multi-pass absorption tank, and the photoelectric detector is used for converting an incident light signal into an original electric signal containing gas absorption information;
the output end of the photoelectric detector is connected with the input end of a preamplifier, and the preamplifier is used for amplifying the original electric signal to obtain an amplified electric signal; one path of output signal of the pre-amplifier enters a first input end of the data acquisition card, the other path of output signal of the pre-amplifier enters a second input end of the phase-locked amplifier, an output end of the phase-locked amplifier is connected with the second input end of the data acquisition card, and an output end of the data acquisition card is connected with signal processing equipment.
Preferably, the laser is a tunable semiconductor laser; the detection system further comprises a laser driving plate, wherein the laser driving plate comprises a current driving module and a temperature driving module, and the current driving module and the temperature driving module are matched to be used so that the tunable semiconductor laser can generate laser beams in a preset wavelength range.
Preferably, a laser collimation unit is arranged between the laser and the multi-pass absorption tank, the laser collimation unit is used for carrying out collimation treatment on outgoing beams of the laser, the output end of the laser is connected with the input end of the laser collimation unit, and the output end of the laser collimation unit is connected with the input end of the multi-pass absorption tank.
Preferably, the laser adopts a fiber laser, and the laser collimation unit is a fiber collimator; the lock-in amplifier adopts a lock-in amplifier with the model number of AD 630.
Preferably, a convex lens is arranged at the light exit window of the multi-pass absorption tank, and the convex lens is used for focusing the outgoing light of the multi-pass absorption tank.
Preferably, the photodetector is disposed at a focal point of the convex lens on a side opposite to the light exit window.
Preferably, the signal processing device adopts an upper computer, and the upper computer adopts a PC.
Preferably, the PC is connected with an alarm device, and the alarm device is used for generating an alarm signal when the PC monitors that the concentration of the gas to be detected exceeds a preset value.
Preferably, the photodetector adopts an InGaAs photodiode; the data acquisition card adopts a data acquisition card with the model PM-512; the laser adopts a distributed feedback laser.
One embodiment of the present disclosure can achieve the following beneficial effects: aiming at the problem of high cost in the production, use and maintenance stages of equipment in the method for measuring the concentration of the gas to be detected with high concentration and low concentration by adopting two sets of independent equipment in the prior art, the utility model provides a variable-range gas concentration detection system with high integration level. The photoelectric detector further converts the laser beam emitted by the multi-pass absorption cell into an original electric signal containing gas absorption information, the preamplifier amplifies the original electric signal and then outputs the signal which is divided into two paths, one path of the signal is directly collected by the data acquisition card, the other path of the signal is demodulated by the lock-in amplifier and then is converted into a harmonic signal containing concentration information, the harmonic signal is also collected by the acquisition card, namely, the data acquisition card collects the direct absorption signal and the second harmonic signal simultaneously, and the concentration information of the gas can be obtained through algorithm inversion because the direct absorption signal and the second harmonic signal show different forms, so that the system can detect the concentration of the gas to be detected with low concentration and detect the concentration of the gas to be detected with high concentration with high precision.
Drawings
In order to more clearly illustrate the embodiments of the present description or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present application, and that other drawings may be obtained according to these drawings without inventive effort to a person skilled in the art.
FIG. 1 is a schematic diagram of a first variable range gas concentration detection system according to the present disclosure;
FIG. 2 is a schematic diagram of a variable range gas concentration detection system according to the first variation of FIG. 1 provided herein;
FIG. 3 is a schematic diagram of a variable range gas concentration detection system according to a second variation of FIG. 1 provided herein;
FIG. 4 is a schematic diagram of a variable range gas concentration detection system according to a third variation of FIG. 1 provided herein;
fig. 5 is a schematic diagram for explaining the operation principle of the variable-range gas concentration detection system provided in the present specification.
Wherein 1 denotes a convex lens.
Detailed Description
The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments.
The embodiment of the application provides a variable-range gas concentration detection system, referring to fig. 1, the system may include a laser, where the laser is used to generate a laser beam required for detecting gas concentration, that is, as a light source of the laser beam, and an output end of the laser is bi-directionally connected with a first input end of a phase-locked amplifier, where the phase-locked amplifier is an amplifier for performing phase-sensitive detection on an alternating signal, and uses a reference signal having the same frequency and phase relation with a detected signal as a reference, and only responds to the detected signal itself and noise components having the same frequency (or frequency multiplication) and the same phase as the reference signal. As shown in fig. 1, a multi-pass absorption cell is disposed in the light emitting direction of the laser, a gas sample to be subjected to concentration detection can be placed in the multi-pass absorption cell, wherein the multi-pass absorption cell is used for increasing the interaction distance between a laser beam and the gas sample to be detected, so that the detection sensitivity can be improved, a light incident window for enabling the laser beam to enter the multi-pass absorption cell is disposed on the multi-pass absorption cell, and a light emitting window for enabling the laser beam to exit the multi-pass absorption cell is disposed on the multi-pass absorption cell, and the interaction distance between the laser beam and the gas sample to be detected can be effectively increased by enabling the light beam entering the multi-pass absorption cell through the light incident window to be reflected in the multi-pass absorption cell. According to different types, the light incidence window and the light emergence window of the multi-pass absorption cell can be at the same end of the multi-pass absorption cell or at different ends.
The system is also provided with a photoelectric detector at a preset distance from the light emergent window of the multi-pass absorption tank, the photoelectric detector can adopt an InGaAs photodiode and the like, the photoelectric detector is used for converting an incident light signal into an original electric signal containing gas absorption information, namely, a light intensity signal of a laser beam after passing through a gas sample in the multi-pass absorption tank is converted into a voltage signal, and the preset distance between the light emergent window of the multi-pass absorption tank and the photoelectric detector can be flexibly set according to an actual scene. The output end of the photoelectric detector is connected with the input end of a preamplifier, and the preamplifier has the function of adjustable gain (amplification factor) and is used for amplifying an original electric signal to obtain an amplified electric signal. In the system, one output signal of the preamplifier enters a first input end of the data acquisition card, the other output signal of the preamplifier enters a second input end of the lock-in amplifier, and the output end of the lock-in amplifier is connected with the second input end of the data acquisition card. The output end of the data acquisition card is connected with signal processing equipment. The data acquisition card can automatically acquire analog or digital signals to be tested of the equipment and send the analog or digital signals to the upper computer for analysis and processing, and the data acquisition card can acquire a plurality of paths of signals according to different types of channels, namely, the board card of the data acquisition card can acquire a plurality of paths of signals.
The working principle of the variable-range gas concentration detection system provided by the utility model is described below: the laser generates laser in a certain wavelength range, the collimated laser beam is emitted into an incident window of the multi-pass absorption cell, and is reflected back and forth for multiple times in the multi-pass absorption cell so as to increase the absorption optical path L of the gas, and finally, the laser beam passes through an emergent window to the detector. Since the cross section of the collimated laser beam has a certain size (the spot diameter is in millimeter level in general), the multi-pass absorption cell exit window is a convex lens with a focal length f, and the detector is arranged at a position away from the multi-pass absorption cell exit window f (namely, focal point). The detector is a photoelectric converter with high sensitivity, and the wavelength response range comprises the light emitting wavelength lambda of the laser. The signal received by the detector is amplified by the pre-amplifier and then divided into two paths: one path is a direct absorption signal, the frequency of the signal is the same as that of a low-frequency sawtooth wave driving signal of the laser, the amplitude of the signal is related to the optical signal received by the detector and the amplification factor of the preamplifier, the stronger the received optical signal is, the larger the amplification factor of the amplifier is, the higher the amplitude is, and the signal is directly collected by the collecting card. The other path of signal is demodulated by the phase-locked amplifier and then is converted into a harmonic signal containing concentration information (in the related art, only one path of signal is sent to the phase-locked amplifier by the preamplifier), the second harmonic signal is generally selected for processing, and the harmonic signal is also collected by the data collecting card. The data acquisition card acquires direct absorption signals and second harmonic signals at the same time, and the acquired signals are processed by the signal processing system. When the multipass absorption cell contains a measured gas (which absorbs in the wavelength lambda range emitted by the laser), the direct absorption signal and the second harmonic signal exhibit different forms: the direct absorption signal is a downward depression of a certain area on the sawtooth wave, and is caused by the light intensity weakening of the light signal at the position after the light signal is absorbed by the gas in the multi-way absorption tank; the second harmonic signal is just opposite, the amplitude of the harmonic signal in the corresponding area is increased due to the gas absorption effect, but the sensitivity of the direct absorption signal and the harmonic signal to the gas concentration change is obviously different, namely, the direct absorption signal can observe obvious concave in the corresponding area only when the measured gas concentration is larger; the sensitivity of the harmonic absorption signal is hundreds or thousands times higher than that of the direct absorption signal, and according to the characteristic, when the gas concentration is lower, the direct absorption signal has no obvious change, the harmonic signal has obvious change, and when the gas concentration is higher than a certain value, the harmonic signal can have the phenomenon of absorption saturation (namely top extinction). The direct absorption signal and the harmonic signal in the system are simultaneously collected by the collecting card, as shown in fig. 5. The upper half part of the graph is a direct absorption signal of gas, namely a voltage signal obtained by amplifying a light intensity signal received by a photoelectric detector through a preamplifier, when a multi-way absorption tank contains measured gas with higher concentration, the light intensity at the wavelength is reduced due to the absorption of the gas, a 'pit' is formed, and the deeper the 'pit', the higher the gas concentration is indicated. The lower half of the graph is the second harmonic absorption signal of the gas, and is suitable for the condition that the concentration of the measured gas is low, the 'concave' of direct absorption can not be observed at the moment, the change of the second harmonic signal is obvious, when the concentration is higher than a certain value, the second harmonic signal can be saturated, namely the top of the waveform can be flattened, and the 'concave' of the direct absorption signal can be gradually displayed. Based on the characteristics, the two paths of signals are simultaneously connected into the data acquisition card in the system, and spectral lines of the calculated signals are selected by judging whether the second harmonic is saturated (top extinction), so that the automatic switching of the high range and the low range of the instrument is realized. The temperature T of the laser and the low-frequency sawtooth wave driving current I can be precisely controlled, and a high-frequency sine wave modulation signal is superposed on the low-frequency sawtooth wave, so that the laser can emit laser with a certain wavelength range lambda.
The gas concentration detection system provided by the utility model aims at the problem that the cost of the device in each stage of production, use and maintenance is high in a method for measuring the concentration of the gas to be detected with high concentration and low concentration by adopting two sets of independent devices in the prior art, and the laser beam for detection is generated by a laser, and is reflected for multiple times in a multi-pass absorption tank containing the gas sample to be detected, so that the interaction distance between the laser beam and the gas sample to be detected can be effectively increased. The photoelectric detector further converts the laser beam emitted by the multi-pass absorption cell into an original electric signal containing gas absorption information, the preamplifier amplifies the original electric signal and then outputs a signal which is divided into two paths, one path of the signal is directly collected by the data acquisition card, the other path of the signal is demodulated by the lock-in amplifier and then is converted into a harmonic signal containing concentration information, the harmonic signal is also collected by the acquisition card, namely, the data acquisition card collects the direct absorption signal and the second harmonic signal simultaneously, and the direct absorption signal and the second harmonic signal show different forms, so that the system can detect the concentration of the gas to be detected with low concentration at high precision and detect the concentration of the gas to be detected with high concentration at high precision.
In order to improve the convergence of the laser beam emitted by the laser, a laser collimation unit can be arranged between the laser and the multi-pass absorption tank, the laser collimation unit is used for carrying out collimation treatment on the emergent beam of the laser, the output end of the laser is connected with the input end of the laser collimation unit, and the output end of the laser collimation unit is connected with the input end of the multi-pass absorption tank. In an alternative scheme, the laser may be an optical fiber laser, where the optical fiber laser uses a rare earth doped glass optical fiber as a gain medium, and correspondingly, the laser collimating unit may be an optical fiber collimator, where the optical fiber collimator is formed by precisely positioning a tail fiber and a self-focusing lens, and may convert transmission light in the optical fiber into collimated light, so as to improve the convergence of the laser beam entering the multipass absorption tank.
Further optimizing scheme can set up the convex lens in the light exit window department of multipass absorption pond, and this convex lens is used for right the outgoing light of multipass absorption pond carries out focusing treatment, and the laser beam that passes through the multiple reflection in the multipass absorption pond probably takes place the divergence of certain degree, through setting up the convex lens in the light exit window of multipass absorption pond, can focus the laser beam that the emergence was gone out the multipass absorption pond effectively to can improve the follow-up precision that carries out the analysis result to the gas absorption information that contains in the laser beam to a certain extent, improve the accuracy of the testing result that detects gas concentration. Based on the scheme, the photoelectric detector can be further arranged at the focus of the convex lens on the side opposite to the light emergent window of the multi-pass absorption cell.
In an alternative embodiment, the phase-locked amplifier may be a phase-locked amplifier with the model of AD630, and may extract and measure weak signals, where the internal resistances are SiCr thin film resistances with high stability, so as to ensure the accuracy and stability of the operation, and the signal processing applications include balanced modulation and demodulation, synchronous detection, phase detection, quadrature detection, phase-sensitive detection, lock-in amplification, square wave multiplication, and so on. The AD630 may be considered to have two preamplifiers integrated therein, one for selecting the precision comparators of the channel preamplifiers, one as a multiplexing switch and output stage integrating op-amp, with high switching speed and fast settling linear amplifiers, with minimal switching distortion due to the fast response time of the comparators, and very low inter-channel crosstalk. The data acquisition card can adopt a data acquisition card with the model number of PM-512, the laser can adopt a distributed feedback laser (Distributed Feedback Lase, DFB), a Bragg grating is built in the data acquisition card, a semiconductor material is used as a medium, and the data acquisition card belongs to a side-emitting semiconductor laser.
In an alternative scheme, the signal processing device can adopt an upper computer, the upper computer adopts a PC, and meanwhile, according to a use scene, the PC can be connected with an alarm device, and the alarm device is used for generating an alarm signal when the PC monitors that the concentration of the gas to be detected exceeds a preset value. The gas concentration detection system provided by the utility model can detect nonflammable gases such as carbon dioxide and also can detect flammable gases such as methane and carbon monoxide. In a possible practical scenario, the mine safety regulations prescribe that the concentration of carbon dioxide in the mine must not exceed five percent, the concentration of oxygen must not be lower than twenty percent, and the system can accurately measure the concentration of low-concentration gas and high-concentration gas, so that the concentration of oxygen and carbon dioxide in the mine can be accurately monitored, an alarm can be given when the concentration of carbon dioxide is monitored to exceed five percent, and an alarm can be given when the concentration of oxygen is monitored to be lower than twenty percent.
In an alternative example, the laser may employ a tunable semiconductor laser, and accordingly, the detection system further includes a laser driver board, which is a circuit board card that provides a driving current for the tunable semiconductor laser, and may include a current driver module and a temperature driver module that cooperate to cause the tunable semiconductor laser to generate a laser beam within a predetermined wavelength range.
In order to more clearly describe the working principle of the variable-range gas concentration detection system provided by the utility model, a specific detection scene for detecting the concentration of methane gas is taken as an example for specific explanation.
In this example, the laser may be a DFB butterfly laser, where the working temperature t=25 ℃, the working current I ranges from 200mA to 205mA, the frequency of the sawtooth current is 200Hz, and a sine wave signal with a small amplitude of 10MHz is superimposed on the basis of 200 Hz. At this time, the central wavelength λ= 1650.9nm of light emitted by the DFB laser is periodically changed at the central wavelength due to the change of the driving current, the wavelength range just can cover a certain absorption line of methane gas, the light beam emitted by the laser becomes a light spot with a cross section of 3mm-5mm after being collimated, and the light beam enters the multipass absorption cell through an incident window of the multipass absorption cell, where the multipass absorption cell can be a white cell, the absorption optical path l=10m, the incident window and the emergent window are located at two sides of the absorption cell, and the effective aperture is 10mm. The incident window is a plane window and forms non-normal incidence with incident light, so that reflected light can be effectively prevented from returning to the laser, damage to the laser is caused, the emergent window is arranged as a convex lens, emergent light is converged into a point, and the photoelectric detector is convenient to receive the emergent light. The photodetector is arranged at the focal point F of the exit window, 15mm from the exit window. The effective detection pixel size of the detection is 0.8mm, and the detection has good wavelength response at 1650.9 nm. The optical signal received by the photodetector is converted into an electrical signal and then transmitted to the preamplifier through the radio frequency line (the photodetector and the preamplifier may also be integrated at this time). The output signal of the preamplifier is divided into two paths: one path is a direct absorption signal, the frequency of the signal is the same as that of a low-frequency sawtooth wave driving signal of the laser, namely 200Hz, the amplitude is related to the optical signal received by the photoelectric detector and the amplification factor of the preamplifier, the stronger the received optical signal is, the larger the amplification factor of the amplifier is, the higher the amplitude is, and the signal is directly collected by the data collecting card. After the other path of signal is demodulated by the phase-locked amplifier, the other path of signal is converted into a harmonic signal containing concentration information, a second harmonic signal is generally selected for processing, the harmonic signal is also collected by a collecting card, and the spectral line states of direct absorption and second harmonic absorption are as follows: the upper half is the direct absorption signal, and the lower half is the second harmonic absorption signal.
In the description of the present utility model, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present utility model and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present utility model.
The foregoing is merely illustrative of specific embodiments of the utility model, and the scope of the utility model is not limited thereto, but is intended to cover any variations or alternatives not contemplated by the inventors. Therefore, the protection scope of the utility model should be subject to the protection scope defined by the claims.
Claims (9)
1. A variable range gas concentration detection system, comprising:
a laser for generating a laser beam required to detect the gas concentration;
the output end of the laser is connected with the first input end of the phase-locked amplifier and is used for generating a reference signal required by the phase-locked amplifier during operation;
a multi-pass absorption tank is arranged in the light emergent direction of the laser, a light incidence window for enabling the laser beam to enter the multi-pass absorption tank is arranged on the multi-pass absorption tank, a photoelectric detector is arranged at a preset distance from the light emergent window of the multi-pass absorption tank, and the photoelectric detector is used for converting an incident light signal into an original electric signal containing gas absorption information;
the output end of the photoelectric detector is connected with the input end of a preamplifier, and the preamplifier is used for amplifying the original electric signal to obtain an amplified electric signal; one path of output signal of the pre-amplifier enters a first input end of the data acquisition card, the other path of output signal of the pre-amplifier enters a second input end of the phase-locked amplifier, an output end of the phase-locked amplifier is connected with the second input end of the data acquisition card, and an output end of the data acquisition card is connected with signal processing equipment.
2. The variable range gas concentration detection system of claim 1 wherein the laser is a tunable semiconductor laser; the detection system further comprises a laser driving plate, wherein the laser driving plate comprises a current driving module and a temperature driving module, and the current driving module and the temperature driving module are matched to be used so that the tunable semiconductor laser can generate laser beams in a preset wavelength range.
3. The variable range gas concentration detection system according to claim 1, wherein a laser collimation unit is disposed between the laser and the multipass absorption cell, the laser collimation unit is used for performing collimation treatment on an outgoing beam of the laser, an output end of the laser is connected with an input end of the laser collimation unit, and an output end of the laser collimation unit is connected with an input end of the multipass absorption cell.
4. A variable range gas concentration detection system according to claim 3, wherein the laser is a fiber laser and the laser collimating unit is a fiber collimator; the lock-in amplifier adopts a lock-in amplifier with the model number of AD 630.
5. The variable range gas concentration detection system according to claim 1, wherein a convex lens is provided at a light exit window of the multipass absorption cell, and the convex lens is configured to focus the outgoing light of the multipass absorption cell.
6. The variable range gas concentration detection system of claim 5, wherein the photodetector is disposed at a focal point on a side of the convex lens opposite the light exit window.
7. The variable range gas concentration detection system of claim 1, wherein the signal processing device is a host computer and the host computer is a PC.
8. The variable range gas concentration detection system of claim 7, wherein the PC is connected to an alarm device for generating an alarm signal when the PC monitors that the concentration of the gas to be detected exceeds a predetermined value.
9. The variable range gas concentration detection system of claim 1, wherein the photodetector employs an ingaas photodiode; the data acquisition card adopts a data acquisition card with the model PM-512; the laser adopts a distributed feedback laser.
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