Anti-interference laser gas telemetry method and system

Abstract

The present invention provides an anti-interference laser gas remote sensing method and system, wherein the method comprises the following steps: reading a signal to be analyzed obtained within a detection period T; dividing the signal to be analyzed into a non-absorption area I and an absorption area II; when it is judged that the quality of the echo signal of the non-absorption area I is qualified and the quality of the first harmonic and second harmonic waveforms of the echo signal of the absorption area II is qualified, further calculating the instantaneous concentration C of the gas IV The laser gas telemetry device obtains the air background value C at this distance based on the detection distance provided by the laser ranging module and the air background curve fitted by the measurement. air , and then use the measured instantaneous concentration value C IV Subtract the air background value C air , that is, the real concentration of the target gas is obtained. The present invention can make the zero point more stable and accurately detect the real concentration of the target gas in the measured space, and is particularly suitable for places that require high-precision, high-sensitivity, and high-accuracy weak gas leakage monitoring.

Description

Technical Field

[0001] The invention relates to the technical field of laser gas telemetry, and in particular to an anti-interference laser gas telemetry method and system. Background Art

[0002] The laser gas telemetry system based on TDLAS technology detects laser light passing through the target gas and irradiating the background reflector. After being reflected by the background reflector, it is received by the photoelectric detector. By analyzing the reflected echo signal, the target gas concentration is inverted. Due to the long measurement distance and the real-time changes of the background reflector, it is easy to cause interference and cause false alarms. The interference factors are mainly the following:

[0003] (1) The measurement distance is long. When the measurement distance is long, the signal-to-noise ratio will be reduced, and the useful signal will be submerged in the noise, causing interference;

[0004] (2) Sudden changes in background reflectors: When background reflectors suddenly change, optical noise will be generated, causing false alarms.

[0005] (3) Interference noise: When the background reflector is a stainless steel bar, double-layer glass, etc., the telemeter return light will produce optical interference, causing false alarms;

[0006] (4) Air background. Since the gas concentration detected by the laser gas telemetry system is the integrated concentration, it is proportional to the average concentration of the air mass and the optical path of the laser beam passing through the air mass. For the air background, the longer the measurement distance, the higher the air background concentration.

[0007] The traditional laser gas telemetry system uses a near-infrared tunable semiconductor laser as the light source and utilizes the absorption peak line of the gas in the near-infrared band. This type of laser gas telemetry has certain advantages in system cost, but due to the long measurement distance, the laser gas detection system receives scattered light intensity, and the light signal is very weak. Sometimes the noise even submerges the real gas concentration information, seriously affecting the sensitivity and accuracy of the system in detecting gas. In addition, the sudden change of light intensity caused by background reflectors, or the optical interference caused by background reflectors are easy to cause interference and cause false alarms.

[0008] At the same time, due to the weak absorption of near-infrared gases, the laser gas remote sensing system generally has low sensitivity, usually at the ppm level, and cannot accurately distinguish the air background at different distances. During long-distance detection, the air background concentration detected by the laser gas remote sensing instrument is relatively large. If it cannot be removed, it will be mistaken for a gas source leak, causing interference to the detection results, and causing zero point fluctuations and false alarms in the laser gas remote sensing instrument.

[0009] In order to improve the detection accuracy, the existing technology usually uses corresponding noise reduction algorithms to process the collected signals. The existing noise reduction algorithms usually use some algorithms (such as least squares method, wavelet analysis) to reduce the noise of the second harmonic signal after obtaining the second harmonic signal. However, these algorithms are aimed at the second harmonic signal detected based on the entire sampling period. Although noise reduction processing has been performed, in actual use, there are still problems such as inaccurate gas detection results due to the influence of reflective objects (such as cement roads, gravel roads, window glass on roadside buildings, various tiles and other environmental factors), which in turn cause false alarms.

[0010] In order to solve the above problems, people have been seeking an ideal technical solution. Summary of the invention

[0011] The purpose of the present invention is to provide an anti-interference laser gas telemetry method and system in view of the deficiencies in the prior art.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A first aspect of the present invention provides an anti-interference laser gas telemetry method, comprising the following steps:

[0014] Read the signal to be analyzed obtained within a detection cycle T; divide the signal to be analyzed into non-absorption area I and absorption area II. When it is judged that the echo signal quality of non-absorption area I is qualified and the first harmonic and second harmonic waveforms of the echo signal of absorption area II are qualified, further calculate the instantaneous concentration of gas C IV ;

[0015] The laser gas telemetry device obtains the air background value C at the distance according to the detection distance provided by the laser ranging module and the measured fitted air background curve. air , and then use the measured instantaneous concentration value C IV Subtract the air background value C air , that is, the actual concentration of the target gas is obtained.

[0016] Based on the above, the instantaneous concentration value C IV The measurement methods include:

[0017] Reading a signal to be analyzed obtained within a detection period T; wherein the signal to be analyzed is an echo signal to be analyzed;

[0018] The signal to be analyzed is divided into a non-absorption zone I and an absorption zone II, wherein the non-absorption zone I corresponds to a sampling start point to an Nth sampling point of a detection cycle T, and the absorption zone II corresponds to a sampling point to an N+1th sampling point to an end point of a detection cycle T;

[0019] Determine whether the quality of the echo signal of the non-absorption area I is qualified. If it is unqualified, the calculation is discarded. If it is qualified, continue to analyze the echo signal of the absorption area II;

[0020] The echo signal of absorption zone II is phase-locked and amplified to obtain the first harmonic and second harmonic waveforms. The quality of the first harmonic and second harmonic waveforms is judged. If they are unqualified, the calculation is discarded. If they are qualified, the instantaneous concentration of the gas C is further calculated. IV .

[0021] Based on the above, when judging whether the echo signal of the non-absorption area I is qualified, the following is performed:

[0022] Perform FFT calculation on the echo signal of non-absorption area I and obtain the amplitude V of the first harmonic f' f ', the amplitude of the second harmonic 2f is V 2f 'To the amplitude of the nth harmonic nf V nf ';

[0023] The signal distortion amount S_Ⅰ of the non-absorption region Ⅰ is calculated using the following formula:

[0024]

[0025] Determine whether the signal distortion amount S_I of the non-absorption area I is greater than the distortion threshold S th _Ⅰ, if so, the echo signal quality of the non-absorption area Ⅰ is judged to be unqualified, otherwise it is judged to be qualified.

[0026] Based on the above, when judging whether the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is qualified, the following is performed:

[0027] First, determine the center position of a maximum point of the standard second harmonic as X 2f , the center positions of the M feature points are X1, X2, ... M , determine the center position Y1 of the zero point of the first harmonic, where M is generally an even number;

[0028] When the position of a maximum value point of the second harmonic after phase-locked amplification of the collected echo signal of the absorption zone II is at X 2f ±∆ 2f In the range, M feature points are located at their center ±∆ M In the range, the position of the zero point of the first harmonic is the same as the position of the maximum point of the second harmonic, both in X 2f ±∆ 2f If the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is within the range, it is determined that the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II is qualified, otherwise it is determined to be unqualified.

[0029] Based on the above, when the first harmonic and second harmonic waveform qualities of the echo signal in the non-absorption area I and the echo signal in the absorption area II after phase-locked amplification are both qualified, the following is further performed:

[0030] According to the first harmonic and second harmonic extracted from absorption zone II, the ratio between the amplitude V2f of the second harmonic and the amplitude Vf of the first harmonic is calculated to obtain the instantaneous concentration value C of the gas to be measured. IV .

[0031] Based on the above, the air background value C air The measurement methods include:

[0032] Select an area without target gas leakage, use laser gas telemetry equipment to measure, record the default air background concentration values ​​corresponding to N different detection distances, and perform a linear fit between every two distances to obtain the air background value C at different detection distances. air ;

[0033] When detecting the target gas concentration, the laser gas telemetry device obtains the air background value C at the detection distance provided by the laser ranging module. air .

[0034] Based on the above, the following methods are used to correct different background values ​​in different regions:

[0035] Select an area where there is no target gas leakage and measure the background concentration at the detection distance L1 , and calculate the background value at the detection distance L1 , and obtain the calibration coefficient ;

[0036] By formula Calculate the actual air background value ;

[0037] By formula Calculate the actual concentration of the target gas.

[0038] A second aspect of the present invention provides an anti-interference laser gas telemetry system, comprising a laser gas telemetry device and a laser ranging module;

[0039] The laser distance measuring module is used to measure the distance between the laser gas telemetry device and the background reflector when performing gas concentration detection;

[0040] The laser ranging module communicates with the laser gas telemetry device to implement the anti-interference laser gas telemetry method.

[0041] Based on the above, the laser in the laser gas telemetry device adopts a mid-infrared semiconductor laser, and the photoelectric detector in the laser gas telemetry device adopts a mid-infrared photoelectric detector.

[0042] The beneficial effects of the present invention are:

[0043] 1) By removing background interference, the present invention can make the zero point more stable and accurately detect the true concentration of the target gas in the measured space, which is particularly suitable for places that require high-precision, high-sensitivity and high-accuracy weak gas leakage monitoring.

[0044] 2) The present invention adopts a method of judging the quality of echo signals by region to calculate the instantaneous concentration value of the gas, divides the signal to be analyzed into non-absorption region I and absorption region II, and judges whether the quality of the echo signal of non-absorption region I is qualified. If it is unqualified, the calculation is discarded, and if it is qualified, the echo signal of absorption region II is continuously analyzed; the echo signal of absorption region II is phase-locked and amplified to obtain the first harmonic and second harmonic waveforms, and the quality of the first harmonic and second harmonic waveforms is judged. If it is unqualified, the calculation is discarded, and if it is qualified, the instantaneous concentration of the gas is further calculated; and then the instantaneous concentration of the gas to be measured is calculated according to the ratio between the amplitude V2f of the second harmonic and the amplitude Vf of the first harmonic of the absorption region II; thereby eliminating abnormal signals to be analyzed, effectively solving the problem of abnormal calculation results of the instantaneous concentration of the gas to be measured caused by various environmental factors such as reflective cement roads, gravel roads, window glass on roadside buildings, various tiles, and irradiated sky, thereby reducing the probability of false alarms;

[0045] 3) Before analyzing the waveform quality of the first harmonic and the second harmonic based on the echo signal quality of the non-absorption zone I and the echo signal of the absorption zone II, the signal quality of the absorption zone II is first detected to determine whether the echo signal of the absorption zone II is distorted. If no distortion occurs, the echo signal quality of the non-absorption zone I is no longer determined, thereby reducing the amount of calculation and improving the detection efficiency on the basis of improving the detection accuracy.

[0046] 4) The mid-infrared semiconductor laser is used as the light source of the laser gas telemetry system. The sensitivity is 2-3 orders of magnitude higher than that of the laser gas telemetry system that uses a near-infrared semiconductor laser as the light source, thus meeting the needs of high-sensitivity monitoring and early warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the principle structure of the system of the present invention.

[0048] Figure 2 is the instantaneous concentration value C in Example 1 of the present invention IV measurement method.

[0049] Figure 3It is a schematic diagram of the echo signal waveform when detecting the gas to be tested (the horizontal axis is the number of points or time, the vertical axis is the amplitude, the unit is mV).

[0050] Figure 4 It is a schematic diagram of the first harmonic and second harmonic of the echo signal of the gas absorption area II after phase-locked amplification and the position of each characteristic point (the horizontal axis is the number of points or time, the vertical axis is the amplitude, the unit is mV). DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described in detail below through specific implementation methods.

[0052] Figure 1 The schematic diagram of the principle structure of the system of the present invention is shown. The anti-interference laser gas telemetry system includes a laser transceiver optical system, a laser control unit, a signal processing unit, and a signal output unit. The detection laser emitted by the laser passes through the collimation system, passes through the target gas, is reflected by the background reflector, and is received by the photoelectric detector as an echo signal absorbed by the target gas. After photoelectric conversion, it is transmitted to the signal processing unit, which performs amplification and filtering on the signal, calculates the instantaneous concentration information of the target gas, and then outputs the instantaneous concentration information of the target gas by the signal output unit.

[0053] Among them, the laser control unit connects the signal processing unit and the laser. The laser control unit includes a current driving unit and a temperature control unit. The wavelength output by the laser is related to the driving current and temperature of the laser. After determining the driving current of the laser, the temperature of the TEC inside the laser is adjusted in real time so that the wavelength output by the laser is always locked on the absorption peak of the target gas. The laser modulation signal output by the signal processing unit is DA converted and transmitted to the laser control unit to drive the laser to emit light (generally using a driving waveform of a triangle wave or a sawtooth wave superimposed on a sine wave). At the same time, the temperature control unit in the laser control unit adjusts the TEC of the mid-infrared semiconductor laser 1 in real time so that the output wavelength of the laser is always stable on the absorption peak of the gas.

[0054] Example 1

[0055] This embodiment provides an anti-interference laser gas telemetry system, including a laser gas telemetry device and a laser ranging module; the laser ranging module is used to measure the distance between the laser gas telemetry device and the background reflector when performing gas concentration detection; the laser ranging module communicates with the laser gas telemetry device to implement an anti-interference laser gas telemetry method.

[0056] Specifically, the laser in the laser gas telemetry device is a mid-infrared semiconductor laser, and the photoelectric detector in the laser gas telemetry device is a mid-infrared photoelectric detector.

[0057] The anti-interference laser gas telemetry method comprises the following steps:

[0058] Read the signal to be analyzed obtained within a detection cycle T; divide the signal to be analyzed into non-absorption area I and absorption area II. When it is judged that the echo signal quality of non-absorption area I is qualified and the first harmonic and second harmonic waveforms of the echo signal of absorption area II are qualified, further calculate the instantaneous concentration of gas C IV .

[0059] The laser gas telemetry device obtains the air background value C at the distance according to the detection distance provided by the laser ranging module and the measured fitted air background curve. air , and then use the measured instantaneous concentration value C IV Subtract the air background value C air , that is, the actual concentration of the target gas is obtained.

[0060] The instantaneous concentration value C IV The measurement method is shown in the flow chart Figure 2 As shown, including:

[0061] Read the signal to be analyzed obtained by the detector within a detection period T; wherein the signal to be analyzed is the target echo signal obtained by the detector; specifically, the detection period T is the same as the period T of the fundamental wave (sawtooth wave, triangular wave, etc.) in the driving waveform of the laser driving circuit, and the period T of the triangular wave is greater than the period T0 of the sine wave.

[0062] The signal to be analyzed is divided into a non-absorption area I and an absorption area II, wherein the non-absorption area I corresponds to a sampling start point to an Nth sampling point of a detection period T, and the absorption area II corresponds to an N+1th sampling point to an end point of a detection period T; wherein N is a natural number greater than or equal to 1; the value of N can be preset and will leave enough redundancy, and can be modified according to actual conditions, such as Figure 3 As shown;

[0063] Determine whether the quality of the echo signal in the non-absorption area I is qualified. If qualified, continue to analyze the echo signal in the absorption area II. If unqualified, abandon the calculation.

[0064] The echo signal of absorption zone II is phase-locked and amplified to obtain the first harmonic and second harmonic waveforms, and the quality of the first harmonic and second harmonic waveforms is judged. If they are qualified, the instantaneous concentration of the gas is further calculated, and if they are unqualified, the calculation is discarded;

[0065] When it is determined that the waveform qualities of the first harmonic and the second harmonic of the echo signal of the non-absorption zone I and the echo signal of the absorption zone II are qualified, the instantaneous concentration value of the gas to be measured is calculated by calculating the ratio between the amplitude V2f of the second harmonic and the amplitude Vf of the first harmonic based on the first harmonic and the second harmonic extracted from the absorption zone II.

[0066] The air background value C air The measurement methods include:

[0067] Select an area without target gas leakage, use laser gas telemetry equipment to measure, record the default air background concentration values ​​corresponding to N different detection distances, and perform a linear fit between every two distances to obtain the air background value C at different detection distances. air ;

[0068] When detecting the target gas concentration, the laser gas telemetry device obtains the air background value C at the detection distance provided by the laser ranging module. air .

[0069] Since the background values ​​in different regions are different, the following methods are used to correct the different background values ​​in different regions:

[0070] Select an area where there is no target gas leakage and measure the background concentration at the detection distance L1 , and calculate the background value at the detection distance L1 , and obtain the calibration coefficient ;

[0071] By formula Calculate the actual air background value ;

[0072] By formula Calculate the actual concentration of the target gas.

[0073] Example 2

[0074] This embodiment takes laser methane detection as an example to specifically explain the instantaneous concentration value C IV The central wavelength of the laser beam output by the laser is 3367nm, the sawtooth wave is used to gradually change the laser output wavelength from 3366nm to 3368nm (within one detection cycle), and the sine wave is used for modulation; the sawtooth wave period is 2.6ms, the sine wave period is 10khz, and the sampling frequency is 200khz;

[0075] When the light intensity in the detection environment is low, or there are glass, corners, and other factors in the detection environment, the echo signal quality of the non-absorption area I will be unqualified, indicating that the echo signal of this detection cycle is too small or seriously disturbed by the external environment, and then the signal of the absorption area will also be disturbed by the environment, which is easy to cause false alarms. th By comparing the results between _Ⅰ, the echo signals with unqualified quality are eliminated, thereby effectively improving the detection accuracy and reducing the calculation amount of phase-locked amplification;

[0076] It can be understood that the non-absorption zone I, as a gas-free absorption zone, can be used as a calculation zone for judging the return light intensity and signal quality, and the absorption zone II, as a gas normal absorption zone, can be used as a gas concentration calculation zone. For judging the signal quality in the gas-free absorption zone, this embodiment provides a signal quality detection method.

[0077] When judging whether the quality of the echo signal of the non-absorption area I is qualified, the following is performed: performing FFT calculation on the echo signal of the non-absorption area I to obtain the amplitude V of the first harmonic f respectively. f ', the amplitude of the second harmonic 2f is V 2f 'To the amplitude of the nth harmonic nf V nf '; The signal distortion amount S_Ⅰ of the non-absorption region Ⅰ is calculated using the following formula:

[0078]

[0079] Determine whether the signal distortion amount S_I of the non-absorption area I is greater than the distortion threshold S th _Ⅰ, if yes, it is determined that the quality of the echo signal of the non-absorption area Ⅰ is unqualified, otherwise it is determined that the quality of the echo signal of the non-absorption area Ⅰ is qualified;

[0080] It should be noted that when no adverse distortion occurs in the non-absorbing region I, the signal distortion amount S of the non-absorbing region I is 1. The more severe the adverse distortion of the non-absorbing region I is, the greater the signal distortion amount S of the non-absorbing region I is.

[0081] Specifically, the value range of n is a natural number greater than 3. Taking into account both the amount of calculation and the accuracy, the value of n can be 4; then the calculation formula for the signal distortion amount S_I of the non-absorption area I can be:

[0082] .

[0083] It should be noted that the amplitude V of the first harmonic f in this embodiment is f ', the amplitude of the second harmonic 2f is V 2f 'To the amplitude of the nth harmonic nf V nf' refers to the harmonic amplitude extracted after FFT calculation based on the echo signal of non-absorption area I, which is used for signal quality evaluation.

[0084] Specifically, the distortion threshold S th The value range of _Ⅰ is 1.05 to 1.2, for example, 1.08;

[0085] Example 3

[0086] It should be noted that: when there are factors such as glass and edges in the detection environment, it will also cause bad distortion in the absorption zone II. When the signal quality of the non-absorption zone I is determined to be qualified, we need to further judge the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification. When it is determined that the waveform quality of the first harmonic and the second harmonic of the echo signal of the non-absorption zone I and the echo signal of the absorption zone II are qualified, the instantaneous concentration value of the gas to be measured is calculated based on the first harmonic and the second harmonic extracted from the absorption zone II, and the ratio between the amplitude V2f of the second harmonic and the amplitude Vf of the first harmonic is obtained.

[0087] The laser beam emitted by the laser is directed to the area where the gas to be tested is located. When the laser output wavelength scans to 3367nm, if it happens to encounter methane gas, the sine wave of absorption zone II (corresponding to 3367nm) will have benign distortion (absorption pit), and at the same time, the characteristic points of the first harmonic and the second harmonic after phase-locked amplification satisfy a certain relationship. We first determine the center position of a maximum point of the second harmonic of benign distortion caused by gas absorption in absorption zone II as X 2f , the center positions of the four characteristic points are X1, X2, X3, and X4, and the center position Y1 of the zero point of the first harmonic is determined. The positions of X1, X2, X3, X4, and Y1 are as follows Figure 4 shown.

[0088] 1) During normal gas measurement

[0089] If methane gas is encountered, the position of a maximum point of the second harmonic after phase-locked amplification in the absorption zone II is at X 2f ±∆ 2f In the range, the four characteristic points are all within the range of X1±∆1, X2±∆2, X3±∆3, and X4±∆4. At the same time, the position of the zero point of the first harmonic is the same as the position of the maximum point of the second harmonic. 2f ±∆ 2f Specifically, ∆ 2f , ∆1, ∆2, ∆3 and ∆4 can be selected in the range of 50~100, for example: 50.

[0090] If no methane gas is encountered, the received echo signal is not distorted, the sine wave in absorption zone II has no absorption pit, and the amplitude of the second harmonic extracted after phase-locked amplification is about 0mV, and the instantaneous concentration value of the gas to be measured is close to 0;

[0091] 2) When the laser beam emitted by the laser encounters background objects such as glass, edges and corners during the gas measurement process

[0092] When the laser output wavelength is scanned to 3367nm, if it happens to encounter methane gas, the sine wave of absorption zone II (corresponding to 3367nm) will be distorted, and the position of a maximum point of the second harmonic of the echo signal after phase-locked amplification is at X 2f ±∆ 2f In the range, the four characteristic points are all within the range of X1±∆1, X2±∆2, X3±∆3, and X4±∆4. At the same time, the position of the zero point of the first harmonic is the same as the position of the maximum point of the second harmonic. 2f ±∆ 2f In range.

[0093] If there is no methane gas, the sine wave in absorption zone II will also be distorted due to interference from background objects such as glass, but the position of a maximum point of the second harmonic of the echo signal after phase-locked amplification is not at X 2f ±∆ 2f The four characteristic points are not in the range of X1±∆1, X2±∆2, X3±∆3, X4±∆4, or the position of the zero point of the first harmonic is different from the position of the maximum point of the second harmonic, and are not in the range of X 2f ±∆ 2f If the absorption in absorption zone II is within the specified range, the absorption in absorption zone II is judged to be unqualified and the measurement is discarded.

[0094] When the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is not determined, the instantaneous concentration of the gas is calculated, and the instantaneous concentration value of the gas to be measured is greater than 0, resulting in the measured instantaneous concentration value of the gas being greater than the actual instantaneous concentration value of the gas, which will cause a false alarm;

[0095] If the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is further determined according to this embodiment, the data will be discarded and the concentration value of the gas to be measured will be close to 0, thereby improving the detection accuracy.

[0096] Example 4

[0097] This embodiment still takes methane laser as an example to specifically explain the instantaneous concentration value C IVThe central wavelength of the output laser beam is 3367nm, and the function of the triangle wave is to gradually change the output wavelength of the laser from 3366nm to 3368nm. The sawtooth wave period is 2.6ms, the sine wave period is 10khz, and the sampling frequency is 200khz.

[0098] When the laser beam emitted by the laser is directed toward the sky, resulting in no background reflectors: when the laser output wavelength is scanned to 3367nm, although no methane gas is encountered, the interference caused by factors such as sunlight causes the sine waves of the non-absorption area I and the absorption area II to be distorted. Although the echo signal of the absorption area II is weak, the characteristic points of the first harmonic and the second harmonic of the distortion after phase-locked amplification meet the judgment conditions in the above-mentioned embodiment 3 and are judged to be qualified.

[0099] If the signal quality of non-absorption zone I is not judged, the measured instantaneous gas concentration value will be greater than the actual instantaneous gas concentration value, triggering an alarm;

[0100] If the quality of the echo signal in the non-absorption region I is determined first in accordance with the present embodiment, the measurement result will be discarded, and the instantaneous concentration value of the gas to be measured will be close to 0, thereby improving the detection accuracy.

[0101] It should be noted that in the prior art, when performing laser telemetry gas detection, the target echo signal is usually obtained within a detection period T for phase-locked amplification calculation to extract the amplitude of the first harmonic. and the amplitude of the second harmonic ;

[0102] However, due to poor lighting conditions caused by weather and other reasons, or the laser beam emitted by the laser irradiates the sky, encounters window glass on roadside buildings, various tiles, etc., it may cause the target echo signal obtained within a detection period T to be locally abnormal (quality failure), and the location where the abnormality occurs in the target echo signal is different under different detection conditions; if the phase-locked amplification calculation and gas instantaneous concentration calculation are still performed according to the existing technology, the calculated gas instantaneous concentration will be greater than the gas instantaneous concentration in the actual environment, thereby causing a false alarm;

[0103] To solve this problem, this embodiment proposes a method for judging the quality of echo signals by region to calculate the instantaneous concentration value of the gas, and calculate the amplitude of the first harmonic in the absorption zone II. and the amplitude of the second harmonic Before that, we first judge the waveform quality of the echo signal in the non-absorption zone I and the first and second harmonics of the echo signal in the absorption zone II after phase-locked amplification, so as to eliminate abnormal signals before calculating the instantaneous concentration of the gas, avoid the impact of unqualified echo signals on the detection results, effectively improve the detection accuracy, reduce the amount of system calculations, and improve the response speed.

[0104] Example 5

[0105] This embodiment provides an anti-interference laser gas telemetry system, including a laser gas telemetry device and a laser ranging module;

[0106] The laser distance measuring module is used to measure the distance between the laser gas telemetry device and the background reflector when performing gas concentration detection;

[0107] The laser ranging module communicates with the laser gas telemetry device to implement the anti-interference laser gas telemetry method described in any one of the above embodiments 1-4.

[0108] Particularly, the laser in the laser gas telemetry device adopts a mid-infrared semiconductor laser, and the photoelectric detector in the laser gas telemetry device adopts a mid-infrared photoelectric detector.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. An anti-interference laser gas telemetry method, characterized in that: The following steps are involved: Read the signal to be analyzed obtained within a detection cycle T; divide the signal to be analyzed into non-absorption area I and absorption area II. When it is judged that the echo signal quality of non-absorption area I is qualified and the first harmonic and second harmonic waveforms of the echo signal of absorption area II are qualified, further calculate the instantaneous concentration of gas C IV ; The laser gas telemetry device obtains the air background value C at the distance according to the detection distance provided by the laser ranging module and the measured fitted air background curve. air , and then use the measured instantaneous concentration value C IV Subtract the air background value C air , that is, the real concentration of the target gas is obtained; Instantaneous concentration value C IV The measurement methods include: Reading a signal to be analyzed obtained within a detection period T; wherein the signal to be analyzed is an echo signal to be analyzed; The signal to be analyzed is divided into a non-absorption zone I and an absorption zone II, wherein the non-absorption zone I corresponds to a sampling start point to an Nth sampling point of a detection cycle T, and the absorption zone II corresponds to a sampling point to an N+1th sampling point to an end point of a detection cycle T; Determine whether the quality of the echo signal of the non-absorption area I is qualified. If it is unqualified, the calculation is discarded. If it is qualified, continue to analyze the echo signal of the absorption area II; The echo signal of absorption zone II is phase-locked and amplified to obtain the first harmonic and second harmonic waveforms. The quality of the first harmonic and second harmonic waveforms is judged. If they are unqualified, the calculation is discarded. If they are qualified, the instantaneous concentration of the gas C is further calculated. IV ; When judging whether the echo signal quality of the non-absorption area I is qualified, executing: Perform FFT calculation on the echo signal of non-absorption area I and obtain the first harmonic f’ The amplitude V f ', the amplitude of the second harmonic 2f is V 2f 'To the amplitude of the nth harmonic nf V nf '; The signal distortion amount S_Ⅰ of the non-absorption region Ⅰ is calculated using the following formula: ， Determine whether the signal distortion amount S_I of the non-absorption area I is greater than the distortion threshold S th _Ⅰ, if yes, the echo signal quality of the non-absorption area Ⅰ is judged to be unqualified, otherwise it is judged to be qualified; When judging whether the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is qualified, the following is performed: First, determine the center position of a maximum point of the standard second harmonic as X 2f , the center positions of the M feature points are X1, X2, ... M , determine the center position Y1 of the zero point of the first harmonic, where M is generally an even number; When the position of a maximum value point of the second harmonic after phase-locked amplification of the collected echo signal of the absorption zone II is at X 2f ±∆ 2f In the range, M feature points are located at their center ±∆ M In the range, the position of the zero point of the first harmonic is the same as the position of the maximum point of the second harmonic, both in X 2f ±∆ 2f If the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II after phase-locked amplification is within the range, it is determined that the waveform quality of the first harmonic and the second harmonic of the echo signal of the absorption zone II is qualified, otherwise it is determined to be unqualified.

2. The anti-interference laser gas telemetry method according to claim 1, characterized in that: When the waveform qualities of the first harmonic and the second harmonic of the echo signal of the non-absorption area I and the echo signal of the absorption area II after phase-locked amplification are both qualified, the following is further performed: According to the first harmonic and second harmonic extracted from absorption zone II, the ratio between the amplitude V2f of the second harmonic and the amplitude Vf of the first harmonic is calculated to obtain the instantaneous concentration value C of the gas to be measured. IV .

3. The anti-interference laser gas remote sensing method according to claim 1, characterized in that: Air background value C air The measurement methods include: Select an area without target gas leakage, use laser gas telemetry equipment to measure, record the default air background concentration values ​​corresponding to N different detection distances, and perform a linear fit between every two distances to obtain the air background value C at different detection distances. air ; When detecting the target gas concentration, the laser gas telemetry device obtains the air background value C at the detection distance provided by the laser ranging module. air .

4. The anti-interference laser gas telemetry method according to claim 1, characterized in that: For different background values ​​in different regions, the following methods are used for correction: Select an area where there is no target gas leakage and measure the air background concentration at the detection distance L1 , and calculate the air background value at the detection distance L1 , and obtain the calibration coefficient ; By formula Calculate the actual air background value ; By formula Calculate the actual concentration of the target gas. 5.An anti-interference laser gas telemetry system, characterized in that: Includes laser gas telemetry equipment and laser ranging modules; The laser distance measuring module is used to measure the distance between the laser gas telemetry device and the background reflector when performing gas concentration detection; The laser ranging module communicates with the laser gas telemetry device to implement the anti-interference laser gas telemetry method according to any one of claims 1 to 4.

6. The anti-interference laser gas telemetry system according to claim 5, characterized in that: The laser in the laser gas remote sensing device adopts a mid-infrared semiconductor laser, and the photoelectric detector in the laser gas remote sensing device adopts a mid-infrared photoelectric detector.

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