CN109916851B - Gas concentration detection method and system of laser telemeter - Google Patents
Gas concentration detection method and system of laser telemeter Download PDFInfo
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- CN109916851B CN109916851B CN201910097609.8A CN201910097609A CN109916851B CN 109916851 B CN109916851 B CN 109916851B CN 201910097609 A CN201910097609 A CN 201910097609A CN 109916851 B CN109916851 B CN 109916851B
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Abstract
The invention discloses a gas concentration detection method of a laser telemeter, which comprises the following steps: acquiring a spectral waveform of a gas absorption signal; obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal; judging whether the gas absorption signal is credible or not according to the signal-to-noise ratio and generating a judgment result; and using the credible gas absorption signal to calculate a gas concentration value based on the judgment result. Meanwhile, the invention also discloses a gas concentration detection system of the laser telemeter. The invention can avoid the false alarm generated by the low signal-to-noise ratio of the signal of the laser telemeter and improve the accuracy of concentration detection.
Description
Technical Field
The invention relates to the technical field of laser spectroscopy, in particular to a gas concentration detection method and system of a laser telemeter.
Background
Gas concentration measurement by reflection echo is a common way of gas telemetry. The light emitted by the light source irradiates the area to be measured through collimation, the light beam reflects the echo back to the photoelectric detector of the remote measuring device after being reflected, and the concentration value of the target gas can be calculated by measuring the absorption of the reflected echo by the target gas on the path. In the prior art, such telemetry devices may generate false positives due to low signal to noise ratios. Therefore, it is necessary to provide a technical solution to improve the concentration detection accuracy of the laser telemeter.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a gas concentration detection method of a laser telemeter in a first aspect, which comprises the following steps:
acquiring a spectral waveform of a gas absorption signal;
obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
judging whether the gas absorption signal is credible or not according to the signal-to-noise ratio and generating a judgment result;
and using the credible gas absorption signal to calculate a gas concentration value based on the judgment result.
Further, the obtaining the signal-to-noise ratio of the gas absorption signal according to the spectral waveform of the gas absorption signal includes:
dividing the spectral waveform of the gas absorption signal into a non-absorption area and an absorption area with an absorption peak;
calculating the signal amplitude of the absorption peak in the absorption region;
calculating the background noise amplitude in the non-absorption region;
calculating the signal-to-noise ratio of the gas absorption signal according to the absorption peak signal amplitude and the background noise amplitude; the signal-to-noise ratio of the gas absorption signal is the absorption peak signal amplitude/the background noise amplitude.
Further, the dividing the spectrum waveform of the gas absorption signal into an absorption region without an absorption region and an absorption region with an absorption peak includes:
determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point;
determining positions of a first limit point, a second limit point, a third limit point and a fourth limit point according to the position of the reference point and preset conditions, wherein the first limit point, the second limit point, the reference point, the third limit point and the fourth limit point are sequentially arranged along the direction of the transverse axis of the spectrum waveform;
determining an absorption region range and a non-absorption region range on the spectral waveform according to the first limit point, the second limit point, the third limit point and the fourth limit point; the sampling time of any sampling point in the absorption area range is later than that of the second limit point and is earlier than that of the third limit point, and the sampling time of any sampling point in the non-absorption area range is later than that of the first limit point and is earlier than that of the second limit point, or is later than that of the third limit point and is earlier than that of the fourth limit point.
Further, the determining whether the gas absorption signal is authentic according to the signal-to-noise ratio and generating a determination result includes:
judging whether the signal-to-noise ratio exceeds a preset threshold value;
when the signal-to-noise ratio exceeds a preset threshold value, taking the gas absorption signal as the credible gas absorption signal;
and when the signal-to-noise ratio does not exceed a preset threshold value, discarding the gas absorption signal.
Further, the acquiring a spectral waveform of a gas absorption signal includes:
obtaining a spectral waveform of the gas absorption signal by using a wavelength scanning direct absorption method based on TDLAS;
or, obtaining the spectral waveform of the gas absorption signal by using a TDLAS-based wavelength modulation absorption method.
The invention provides a gas concentration detection system of a laser telemeter in a second aspect, which comprises the following modules:
the acquisition module is used for acquiring the spectral waveform of the gas absorption signal;
the calculation module is used for obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
the credibility judgment module is used for judging whether the gas absorption signal is credible according to the signal-to-noise ratio and generating a judgment result;
and the selecting module is used for calculating the gas concentration value by using the credible gas absorption signal based on the judgment result.
Further, the calculation module includes:
the dividing module is used for dividing the spectrum waveform of the gas absorption signal into a non-absorption area and an absorption area with an absorption peak;
the signal-to-noise ratio calculation module is used for calculating the amplitude of an absorption peak signal in the absorption region, calculating the amplitude of background noise in the non-absorption region and calculating the signal-to-noise ratio of the gas absorption signal according to the amplitude of the absorption peak signal and the amplitude of the background noise; the signal-to-noise ratio of the gas absorption signal is absorption peak signal amplitude/background noise amplitude.
Further, the dividing module includes:
the reference point determining module is used for determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point;
a limit point determining module, configured to determine positions of a first limit point, a second limit point, a third limit point, and a fourth limit point according to a position of the reference point and a preset condition, where the first limit point, the second limit point, the reference point, the third limit point, and the fourth limit point are sequentially arranged along a horizontal axis direction of the spectral waveform;
a range determination module to determine an absorption region range and a non-absorption region range on the spectral waveform according to the first, second, third, and fourth limit points; the sampling time of any sampling point in the range of the absorption area is later than that of the second limit point and earlier than that of the third limit point; the sampling time of any sampling point in the non-absorption area range is later than the sampling time of the first limit point and is earlier than the sampling time of the second limit point, or is later than the sampling time of the third limit point and is earlier than the sampling time of the fourth limit point.
Further, the credibility judgment module comprises:
the signal-to-noise ratio judging module is used for judging whether the signal-to-noise ratio exceeds a preset threshold value;
a result generation module, configured to take the gas absorption signal as the trusted gas absorption signal when the signal-to-noise ratio exceeds a preset threshold; and when the signal-to-noise ratio does not exceed a preset threshold value, discarding the gas absorption signal.
Further, the obtaining module comprises:
a first acquisition module for acquiring a spectral waveform of the gas absorption signal using a wavelength scanning direct absorption method based on TDLAS,
or, the second acquisition module is used for acquiring the spectrum waveform of the gas absorption signal by using a wavelength modulation absorption method based on TDLAS.
The implementation of the invention has the following beneficial effects: the invention divides the spectrum waveform of the gas absorption signal into an absorption area and a non-absorption area according to the reference point position corresponding to the absorption peak and the preset condition, obtains the signal-to-noise ratio for evaluating the signal quality by analyzing the signal amplitude of the absorption area and the noise amplitude of the non-absorption area, selects the credible gas absorption signal according to the signal quality evaluation result to calculate the concentration value, and discards the incredible echo signal. The invention can avoid the false alarm generated by the low signal-to-noise ratio of the signal of the laser telemeter and improve the accuracy of concentration detection.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a flow chart of a method of improving the accuracy of concentration detection by a laser telemeter according to an embodiment of the present invention;
fig. 2 is a flowchart of step S200;
FIG. 3 is a schematic illustration of the division of the absorbent and non-absorbent regions provided by an embodiment of the present invention;
fig. 4 is a flowchart of step S210;
fig. 5 is a flowchart of step S300;
FIG. 6 is a diagram illustrating the relationship between detected light intensity and fitted light intensity provided by an embodiment of the present invention;
FIG. 7 is a schematic illustration of an absorbance curve provided by an embodiment of the present invention;
FIG. 8 is a block diagram of a system for improving the accuracy of laser telemeter concentration detection according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. Examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout.
Examples
In the prior art, a telemetry device may generate false alarm due to low signal-to-noise ratio, which causes several common situations that the signal-to-noise ratio of a gas absorption signal is low as follows:
1) the gas absorption signal is easily submerged in electronic and optical noise when the gas absorption signal is weak due to low gas concentration or short optical path.
2) The telemeter receives too little reflected light (the telemeter irradiates too far, or the reflectivity of the reflecting surface is too low, or the included angle between the reflecting surface and the laser is too small), and then the electrical noise is dominant.
3) When the optical noise is too large, for example, when the telemeter transmits double-layer glass, or is coated with anti-infrared reflection film glass, or polarized glass, an F-P interference cavity is easily formed between the front and back surfaces of the glass or between the glasses, so that optical interference fringes are formed.
4) The reflective surface may be of a material or construction that is unique to the reflective surface, such as a reflective surface of a construction like a multi-layer screen.
5) Optical noise caused by a drastic change in ambient light, such as optical noise having the same frequency as the signal is easily generated and absorbed when the flicker frequency of the ambient light and the signal frequency are close to each other.
In order to avoid the false alarm possibly generated by the low signal-to-noise ratio of the signal of the laser telemeter and improve the accuracy of concentration detection, the embodiment provides a method for improving the accuracy of concentration detection of the laser telemeter.
Fig. 1 is a flowchart of a method for improving the concentration detection accuracy of a laser telemeter according to an embodiment of the present invention, and fig. 1 shows the method including the following steps:
s100: acquiring a spectral waveform of a gas absorption signal;
s200: obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
s300: judging whether the gas absorption signal is credible or not according to the signal-to-noise ratio and generating a judgment result;
s400: the trusted gas absorption signal is used to calculate a gas concentration value based on the determination.
Fig. 2 is a flowchart of step S200, fig. 3 is a schematic diagram of dividing an absorption region and a non-absorption region according to an embodiment of the present invention, and with reference to fig. 2 and fig. 3, specifically, step S200: obtaining the signal-to-noise ratio of the gas absorption signal according to the spectral waveform of the gas absorption signal, and comprises the following sub-steps:
s210: dividing the spectral waveform of the gas absorption signal into a non-absorption area and an absorption area with an absorption peak;
s220: calculating the signal amplitude of an absorption peak in the absorption region;
referring to fig. 3, the white area is the absorption area with absorption peak, and the calculated signal amplitude of the absorption peak is 3 × 10-4。
S230: calculating the background noise amplitude in the non-absorption region;
referring to fig. 3, the gray background part is a non-gas absorption area, and the calculated background noise amplitude is 2 × 10-4。
S240: calculating the signal-to-noise ratio of the gas absorption signal according to the absorption peak signal amplitude and the background noise amplitude; the signal-to-noise ratio of the gas absorption signal is the absorption peak signal amplitude/background noise amplitude.
Fig. 4 is a flowchart of step S210, and referring to fig. 4, since the wavelength corresponding to the gas absorption peak is determined, specifically, step S210: the method comprises the following substeps of dividing the spectral waveform of a gas absorption signal into absorption regions with no absorption region and absorption regions with absorption peaks:
s211: determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point;
s212: determining the positions of a first limit point, a second limit point, a third limit point and a fourth limit point according to the position of a reference point and preset conditions, wherein the first limit point, the second limit point, the reference point, the third limit point and the fourth limit point are sequentially arranged along the direction of a transverse axis of the spectrum waveform;
in an embodiment, referring to fig. 3 (in fig. 3, the sampling point numbers correspond to the sampling times one to one), the preset condition includes a signal amplitude variation range of the spectral waveform, and the non-absorption region is divided according to the signal amplitude variation range of the spectral waveform, for example, a region where the signal amplitudes on both sides of the absorption peak are significantly decreased and tend to change steadily. Determining the position relation between each limit point and a reference point of a non-absorption area and an absorption area with an absorption peak according to a preset condition, wherein:
the first limit point A is positioned on the left side of the absorption peak, the distance between the first limit point A and the reference point is a first preset distance, and the first preset distance is a sampling time interval between the sampling time of the corresponding reference point and the sampling time of the first limit point A;
a second limit point B is positioned on the left side of the absorption peak, the second limit point B is positioned at the junction of the gray area and the white area in the figure, the distance between the second limit point B and the reference point is a second preset distance, the second preset distance is a sampling time interval between the sampling time of the corresponding reference point and the sampling time of the second limit point B, and the second preset distance is smaller than the first preset distance;
a third limit point C is positioned at the right side of the absorption peak, the third limit point C is positioned at the junction of the white area and the gray area in the figure, the distance between the third limit point C and the reference point is a third preset distance, and the third preset distance corresponds to the sampling time interval between the sampling time of the third limit point C and the sampling time of the reference point;
the fourth limit point D is positioned on the right side of the absorption peak, the distance between the fourth limit point D and the reference point is a fourth preset distance, the fourth preset distance corresponds to the sampling time interval between the sampling time of the fourth limit point D and the sampling time of the reference point, and the third preset distance is smaller than the fourth preset distance.
It should be noted that the second preset distance and the third preset distance may be equal or unequal, and the first preset distance and the fourth preset distance may be equal or unequal.
S213: determining an absorption region range (white region in fig. 3) and a non-absorption region range (gray region in fig. 3) on the spectral waveform according to the first limit point, the second limit point, the third limit point and the fourth limit point; the sampling time of any sampling point in the absorption area range is later than the sampling time of the second limit point B and is earlier than the sampling time of the third limit point C, and the sampling time of any sampling point in the non-absorption area range is later than the sampling time of the first limit point A and is earlier than the sampling time of the second limit point B, or is later than the sampling time of the third limit point C and is earlier than the sampling time of the fourth limit point D.
Fig. 5 is a flowchart of step S300, please refer to fig. 5, specifically, step S300: judging whether the gas absorption signal is credible or not according to the signal-to-noise ratio and generating a judgment result, wherein the method comprises the following substeps:
s310: judging whether the signal-to-noise ratio exceeds a preset threshold value;
in one embodiment, the preset threshold is 2, the SNR calculated in step S240 is 1.5, and is compared with the preset threshold 2, the reliability of the signal is determined according to the comparison result, and it is determined whether the absorption peak signal can be used for gas concentration calculation; since the calculated SNR is smaller than the preset threshold, the process goes to step S330.
It should be noted that the foregoing example is only used for illustrating the present embodiment, and should not be construed as limiting the value range of the preset threshold in the present embodiment, and the preset threshold may also be set to other values according to actual needs.
S320: when the signal-to-noise ratio exceeds a preset threshold value, taking the gas absorption signal as a credible gas absorption signal; that is, if the signal-to-noise ratio exceeds a set threshold, the quality of the current spectral data is considered to be high, the absorption signal is credible, and the concentration value can be calculated according to the absorption signal;
s330: and when the signal-to-noise ratio does not exceed a preset threshold value, discarding the gas absorption signal. That is, if the signal-to-noise ratio does not exceed the set threshold, it is determined that the quality of the current spectral data is poor, the absorption signal is not reliable, and the gas concentration value cannot be calculated according to the current absorption signal, so that the current data is discarded.
In particular, the spectral waveform of the gas absorption signal is obtained in one embodiment based on tunable semiconductor laser absorption spectroscopy (TDLAS)).
TDLAS is a method for detecting a given gas to be measured by using the wavelength tuning characteristic of a semiconductor laser, thereby obtaining information on the concentration of the gas to be measured, and the like. The TDLAS has the advantages of high measurement precision, quick response and non-contact measurement. Currently, TDLAS-based gas detection is mainly performed by a wavelength scanning direct absorption method and a wavelength modulation absorption method (harmonic method). The tunable semiconductor laser has the advantage that the output wavelength of the tunable semiconductor laser can be adjusted within a certain range, and can be used for simultaneously detecting various gases.
Fig. 6 is a schematic diagram showing a relationship between detected light intensity and fitted light intensity provided by the embodiment of the present invention, where as shown in fig. 6, the detected light intensity is shown by a solid line in the diagram, and the fitted light intensity is shown by a dotted line in the diagram (i.e., light intensity not absorbed by gas). In one embodiment, the fitting light intensity is subtracted from the detected light intensity by using a wavelength scanning direct absorption method based on TDLAS to obtain a gas absorption signal, and then the absorbance (the absorbance curve is shown in FIG. 7) is obtained according to the Beer-Lambert law, so that the target gas concentration is inverted.
The Beer-Lambert law describes the relationship between the intensity of light absorbed by a substance at a certain wavelength and the concentration of a light-absorbing substance and the transmission distance of light in the light-absorbing substance, and indicates that when a light beam with a frequency v passes through the light-absorbing substance, the light intensity of the light beam passing through the gas to be measured changes as follows:
I(v)＝I0(v)exp[-σ(v)CL]＝I0(v)exp[-A(v)]
wherein, I (v) -the transmitted light intensity of the light beam passing through the measured gas;
I0(v) -an incident light intensity;
σ (v) -measured gas molecule absorption cross section;
c-concentration of the gas to be detected;
an L-optical path;
a (v) -absorbance;
alternatively, the gas absorption signal may also be obtained in one embodiment using wavelength modulated absorption based on TDLAS (harmonic method). The TDLAS is combined with the Wavelength Modulation Spectrum (WMS) to measure the gas concentration, and the method has the advantages of high sensitivity, good selectivity, long-term stability and the like.
It should be noted that, for the sake of simplicity, each of the above-mentioned method embodiments is described as a series of steps, but those skilled in the art should understand that the present invention is not limited by the described sequence of steps, because some steps can be performed in other sequences or simultaneously according to the present invention. Further, the above embodiments may be arbitrarily combined to obtain other embodiments.
Based on the same idea as the method for improving the concentration detection accuracy of the laser telemeter in the above embodiment, the present invention also provides a system for improving the concentration detection accuracy of the laser telemeter, which can be used to execute the above method for improving the concentration detection accuracy of the laser telemeter. For ease of illustration, the schematic structural diagram of the embodiment of the system for improving the accuracy of concentration detection of a laser telemeter only shows the parts related to the embodiment of the present invention, and those skilled in the art will appreciate that the illustrated structure does not constitute a limitation of the system, and may include more or less components than those illustrated, or combine some components, or arrange different components.
Fig. 8 is a block diagram of a system for improving the accuracy of detecting the concentration of a laser telemeter according to an embodiment of the present invention, and referring to fig. 8, the system for improving the accuracy of detecting the concentration of a laser telemeter according to the embodiment includes an obtaining module 100, a calculating module 200, a confidence determining module 300, and a selecting module 400. It will be appreciated that the modules referred to above are referred to as computer programs or program segments for performing one or more particular functions, and that the distinction of modules does not imply that actual program code must also be separated. The modules are detailed as follows:
an obtaining module 100, configured to obtain a spectral waveform of a gas absorption signal;
the calculation module 200 is used for obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
the credibility judgment module 300 is used for judging whether the gas absorption signal is credible according to the signal-to-noise ratio and generating a judgment result;
and the selecting module 400 is used for calculating the gas concentration value by using the credible gas absorption signal based on the judgment result.
Further, the calculation module 200 includes a division module and a signal-to-noise ratio calculation module, and the functions of each sub-module are described as follows:
the dividing module is used for dividing the spectrum waveform of the gas absorption signal into a non-absorption area and an absorption area with an absorption peak;
and the signal-to-noise ratio calculation module is used for calculating the amplitude of the absorption peak signal in the absorption region, calculating the amplitude of background noise in the non-absorption region and calculating the signal-to-noise ratio of the gas absorption signal according to the amplitude of the absorption peak signal and the amplitude of the background noise.
Referring to fig. 3, the white area is the absorption area with absorption peak, and the calculated signal amplitude of the absorption peak is 3 × 10-4(ii) a The gray background part in the figure is a non-gas absorption area, and the calculated amplitude of the background noise is 2 multiplied by 10-4(ii) a The signal-to-noise ratio of the gas absorption signal is the absorption peak signal amplitude/background noise amplitude.
It should be noted that fig. 3 shows only one example of calculation with respect to actual measurement results, and in practical applications, the absorption peak signal amplitude, the background noise amplitude, and the signal-to-noise ratio may be affected by various factors such as the kind of the gas to be measured, the temperature, and the environment. The magnitudes of the absorption peak signal amplitude, the background noise amplitude, and the signal-to-noise ratio may be other values besides the case shown in fig. 3, which is not limited in this embodiment.
Specifically, the dividing module comprises a reference point determining module, a boundary point determining module and a range determining module, and the functions of the sub-modules are described as follows:
the reference point determining module is used for determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point;
the boundary point determining module is used for determining the positions of a first boundary point, a second boundary point, a third boundary point and a fourth boundary point according to the position of a reference point and preset conditions, wherein the first boundary point, the second boundary point, the reference point, the third boundary point and the fourth boundary point are sequentially arranged along the direction of a transverse axis of the spectrum waveform;
a range determination module for determining an absorption region range (white region in fig. 3) and a non-absorption region range (gray region in fig. 3) on the spectral waveform according to the first limit point, the second limit point, the third limit point and the fourth limit point; the sampling time of any sampling point in the range of the absorption area is later than that of the second limit point and earlier than that of the third limit point; the sampling time of any sampling point in the non-absorption area range is later than the sampling time of the first limit point and is earlier than the sampling time of the second limit point, or is later than the sampling time of the third limit point and is earlier than the sampling time of the fourth limit point.
Specifically, the trusted judgment module 300 includes a signal-to-noise ratio judgment module and a result generation module, and the function of each sub-module is described as follows:
the signal-to-noise ratio judging module is used for judging whether the signal-to-noise ratio exceeds a preset threshold value; comparing the calculated signal-to-noise ratio with a set threshold, judging the reliability of the signal according to the comparison result, and determining whether the absorption peak signal can be used for calculating the gas concentration;
in one embodiment, the preset threshold is 2, the SNR calculated in step S240 is 1.5, and is compared with the preset threshold 2, the reliability of the signal is determined according to the comparison result, and it is determined whether the absorption peak signal can be used for gas concentration calculation; and the steering result generating module is used for generating a steering result at the moment when the calculated signal-to-noise ratio SNR is smaller than a preset threshold value.
It should be noted that the foregoing example is only used for illustrating the present embodiment, and should not be construed as limiting the value range of the preset threshold in the present embodiment, and the preset threshold may also be set to other values according to actual needs.
The result generation module is used for taking the gas absorption signal as a credible gas absorption signal when the signal-to-noise ratio exceeds a preset threshold; that is, if the signal-to-noise ratio exceeds a set threshold, the quality of the current spectral data is considered to be high, the absorption signal is credible, and the concentration value can be calculated according to the absorption signal;
the result generation module is also used for abandoning the gas absorption signal when the signal-to-noise ratio does not exceed a preset threshold value. That is, if the signal-to-noise ratio does not exceed the set threshold, it is determined that the quality of the current spectral data is poor, the absorption signal is not reliable, and the gas concentration value cannot be calculated according to the current absorption signal, so that the current data is discarded.
Further, the obtaining module 100 includes a first obtaining module or a second obtaining module, and functions of the sub-modules are described as follows:
the device comprises a first acquisition module, a second acquisition module and a third acquisition module, wherein the first acquisition module is used for acquiring the spectral waveform of a gas absorption signal by using a TDLAS-based wavelength scanning direct absorption method; and the second acquisition module is used for acquiring the spectrum waveform of the gas absorption signal by using a TDLAS-based wavelength modulation absorption method. The contents of the wavelength scanning direct absorption method and the wavelength modulation absorption method based on the TDLAS may refer to the contents described in the above embodiments, and are not repeated herein.
In this embodiment, the spectral waveform of the gas absorption signal is divided into an absorption region and a non-absorption region according to the reference point position corresponding to the absorption peak and the preset condition, a signal-to-noise ratio for evaluating the signal quality is obtained by analyzing the signal amplitude of the absorption region and the noise amplitude of the non-absorption region, a reliable gas absorption signal is selected according to the signal quality evaluation result to calculate the concentration value, and unreliable data is discarded. The invention can avoid the false alarm generated by the low signal-to-noise ratio of the signal of the laser telemeter and improve the accuracy of concentration detection.
In the foregoing embodiments, the descriptions of the embodiments have respective emphasis, and reference may be made to related descriptions of other embodiments for parts that are not described in detail in a certain embodiment.
Those of skill in the art will further appreciate that the various illustrative logical blocks, units, and steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate the interchangeability of hardware and software, various illustrative components, elements, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design requirements of the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments.
It should be noted that the above-mentioned embodiments are only some specific embodiments of the present invention, and should not be construed as limiting the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A gas concentration detection method of a laser telemeter is characterized by comprising the following steps:
acquiring a spectral waveform of a gas absorption signal, wherein the gas absorption signal is obtained by deducting fitting light intensity from detected light intensity by using a wavelength scanning direct absorption method based on TDLAS; the fitting light intensity is light intensity which is not absorbed by gas;
obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
judging whether the gas absorption signal is credible or not according to the signal-to-noise ratio and generating a judgment result;
using the credible gas absorption signal to calculate a gas concentration value based on the judgment result;
the obtaining of the signal-to-noise ratio of the gas absorption signal according to the spectral waveform of the gas absorption signal includes:
dividing the spectrum waveform of the gas absorption signal into a non-absorption region and an absorption region with an absorption peak according to the signal amplitude variation amplitude of the spectrum waveform;
calculating the signal amplitude of the absorption peak in the absorption region;
calculating the background noise amplitude in the non-absorption region;
calculating the signal-to-noise ratio of the gas absorption signal according to the absorption peak signal amplitude and the background noise amplitude, wherein the signal-to-noise ratio of the gas absorption signal = the absorption peak signal amplitude/the background noise amplitude;
the method for dividing the spectrum waveform of the gas absorption signal into a non-absorption region and an absorption region with an absorption peak according to the signal amplitude variation amplitude of the spectrum waveform comprises the following steps:
determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point; wherein the wavelength corresponding to the gas absorption peak is determined;
determining positions of a first limit point, a second limit point, a third limit point and a fourth limit point according to the position of the reference point and the signal amplitude variation amplitude of the spectrum waveform, wherein the first limit point, the second limit point, the reference point, the third limit point and the fourth limit point are sequentially arranged along the direction of a transverse axis of the spectrum waveform;
determining an absorption region range and a non-absorption region range on the spectral waveform according to the first limit point, the second limit point, the third limit point and the fourth limit point; the sampling time of any sampling point in the absorption area range is later than that of the second limit point and is earlier than that of the third limit point, and the sampling time of any sampling point in the non-absorption area range is later than that of the first limit point and is earlier than that of the second limit point, or is later than that of the third limit point and is earlier than that of the fourth limit point.
2. The method of claim 1, wherein said determining whether the gas absorption signal is authentic based on the signal-to-noise ratio and generating a determination comprises:
judging whether the signal-to-noise ratio exceeds a preset threshold value;
when the signal-to-noise ratio exceeds a preset threshold value, taking the gas absorption signal as the credible gas absorption signal;
and when the signal-to-noise ratio does not exceed a preset threshold value, discarding the gas absorption signal.
3. A gas concentration detection system of a laser telemeter, comprising:
the device comprises an acquisition module, a detection module and a control module, wherein the acquisition module is used for acquiring the spectral waveform of a gas absorption signal, and the gas absorption signal is obtained by deducting fitting light intensity from detected light intensity by using a wavelength scanning direct absorption method based on TDLAS; the fitting light intensity is light intensity which is not absorbed by gas;
the calculation module is used for obtaining the signal-to-noise ratio of the gas absorption signal according to the spectrum waveform of the gas absorption signal;
the credibility judgment module is used for judging whether the gas absorption signal is credible according to the signal-to-noise ratio and generating a judgment result;
the selection module is used for using the credible gas absorption signal to calculate a gas concentration value based on the judgment result;
the calculation module comprises:
the dividing module is used for dividing the spectrum waveform of the gas absorption signal into a non-absorption area and an absorption area with an absorption peak according to the signal amplitude variation amplitude of the spectrum waveform;
the signal-to-noise ratio calculation module is used for calculating the amplitude of an absorption peak signal in the absorption region, calculating the amplitude of background noise in the non-absorption region and calculating the signal-to-noise ratio of the gas absorption signal according to the amplitude of the absorption peak signal and the amplitude of the background noise; the signal-to-noise ratio of the gas absorption signal = absorption peak signal amplitude/background noise amplitude; the dividing module includes:
the reference point determining module is used for determining an absorption peak on a spectrum waveform of the gas absorption signal, and taking a sampling point corresponding to the absorption peak as a reference point; wherein the wavelength corresponding to the gas absorption peak is determined;
a limit point determining module, configured to determine positions of a first limit point, a second limit point, a third limit point, and a fourth limit point according to a position of the reference point and a signal amplitude variation amplitude of the spectral waveform, where the first limit point, the second limit point, the reference point, the third limit point, and the fourth limit point are sequentially arranged along a horizontal axis direction of the spectral waveform;
a range determination module to determine an absorption region range and a non-absorption region range on the spectral waveform according to the first, second, third, and fourth limit points; the sampling time of any sampling point in the range of the absorption area is later than that of the second limit point and earlier than that of the third limit point; the sampling time of any sampling point in the non-absorption area range is later than the sampling time of the first limit point and is earlier than the sampling time of the second limit point, or is later than the sampling time of the third limit point and is earlier than the sampling time of the fourth limit point.
4. The system of claim 3, wherein the trusted judgment module comprises:
the signal-to-noise ratio judging module is used for judging whether the signal-to-noise ratio exceeds a preset threshold value;
a result generation module, configured to take the gas absorption signal as the trusted gas absorption signal when the signal-to-noise ratio exceeds a preset threshold;
and when the signal-to-noise ratio does not exceed a preset threshold value, discarding the gas absorption signal.
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