CN108061722B - Detection device and detection method for carbon monoxide concentration - Google Patents
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- 238000001514 detection method Methods 0.000 title claims abstract description 84
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Abstract
The invention discloses a device and a method for detecting carbon monoxide concentration.A first beam splitter in the detection device divides a light beam emitted by a light source into a calibration light beam and a detection light beam; the calibration light beam irradiates the photoelectric detector after passing through the collimator and the calibration absorption cell to obtain a calibration electric signal; the second beam splitter splits the detection beam into a reference beam and a measurement beam; the reference beam irradiates a photoelectric detector after passing through a collimator to obtain a reference electric signal; the measuring light beam is emitted and output from the center of the Fresnel lens after passing through the collimator, and irradiates a reflection end after passing through a region to be measured, and the reflection end reflects the light beam to the photoelectric detector in the original path to obtain a measuring electric signal; the differential amplifier carries out differential operation on the reference electric signal and the measurement electric signal to obtain a differential signal; and the processor determines the concentration of carbon monoxide in the area to be detected according to the calibration electrical signal, the reference electrical signal and the differential signal. The detection device and the detection method provided by the invention can improve the detection precision of the laser spectrum measurement of the carbon monoxide concentration in the open area.
Description
Technical Field
The invention relates to the field of laser online detection, in particular to a detection device and a detection method for carbon monoxide concentration.
Background
CO is a common flammable, explosive and toxic process gas in the chemical industry, the metallurgical industry and other industries, and the environmental CO concentration monitoring technology can provide a reliable basis for gas leakage safety early warning of hazardous chemical areas. The optical detection method has the outstanding advantages of non-contact measurement, high sensitivity, long service life and the like, can realize the complete coverage of regional safety monitoring by combining with a long optical path technology, and is an important direction for the development of the current industrial safety monitoring technology.
The infrared semiconductor laser spectrum detection technology is based on the fingerprint absorption characteristic of gas molecules to infrared spectrum, and realizes qualitative and quantitative detection of gas by utilizing the characteristic spectrum absorption of target gas molecules. In the field of regional safety monitoring, the laser technology has the characteristic of high optical power density, so that continuous gas leakage safety monitoring in a kilometer range can be realized.
The direct absorption spectrum technology and the balance detection technology are the main detection methods of the existing infrared laser spectrum detection method. The direct absorption spectrum technology is to directly detect through transmitted light intensity and realize direct correction of light intensity change by utilizing background light intensity fitting and normalization processing, but in general, gas absorption is relatively weak, and a direct absorption spectrum shows a small change on a strong background, so that the signal-to-noise ratio and the sensitivity of a measurement signal are low, and the detection precision of gas concentration is reduced. The balance detection technology is a high-sensitivity detection technology based on double-light-path detection, and achieves the purpose of effectively suppressing background and common-mode noise by utilizing differential cancellation processing of non-absorption reference light path signals and external detection light path signals. However, the automatic balance detection technology cannot acquire a light intensity signal, so that the normalization processing of an absorption signal and the light intensity is difficult to complete, and the detection precision of the gas concentration is reduced. Especially when the measuring environment is an open area, the light intensity signal has large fluctuation due to environmental factors such as dust, fog and haze in the environment, so that the detection precision of the concentration of carbon monoxide can be further reduced.
Therefore, how to improve the detection accuracy of the carbon monoxide concentration in the open area becomes a technical problem that needs to be solved by those skilled in the art.
Disclosure of Invention
The invention aims to provide a device and a method for detecting carbon monoxide concentration, which aim to improve the detection precision of the carbon monoxide concentration in an open area.
In order to achieve the purpose, the invention provides the following scheme:
a detection device for carbon monoxide concentration takes a laser as a detection light source, and the laser emits a near infrared light beam with the wavelength periodically and continuously scanned in a set wavelength range; a first beam splitter splits the near-infrared beam into a calibration beam and a detection beam;
the calibration light beam is collimated by a calibration light collimator to obtain a collimated calibration light beam, the collimated calibration light beam irradiates a calibration photoelectric detector for photoelectric conversion after passing through a calibration absorption cell to obtain a calibration electric signal, the calibration photoelectric detector sends the calibration electric signal to a processor, wherein carbon monoxide gas with known concentration under standard atmospheric pressure is sealed in the calibration absorption cell;
a second beam splitter splits the detection beam into a reference beam and a measurement beam;
the reference light beam is collimated by a reference light collimator and then is irradiated onto a reference light photoelectric detector for photoelectric conversion to obtain reference electric signals, and the reference electric signals are respectively sent to a differential amplification circuit and the processor by the reference light photoelectric detector;
the measuring light beam is collimated by a measuring light collimator and then emitted and output through the center of a Fresnel lens, the light beam emitted and output by the Fresnel lens irradiates a reflection end after passing through a region to be measured, wherein the Fresnel lens and the reflection end are correspondingly arranged at two ends of the region to be measured, the reflection end reflects a light beam original path to a measuring photoelectric detector to obtain a measuring electric signal, and the measuring photoelectric detector sends the measuring electric signal to the differential amplifier;
the differential amplifier carries out differential operation on the reference electric signal and the measurement electric signal to obtain a differential signal, and sends the differential signal to the processor; and the processor determines the concentration of the carbon monoxide in the area to be detected according to the calibration electrical signal, the reference electrical signal and the differential signal.
Optionally, the detection device further includes a display connected to the processor, and configured to display the concentration of carbon monoxide in the region to be detected.
Optionally, detection device still includes laser controller and signal generator, laser controller with the laser instrument is connected, signal generator with the laser controller is connected, signal generator is used for producing the sawtooth wave signal, the laser controller will the sawtooth wave signal with the drive current that the laser controller predetermines the direct current stack that generates the laser instrument, the laser instrument basis the laser controller predetermine the temperature with the drive current emission wavelength is at the near infrared light beam of the periodic continuous scanning of settlement wavelength range.
Optionally, the signal generator is connected to the processor, and the signal generator is further configured to generate a rectangular wave signal synchronized with the sawtooth wave signal, and the processor synchronously acquires the calibration electrical signal, the reference electrical signal, and the differential signal according to the rectangular wave signal.
A method for detecting a concentration of carbon monoxide, the method being used for the detection apparatus, the method comprising:
acquiring a calibration electrical signal, a reference electrical signal and a differential signal;
respectively carrying out discretization data acquisition on the calibration electrical signal, the reference electrical signal and the differential signal to obtain a discretization calibration signal corresponding to the calibration electrical signal, a discretization reference signal corresponding to the reference electrical signal and a discretization differential signal corresponding to the differential signal;
fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete differential signal to obtain a background signal of the differential signal;
fitting the discrete reference signal to obtain a background signal of the reference signal;
determining a background signal of a measurement signal according to a background signal of the differential signal, a gain of a differential amplifier and a background signal of the reference signal;
determining a discrete absorption signal according to a background signal of the differential signal, the discrete differential signal and a gain of the differential amplifier;
determining an integral absorption line strength of the measurement signal from the discrete absorption signal and a background signal of the measurement signal;
fitting data of a background spectrum area without carbon monoxide absorption in the spectrogram of the discrete calibration signal to obtain a background signal of the calibration signal;
carrying out normalization processing on a background signal of the calibration signal and the discrete calibration signal to obtain a normalized calibration signal;
fitting the normalized calibration signal to obtain the integral absorption line intensity of the calibration signal;
and determining the concentration of the carbon monoxide in the area to be measured according to the integral absorption line intensity of the measurement signal, the integral absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement light path and the concentration of the carbon monoxide gas in the calibration absorption cell.
Optionally, before fitting the data of the background spectral region without carbon monoxide absorption in the spectrogram of the discrete differential signal, the method further includes:
acquiring a corrected discrete calibration signal, wherein the corrected discrete calibration signal is an average value of the discrete calibration signals of a plurality of periods;
acquiring a corrected discrete reference signal, wherein the corrected discrete reference signal is an average value of the discrete reference signals of a plurality of periods;
acquiring a corrected discrete differential signal, wherein the corrected discrete differential signal is an average value of the discrete differential signals of a plurality of periods.
Optionally, the determining an integrated absorption line strength of the measurement signal according to the discrete absorption signal and a background signal of the measurement signal specifically includes:
determining a normalized absorption signal from the discrete absorption signal and a background signal of the measurement signal;
and fitting the normalized signal by adopting a Lorentz function to obtain the integral absorption line intensity of the measurement signal.
Optionally, the determining the background signal of the measurement signal according to the background signal of the differential signal, the gain of the differential amplifier, and the background signal of the reference signal specifically includes:
according to the formula:
determining a background signal of the measurement signal, wherein sb (n) represents the background signal of the measurement signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and rb (n) represents the background signal of the reference signal.
Optionally, the determining a discrete absorption signal according to a background signal of the differential signal, the discrete differential signal, and a gain of the differential amplifier specifically includes:
according to the formula:
determining a discrete absorption signal, wherein A (n) represents the discrete absorption signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and M (n) represents the discrete differential signal.
Optionally, the determining the concentration of carbon monoxide in the region to be measured according to the integrated absorption line intensity of the measurement signal, the integrated absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement optical path, and the concentration of carbon monoxide gas in the calibration absorption cell specifically includes:
according to the formula:
determining the concentration of carbon monoxide in the region to be measured, wherein C represents the average concentration of carbon monoxide in the region to be measured, AS represents the integrated absorption line intensity of the measurement signal, AJ represents the integrated absorption line intensity of the calibration signal, and L0Indicating the length of the calibration cell, L indicating the measuring pathLength, C0Indicating the concentration of carbon monoxide gas in the calibration cell.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the near-infrared light beam emitted by the laser is divided into the calibration light beam and the detection light beam, wherein the detection light beam is divided into the reference light beam and the measurement light beam, and common-mode components of signals of the reference light path and the measurement light path are offset by utilizing signal cancellation processing technologies in the reference light path and the measurement light path, so that not only can additional noise in the transmission process of the laser noise and the light beam be suppressed, the signal-to-noise ratio of a differential signal be improved, but also the direct-current component of the measurement signal can be reduced, and the detection precision of the concentration of the carbon monoxide is improved. Meanwhile, the invention obtains the light intensity change information of the measuring light path by constructing the background signals of the differential signal and the reference signal, eliminates the influence of light intensity fluctuation caused by the light beam transmission characteristic change of the measuring light path on the detection precision by utilizing normalization processing, and further ensures the detection precision of the carbon monoxide concentration in the open area.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a detection apparatus provided in embodiment 1 of the present invention;
fig. 2 is a flowchart of a detection method provided in embodiment 2 of the present invention.
Detailed Description
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 only a part of the embodiments of the present invention, and not all of the embodiments. 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.
The invention aims to provide a device and a method for detecting carbon monoxide concentration, which aim to improve the detection precision of the carbon monoxide concentration in an open area.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1:
as shown in fig. 1, a carbon monoxide concentration detection device, which uses a laser 1 as a detection light source, wherein the laser 1 emits a near infrared light beam with a wavelength periodically and continuously scanned in a set wavelength range; a first beam splitter 2 splits the near infrared beam into a calibration beam and a detection beam;
the calibration light beam is collimated by a calibration light collimator 3 to obtain a collimated calibration light beam, the collimated calibration light beam irradiates a calibration photoelectric detector 5 through a calibration absorption cell 4 to perform photoelectric conversion, so as to obtain a calibration electric signal, the calibration photoelectric detector 5 sends the calibration electric signal to a processor 6, wherein carbon monoxide gas with known concentration under standard atmospheric pressure is sealed in the calibration absorption cell 4;
a second beam splitter 7 splits the detection beam into a reference beam and a measuring beam;
the reference light beam is collimated by a reference light collimator 8 and then irradiates a reference light photoelectric detector 9 for photoelectric conversion to obtain a reference electric signal, and the reference electric signal is respectively sent to a differential amplification circuit 10 and the processor 6 by the reference light photoelectric detector 9;
the measuring light beam is collimated by a measuring light collimator 11 and then emitted and output through the center of a Fresnel lens 12, the light beam emitted and output by the Fresnel lens 12 passes through a region to be measured and then irradiates a reflection end 13, wherein the Fresnel lens 12 and the reflection end 13 are correspondingly arranged at two ends of the region to be measured, the reflection end 13 reflects a light beam original circuit onto a measuring photoelectric detector 14 to obtain a measuring electric signal, and the measuring photoelectric detector 14 sends the measuring electric signal to the differential amplifier 10;
the differential amplifier 10 performs differential operation on the reference electrical signal and the measurement electrical signal to obtain a differential signal, and sends the differential signal to the processor 6; the processor 6 determines the concentration of carbon monoxide in the region to be measured according to the calibration electrical signal, the reference electrical signal and the differential signal.
Preferably, in this embodiment, the detection apparatus further includes a display 15 connected to the processor 6, and configured to display the concentration of carbon monoxide in the region to be detected. The detection device further comprises a laser controller 16 and a signal generator 17, the laser controller 16 is connected with the laser 1, the signal generator 17 is connected with the laser controller 16, the signal generator 17 is used for generating sawtooth wave signals with adjustable amplitude, the laser controller 16 is used for superposing the sawtooth wave signals and direct current generated by the laser controller 16 in a preset mode to generate driving current of the laser 1, and the laser 1 is used for emitting near-infrared light beams with periodic continuous scanning wavelength in a set wavelength range according to the preset temperature of the laser controller 16. Wherein, the wavelength range is set as (1566.6396nm-a, 1566.6396nm + a), a is constant, and the unit is nm. The wavelength range can be correspondingly adjusted by adjusting the amplitude of the sawtooth wave signal. The signal generator 17 is connected with the processor 6, the signal generator 17 is further configured to generate a rectangular wave signal synchronized with the sawtooth wave signal, and the processor 6 synchronously acquires the calibration electrical signal, the reference electrical signal and the differential signal according to the rectangular wave signal.
As shown in fig. 1, in the present embodiment, a near infrared distributed feedback semiconductor laser (DFB) that outputs a near infrared signal with a center wavelength of about 1.57 μm is used as a detection light source of CO gas, a laser controller 16 tunes the center wavelength of a light beam output from the laser 1 to the middle of a CO absorption spectrum line by controlling the temperature of a semiconductor and the driving current of the laser 1, and a signal generation circuit 17 generates two signals, one is a 100Hz sawtooth wave signal, and the other is a rectangular wave signal synchronized with the sawtooth wave signal. The signal generating circuit 17 sends the rectangular wave signal to the processor 6 as a trigger signal for the processor 6 to perform signal acquisition, so as to ensure the synchronization of the scanning signal emitted by the laser and the periodic signal acquired by the processor in the time domain.
As shown in fig. 1, the present embodiment is provided with a main cabinet 18, wherein the laser 1, the first beam splitter 2, the calibration light collimator 3, the calibration absorption cell 4, the calibration photo-detector 5, the processor 6, the differential amplification circuit 10, the display 15, the laser controller 16, and the signal generator 17 are all disposed in the main cabinet 18 to constitute an instrument main body. The present embodiment is further provided with an emitting end housing 19, wherein the second beam splitter 7, the reference light collimator 8, the reference light photodetector 9, the measuring light collimator 11, the fresnel lens 12, and the measuring light photodetector 14 are all disposed in the emitting end housing 19 to form an emitting end, wherein a window is disposed on the emitting end housing 19, the window is located on an outgoing light path of the emitting end, and a quartz window 20 is disposed on the window.
The light beam emitted by the laser 1 is coupled and output by the optical fiber, the first beam splitter 2 is a 1 x 2 optical fiber beam splitter, the first beam splitter 2 splits the light beam into two beams according to the ratio of 1:9, the weaker light beam is used as a calibration light beam, and the stronger light beam is used as a detection light beam. In this embodiment, a first low-pass filtering and amplifying circuit 27 is disposed between the calibration photo-detector 5 and the processor 6, the calibration photo-detector 5 sends the calibration electrical signal to the first low-pass filtering and amplifying circuit 27 for filtering and amplifying as a calibration signal, and the processor 6 performs data acquisition and data processing on the calibration signal.
In this embodiment, an input fiber coupler 23 is further provided on the transmitting end housing 19. The detection light beam is connected with an external light path through an output optical fiber coupler 21, transmitted to the transmitting end through a single mode optical fiber 22, and connected with an optical system in the transmitting end. The light beam coupled into the transmitting end is split by a second beam splitter 7 into 2: 8, and the second beam splitter 7 is a 1 × 2 fiber beam splitter, wherein the weaker beam is used as a reference beam and the stronger beam is used as a measuring beam. The reference beam is collimated by a reference light collimator 8 and then irradiated onto a reference light photoelectric detector 9 for photoelectric conversion to obtain a calibration electric signal, the reference light photoelectric detector 9 connects the reference electric signal with a host through a first signal transmission cable interface 24, the signal is transmitted back to the host through a multi-core signal transmission cable 25 and is transmitted to a second low-pass filtering and amplifying circuit 28 through a second signal transmission cable interface 26 on a host case 18, the output signal after filtering and amplifying is divided into two paths, one path is sent to a processor 6 for analog-to-digital conversion and digital signal acquisition, and the other path is sent to a differential amplifying circuit 10. The measuring light beam is collimated by a measuring light collimator 11 and emitted and output from the center of a Fresnel lens 12 at an emitting end, the light beam returns according to an original light path after being reflected by a reflecting end 13 arranged at the other end of the light path after passing through a detection area, a reflected light beam is collected by the Fresnel lens 12 and focused on a photosensitive surface of a measuring light photoelectric detector 14, wherein the measuring light photoelectric detector 14 is an infrared photoelectric detector, the light beam is subjected to photoelectric conversion by the infrared photoelectric detector, an output signal is connected with a host through a first signal transmission cable interface 24, the signal is transmitted back to the host through a multi-core signal transmission cable 25, the signal is transmitted to a third low-pass filtering and amplifying circuit 29 through a second signal transmission cable interface 26, and the filtered and amplified output signal is sent to a differential amplifying circuit 10 as a measuring signal. The differential amplification circuit 10 performs differential operation on the received signals, outputs signals serving as differential signals to the processor 6 for analog-to-digital conversion and digital signal acquisition, and the processor 6 performs data processing on the synchronously acquired reference signals, calibration signals and differential signals to calculate and obtain the average CO gas concentration in the detection optical path, and displays the average CO gas concentration on the liquid crystal display 15, wherein the display 15 in the embodiment is a liquid crystal display. As shown in fig. 1, an air outlet provided with a fan 33 is formed on one side wall of the main cabinet 18, and the heat in the main cabinet 18 is dissipated by the fan 33. A dc stabilized power supply 32 is further disposed in the main chassis 18, the dc stabilized power supply 32 is used for supplying electric energy to each electric device, and the dc stabilized power supply 32 is connected to the main power socket 30 and is connected to an external power supply through the main power socket 30. A main power switch 31 connected to the dc regulated power supply 32 is further provided on a side wall of the main cabinet 18, and the detection device is turned on or off by the main power switch 31.
In the embodiment, a near-infrared semiconductor laser is used as a detection light source, and the CO gas concentration in a hazardous chemical region is subjected to high-sensitivity and high-resolution online detection by detecting an isolated characteristic absorption spectral line of the CO gas near a near-infrared spectral region of 1.56 microns and combining with a long-range optical system.
Example 2:
as shown in fig. 2, a method for detecting a carbon monoxide concentration, which is used in the detection apparatus described in embodiment 1, includes:
step 201: a calibration electrical signal, a reference electrical signal, and a differential signal are acquired.
Step 202: and respectively carrying out discretization data acquisition on the calibration electric signal, the reference electric signal and the differential signal to obtain a discretization calibration signal corresponding to the calibration electric signal, a discretization reference signal corresponding to the reference electric signal and a discretization differential signal corresponding to the differential signal.
Step 203: and fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete differential signal to obtain the background signal of the differential signal.
The reference signal does not contain CO gas absorption features and appears as a sloping background; when the measuring light passes through the detection area, if CO gas exists in the measuring light path, absorption is generated in the scanning period of the measuring light, and a measuring signal S0Contains absorption information, which is represented as a characteristic absorption on a slope background. By adjusting the gains of the first low-pass filtering amplifier circuit 27 and the second low-pass filtering amplifier circuit 28, the difference signal output by the difference amplifier circuit 10 is completely cancelled at the part without gas absorption under ideal conditions, but in actual working conditions, due to the change of the measured light path extinction, the ideal cancellation effect cannot be achieved, a certain background is shown, and the light path extinction characteristic can be obtained by utilizing the background characteristic. Defining the background signal of the discrete difference signal M (n) as delta (n), and fitting blank regions without CO spectrum absorption in the data sequence of the discrete difference signal M (n)The fitting function is obtained as:
δ(n)＝a0+a1n+a2n2
wherein: a is0、a1、a2Representing the fitting parameters of the differential signal and n representing the discrete point data number of the signal time sequence sampling.
Step 204: and fitting the discrete reference signal to obtain a background signal of the reference signal.
The reference signal does not contain CO gas absorption characteristics and is represented by a slope background, the background of the reference signal can be directly obtained by fitting a data sequence of the reference signal, and the fitting function is as follows:
RB(n)＝b0+b1n+b2n2
wherein: b0、b1、b2Representing the fitting parameters of the reference signal.
Step 205: and determining the background signal of the measuring signal according to the background signal of the differential signal, the gain of the differential amplifier and the background signal of the reference signal.
Step 206: and determining a discrete absorption signal according to the background signal of the differential signal, the discrete differential signal and the gain of the differential amplifier.
Step 207: and determining the integral absorption line intensity of the measuring signal according to the discrete absorption signal and the background signal of the measuring signal.
Step 208: and fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete calibration signal to obtain the background signal of the calibration signal.
Step 209: and carrying out normalization processing on the background signal of the calibration signal and the discrete calibration signal to obtain a normalized calibration signal.
Step 210: and fitting the normalized calibration signal to obtain the integral absorption line intensity of the calibration signal.
The calibration signal is a calibration optical path direct absorption spectrum signal, and similar to the calculation method for measuring the optical path integral absorption line intensity, a background signal JB (n) of the calibration signal is obtained through background fitting of the calibration signal, the background signal is used for carrying out normalization processing on the calibration signal to obtain a normalized calibration signal JC (n), and a Lorentz function is used for fitting the normalized calibration signal JC (n) to obtain the integral absorption line intensity AJ of the calibration signal.
The background signal JB (n) of the calibration signal is also obtained by fitting a data segment without CO gas absorption in the data sequence of the calibration signal J (n), and the fitting formula is as follows:
JB(n)＝c0+c1n+c2n2
wherein: c. C0、c1、c2Are the fitting parameters of the calibration signal.
The normalized calibration signal JC (n) obtained by the normalization processing of the calibration signal has the formula:
the fit equation for the integrated absorption line intensity AJ of the calibration signal is:
wherein: AJ. Gamma's'L、n'0Are fitting parameters.
Step 211: and determining the concentration of the carbon monoxide in the area to be measured according to the integral absorption line intensity of the measurement signal, the integral absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement light path and the concentration of the carbon monoxide gas in the calibration absorption cell.
Preferably, in performing step 203: before fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete differential signal, the method further comprises the following steps:
acquiring a corrected discrete calibration signal, wherein the corrected discrete calibration signal is an average value of the discrete calibration signals of a plurality of periods;
acquiring a corrected discrete reference signal, wherein the corrected discrete reference signal is an average value of the discrete reference signals of a plurality of periods;
acquiring a corrected discrete differential signal, wherein the corrected discrete differential signal is an average value of the discrete differential signals of a plurality of periods.
Specifically, step 207: determining an integral absorption line strength of the measurement signal according to the discrete absorption signal and a background signal of the measurement signal, specifically comprising:
step 2071: determining a normalized absorption signal from the discrete absorption signal and a background signal of the measurement signal.
In order to eliminate the influence of extinction change of the measuring light path on detection, the invention adopts a normalized absorption signal sigma (n) to carry out inverse calculation of gas concentration, and the calculation formula is as follows:
step 2072: and fitting the normalized signal by adopting a Lorentz function to obtain the integral absorption line intensity of the measurement signal.
The normalized absorption signal is represented by a gas molecule absorption line type and can be described by a Lorentzian function under normal pressure, the integral absorption line intensity AS of the measurement signal is defined AS the integral area, and the fitting function relationship is AS follows:
wherein: AS, gammaL、n0Both represent fitting parameters.
Specifically, step 205: determining a background signal of the measurement signal according to the background signal of the differential signal, the gain of the differential amplifier and the background signal of the reference signal, specifically comprising:
according to the formula:
determiningThe background signal of the measurement signal, wherein sb (n) represents the background signal of the measurement signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and rb (n) represents the background signal of the reference signal.
Specifically, step 206: determining a discrete absorption signal according to a background signal of the differential signal, the discrete differential signal and a gain of the differential amplifier, specifically comprising:
according to the formula:
determining a discrete absorption signal, wherein A (n) represents the discrete absorption signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and M (n) represents the discrete differential signal.
Specifically, step 211: determining the concentration of carbon monoxide in the region to be measured according to the integrated absorption line intensity of the measurement signal, the integrated absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement optical path and the concentration of carbon monoxide gas in the calibration absorption cell, and specifically comprises:
according to the formula:
determining the concentration of carbon monoxide in the region to be measured, wherein C represents the average concentration of carbon monoxide in the region to be measured, AS represents the integrated absorption line intensity of the measurement signal, AJ represents the integrated absorption line intensity of the calibration signal, and L0Denotes the length of the calibration cell, L denotes the length of the measuring beam path, C0Indicating the concentration of carbon monoxide gas in the calibration cell.
The detection method provided by this embodiment cancels the common mode components of the signals of the reference optical path and the measurement optical path by using the cancellation processing of the signals of the reference optical path and the measurement optical path, so as to achieve the purpose of suppressing laser noise and additional noise in the transmission process of the light beam, and on the other hand, reduce the direct current component of the detection signal, achieve effective amplification of the absorption signal, and increase the dynamic measurement range of the detection system.
The invention obtains the light intensity change information of the measuring light path by constructing the background signal of the measuring light path, eliminates the influence of light intensity fluctuation caused by the change of the transmission characteristic of the light beam of the measuring light path on the detection by utilizing the normalization processing, and realizes the accurate online detection of the carbon monoxide concentration in the open area by combining with the built-in calibration pool.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. A carbon monoxide concentration detection device is characterized in that: the detection device takes a laser as a detection light source, and the laser emits a near-infrared light beam with the wavelength periodically and continuously scanned in a set wavelength range; a first beam splitter splits the near-infrared beam into a calibration beam and a detection beam;
the calibration light beam is collimated by a calibration light collimator to obtain a collimated calibration light beam, the collimated calibration light beam irradiates a calibration photoelectric detector for photoelectric conversion after passing through a calibration absorption cell to obtain a calibration electric signal, the calibration photoelectric detector sends the calibration electric signal to a processor, wherein carbon monoxide gas with known concentration under standard atmospheric pressure is sealed in the calibration absorption cell;
a second beam splitter splits the detection beam into a reference beam and a measurement beam;
the reference light beam is collimated by a reference light collimator and then is irradiated onto a reference light photoelectric detector for photoelectric conversion to obtain reference electric signals, and the reference electric signals are respectively sent to a differential amplification circuit and the processor by the reference light photoelectric detector;
the measuring light beam is collimated by a measuring light collimator and then emitted and output through the center of a Fresnel lens, the light beam emitted and output by the Fresnel lens irradiates a reflection end after passing through a region to be measured, wherein the Fresnel lens and the reflection end are correspondingly arranged at two ends of the region to be measured, the reflection end reflects a light beam original path to a measuring photoelectric detector to obtain a measuring electric signal, and the measuring photoelectric detector sends the measuring electric signal to a differential amplifier;
the differential amplifier carries out differential operation on the reference electric signal and the measurement electric signal to obtain a differential signal, and sends the differential signal to the processor; the processor determines the concentration of carbon monoxide in the region to be detected according to the calibration electrical signal, the reference electrical signal and the differential signal, and specifically includes:
respectively carrying out discretization data acquisition on the calibration electrical signal, the reference electrical signal and the differential signal to obtain a discretization calibration signal corresponding to the calibration electrical signal, a discretization reference signal corresponding to the reference electrical signal and a discretization differential signal corresponding to the differential signal;
fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete differential signal to obtain a background signal of the differential signal;
fitting the discrete reference signal to obtain a background signal of the reference signal;
determining a background signal of a measurement signal according to a background signal of the differential signal, a gain of a differential amplifier and a background signal of the reference signal;
determining a discrete absorption signal according to a background signal of the differential signal, the discrete differential signal and a gain of the differential amplifier;
determining an integral absorption line strength of the measurement signal from the discrete absorption signal and a background signal of the measurement signal;
fitting data of a background spectrum area without carbon monoxide absorption in the spectrogram of the discrete calibration signal to obtain a background signal of the calibration signal;
carrying out normalization processing on a background signal of the calibration signal and the discrete calibration signal to obtain a normalized calibration signal;
fitting the normalized calibration signal to obtain the integral absorption line intensity of the calibration signal;
and determining the concentration of the carbon monoxide in the area to be measured according to the integral absorption line intensity of the measurement signal, the integral absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement light path and the concentration of the carbon monoxide gas in the calibration absorption cell.
2. The detection device according to claim 1, wherein: the detection device further comprises a display connected with the processor and used for displaying the concentration of the carbon monoxide in the area to be detected.
3. The detection device according to claim 1, wherein: the detection device further comprises a laser controller and a signal generator, the laser controller is connected with the laser, the signal generator is connected with the laser controller, the signal generator is used for generating sawtooth wave signals, the laser controller is used for superposing the sawtooth wave signals and direct current generated by the laser controller in advance to generate driving current of the laser, and the laser is used for emitting near-infrared light beams periodically and continuously scanned within a set wavelength range according to preset temperature of the laser controller and the driving current.
4. The detection device according to claim 1, wherein: the signal generator is connected with the processor and is also used for generating a rectangular wave signal synchronous with the sawtooth wave signal, and the processor synchronously acquires the calibration electric signal, the reference electric signal and the differential signal according to the rectangular wave signal.
5. A detection method of a carbon monoxide concentration, characterized in that the detection method is used for the detection apparatus according to any one of claims 1 to 4, the detection method comprising:
acquiring a calibration electrical signal, a reference electrical signal and a differential signal;
respectively carrying out discretization data acquisition on the calibration electrical signal, the reference electrical signal and the differential signal to obtain a discretization calibration signal corresponding to the calibration electrical signal, a discretization reference signal corresponding to the reference electrical signal and a discretization differential signal corresponding to the differential signal;
fitting data of a background spectrum region without carbon monoxide absorption in the spectrogram of the discrete differential signal to obtain a background signal of the differential signal;
fitting the discrete reference signal to obtain a background signal of the reference signal;
determining a background signal of a measurement signal according to a background signal of the differential signal, a gain of a differential amplifier and a background signal of the reference signal;
determining a discrete absorption signal according to a background signal of the differential signal, the discrete differential signal and a gain of the differential amplifier;
determining an integral absorption line strength of the measurement signal from the discrete absorption signal and a background signal of the measurement signal;
fitting data of a background spectrum area without carbon monoxide absorption in the spectrogram of the discrete calibration signal to obtain a background signal of the calibration signal;
carrying out normalization processing on a background signal of the calibration signal and the discrete calibration signal to obtain a normalized calibration signal;
fitting the normalized calibration signal to obtain the integral absorption line intensity of the calibration signal;
and determining the concentration of the carbon monoxide in the area to be measured according to the integral absorption line intensity of the measurement signal, the integral absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measurement light path and the concentration of the carbon monoxide gas in the calibration absorption cell.
6. The detection method according to claim 5, wherein before fitting the data of the background spectral region without carbon monoxide absorption in the spectrogram of the discrete differential signals, further comprising:
acquiring a corrected discrete calibration signal, wherein the corrected discrete calibration signal is an average value of the discrete calibration signals of a plurality of periods;
acquiring a corrected discrete reference signal, wherein the corrected discrete reference signal is an average value of the discrete reference signals of a plurality of periods;
acquiring a corrected discrete differential signal, wherein the corrected discrete differential signal is an average value of the discrete differential signals of a plurality of periods.
7. The detection method according to claim 5, wherein the determining an integrated absorption line strength of the measurement signal from the discrete absorption signal and a background signal of the measurement signal comprises:
determining a normalized absorption signal from the discrete absorption signal and a background signal of the measurement signal;
and fitting the normalized signal by adopting a Lorentz function to obtain the integral absorption line intensity of the measurement signal.
8. The detection method according to claim 5, wherein determining the background signal of the measurement signal from the background signal of the differential signal, the gain of the differential amplifier and the background signal of the reference signal comprises:
according to the formula:
determining a background signal of the measurement signal, wherein sb (n) represents the background signal of the measurement signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and rb (n) represents the background signal of the reference signal.
9. The detection method according to claim 5, wherein the determining a discrete absorption signal according to a background signal of a differential signal, the discrete differential signal and a gain of a differential amplifier comprises:
according to the formula:
determining a discrete absorption signal, wherein A (n) represents the discrete absorption signal, δ (n) represents the background signal of the differential signal, G represents the gain of the differential amplifier, and M (n) represents the discrete differential signal.
10. The detecting method according to claim 5, wherein the determining the concentration of carbon monoxide in the region to be detected according to the integrated absorption line intensity of the measuring signal, the integrated absorption line intensity of the calibration signal, the length of the calibration absorption cell, the length of the measuring optical path and the concentration of carbon monoxide gas in the calibration absorption cell specifically comprises:
according to the formula:
determining the concentration of carbon monoxide in the region to be measured, wherein C represents the average concentration of carbon monoxide in the region to be measured, AS represents the integrated absorption line intensity of the measurement signal, AJ represents the integrated absorption line intensity of the calibration signal, and L0Denotes the length of the calibration cell, L denotes the length of the measuring beam path, C0Indicating the concentration of carbon monoxide gas in the calibration cell.
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