CN116818712A - Device and method for measuring concentration of various trace gases - Google Patents
Device and method for measuring concentration of various trace gases Download PDFInfo
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- 229910000530 Gallium indium arsenide Inorganic materials 0.000 claims description 3
- OYLGJCQECKOTOL-UHFFFAOYSA-L barium fluoride Chemical compound [F-].[F-].[Ba+2] OYLGJCQECKOTOL-UHFFFAOYSA-L 0.000 claims description 3
- 229910001632 barium fluoride Inorganic materials 0.000 claims description 3
- KXNLCSXBJCPWGL-UHFFFAOYSA-N [Ga].[As].[In] Chemical compound [Ga].[As].[In] KXNLCSXBJCPWGL-UHFFFAOYSA-N 0.000 claims description 2
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Abstract
A plurality of trace gas concentration measurement apparatus comprising: the laser module is suitable for outputting a measuring beam, the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks; a gas chamber; a conversion unit adapted to convert the measuring beam emitted from the gas cell into an electrical signal, the electrical signal being superimposed with first modulation signals of different frequencies; the processing module comprises a phase-locked processing circuit and is configured to perform phase-sensitive detection and narrow-band filtering on the electric signals so as to obtain harmonic signals with a plurality of different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected; a division circuit configured to normalize the second harmonic signal with a first one of the harmonic signals; and the calculating circuit is configured to carry out numerical fitting according to the function relation between the normalized second harmonic signal and the concentration of the gas to be measured to obtain the concentration information of each gas to be measured.
Description
Technical Field
The invention belongs to the technical field of gas detection, and particularly relates to a device and a method for measuring the concentration of various trace gases.
Background
With the development of environmental protection and gas measurement technology, the requirements of many fields on gas measurement instruments are higher and higher, and particularly in the aspect of trace gas detection, higher detection precision is required. The method has urgent application requirements for real-time high-precision monitoring in the control of toxic and harmful gases such as carbon dioxide, ammonia, carbon monoxide, methane, hydrogen chloride and the like generated in petrochemical production processes and industrial and agricultural production processes. How to perform on-line sensing and monitoring on multiple component gases in a space environment becomes an important problem in the fields of meteorological environment and industrial control.
The electrochemical measurement method aiming at the detection of the multi-component gas in the current market has the defects of lower detection precision, slower response time and the like. In view of this, there is a need for improvements in existing detection schemes to address the above-mentioned problems.
Disclosure of Invention
In view of the above, the present invention provides a plurality of trace gas concentration measuring apparatuses and a plurality of trace gas concentration measuring methods, so as to at least partially solve at least one of the above technical problems.
An aspect of the present disclosure provides a plurality of trace gas concentration measurement apparatuses, comprising: the laser module is suitable for outputting a measuring beam, the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks; a gas chamber adapted to contain a plurality of trace amounts of the gas to be measured; a conversion unit adapted to convert the measuring beam emitted from the gas cell into an electrical signal superimposed with the first modulated signal of the different frequency; and a processing module comprising: the phase-locked processing circuit is configured to perform phase-sensitive detection and narrow-band filtering on the electric signals so as to obtain a plurality of harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected; a division circuit configured to normalize a second harmonic signal with a first one of the harmonic signals; and the calculating circuit is configured to carry out numerical fitting according to the normalized function relation between the second harmonic signal and the concentration of the gas to be measured, so as to obtain the concentration information of each gas to be measured.
According to an embodiment of the present disclosure, the laser module includes: a plurality of lasers, each laser adapted to emit an initial beam of light having a wavelength range including an absorption peak of one of the gases under test; a modulating unit, adapted to modulate a plurality of the lasers based on a plurality of second modulation signals with the same frequency to lock a plurality of the absorption peaks, and respectively superimpose first modulation signals with different frequencies on a plurality of the lasers based on a plurality of the locked absorption peaks; and a coupling unit adapted to couple a plurality of initial light beams from a plurality of said lasers into a measuring light beam.
According to an embodiment of the present disclosure, the laser module further includes: and the temperature control unit is suitable for adjusting the temperature inside the lasers so as to control the wavelength range of the initial light beams emitted by the multiple lasers.
According to an embodiment of the disclosure, the first modulation signal comprises a high frequency sinusoidal modulation signal and the second modulation signal comprises a low frequency sawtooth signal, wherein the frequency range of the high frequency sinusoidal modulation signal is 5 kHz-20 kHz, and the frequency range of the low frequency sawtooth signal is 1 Hz-100 Hz.
According to the embodiment of the disclosure, a long-optical-path gas absorption cell cavity is formed in the gas chamber, a light beam inlet and a light beam outlet are respectively arranged at two ends of the gas chamber, and barium fluoride wedge-shaped light windows are respectively arranged at the light beam inlet and the light beam outlet.
According to an embodiment of the disclosure, the measuring beam is incident into the gas chamber at the same angle as the included angle of the beam inlet in the X-axis, Y-axis and Z-axis; preferably, the measuring beam passing through the gas cell exits at the same angle as the included angle of the beam outlet in the X-axis, Y-axis, Z-axis.
According to an embodiment of the disclosure, the conversion unit comprises a photodetector comprising an indium gallium arsenide based planar photodetector.
Another aspect of the present disclosure also provides a plurality of trace gas concentration measurement methods, comprising: generating a measuring beam, wherein the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks; injecting measuring beams into a gas chamber containing a plurality of gases to be measured; converting the measuring beam emitted from the gas cell into an electrical signal, the electrical signal being superimposed with the first modulated signal of different frequency; performing phase-sensitive detection and narrow-band filtering on the electric signals to obtain harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected; normalizing the second harmonic signal by adopting a first harmonic signal in the harmonic signals; and performing numerical fitting according to the normalized function relation between the second harmonic signal and the concentration of the gas to be measured to obtain the concentration information of each gas to be measured.
According to an embodiment of the present disclosure, the step of generating the measuring beam comprises: generating a plurality of initial light beams by using a plurality of lasers respectively, wherein the wavelength range of each initial light beam comprises an absorption peak of one gas to be detected in the gas to be detected; modulating a plurality of lasers based on a plurality of second modulation signals with the same frequency to lock a plurality of absorption peaks, and respectively superposing first modulation signals with different frequencies on the plurality of lasers based on the plurality of locked absorption peaks; and coupling a plurality of initial beams from a plurality of said lasers into a measuring beam.
According to the embodiment of the disclosure, the concentration information of the measured gas to be measured is corrected by using the noise equivalent gas concentration to be measured as a correction factor.
According to the multiple trace gas concentration measuring device disclosed by the embodiment of the disclosure, as the laser module is formed by respectively superposing the first modulation signals with different frequencies on the positions of the absorption peaks, the modulation frequency range of single modulation is reduced, and the response time is accelerated; furthermore, the division circuit normalizes the second harmonic signal by adopting the first harmonic signal in the harmonic signals, so that the influence of power jitter of the laser and transmission loss in an optical path is eliminated, and the detection precision is improved.
Drawings
FIG. 1 is a simplified structural flow diagram of a variety of trace gas concentration measurement apparatus according to an illustrative embodiment of the present disclosure;
FIG. 2 is a simplified measurement flow diagram of a plurality of trace gas concentration measurement methods according to another exemplary embodiment of the present disclosure;
fig. 3 is a characteristic absorption spectrum diagram of a gas to be measured with a strong absorption peak in a near infrared band in the embodiment.
Description of the reference numerals
1: a modulation unit;
2: a laser module;
3: and a processing module.
Detailed Description
For the purposes of promoting an understanding of the principles and advantages of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. This disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. In the drawings, the size of layers and regions, as well as the relative sizes, may be exaggerated for the same elements throughout.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present disclosure. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the concepts of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and/or the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.
For the convenience of those skilled in the art to understand the technical solutions of the present disclosure, the following technical terms will be explained.
Where expressions like at least one of "A, B and C, etc. are used, the expressions should generally be interpreted in accordance with the meaning as commonly understood by those skilled in the art (e.g.," a system having at least one of A, B and C "shall include, but not be limited to, a system having a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.). Where a formulation similar to at least one of "A, B or C, etc." is used, in general such a formulation should be interpreted in accordance with the ordinary understanding of one skilled in the art (e.g. "a system with at least one of A, B or C" would include but not be limited to systems with a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.).
FIG. 1 is a simplified structural flow diagram of a variety of trace gas concentration measurement apparatus according to an illustrative embodiment of the present disclosure;
embodiments of the present disclosure provide a variety of trace gas concentration measurement apparatuses, as shown in fig. 1, including a laser module 2, a gas cell, a conversion unit, and a processing module 3, wherein the processing module 3 includes a phase-locked processing circuit, a division circuit, and a calculation circuit.
The laser module 2 is suitable for outputting a measuring beam, the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks; the gas chamber is suitable for accommodating a plurality of gases to be tested; a conversion unit adapted to convert the measuring beam emitted from the gas cell into an electrical signal, the electrical signal being superimposed with first modulation signals of different frequencies; the phase-locked processing circuit is configured to perform phase-sensitive detection and narrow-band filtering on the electric signals so as to obtain a plurality of harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected; the division circuit is configured to normalize the second harmonic signal with a first harmonic signal of the harmonic signals; and the calculating circuit is configured to perform numerical fitting according to the normalized function relation between the second harmonic signal and the concentration of the gas to be measured, so as to obtain the concentration information of each gas to be measured.
The various trace gas concentration measuring devices according to the embodiments of the present disclosure employ an adjustable semiconductor laser absorption spectroscopy (Tunable Diode Laser Absorption Spectroscopy, TDLAS) technique and a frequency division multiplexing technique, which can effectively implement real-time trace detection of multi-component gases. The laser module is used for respectively superposing the first modulation signals with different frequencies on the positions of the absorption peaks, so that the modulation frequency range of single modulation is reduced, and the response time is shortened; furthermore, the division circuit normalizes the second harmonic signal by adopting the first harmonic signal in the harmonic signals, so that the influence of power jitter of the laser and transmission loss in an optical path is eliminated, and the detection precision is improved.
In one exemplary embodiment, the laser module 2 includes: each laser is adapted to emit a plurality of lasers having a wavelength range including an initial beam of an absorption peak of one of the gases under test; a modulation unit adapted to modulate the plurality of lasers based on a plurality of second modulation signals having the same frequency to lock the plurality of absorption peaks and to superimpose first modulation signals having different frequencies on the plurality of lasers based on the plurality of locked absorption peaks, respectively; a coupling unit adapted to couple a plurality of initial light beams from a plurality of lasers into a measuring light beam; and a temperature control unit adapted to adjust the temperature inside the lasers to control the wavelength ranges of the initial light beams emitted by the plurality of lasers. Fig. 3 is a characteristic absorption spectrum diagram of a gas to be measured with a strong absorption peak in a near infrared band in the embodiment.
In detail, taking the gas to be measured as carbon dioxide, ammonia, carbon monoxide, methane and hydrogen chloride as examples, as shown in fig. 3, the gas to be measured has strong absorption peaks in the near infrared band, and a laser can be selected for laser distributed feedback (Distributed Feedback Laser, DFB), and the laser can generate laser with a wavelength corresponding to the absorption peak of the gas to be measured within the range of 1400-1800nm, and has a narrower line width and a higher side mode rejection ratio. The tuning range of each laser can cover the near infrared absorption spectrum line of the corresponding gas to be detected.
Further, the laser module 2 is controlled by the microprocessor, and besides the temperature control unit and the modulation unit 1, the laser module 2 further comprises a constant current driving unit, wherein the constant current driving unit is used for controlling working currents of a plurality of lasers and providing stable direct current driving currents which are not influenced by voltage of a load terminal for the plurality of lasers. In some embodiments, the plurality of lasers may be arranged in a laser array, and the temperature control unit is configured to control the operating temperatures of the plurality of lasers such that each laser output wavelength is at a corresponding absorption peak of near infrared absorption or a center wavelength (λ) of infrared absorption of the gas to be measured 1 、λ 2 、λ 3 ...λ n ) Nearby, the wavelength is secondarily calibrated by adjusting the working current of each laser. The temperature control unit can select a closed-loop negative feedback structure to control the temperature, and the temperature control chip can adopt a MAX1978 chip. The thermistor, the PID system network and the temperature control chip in the laser package cooperate together to realize the working temperature control of the laser.
Further, the microprocessor controls the second modulation unit in the modulation unit 1 to modulate the injection current of each laser based on the low-frequency sawtooth wave signal with the same frequency, and periodically changes the magnitude of the current control signal of each laser to make the wavelength of the initial light beam emitted by each laser respectively sweep the target absorption peak of the corresponding gas to be detected within one current modulation period so as to lock the absorption peak or the infrared absorption center wavelength (lambda 1 、λ 2 、λ 3 ...λ n ). The first one of the modulation units 1 is arranged to absorb the light at each of the different absorption peaks (lambda 1 、λ 2 、λ 3 ...λ n ) Bit positionPut on different frequencies f m (m=1, 2, 3..n). Because each high-frequency sinusoidal modulation signal only corresponds to one gas, the high-frequency sinusoidal modulation signal is a small signal, the modulation frequency range is reduced, the effect of quick response time is realized, the laser scans back and forth at the target absorption peak twice in each modulation period in the modulation process, and the detection performance is improved. The frequency range of the high-frequency sinusoidal modulation signal is 5 kHz-20 kHz, and the frequency range of the low-frequency sawtooth wave signal is 1 Hz-100 Hz.
In one embodiment, a high frequency sinusoidal modulation signal superimposed with different frequencies may be generated on a wavelength sweep basis for each laser in the laser array separately by a multi-stage modulation circuit. The modulation current is controlled by the microprocessor chip and the parallel resistor connected with the microprocessor chip.
In detail, the optical power and peak wavelength of the initial beam emitted by each laser can be expressed as:
I s (t)＝I 0 +i 0 ·cos(2πf m t+φ)； (1)
λ(t)＝λ 0 +a·cos(2πf m t)； (2)
wherein I is 0 I is the average intensity when no high frequency modulation is applied 0 Amplitude is linearly modulated for laser intensity); lambda (lambda) 0 For the wavelength range of the initial beam emitted when the laser is not modulated, f m (m=1, 2, 3..n.) is the absorption peak or the center wavelength (λ) of infrared absorption of each gas to be measured 1 、λ 2 、λ 3 ...λ n ) The frequencies of the different high-frequency sinusoidal modulation signals superimposed on the positions; phi is the phase shift between the first modulated signal and the second modulated signal; t is the modulation time; a is the frequency modulation amplitude.
Further, the number of the lasers is set to be the same as the number of the gases to be measured, so that the wavelength range of the initial light beam generated by the laser emission array comprises absorption peaks of all the gases to be measured in the gas chamber. The multiple initial light beams emitted by the multiple lasers are output through the tail fibers and then connected with the optical fiber adapter, are coupled into measuring light beams of single light through the coupling unit such as the optical coupler, realize single-fiber output, and then realize that the measuring light beams are incident into the air inlet chamber at a certain angle through the light path unit. In detail, the optical path unit includes an optical isolator and an optical fiber collimator lens. The measuring beam is emitted into the air chamber through the optical fiber, the optical isolator and the optical fiber collimating lens, and the measuring beam is absorbed by the gas to be measured in the air chamber and then emitted to the conversion unit such as the photoelectric detector, and the photoelectric detector converts the measuring beam into an electric signal such as a photocurrent signal.
Further, the optical fiber collimating lens and the photoelectric detector are respectively arranged at the outer sides of the optical windows at the two sides of the air chamber, and the effective absorption optical path is maximized by adjusting the proper incidence angle of the measuring beam.
In detail, the air chamber is connected with a multi-component gas generating device, and the gas generating device consists of a high-precision mass flow monitor, an automatic standard gas diluter and a vacuum negative pressure exhaust valve and is used for generating single-component and multi-component mixed gas under different reference concentrations. A long-optical-path gas absorption cell cavity is formed in the gas chamber, spherical reflectors with off-axis holes are respectively arranged on the left side and the right side of the cavity to increase the gas absorption optical path, an air inlet and an air outlet of the gas chamber are respectively matched with the off-axis holes, a light beam inlet and a light beam outlet are respectively arranged at two ends of the gas chamber, and barium fluoride wedge-shaped light windows are respectively arranged at the light beam inlet and the light beam outlet to reduce incidence loss and influence caused by interference.
In detail, in order to ensure that the measuring beam can be effectively received by the photosensitive surface of the photoelectric detector after being absorbed, the measuring beam can be arranged to be injected into the air chamber at the same angle with the included angles formed by the beam inlets in the X axis, the Y axis and the Z axis; the measuring beam passing through the air chamber exits at the same angle as the included angle formed by the beam outlet in the X axis, the Y axis and the Z axis.
Further, the photoelectric detector can be a planar photoelectric detector based on InGaAs, and weak signal detection requirements in the aspects of photosensitive surface size, working wavelength, responsivity, dark current and the like are met.
The received signal received by the photoelectric detector is strongest by adjusting the incidence angle of the measuring beam and the angle of the photosensitive surface of the photoelectric detector. The influence caused by the difference of responsivity of the photoelectric detector at different wavelengths is reduced by adopting a proportional calibration algorithm.
In detail, the optical power of the measuring beam after being absorbed by the various gases to be measured in the gas cell can be expressed as:
I(t)＝I s (t)exp{-α(λ)·CL}＝[I 0 +i 0 ·cos(2πf m t+φ)]exp[-α(λ)·CL]； (3)
wherein alpha (lambda) is the absorption coefficient of each gas molecule to be measured, C is the concentration of the gas to be measured, and L is the path length of the measuring beam through the uniform absorption medium.
Further, the processing module 3 includes a multi-stage signal amplifying circuit in addition to the phase-locked processing circuit, the dividing circuit, and the calculating circuit. The multi-stage signal amplifying circuit is connected with the photoelectric detector, converts a photocurrent signal from the photoelectric detector into a voltage signal and performs program-controlled amplification on the voltage signal to adjust the voltage signal to an optimal range suitable for harmonic detection.
Further, the phase-locked processing circuit performs phase-sensitive detection and narrow-band filtering on the electric signal, namely the voltage signal, so as to obtain a plurality of harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected. In detail, the phase-lock processing circuit superimposes the first modulated signals of different frequencies on the plurality of absorption peak positions, respectively, based on the first modulating unit. The phase-locked processing circuit extracts harmonic signals with different absorption peaks after being absorbed by each gas to be detected in a plurality of trace gases based on the first modulation signals with different frequencies respectively in the process of carrying out phase-sensitive detection and narrow-band filtering on the electric signals by the phase-locked processing circuit. The harmonic signals corresponding to each gas to be measured comprise a first harmonic signal and a second harmonic signal. The processed signal noise suppression effect is obvious, and the signal to noise ratio is improved well.
Specifically, fourier series expansion is performed on (3):
wherein,,ω m ＝2πf m for modulating the signal angular frequency; k is the number of stages; exp-alpha (lambda) CL]Is a laser transmissivity.
The quadrature terms of the detected signal after phase lock amplification and low pass filtering can be expressed as:
the processed first and second harmonic signals can be expressed as:
wherein X is 1f 、Y 1f Two orthogonal components that are first harmonic signals; x is X 2f 、Y 2f Two orthogonal components of the second harmonic signal; g is the photodetector gain; h 0 、H 1 、H 2 、H 3 Is the fourier coefficient of the laser transmissivity.
Advancing oneThe division circuit normalizes the extracted harmonic signals with different frequencies, and the first harmonic signal S is adopted in the corresponding treatment process of each gas to be detected 1f For second harmonic signal S 2f Normalization is carried out to eliminate the dependence of the second harmonic signal on the power jitter of the laser light source and a smoothing filter circuit is introduced to carry out noise filtering on the collected harmonic signal.
Further, the computing circuit carries out numerical fitting according to the function relation between the normalized second harmonic signal and the concentration of the gas to be detected, and concentration information of each gas to be detected is obtained.
In detail, at the absorption peak of each gas to be measured, when the concentration of the gas to be measured is small, the normalized second harmonic signal can be expressed as:
each gas to be detected has an independent molecular transition absorption line type, and the functional relation between the concentration information of the gas to be detected and the normalized second harmonic signal intensity can be obtained by the formula (11) under the weak absorption condition, so that the concentration information of each trace gas to be detected can be inverted.
In one exemplary embodiment, the signal accumulation circuit is used for carrying out multi-time acquisition averaging on the multi-period signal so as to effectively reduce the influence of disturbance and noise.
In an exemplary embodiment, the laser module 2 and the processing module 3 are both connected with a data display module, the data display module is connected to communicate with an upper computer through a serial server, and meanwhile receives an instruction sent by a serial port, executes a corresponding program, sends sampling data and an operation result back to a serial port screen, and monitors the operation result in real time and is simultaneously used for displaying multiple kinds of concentration information of gas to be detected after multi-period average and smooth filtration. For example, the data display module may include a display start circuit and a liquid crystal display. In an exemplary embodiment, a continuous cross-correlation operation is performed on the absorption spectrum line region and the non-absorption background spectrum line region in the scanning bandwidth of each laser before the modulation unit 1 modulates, background signals are extracted in real time, and background elimination processing is performed to filter out low-frequency noise signals and adjust the phenomenon of wavelength drift in the long-term monitoring process.
In an exemplary embodiment, the measured concentration information of the gas to be measured is corrected in the normalization process by using the noise equivalent concentration of the gas to be measured as a correction factor.
FIG. 2 is a simplified measurement flow diagram of a plurality of trace gas concentration measurement methods according to another exemplary embodiment of the present disclosure;
another embodiment of the present disclosure provides a method for measuring concentration of a plurality of trace gases, as shown in fig. 2, the method including generating a plurality of absorption peaks having a wavelength range including a plurality of gases to be measured, and superimposing measuring beams of first modulated signals of different frequencies on positions of the plurality of absorption peaks, respectively; injecting measuring light beams into a gas chamber containing a plurality of gases to be measured, converting the measuring light beams emitted from the gas chamber into electric signals, and superposing the electric signals with first modulation signals with different frequencies; performing phase-sensitive detection and narrow-band filtering on the electric signals to obtain harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected; normalizing the second harmonic signal by adopting a first harmonic signal in the harmonic signals; and performing numerical fitting according to the normalized function relation between the second harmonic signal and the concentration of the gas to be measured to obtain the concentration information of each gas to be measured.
In one exemplary embodiment, the step of generating the measuring beam includes generating a plurality of initial beams, respectively, using a plurality of lasers, each of the initial beams having a wavelength range including an absorption peak of one of the gases under test; modulating the plurality of lasers based on the plurality of second modulation signals with the same frequency to lock the plurality of absorption peaks, and respectively superposing the first modulation signals with different frequencies on the plurality of lasers based on the plurality of locked absorption peaks; and coupling the plurality of initial beams from the plurality of lasers into a measurement beam.
In one exemplary embodiment, a plurality of trace gas concentration measurement methods steps a through E.
Specifically, in step a, the absorption peak of each gas to be measured is selected as a target absorption peak, the output wavelength of each laser in the laser arrays of the plurality of lasers is adjusted to correspond to the target absorption peak through secondary adjustment, and the wavelength is locked;
b, the injection current of each laser is tuned by a low-frequency sawtooth wave signal with the same frequency, and then high-frequency sinusoidal modulation signals with different frequencies are overlapped on the corresponding target absorption peak positions;
in step C, the modulated laser is emitted to be coupled into a measuring beam of single beam light, and the measuring beam is incident to a gas chamber containing multiple gases to be measured; photoelectric conversion is realized by using a conversion unit based on the measuring light beam emitted from the air chamber, a detection current is generated, and current-voltage conversion and multistage signal amplification are carried out on the detection current;
in the step D, phase-sensitive detection and narrow-band filtering are carried out on detection signals overlapped with high-frequency modulation signals with different frequencies by utilizing a phase-locked amplifying circuit, so as to obtain the intensity of second harmonic waves generated by absorption at the wavelength corresponding to the target absorption peak in the gas to be detected;
and E, carrying out normalization processing on the extracted harmonic signals with different frequencies, and obtaining concentration information of each gas to be detected according to the second harmonic intensity at each target absorption peak and the corresponding fundamental wave intensity.
In the step A, the wavelength of the emitted laser is transplanted into the non-absorption spectrum line area by changing the central current of the laser, the background signal is extracted, and the wavelength scanning range is adjusted in real time by using the background signal.
In step E, the measured concentration of the gas to be measured is corrected by using the noise equivalent concentration of the gas to be measured as a correction factor. The noise equivalent gas concentration to be detected is obtained by testing a device for detecting the concentration of various gases to be detected in real time based on the TDLAS technology in an environment without absorbing the gases to be detected.
It should be further noted that, the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only referring to the directions of the drawings, and are not intended to limit the scope of the present disclosure. Like elements are denoted by like or similar reference numerals throughout the drawings. In the event that an understanding of the present disclosure may be made, conventional structures or constructions will be omitted, and the shapes and dimensions of the various parts in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure.
Unless otherwise known, numerical parameters in this specification and the appended claims are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". In general, the meaning of expression is meant to include a variation of + -10% in some embodiments, a variation of + -5% in some embodiments, a variation of + -1% in some embodiments, and a variation of + -0.5% in some embodiments by a particular amount.
The use of ordinal numbers such as "first," "second," "third," etc., in the description and the claims to modify a corresponding element does not by itself connote any ordinal number of elements or the order of manufacturing or use of the ordinal numbers in a particular claim, merely for enabling an element having a particular name to be clearly distinguished from another element having the same name.
Furthermore, unless specifically described or steps must occur in sequence, the order of the above steps is not limited to the list above and may be changed or rearranged according to the desired design. In addition, the above embodiments may be mixed with each other or other embodiments based on design and reliability, i.e. the technical features of the different embodiments may be freely combined to form more embodiments.
While the foregoing is directed to embodiments of the present disclosure, other and further details of the invention may be had by the present application, it is to be understood that the foregoing description is merely exemplary of the present disclosure and that no limitations are intended to the scope of the disclosure, except insofar as modifications, equivalents, improvements or modifications may be made without departing from the spirit and principles of the present disclosure.
Claims (10)
1. A plurality of trace gas concentration measurement apparatus comprising:
the laser module is suitable for outputting a measuring beam, the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks;
a gas chamber adapted to contain a plurality of trace amounts of the gas to be measured;
a conversion unit adapted to convert the measuring beam emitted from the gas cell into an electrical signal superimposed with the first modulated signal of the different frequency; and
a processing module, comprising:
the phase-locked processing circuit is configured to perform phase-sensitive detection and narrow-band filtering on the electric signals so as to obtain a plurality of harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected;
a division circuit configured to normalize a second harmonic signal with a first one of the harmonic signals; and
and the calculating circuit is configured to carry out numerical fitting according to the function relation between the normalized second harmonic signal and the concentration of the gas to be measured to obtain the concentration information of each gas to be measured.
2. The plurality of trace gas concentration measurement apparatus according to claim 1, wherein the laser module comprises:
a plurality of lasers, each laser adapted to emit an initial beam of light having a wavelength range including an absorption peak of one of the gases under test;
a modulating unit, adapted to modulate a plurality of the lasers based on a plurality of second modulation signals with the same frequency to lock a plurality of the absorption peaks, and respectively superimpose first modulation signals with different frequencies on a plurality of the lasers based on a plurality of the locked absorption peaks; and
and a coupling unit adapted to couple a plurality of initial light beams from a plurality of said lasers into a measuring light beam.
3. The plurality of trace gas concentration measurement apparatus according to claim 2, wherein the laser module further comprises: and the temperature control unit is suitable for adjusting the temperature inside the lasers so as to control the wavelength range of the initial light beams emitted by the multiple lasers.
4. The plurality of trace gas concentration measurement apparatus according to claim 2, wherein the first modulated signal comprises a high frequency sinusoidal modulated signal and the second modulated signal comprises a low frequency sawtooth signal, wherein the high frequency sinusoidal modulated signal has a frequency range of 5kHz to 20kHz and the low frequency sawtooth signal has a frequency range of 1Hz to 100Hz.
5. The multiple trace gas concentration measuring apparatus according to any one of claims 1 to 4, wherein a long optical path gas absorption cell cavity is formed in the gas chamber, a beam inlet and a beam outlet are respectively provided at both ends of the gas chamber, and barium fluoride wedge-shaped optical windows are respectively provided at the beam inlet and the beam outlet.
6. The plurality of trace gas concentration measurement apparatus according to claim 5, wherein the measurement beam is incident on the gas chamber at the same angle as the beam inlet is at an angle in the X-axis, Y-axis, Z-axis;
preferably, the measuring beam passing through the gas cell exits at the same angle as the included angle of the beam outlet in the X-axis, Y-axis, Z-axis.
7. The plurality of trace gas concentration measurement apparatus according to any one of claims 1 to 4, wherein the conversion unit comprises a photodetector comprising an indium gallium arsenide based planar photodetector.
8. A method of measuring the concentration of a plurality of trace gases, comprising:
generating a measuring beam, wherein the wavelength range of the measuring beam comprises a plurality of absorption peaks of a plurality of gases to be measured, and first modulation signals with different frequencies are respectively overlapped on the positions of the plurality of absorption peaks;
injecting measuring beams into a gas chamber containing a plurality of gases to be measured;
converting the measuring beam emitted from the gas cell into an electrical signal, the electrical signal being superimposed with the first modulated signal of different frequency;
performing phase-sensitive detection and narrow-band filtering on the electric signals to obtain harmonic signals with different frequencies, which are generated due to absorption, at wavelengths corresponding to a plurality of target absorption peaks in a plurality of gases to be detected;
normalizing the second harmonic signal by adopting a first harmonic signal in the harmonic signals; and
and performing numerical fitting according to the normalized function relation between the second harmonic signal and the concentration of the gas to be measured to obtain the concentration information of each gas to be measured.
9. The plurality of trace gas concentration measurement methods according to claim 8, wherein the step of generating a measurement beam comprises:
generating a plurality of initial light beams by using a plurality of lasers respectively, wherein the wavelength range of each initial light beam comprises an absorption peak of one gas to be detected in the gas to be detected;
modulating a plurality of lasers based on a plurality of second modulation signals with the same frequency to lock a plurality of absorption peaks, and respectively superposing first modulation signals with different frequencies on the plurality of lasers based on the plurality of locked absorption peaks; and
a plurality of initial beams from a plurality of said lasers are coupled into a measuring beam.
10. The method for measuring the concentration of a plurality of trace gases according to claim 8, wherein the measured concentration information of the gas to be measured is corrected using the noise equivalent concentration of the gas to be measured as a correction factor.
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