A gas detection self-calibration system and method based on TDLAS

Abstract

This invention discloses a gas detection self-calibration system and method based on TDLAS. The gas detection self-calibration system consists of a beam splitter, a standard gas chamber, a first converging mirror, and a light intensity detector. The beam splitter receives the measurement beam generated after passing through a collimating mirror from a laser. The standard gas chamber absorbs the measurement beam. The first converging mirror converges the measurement beam absorbed by the standard gas chamber. The light intensity detector generates a photoelectric signal based on the converged measurement beam and transmits it to the detection control system. The detection control system modulates the measurement beam based on the photoelectric signal. The detection control system is electrically connected to the laser and the light intensity detector. This invention uses the data characteristics of the received signal obtained by the detector in the calibration optical path to control the temperature of the laser through feedback, so that the laser wavelength can always be strictly aligned with the center position of the gas absorption peak under different operating conditions, thereby achieving laser center wavelength calibration in complex environments.

Description

Technical Field

[0001] This invention relates to the field of infrared absorption spectroscopy, and in particular to a gas detection self-calibration system and method based on TDLAS. Background Technology

[0002] Wavelength modulation methods are mainly divided into two types: peak-fixing and peak-sweeping. Peak-sweeping modulates the laser output by superimposing a low-frequency sawtooth or triangular wave with a high-frequency sine wave. Peak-fixing modulates the laser output by superimposing a high-frequency sine wave drive signal when the laser output wavelength coincides with the gas absorption peak. Peak-fixing can obtain a large amount of gas concentration data from the absorption waveform. In scenarios where laser temperature control accuracy is high or environmental changes are small, a higher signal-to-noise ratio can be achieved by averaging the measurement results.

[0003] When using the peak-fixing method to measure gas concentration, the wavelength of the laser corresponding to the zero-crossing point of the sinusoidal signal should be aligned with the center wavelength of the absorption peak of the object being measured. However, in different operating environments, the peak position of the gas absorption peak and the center wavelength of the laser may shift due to the influence of ambient air pressure, temperature, humidity, and the electrical parameters of the system itself. This can lead to problems such as a shorter measurement distance, lower sensitivity, and in severe cases, even failure to measure the target gas.

[0004] In summary, achieving automatic calibration of the system under complex environments in TDLAS technology is a current research challenge. Therefore, there is an urgent need for a self-calibration method for TDLAS that can achieve strict alignment between the center wavelength and the gas absorption peak position, providing a new solution for the measurement and calibration of wavelength modulation technology. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of automatic laser wavelength calibration in complex environments. It proposes a gas detection self-calibration system and method based on TDLAS for achieving laser center wavelength calibration in complex environments.

[0006] To achieve the above technical objectives, the present invention provides a gas detection self-calibration system based on TDLAS, comprising:

[0007] A beam splitter is used to receive the measurement beam generated by a laser after passing through a collimating lens;

[0008] A standard gas chamber is used to absorb the measurement beam.

[0009] The first converging lens is used to converge the measurement beam absorbed by the standard gas cell;

[0010] A light intensity detector is used to generate a photoelectric signal based on the converged measurement beam and transmit it to the detection and control system. The detection and control system modulates the measurement beam based on the photoelectric signal. The detection and control system is electrically connected to the laser and the light intensity detector.

[0011] Preferably, the detection and control system is used to modulate the measurement beam using a sawtooth wave signal and a sinusoidal signal superimposed with a fixed DC bias as driving signals.

[0012] Preferably, the detection and control system is also used to perform phase-locked amplification of the photoelectric signal according to Beer-Lambert's law to obtain the second harmonic of the photoelectric signal;

[0013] By adjusting the temperature parameters of the laser, the peak position of the second harmonic curve is changed, aligning the laser's output wavelength with the gas absorption peak, thus calibrating the TDLAS gas detection system. The TDLAS gas detection system consists of a laser, collimating mirror, reflecting surface, detection control system, photodetector, and second converging mirror arranged sequentially. After the measurement beam passes through the gas being measured, it is reflected by the reflecting surface to the second converging mirror, where it is then focused and collected by the photodetector before being transmitted to the detection control system to detect the type and concentration of the gas in the gas being measured.

[0014] This invention also provides a gas detection self-calibration method based on TDLAS, applied to a gas detection self-calibration system, comprising the following steps:

[0015] The drive signal generated by the detection and control system is acquired at the first moment corresponding to the start phase of the first cycle, and at the second moment corresponding to the start phase of the second cycle.

[0016] The third moment corresponds to the peak value of the second harmonic of the photoelectric signal generated by the measurement beam produced by the laser after passing through the collimating lens and collected by the detection and control system.

[0017] Based on the first and second moments, and according to the third moment, it is determined whether the output waveform of the laser has shifted. If a shift occurs, the output wavelength of the laser is modulated to align with the gas absorption peak by adjusting the temperature parameter value of the laser based on the first difference between the second and third moments, in order to calibrate the TDLAS gas detection system. Otherwise, the TDLAS gas detection system is not calibrated.

[0018] Preferably, in the process of obtaining the second harmonic, the photoelectric signal is amplified by lock-in based on Beer-Lambert's law to obtain the second harmonic of the photoelectric signal.

[0019] Preferably, in the process of determining whether the output waveform has shifted, the second difference between the first time and the second time is used to determine whether the output waveform has shifted. When the second difference remains constant, it is determined that the output waveform has not shifted; otherwise, it is determined that the output waveform has shifted.

[0020] Preferably, during the modulation of the output wavelength, the temperature parameter value is adjusted to make the first difference 0, thereby aligning the modulated output wavelength with the gas absorption peak for calibration of the TDLAS gas detection system.

[0021] Preferably, after calibrating the TDLAS gas detection system, the laser drive signal is changed to a sine wave signal superimposed with a fixed DC bias. According to Beer-Lambert's law, the gas concentration measurement of the gas being measured is calibrated based on the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal generated by the sine wave signal.

[0022] Preferably, during the process of changing the dynamic signal to a sinusoidal signal, after controlling the sinusoidal signal to be equal to the current value corresponding to the third moment, concentration calibration is performed based on the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal.

[0023] Preferably, after concentration calibration, the gas detection self-calibration system is disconnected from the TDLAS gas detection system, and the TDLAS gas detection system is controlled to detect the gas to be measured.

[0024] The present invention discloses the following technical effects:

[0025] This invention uses the data characteristics of the received signal obtained by the detector in the calibration optical path to control the temperature of the laser, so that the laser wavelength can always be strictly aligned with the center position of the gas absorption peak under different operating conditions, thereby realizing laser center wavelength calibration in complex environments. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the calibration system described in this invention;

[0028] Figure 2 The driving signal and second harmonic curve described in this invention;

[0029] Figure 3This is a schematic diagram of the telemetry optical path described in this invention;

[0030] Figure 4 This is a schematic diagram of the calibration optical path according to the present invention, wherein 1 is a laser, 2 is a collimating lens, 3 is a beam splitter, 4 is a reflecting surface, 5 is a standard gas cell, 6 is a first converging lens, 7 is a light intensity detector, 8 is a detection and control system, 9 is a photodetector, 10 is a second converging lens, and 11 is a calibration system. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0032] like Figure 1-4 As shown, the present invention provides a gas detection self-calibration system based on TDLAS, characterized in that it includes:

[0033] Beam splitter 3 is used to receive the measurement beam generated by the laser 1 after passing through collimating lens 2;

[0034] Standard gas chamber 5 is used to absorb the measurement beam;

[0035] The first converging mirror 6 is used to converge the measurement beam absorbed by the standard gas chamber 5;

[0036] The light intensity detector 7 is used to generate a photoelectric signal based on the converged measurement beam and transmit it to the detection and control system 8. The detection and control system 8 modulates the measurement beam based on the photoelectric signal. The detection and control system 8 is electrically connected to the laser 1 and the light intensity detector 7.

[0037] More preferably, the detection and control system 8 provided by the present invention is used to modulate the measurement beam using a sawtooth wave signal and a sinusoidal signal superimposed with a fixed DC bias as driving signals.

[0038] More preferably, the detection and control system 8 provided by the present invention is also used to perform phase-locked amplification of the photoelectric signal according to Beer-Lambert's law to obtain the second harmonic of the photoelectric signal;

[0039] By adjusting the temperature parameter value of laser 1, the peak position of the second harmonic curve is changed, so that the output wavelength of laser 1 is aligned with the gas absorption peak, and the TDLAS gas detection system is calibrated. The TDLAS gas detection system consists of laser 1, collimating lens 2, reflecting surface 4, detection control system 8, photodetector 9, and second converging lens 10 arranged in sequence. After the measurement beam passes through the gas to be measured, it is reflected by reflecting surface 4 and then converged by second converging lens 10. After being collected by photodetector 9, it is transmitted to detection control system 8 to detect the gas type and gas concentration in the gas to be measured.

[0040] This invention provides a gas detection self-calibration method based on TDLAS, applied to a gas detection self-calibration system, comprising the following steps:

[0041] The drive signal generated by the detection and control system 8 is acquired at the first moment corresponding to the start phase of the first cycle, and at the second moment corresponding to the start phase of the second cycle.

[0042] The third moment corresponds to the peak value of the second harmonic of the photoelectric signal generated by the measurement beam produced by the laser 1 after passing through the collimating lens 2 and collected by the detection and control system 8.

[0043] Based on the first and second moments, and according to the third moment, it is determined whether the output waveform of laser 1 has shifted. If a shift occurs, the output wavelength of laser 1 is modulated to align with the gas absorption peak by adjusting the temperature parameter value of laser 1 according to the first difference between the second and third moments, in order to calibrate the TDLAS gas detection system. Otherwise, the TDLAS gas detection system is not calibrated.

[0044] More preferably, in the process of obtaining the second harmonic, based on Beer-Lambert's law, the present invention performs phase-locked amplification on the photoelectric signal to obtain the second harmonic of the photoelectric signal.

[0045] More preferably, in the process of determining whether the output waveform has shifted, the present invention determines whether the output waveform has shifted based on the second difference between the first time and the second time. When the second difference remains constant, it is determined that the output waveform has not shifted; otherwise, it is determined that the output waveform has shifted.

[0046] More preferably, during the modulation of the output wavelength, the present invention adjusts the temperature parameter value to make the first difference 0, thereby aligning the modulated output wavelength with the gas absorption peak position for calibration of the TDLAS gas detection system.

[0047] More preferably, after calibrating the TDLAS gas detection system, the present invention changes the driving signal of the laser 1 to a sine wave signal superimposed with a fixed DC bias. According to Beer-Lambert's law, the gas concentration measurement of the gas being measured is calibrated based on the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal generated by the sine wave signal.

[0048] More preferably, in the process of changing the dynamic signal to a sine wave signal, after the present invention controls the sine wave signal to be equal to the current value corresponding to the third moment, the concentration is calibrated according to the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal.

[0049] More preferably, after concentration calibration, the present invention separates the gas detection self-calibration system from the TDLAS gas detection system and controls the TDLAS gas detection system to detect the gas to be measured.

[0050] The gas detection self-calibration method mentioned in this invention is achieved through the following technical solution.

[0051] Laser 1 is turned on, and the emitted light is collimated by collimating lens 2 to generate a measurement beam. This beam passes through a standard gas chamber with a known gas concentration and is then focused by the receiving lens of the first converging lens 6. Finally, it is collected by the light intensity detector 7. The detection and control system 8 is then activated, using a sawtooth wave signal and a sinusoidal signal superimposed with a fixed DC bias as driving signals to modulate the measurement light. The driving signals are as follows: Figure 2 As shown in (a), the output wavelength of laser 1 at time t2 is the wavelength corresponding to the absorption peak of the gas being measured. At the beginning of each cycle, a synchronous pulse width signal is generated to mark the 0-phase point of the driving signal, as shown in (a). Figure 2 As shown in (b).

[0052] After the photoelectric signal collected by the light intensity detector 7 is transmitted to the detection and control system 8, it is further amplified by lock-in according to Beer-Lambert's law to obtain the second harmonic of the photoelectric signal, such as... Figure 2 As shown in (c), t0 and t3 are the times corresponding to the starting phases of the two cycles of the driving signal, and t2 is the corresponding point of the peak value of the second harmonic curve. The peak value position of the second harmonic curve t2 is t2-t0=Δt1 away from the starting time t0. When the center wavelength of laser 1 is aligned with the gas absorption peak, Δt1 remains constant; when the wavelength of laser 1 shifts, or when the gas absorption peak shifts due to environmental influences, the peak value position of the second harmonic curve will also change, such as... Figure 2 As shown in (d), t1 is t1-t0=Δt3 away from the starting time t0.

[0053] The wavelength of laser 1 can be modulated by changing the drive current and temperature parameters. However, changing the drive current to alter the laser wavelength affects the laser's output power, thus impacting the gas measurement distance. Therefore, changing the temperature parameters allows for wavelength adjustment without affecting the laser's output power, enabling alignment of the laser's output wavelength with the gas absorption peak. By adjusting the temperature parameters of laser 1, the peak position of the second harmonic distortion curve can be altered, i.e., the wavelength of the laser can be changed. Figure 2 The width of Δt3 in (d). In wavelength calibration mode, the temperature parameter value is adjusted in real time. When Δt3 equals 0, the second harmonic peak position will stably appear in the middle position between t0 and t3. At this time, the wavelength of laser 1 is aligned with the gas absorption peak position, thereby realizing the automatic calibration of the gas detection system based on TDLAS.

[0054] Traditional telemetry optical path diagram Figure 3 As shown in the figure, combined with the wavelength modulation spectrum calibration method proposed in this paper, in the process of... Figure 3 When the telemetry system shown is calibrated, the calibration system 11 is coupled into the system by controlling the mechanical switching device or the guide rail. Figure 3 In the optical path system shown, the calibration system 11 consists of a beam splitter 3, a standard gas cell 5, a converging lens 6, and a light intensity detector 7. The overall optical path during calibration is as follows: Figure 4 As shown.

[0055] use Figure 4 The optical path system shown and the method proposed in this paper can realize the automatic calibration of the gas detection system. After determining the driving parameters of laser 1, the driving signal of laser 1 is changed to a sine wave signal superimposed with a fixed DC bias. The laser signal is absorbed by the gas in the standard gas chamber. According to Beer-Lambert's law, the relationship between the second harmonic and the fundamental component extracted from the photoelectric signal can further realize the calibration of gas measurement.

[0056] use Figure 4 The optical path system shown and the method proposed in this paper can realize the automatic calibration of the wavelength of the measurement beam of the gas detection system.

[0057] After determining the driving parameters of laser 1, the driving signal of laser 1 is changed to a sine wave signal superimposed with a fixed DC bias, wherein the DC bias signal and... Figure 2 In (a), the current values ​​at time t2 are equal. At this time, the measurement beam emitted by laser 1 is partially absorbed after passing through the standard gas chamber 5. According to Beer-Lambert's law, the concentration calibration of gas detection can be further realized by using the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal.

[0058] After calibration, the calibration system 11 can be disconnected from the optical path by controlling the mechanical switching device or the guide rail, allowing the measurement system to return to its normal state. Figure 3 The optical path state shown allows the device to enter the normal gas measurement mode.

[0059] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The words "comprising" or "including" do not exclude the presence of components or steps not listed in the claims. The words "a" or "an" preceding a component do not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0061] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A gas detection self-calibration method based on TDLAS, applied to a gas detection self-calibration system, characterized in that, The gas detection self-calibration system includes: a beam splitter (3) for receiving a measurement beam generated by a laser (1) through a collimating lens (2); a standard gas chamber (5) for absorbing the measurement beam; a first converging lens (6) for converging the measurement beam absorbed by the standard gas chamber (5); and a light intensity detector (7) for generating a photoelectric signal based on the converged measurement beam and transmitting it to a detection control system (8). The detection control system (8) modulates the measurement beam based on the photoelectric signal. The detection control system (8) is electrically connected to the laser (1) and the light intensity detector (7). The self-calibration method includes the following steps: The drive signal generated by the detection and control system (8) is acquired at the first moment corresponding to the start phase of the first cycle, and at the second moment corresponding to the start phase of the second cycle. The third moment corresponding to the peak value of the second harmonic of the photoelectric signal generated by the measurement beam generated by the laser (1) through the collimating lens (2) is acquired by the detection control system (8); Based on the first time and the second time, and according to the third time, it is determined whether the output waveform of the laser (1) has shifted. If a shift occurs, the temperature parameter value of the laser (1) is adjusted according to the first difference between the second time and the third time so that the first difference is 0. The output wavelength of the laser (1) is modulated to align with the gas absorption peak for calibrating the TDLAS gas detection system. Otherwise, the TDLAS gas detection system is not calibrated.

2. The gas detection self-calibration method based on TDLAS according to claim 1, characterized in that, The detection and control system (8) is used to modulate the measurement beam using a sawtooth wave signal and a sinusoidal signal superimposed with a fixed DC bias as driving signals.

3. The gas detection self-calibration method based on TDLAS according to claim 2, characterized in that, The detection and control system (8) is also used to perform phase-locked amplification of the photoelectric signal according to Beer-Lambert's law to obtain the second harmonic of the photoelectric signal; By adjusting the temperature parameter value of the laser (1), the peak position of the second harmonic curve is changed, so that the output wavelength of the laser (1) is aligned with the gas absorption peak, and the TDLAS gas detection system is calibrated. The TDLAS gas detection system consists of the laser (1), the collimating mirror (2), the reflecting surface (4), the detection control system (8), the photodetector (9), and the second converging mirror (10) arranged in sequence. After the measurement beam passes through the gas to be measured, it is reflected by the reflecting surface (4) to the second converging mirror (10) and then collected by the photodetector (9) and transmitted to the detection control system (8) for detecting the gas type and gas concentration in the gas to be measured.

4. A gas detection self-calibration method based on TDLAS according to any one of claims 1 to 3, characterized in that: In the process of determining whether the output waveform has shifted, the second difference between the first time and the second time is used to determine whether the output waveform has shifted. When the second difference remains constant, it is determined that the output waveform has not shifted; otherwise, it is determined that the output waveform has shifted.

5. The gas detection self-calibration method based on TDLAS according to claim 4, characterized in that: After calibrating the TDLAS gas detection system, the driving signal of the laser (1) is changed to a sine wave signal superimposed with a fixed DC bias. According to Beer-Lambert's law, the gas concentration measurement of the gas being measured is calibrated based on the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal generated by the sine wave signal.

6. The gas detection self-calibration method based on TDLAS according to claim 5, characterized in that: During the process of changing the dynamic signal to a sine wave signal, after controlling the sine wave signal to be equal to the current value corresponding to the third moment, concentration calibration is performed based on the relationship between the second harmonic and the fundamental component extracted from the light intensity response signal.

7. The gas detection self-calibration method based on TDLAS according to claim 6, characterized in that: After concentration calibration, the gas detection self-calibration system is disconnected from the TDLAS gas detection system, and the TDLAS gas detection system is then controlled to detect the gas to be measured.

Images