Multi-gas detection device based on TDLAS (Tunable Diode Laser Absorption Spectroscopy) technology

Abstract

The utility model discloses a TDLAS (tunable diode laser absorption spectroscopy) technology-based multi-gas detection device. The device comprises a plurality of paths of lasers with different wavelengths, a laser coupling device, a multi-reflection gas chamber, a detector and a data processing module, the device modulates a plurality of lasers with different wavelengths at different frequencies, then light emitted by the different lasers is coupled and then enters a multi-reflection gas chamber to react with detected gas, the output light passes through a detector, and a signal generated by the detector is demodulated by adopting a demodulation frequency which is the same as the modulation frequency. And the concentrations of different gas components are extracted. According to the device, various gas components can be analyzed under the condition that only one gas chamber and one detector are used, the size and the weight of gas analysis equipment are effectively reduced, and the manufacturing cost is reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to optical gas analysis field especially relates to a variety of gas detection device based on TDLAS technique. BACKGROUND

[0002] The gas detection technology principle based on laser absorption spectrum is:

[0003] Due to the existence of gas molecule absorption spectrum, when light passes through the gas, if the light source spectrum coincides with the absorption spectrum of the gas to be measured, part of the light energy will be absorbed by the gas to be measured, and the output light intensity will be weakened, when the gas concentration is low, the absorption of specific wavelength light energy by the gas meets the Beer-Lambert law.

[0004] According to the law, a specific gas only absorbs a specific wavelength spectrum, and the absorption intensity is proportional to the gas concentration, and the concentration of the specific gas can be calculated by detecting the absorption intensity of the gas.

[0005] The existing variety of gas detection methods often integrate multiple single detection devices into a device for detection, such as Figure 1 As shown, this detection method needs to use multiple detection chambers, which is high in cost and large in size. SUMMARY

[0006] The present disclosure provides a variety of gas detection device based on TDLAS (Tunable diode laser absorption spectroscopy) technology, which can realize the detection of multiple gas components under the condition of using only one gas chamber and one detector, effectively reducing the size and cost of the device.

[0007] The principle of TDLAS modulation spectrum technology is:

[0008] If the wavelength of the light source is directly locked on the gas absorption peak, when the light source deviates from the gas absorption peak due to temperature and other factors, the absorption coefficient will change, causing the detection result to change. In order to avoid this influence and improve the signal-to-noise ratio, the wavelength of the light source can be modulated, a high-frequency sinusoidal modulation signal is superimposed on the laser scanning signal, so that the instantaneous frequency and light intensity of the light source can periodically change according to the sinusoidal function and scan the gas absorption peak. The harmonic signal generated after the interaction of the light source and the gas absorption peak can be analyzed to obtain the concentration of the gas to be measured.

[0009] The variety of gas detection device based on TDLAS technology provided by the present disclosure comprises:

[0010] A plurality of lasers of different wavelengths, a laser coupling device, a multi-reflection gas chamber, a detector, and a data processing module; wherein:

[0011] The data processing module is configured to modulate the plurality of lasers of different wavelengths at different frequencies, and demodulate the signals generated by the detector using reference signals of the same frequency as the modulation signals, and calculate the concentration values of each kind of absorbing gas.

[0012] The laser coupling device is configured to couple the modulated plurality of lasers.

[0013] The multi-reflection gas chamber is configured to sufficiently absorb the coupled laser.

[0014] The detector is configured to detect the light emitted by the multi-reflection gas chamber.

[0015] Further, the lasers are DFB distributed feedback lasers.

[0016] Further, the data processing module comprises a plurality of modulation sub-modules and a plurality of demodulation sub-modules, wherein:

[0017] The modulation sub-modules are configured to modulate the lasers, and the modulation sub-modules corresponding to the lasers of different wavelengths use different modulation frequencies.

[0018] The demodulation frequency of one demodulation sub-module corresponds to the modulation frequency of one modulation sub-module, and the demodulation sub-module is configured to demodulate the signals generated by the detector using reference signals of the same frequency as the modulation signals.

[0019] Further, the modulation sub-modules use a dual-frequency modulation method of superimposing high-frequency sine waves on low-frequency sawtooth waves to modulate the lasers, and the modulation sub-modules corresponding to the lasers of different wavelengths use high-frequency sine waves of different frequencies.

[0020] Further, the modulation sub-modules comprise an FPGA board and a modulation signal generation component, wherein the FPGA board is configured to control the modulation signal generation component to generate sawtooth wave signals and sine wave signals for modulating the lasers, and the two signals are superimposed as the final modulation signals.

[0021] The lasers comprise a current driving component and a temperature control component, wherein the current driving component is configured to tune the current input to the lasers under the action of the final modulation signals, and the temperature control component is configured to keep the lasers at a constant temperature.

[0022] Further, the laser coupling device uses an optical fiber coupler.

[0023] Compared with the prior art, the present disclosure has the following advantages: (1) the analysis of multiple gas components can be realized using only one gas chamber and one detector; (2) the device size and weight are effectively reduced, and the manufacturing cost is reduced; (3) the influence of temperature and current jitter on the stability of the system detection signal is well eliminated by double-frequency modulation of the laser. BRIEF DESCRIPTION OF DRAWINGS

[0024] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the figures, and wherein:

[0025] Figure 1 Prior art gas detection schematic diagram;

[0026] Figure 2 System structure diagram according to an exemplary embodiment of the present disclosure;

[0027] Figure 3 DFB laser center wavelength change with current and temperature relationship diagram;

[0028] Figure 4 Single-component system principle block diagram;

[0029] Figure 5 Laser double-frequency modulation implementation block diagram;

[0030] Figure 6 Demodulation technique principle block diagram. DETAILED DESCRIPTION

[0031] Preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0032] The present disclosure provides a new TDLAS-based multi-gas detection device, which can realize the analysis of multiple gas components using only one gas chamber and one detector.

[0033] According to an exemplary embodiment of the present disclosure, as shown in the accompanying drawings, the main working process includes the following steps: Figure 2

[0034] Step 1: Modulate the laser of different wavelengths at different frequencies;

[0035] Step 2: Couple the multi-channel laser; ​

[0036] Step 3: The coupled light is injected into the multi-reflection gas chamber through the collimator, and after being fully absorbed, the light is emitted, and a detector receives the light signal;

[0037] Step 4: A reference signal with the same frequency as the modulation signal is selected to demodulate the signal received by the detector, and the concentration values of multiple gases are calculated.

[0038] In this embodiment, a DFB (Distributed Feedback Laser) distributed feedback laser is applied, and the relationship between the central wavelength and the current and temperature is shown in the attached Figure 3 .

[0039] In this embodiment, the system principle block diagram for single-component gas is shown in the attached Figure 4 .

[0040] 1. Implementation of wavelength modulation

[0041] In this embodiment, the wavelength modulation of the laser adopts a double-frequency modulation method, and the implementation method is shown in the attached Figure 5 , that is, a high-frequency sinusoidal modulation is superimposed on a low-frequency sawtooth wave, which well eliminates the influence of temperature and current jitter on the stability of the system detection signal.

[0042] The scanning start wavelength is determined by setting the temperature and reference current of the laser, the speed and range of wavelength scanning are controlled by the sawtooth wave, and it is ensured that the scanning passes through the absorption line and is separated from other gas absorption lines, so that the problem of background gas interference can be solved. Moreover, through the sawtooth wave scanning, the measurement error caused by the drift of the laser central wavelength to the system can be avoided. The sawtooth wave and the sinusoidal wave are superimposed as the final modulation signal acting on the current drive of the laser, and the laser generates the required modulation light through the tuning current and the temperature control module together.

[0043] 2. Demodulation

[0044] Since the detector receives the modulation signals of multiple lasers, the output signal of the detector is in a state of superposition of multiple frequencies and also increases noise information, and the signal can be represented as:

[0045] A1cos(ω1t+α1)+A2cos(ω2t+α2)+A3cos(ω3t+α3)+……+A n cos(ω n t+α n )+n(t)

[0046] Where ω1, ω2…ω n represent the modulation frequencies of different lasers,

[0047] α1, α2…α nmodulation initial phase angle representing different lasers,

[0048] A1, A2, A n modulation amplitude representing different lasers,

[0049] n(t) represents a noise signal.

[0050] The superimposed signal cannot directly obtain information, and needs to be demodulated to extract useful signals. Figure 6 For example:

[0051] When the laser 1 works, the frequency of the reference signal given by the demodulation signal is ω1, at this time the light of other frequencies received by the detector will be filtered out by the filter, and similarly, when the laser n works, the frequency of the reference signal of the demodulation signal is ωn, at this time the light of other frequencies received by the detector will be filtered out by the filter. n Through a series of demodulation processes, the output signal of the detector can be extracted to obtain the concentration information of the gas detected by the laser.

[0052] In this embodiment, different frequencies of wavelength modulation are performed on a plurality of lasers, the light emitted by the different lasers is coupled through a fiber coupler, the coupled laser enters the multi-reflection gas chamber and reacts with the measured gas, and the optical signal is detected by a photodetector. The detector signal is amplified, filtered and processed into a data processing module. Through a specific demodulation algorithm, the concentration of different gas components is extracted.

[0053] The above technical solution is only an exemplary embodiment of the present application, and for those skilled in the art, on the basis of the application method and principle disclosed in the present application, various types of improvements or modifications can be easily made, and the method described in the above embodiment is not limited to the method described in the above embodiment. Therefore, the above-described method is only preferred, and does not have a limiting meaning.

Claims

1. A multi-gas detection device based on TDLAS technology, characterized in that, The application relates to a multi-wavelength laser absorption gas concentration detection device. The device comprises a plurality of lasers of different wavelengths, a laser coupling device, a multi-reflection gas chamber, a detector and a data processing module. The data processing module is used for modulating the lasers of different wavelengths at different frequencies and demodulating the signals generated by the detector using reference signals of the same frequency as the modulation signal frequency, so as to calculate the concentration value of each kind of absorption gas. The laser coupling device is used for coupling the modulated multi-wavelength lasers. The multi-reflection gas chamber is used for fully absorbing the coupled lasers. The detector is used for detecting the light emitted by the multi-reflection gas chamber.

2. The apparatus of claim 1, wherein, The laser adopts a DFB distributed feedback laser.

3. The apparatus of claim 1, wherein, The data processing module comprises a plurality of modulation sub-modules and a plurality of demodulation sub-modules. The modulation sub-modules are used for modulating the lasers, and the modulation frequencies of the modulation sub-modules are different, so as to modulate the lasers of different wavelengths. The demodulation sub-modules are used for demodulating the signals generated by the detector using reference signals of the same frequency as the modulation signal frequency, and the demodulation frequency of one demodulation sub-module is the same as the modulation frequency of one modulation sub-module.

4. The apparatus of claim 3, wherein, The modulation sub-modules all adopt a double-frequency modulation mode of superimposing a high-frequency sine wave on a low-frequency sawtooth wave, and the high-frequency sine wave frequencies of the modulation sub-modules for modulating the lasers of different wavelengths are different.

5. The apparatus of claim 3, wherein, The modulation sub-modules comprise an FPGA board and a modulation signal generating component. The FPGA board is used for controlling the modulation signal generating component to generate sawtooth wave and sine wave signals for modulating the lasers, and the two signals are superimposed as the final modulation signal.

6. The apparatus of any one of claims 1-5, wherein, The laser comprises a current driving component and a temperature control component. The current driving component is used for tuning the current input to the laser under the action of the final modulation signal. The temperature control component is used for keeping the laser at a constant temperature. The laser coupling device adopts an optical fiber coupler.

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