Photoacoustic sensing detection system based on microphone photoacoustic cell

Abstract

According to the opto-acoustic sensing detection system based on the microphone opto-acoustic cell, a signal generator is in signal connection with an adder, the adder is in signal connection with a laser, the opto-acoustic cell is arranged on the downstream of an optical path of the laser, and a pressure control unit, a temperature control unit, the microphone and an air inlet filter are arranged on the opto-acoustic cell. And the lock-in amplifier is in signal connection with the photoacoustic cell, the computer and the signal generator. According to the application, full-range greenhouse gas accurate measurement is realized through the pressure control unit, the temperature control unit and the gas inlet filter, the system stability is good, and wide-range greenhouse gas detection is realized through combination of the gas inlet filter and the photoacoustic cell.

Description

Technical Field

[0001] The present application relates to the technical field of photoacoustic spectroscopy gas detection, and in particular to a photoacoustic sensing detection system based on a microphone photoacoustic cell. Background Art

[0002] With the continuous advancement of industrialization, the consumption of fossil fuels has continued to increase, and the corresponding greenhouse gas emissions have also continued to increase. Thermal power, steel, oil and gas mining, coal mining, waste treatment and other industries are key emission units. Therefore, CO 2 and CH 4 The emission monitoring of greenhouse gases such as carbon dioxide and carbon monoxide is particularly urgent. At present, there are many types of gas sensors, which are divided into four major detection methods according to different detection principles: electrical method, electrochemical method, optical method and others. Compared with other methods, gas sensors based on optical methods have the characteristics of high detection sensitivity, good selectivity and fast response speed. They are ideal methods for real-time monitoring of multiple gases. Commonly used optical gas concentration monitoring technologies include non-dispersive infrared absorption method, Fourier transform infrared spectroscopy, portable Fourier transform infrared spectroscopy, tunable laser method and photoacoustic spectroscopy.

[0003] Since these key industries have the characteristics of high emission concentration and large variation range, gas detection needs to have the ability to respond quickly over a wide range.

[0004] Existing optical detection technology is mainly based on tunable optical absorption method. Laser has problems such as Mie scattering and Rayleigh scattering in high-concentration gas, and the system detection signal stability is poor. Utility Model Content

[0005] The embodiment of the present application provides a photoacoustic sensing detection system based on a microphone photoacoustic cell, which is used to solve the problem in the prior art that the laser based on the tunable optical absorption method has Mie scattering and Rayleigh scattering in high-concentration gas, the system detection signal stability is poor, and it is not suitable for large-scale greenhouse gas detection.

[0006] On the one hand, the embodiment of the present application provides a photoacoustic sensing detection system based on a microphone photoacoustic cell, comprising:

[0007] A signal generator, the signal of the signal generator is connected to an adder, the signal of the adder is connected to a laser, a photoacoustic cell is arranged downstream of the optical path of the laser, a pressure control unit, a temperature control unit, a microphone and an air intake filter are arranged on the photoacoustic cell, and a phase-locked amplifier signal is connected to the photoacoustic cell, a computer and the signal generator.

[0008] In a possible implementation manner, the signals transmitted between the signal generator and the adder are respectively a sine wave signal and a sawtooth wave signal.

[0009] In a possible implementation manner, the signal generator is connected to a reference signal input terminal of the lock-in amplifier through the sinusoidal signal.

[0010] In a possible implementation manner, a signal output end of the microphone is connected to a signal input end of the lock-in amplifier.

[0011] In a possible implementation manner, a signal output terminal of the lock-in amplifier is connected to the computer.

[0012] In a possible implementation, the laser is modularly configured, and the laser wavelength is selected according to the type of gas to be measured. In a possible implementation, the gas input port and the gas output port of the photoacoustic cell are respectively provided with a boost module and an electric control valve module of the pressure control unit, the pressure sensor of the pressure control unit is arranged in the photoacoustic cell, and the gas input port of the photoacoustic cell is also provided with an air intake filter.

[0013] In a possible implementation, the temperature control unit includes a temperature sensor, a heating device, and a heat dissipation device, and the temperature sensor is disposed inside the photoacoustic cell.

[0014] The photoacoustic sensing detection system based on the microphone photoacoustic cell in the present application has the following advantages:

[0015] (1) Accurate measurement of greenhouse gases over the entire range is achieved through the pressure control unit, temperature control unit and air intake filter, and the system has good stability.

[0016] (2) A wide range of greenhouse gas detection can be achieved by combining an air intake filter with a photoacoustic cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a photoacoustic sensing detection system based on a microphone photoacoustic cell provided in an embodiment of the present application;

[0019] Figure 2 This is a graph of the full-range stability test results of a photoacoustic sensing detection system based on a microphone photoacoustic cell provided in an embodiment of the present application.

[0020] Explanation of the numbers in the figure: 1. Signal generator; 2. Adder; 3. Laser; 4. Photoacoustic cell; 42. Pressure control unit; 43. Temperature control unit; 44. Microphone; 45. Air intake filter; 5. Lock-in amplifier; 6. Computer. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0022] Figure 1 A schematic diagram of the structure of a photoacoustic sensing detection system based on a microphone photoacoustic cell provided in an embodiment of the present application; an embodiment of the present application provides a photoacoustic sensing detection system based on a microphone photoacoustic cell, comprising:

[0023] A signal generator 1, wherein the signal of the signal generator 1 is connected to an adder 2, wherein the signal of the adder 2 is connected to a laser 3, wherein a photoacoustic cell 4 is arranged downstream of the optical path of the laser 3, wherein a pressure control unit 42, a temperature control unit 43, a microphone 44 and an air intake filter 45 are arranged on the photoacoustic cell 4, and a lock-in amplifier 5 is connected to the photoacoustic cell 4, a computer 6 and the signal generator 1;

[0024] The signals transmitted between the signal generator 1 and the adder 2 are respectively a sine signal and a sawtooth wave signal. The signal generator 1 is connected to the reference signal input end of the phase-locked amplifier 5 through the sine signal. The signal output end of the microphone 44 is connected to the signal input end of the phase-locked amplifier 5. The signal output end of the phase-locked amplifier 5 is connected to the computer 6. The laser 3 is modularly arranged. The laser 3 selects the laser wavelength according to the type of gas to be measured. The gas input port and the gas output port of the photoacoustic cell 4 are respectively provided with a boosting module and an electric control valve module of the pressure control unit 42. The pressure sensor of the pressure control unit 42 is arranged in the photoacoustic cell 4. The gas input port of the photoacoustic cell 4 is also provided with an air intake filter 45.

[0025] The temperature control unit 43 includes a temperature sensor, a heating device and a heat dissipation device. The temperature sensor is arranged inside the photoacoustic cell 4 .

[0026] Exemplarily, one channel of the signal generator 1 outputs a sinusoidal signal for modulating the laser 3; one channel outputs a sawtooth signal for realizing wavelength scanning of the laser 3. The two channel outputs of the signal generator are connected to the modulation port of the laser 3 after passing through the adder 2. The output laser of the laser 3 is connected to the photoacoustic pool 4 to excite the gas and detect the photoacoustic signal. In order to ensure higher stability, a temperature control unit 43 and a pressure control unit 42 are installed on the periphery of the photoacoustic pool 4; in order to ensure the cleanliness of the system, an air intake filter 45 is installed at the air inlet; the function of the air intake filter 45 is to physically isolate particulate matter in the intake air to prevent contamination of the photoacoustic pool 4.

[0027] The boosting module of the pressure control unit 42 is a boosting fan, which is arranged at the gas input port of the photoacoustic pool 4. The electric control valve module of the pressure control unit 42 is arranged at the gas output port of the photoacoustic pool 4. The gas flow rate control of the boosting module is combined with the gas flow control of the electric control valve module to achieve the pressure control inside the entire photoacoustic pool 4. The pressure inside the photoacoustic pool 4 is monitored by the pressure sensor of the pressure control unit 42, so that the pressure inside the photoacoustic pool 4 is within the set threshold range.

[0028] The temperature control unit 43 is arranged to wrap the photoacoustic pool 4 as a whole. The heating device of the temperature control unit 43 is a hot air blower, which heats the entire photoacoustic pool 4 by hot air. The temperature control unit 43 dissipates heat from the photoacoustic pool 4 through a heat dissipation device. The heat dissipation device is a heat sink with a fan, and the heat sink is attached to the pool wall of the photoacoustic pool 4. The temperature control unit 43 monitors the temperature inside the photoacoustic pool 4 through a temperature sensor. When the temperature inside the photoacoustic pool 4 reaches the specified temperature, the heat dissipation device and the heating device are started and stopped to maintain the temperature balance inside the photoacoustic pool 4.

[0029] The temperature control unit 43 maintains a constant temperature in the photoacoustic cell 4 by actively heating and dissipating heat. This is because when the temperature rises, the thermal motion of the gas molecules intensifies, resulting in Doppler broadening (proportional to the square root of the temperature). This will make the absorption peak wider and the peak absorption coefficient lower, thereby weakening the photoacoustic signal.

[0030] The pressure control unit 42 controls the pressure of the gas entering and leaving the photoacoustic cell 4 so that a relative temperature pressure is maintained in the cavity of the photoacoustic cell 4. This is because the increase in pressure leads to an increase in the frequency of molecular collisions, and the absorption line width (Lorentz broadening) increases accordingly, and the peak absorption coefficient decreases. If the light source line width is narrower than the absorption line width, the signal will be weakened; if the light source covers the entire broadened line type, the integrated absorption intensity may remain unchanged. In addition, pressure changes may change the resonant frequency of the photoacoustic cell 4, and the detection system needs to be adjusted to maintain sensitivity.

[0031] In order to improve the signal-to-noise ratio of the signal, the sinusoidal signal of the signal generator 1 is connected to the reference signal input terminal of the phase-locked amplifier 5, and the output electrical signal of the microphone 44 in the photoacoustic cell 4 is connected to the signal input terminal of the phase-locked amplifier 5 to achieve phase-locked detection. Finally, the output signal of the phase-locked amplifier 5 is connected to the computer 6 for data storage, display and post-processing. Using this system, accurate measurement within the range of 80000ppm-200000ppm can be achieved.

[0032] Optionally, the selection of the laser 1 is determined according to the absorption wavelength of the detection gas, and may be a DFB laser, a QCL laser, or other lasers.

[0033] In a possible embodiment, Figure 2 As shown, the horizontal axis is CO 2 The vertical axis is the gas concentration, and the vertical axis is the voltage signal output by the photoacoustic cell.

[0034] When testing, Figure 1 Different concentrations of CO are introduced into the air inlet above the middle air inlet filter 45. 2 The gas enters the photoacoustic cell 4 after passing through the air inlet filter 45 and the pressure control unit 42. The gas is ventilated for 5 minutes each time. After the system is stable, the average voltage of the last five minutes is taken as the voltage value, and the concentration and voltage value curves are obtained in turn. Finally, the test results of the full-scale stability test of the system are obtained.

[0035] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0036] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A photoacoustic sensing detection system based on a microphone photoacoustic cell, characterized in that: include: A signal generator (1), wherein the signal generator (1) is signal-connected to an adder (2), wherein the adder (2) is signal-connected to a laser (3), wherein a photoacoustic cell (4) is disposed downstream of the optical path of the laser (3), wherein a pressure control unit (42), a temperature control unit (43), a microphone (44) and an air intake filter (45) are disposed on the photoacoustic cell (4), and a phase-locked amplifier (5) is signal-connected to the photoacoustic cell (4), a computer (6) and the signal generator (1).

2. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The signals transmitted between the signal generator (1) and the adder (2) are respectively a sine wave signal and a sawtooth wave signal.

3. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 2, characterized in that: The signal generator (1) is connected to the reference signal input terminal of the lock-in amplifier (5) via the sinusoidal signal.

4. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The signal output end of the microphone (44) is connected to the signal input end of the lock-in amplifier (5).

5. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The signal output end of the lock-in amplifier (5) is connected to the computer (6).

6. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The laser (3) is modularly configured, and the laser wavelength of the laser (3) is selected according to the type of gas to be measured.

7. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The gas input port and the gas output port of the photoacoustic cell (4) are respectively provided with a pressurizing module and an electric control valve module of the pressure control unit (42); the pressure sensor of the pressure control unit (42) is arranged in the photoacoustic cell (4); and the gas input port of the photoacoustic cell (4) is also provided with an air intake filter (45).

8. The photoacoustic sensing detection system based on a microphone photoacoustic cell according to claim 1, characterized in that: The temperature control unit (43) comprises a temperature sensor, a heating device and a heat dissipation device, and the temperature sensor is arranged inside the photoacoustic cell (4).

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