Photoacoustic cell for gas photoacoustic spectrum detection

Abstract

The invention provides a photoacoustic cell for gas photoacoustic spectrum detection, which belongs to the technical field of gas measurement, and comprises a first photoacoustic cell group, a second photoacoustic cell group, a light source, a light source segmentation assembly and a signal processor, the first photoacoustic cell group comprises a first photoacoustic cell and a second photoacoustic cell, and the first photoacoustic cell and the second photoacoustic cell are communicated with each other and are symmetrically arranged; a first air inlet and a first air outlet are formed in the communication part of the first photoacoustic cell and the second photoacoustic cell; the second photoacoustic cell group comprises a third photoacoustic cell and a fourth photoacoustic cell, and the third photoacoustic cell and the fourth photoacoustic cell are communicated with each other and are symmetrically arranged; a second air inlet and a second air outlet are formed in the communication part of the third photoacoustic cell and the fourth photoacoustic cell; the first photoacoustic cell and the fourth photoacoustic cell have the same structure, and the second photoacoustic cell and the third photoacoustic cell have the same structure. The photoacoustic cell for gas photoacoustic spectrum detection is high in detection sensitivity and more stable and accurate in measurement result.

Description

Technical Field

[0001] The invention relates to the technical field of gas measurement, in particular to a photoacoustic cell for gas photoacoustic spectrum detection. Background Art

[0002] The existing gas concentration measurement methods mainly include gas chromatography and photoacoustic spectroscopy. Gas chromatography requires standard gas and carrier gas, and the chromatographic column needs to be replaced and calibrated regularly, which makes the measurement and maintenance work more complicated.

[0003] Traditional photoacoustic spectroscopy technology generally only sets up one photoacoustic cell. Each time a measurement is made, it is necessary to first flush pure gas, measure the background signal in the photoacoustic value, and then fill the gas to be tested, and measure the signal change of the gas to be tested. However, the gas to be tested contains the background signal, and finally the signal in the gas to be tested needs to be subtracted from the background signal to obtain the pure signal of the gas to be tested. However, the background signal keeps changing, causing the signal of the gas to be tested to deviate, and the final measurement result is inaccurate.

[0004] The invention patent with application number 202311150394.4 discloses a gas concentration measurement system and method based on a series dual photoacoustic cell. Two photoacoustic cells in series are used to reduce the impact of background signals. However, when the series connection is used, the energy of the infrared light source will decay after passing through the first photoacoustic cell, resulting in inaccurate measurements. The invention patent with application number 202311559000.0 discloses a parallel dual photoacoustic cell gas concentration measurement method and device. The two photoacoustic cells are set in parallel, which solves the problem of energy attenuation when the photoacoustic cells are connected in series and improves the measurement accuracy. However, the detection sensitivity of this measurement method is low, and the effect is not ideal when measuring trace gases. Summary of the invention

[0005] The object of the present invention is to provide a photoacoustic cell for gas photoacoustic spectroscopy detection, which has high detection sensitivity and more stable and accurate measurement results.

[0006] To achieve the above object, the present invention provides a photoacoustic cell for gas photoacoustic spectroscopy detection, comprising a first photoacoustic cell group and a second photoacoustic cell group, and also comprising a light source, a light source splitting component and a signal processor;

[0007] The first photoacoustic cell group includes a first photoacoustic cell and a second photoacoustic cell, the first photoacoustic cell and the second photoacoustic cell are interconnected and symmetrically arranged;

[0008] A first air inlet and a first air outlet are provided at the connection point between the first photoacoustic cell and the second photoacoustic cell;

[0009] The second photoacoustic cell group includes a third photoacoustic cell and a fourth photoacoustic cell, the third photoacoustic cell and the fourth photoacoustic cell are interconnected and symmetrically arranged;

[0010] A second air inlet and a second air outlet are provided at the connection point between the third photoacoustic cell and the fourth photoacoustic cell;

[0011] The first photoacoustic cell and the fourth photoacoustic cell have the same structure, and the second photoacoustic cell and the third photoacoustic cell have the same structure.

[0012] Preferably, a window is provided at the end of the second photoacoustic cell, a truncated cone-shaped buffer chamber is provided inside the window, the inside of the truncated cone-shaped buffer chamber is connected to the second resonant cavity, and the other end of the second resonant cavity is also connected to the truncated cone-shaped buffer chamber;

[0013] A second sound sensor is also arranged on the second photoacoustic cell.

[0014] Preferably, the first photoacoustic cell comprises a buffer chamber and a first resonant cavity, the buffer chamber is connected to the first resonant cavity, and the other end of the first resonant cavity is also connected to the buffer chamber;

[0015] A first sound sensor is also arranged on the first photoacoustic cell.

[0016] Preferably, the first sound sensor on the first photoacoustic cell and the second sound sensor on the second photoacoustic cell are both connected to the first differential amplifier;

[0017] The second sound sensor on the third photoacoustic cell and the first sound sensor on the fourth photoacoustic cell are both connected to the second differential amplifier.

[0018] Preferably, the output terminals of the first differential amplifier and the second differential amplifier are both connected to the input terminal of the signal processor.

[0019] Preferably, the light source segmentation assembly includes a converging mirror, a filter, a chopper, an infrared semi-reflecting mirror and an infrared total reflecting mirror, the converging mirror is arranged directly below the light source, the filter is arranged directly below the converging mirror, the chopper is arranged directly below the filter, the infrared semi-reflecting mirror is arranged directly below the chopper and located at the top of the window of the second photoacoustic cell, and the infrared total reflecting mirror is arranged on the reflected light path of the infrared semi-reflecting mirror and located at the top of the window of the third photoacoustic cell.

[0020] Preferably, the first sound sensor and the second sound sensor are any one of a microphone and an optical fiber sound sensor.

[0021] Preferably, the first resonant cavity and the second resonant cavity have the same structure, and the ratio of the length of the resonant cavity to its cross-sectional area is greater than 10.

[0022] Preferably, the light source is an infrared light source.

[0023] Therefore, the present invention adopts the above-mentioned photoacoustic cell for gas photoacoustic spectroscopy detection, and the technical effects are as follows:

[0024] (1) The first photoacoustic cell group and the second photoacoustic cell group are filled with the gas to be tested and the pure gas, respectively, and the first sound signal and the second sound signal are collected, respectively. After the infrared light passes through the second photoacoustic cell, opposite sound signals are generated in the first resonant cavity and the second resonant cavity, and a double sound signal (the first sound signal) is obtained by subtracting them through a differential amplifier; similarly, the second sound signal is obtained. Therefore, the photoacoustic cell proposed in the present invention improves the sensitivity of gas detection.

[0025] (2) The buffer chamber is set to be in a truncated cone shape, which effectively improves the detection sensitivity of the photoacoustic cell, and cooperates with the first photoacoustic cell group and the second photoacoustic cell group to achieve the effect of doubly improving the detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of the structure of a photoacoustic cell for gas photoacoustic spectroscopy detection.

[0027] Reference numerals

[0028] 1. Light source; 2. Converging mirror; 3. Filter; 4. Chopper; 5. Infrared half-reflecting mirror; 6. Infrared total-reflecting mirror; 7. First photoacoustic cell; 8. Second photoacoustic cell; 9. Third photoacoustic cell; 10. Fourth photoacoustic cell; 11. First air inlet; 12. First air outlet; 13. Second air inlet; 14. Second air outlet; 15. Window; 16. Cone-shaped buffer chamber; 17. Second resonant cavity; 18. Second sound sensor; 19. Buffer chamber; 20. First resonant cavity; 21. First sound sensor; 22. First differential amplifier; 23. Second differential amplifier; 24. Signal processor. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0030] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0031] Embodiment 1

[0032] like Figure 1 , which is a schematic diagram of the structure of a photoacoustic cell for gas photoacoustic spectroscopy detection according to the present invention, including a first photoacoustic cell group and a second photoacoustic cell group. It also includes a light source 1, a light source segmentation component and a signal processor 24. In this embodiment, the light source 1 is an infrared light source.

[0033] The first photoacoustic cell group is used to be filled with the gas to be tested, and the second photoacoustic cell group is used to be filled with pure gas.

[0034] The first photoacoustic cell group includes a first photoacoustic cell 7 and a second photoacoustic cell 8 . The first photoacoustic cell 7 and the second photoacoustic cell 8 are interconnected and symmetrically arranged.

[0035] A first air inlet 11 and a first air outlet 12 are provided at the connection point between the first photoacoustic cell 7 and the second photoacoustic cell 8;

[0036] The first photoacoustic cell 7 includes a buffer chamber 19 and a first resonant cavity 20, the buffer chamber 19 is connected to the first resonant cavity 20, and the other end of the first resonant cavity 20 is connected to another buffer chamber 19;

[0037] A first sound sensor 21 is also provided on the first photoacoustic cell 7. A second sound sensor 18 is provided on the second photoacoustic cell 8. The second sound sensor 18 collects the sound signal generated after the light beam passes through.

[0038] A window 15 is provided at the end of the second photoacoustic cell 8, a truncated cone-shaped buffer chamber 16 is provided inside the window 15, a second resonant cavity 17 is provided inside the truncated cone-shaped buffer chamber 16, and the second resonant cavity 17 is communicated with the truncated cone-shaped buffer chamber 16;

[0039] The first sound sensor 21 on the first photoacoustic cell 7 and the second sound sensor 18 on the second photoacoustic cell 8 are both connected to the first differential amplifier 22;

[0040] The first resonant cavity 20 and the second resonant cavity 17 have the same structure, and the ratio of the length of the resonant cavity to its cross-sectional area is greater than 10.

[0041] When the light beam is projected into the second photoacoustic pool 8 through the window 15, the gas to be measured in the second photoacoustic pool 8 absorbs the infrared light source and is excited by the light to generate heat, thereby expanding. At this time, the gas to be measured in the first photoacoustic pool 7 does not expand instantly because it is not illuminated by light. Therefore, the gas in the second photoacoustic pool 8 will compress the gas in the first photoacoustic pool 7 after expansion, so that the phases of the sound signals generated by the first resonant cavity 20 and the second resonant cavity 17 are opposite, and then the first sound sensor 21 and the second sound sensor 18 transmit the collected sound signals to the first differential amplifier 22, and the first differential amplifier 22 subtracts the two sound signals to obtain a double sound signal.

[0042] The second photoacoustic cell group includes a third photoacoustic cell 9 and a fourth photoacoustic cell 10, and the third photoacoustic cell 9 and the fourth photoacoustic cell 10 are interconnected and symmetrically arranged;

[0043] A second air inlet 13 and a second air outlet 14 are provided at the connection point between the third photoacoustic cell 9 and the fourth photoacoustic cell 10;

[0044] The third photoacoustic cell 9 is also provided with a second sound sensor 18. The second sound sensor 18 collects the sound signal generated after the light beam passes through. The fourth photoacoustic cell 10 is also provided with a first sound sensor 21.

[0045] The second acoustic sensor 18 on the third photoacoustic cell 9 and the first acoustic sensor 21 on the fourth photoacoustic cell 10 are both connected to the second differential amplifier 23 .

[0046] When the light beam is incident into the third photoacoustic cell 9 through the window 15, the pure gas in the second photoacoustic cell 9 absorbs the infrared light source and is excited by the light to generate heat, thereby expanding. At this time, the pure gas in the fourth photoacoustic cell 10 does not expand instantly because it is not illuminated. Therefore, the gas in the fourth photoacoustic cell 10 will compress the gas in the third photoacoustic cell 9 after expansion, so that the phases of the sound signals generated by the first resonant cavity 20 and the second resonant cavity 17 are opposite, and then the first sound sensor 21 and the second sound sensor 18 transmit the collected sound signals to the second differential amplifier 23, and the second differential amplifier 23 subtracts the two sound signals to obtain a double sound signal.

[0047] The output ends of the first differential amplifier 22 and the second differential amplifier 23 are both connected to the input end of the signal processor 24. The two doubled sound signals obtained by the first photoacoustic cell group and the second photoacoustic cell group are processed by the signal processor 24.

[0048] The signal processor can adopt a terminal with computing processing capability such as a single chip microcomputer and an industrial computer.

[0049] The first photoacoustic cell 7 and the fourth photoacoustic cell 10 have the same structure, and the second photoacoustic cell 8 and the third photoacoustic cell 9 have the same structure.

[0050] The light source dividing component comprises a converging mirror 2 , a filter 3 , a chopper 4 , an infrared half-reflecting mirror 5 and an infrared total-reflecting mirror 6 .

[0051] The converging mirror 2 is arranged directly below the light source 1, the filter 3 is arranged directly below the converging mirror 2, the chopper 4 is arranged directly below the filter 3, the infrared half-reflecting mirror 5 is arranged directly below the chopper 4 and located at the top of the window 15 of the second photoacoustic cell 8, and the infrared total reflection mirror 6 is arranged on the reflection light path of the infrared half-reflecting mirror 5 and located at the top of the window 15 of the third photoacoustic cell 9.

[0052] The converging mirror 2 converges the infrared light beam emitted by the light source 1 into a parallel light beam, filters out stray light through the filter 3 with a specific central wavelength corresponding to the absorption peak of the gas to be measured, and then passes through the chopper 4 to make the continuously emitted infrared light beam form an infrared pulse light with a certain period of time. The infrared pulse light is divided into a first light beam and a second light beam by an infrared semi-reflecting mirror 5. The first light beam is transmitted light and directly enters the second photoacoustic cell 8. The second light beam is reflected light and is reflected by the infrared total reflection mirror 6 into the third photoacoustic cell 9.

[0053] The first sound sensor 21 and the second sound sensor 18 are any one of a microphone and an optical fiber sound sensor. In this embodiment, a microphone is used.

[0054] The working process of the present invention is as follows:

[0055] First, the first air inlet, the first air outlet, the second air inlet and the second air outlet of the first photoacoustic cell group and the second photoacoustic cell group are opened, and the gas to be measured and the pure gas are respectively charged into the first photoacoustic cell group and the second photoacoustic cell group. The infrared light beam emitted by the light source is divided into the first light beam and the second light beam by the light source splitting component, the first light beam enters the second photoacoustic cell, and the second light beam enters the third photoacoustic cell. The gas in the second photoacoustic cell and the third photoacoustic cell expands due to the excitation of light, thereby squeezing the first photoacoustic cell and the fourth photoacoustic cell. The first sound sensor and the second sound sensor collect corresponding sound signals and transmit them to the first differential amplifier and the second differential amplifier to obtain two double sound signals, which are then transmitted to the signal processor for processing, and finally the concentration of the gas to be measured is obtained.

[0056] During the working process, in order to reduce the influence of background signals, pure gas is filled into the first photoacoustic cell group and the second photoacoustic cell group, and the proportional coefficient is calculated; the first photoacoustic cell group is filled with the gas to be tested, and the second photoacoustic cell group is filled with pure gas, and the sound signal of the gas to be tested is calculated by the proportional coefficient; the sound signals generated by the gas to be tested of different concentrations are recorded, and the linear relationship between the gas concentration and the sound signal is obtained by measuring the data; for the gas of unknown concentration, after the sound signal is measured, the corresponding concentration can be obtained by using the relationship between the gas concentration and the sound signal. The calculation here is the prior art and will not be elaborated in detail in the present invention.

[0057] The innovation of the present invention is that on the basis of the parallel dual photoacoustic cell gas concentration measurement device, each photoacoustic cell is again connected in parallel with a photoacoustic cell, so as to obtain a double sound signal and improve the sensitivity of detection. In addition, the buffer chamber is set to a truncated cone shape to also improve the sensitivity of detection. The above two technologies are combined together to further improve the sensitivity of detection.

[0058] Therefore, the present invention adopts the above-mentioned photoacoustic cell for gas photoacoustic spectroscopy detection, which has high detection sensitivity and more stable and accurate measurement results.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A photoacoustic cell for gas photoacoustic spectroscopy detection, comprising a first photoacoustic cell group and a second photoacoustic cell group, characterized in that: Also includes a light source, a light source splitting component and a signal processor; The first photoacoustic cell group includes a first photoacoustic cell and a second photoacoustic cell, the first photoacoustic cell and the second photoacoustic cell are interconnected and symmetrically arranged; A first air inlet and a first air outlet are provided at the connection point between the first photoacoustic cell and the second photoacoustic cell; The second photoacoustic cell group includes a third photoacoustic cell and a fourth photoacoustic cell, the third photoacoustic cell and the fourth photoacoustic cell are interconnected and symmetrically arranged; A second air inlet and a second air outlet are provided at the connection point between the third photoacoustic cell and the fourth photoacoustic cell; The first photoacoustic cell and the fourth photoacoustic cell have the same structure, and the second photoacoustic cell and the third photoacoustic cell have the same structure.

2. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 1, characterized in that: A window is provided at the end of the second photoacoustic cell, a truncated cone-shaped buffer chamber is provided inside the window, the inside of the truncated cone-shaped buffer chamber is communicated with the second resonant cavity, and the other end of the second resonant cavity is also communicated with the truncated cone-shaped buffer chamber; A second sound sensor is also arranged on the second photoacoustic cell.

3. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 2, characterized in that: The first photoacoustic cell comprises a buffer chamber and a first resonant cavity, the buffer chamber is connected to the first resonant cavity, and the other end of the first resonant cavity is also connected to the buffer chamber; A first sound sensor is also arranged on the first photoacoustic cell.

4. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 3, characterized in that: The first sound sensor on the first photoacoustic cell and the second sound sensor on the second photoacoustic cell are both connected to the first differential amplifier; The second sound sensor on the third photoacoustic cell and the first sound sensor on the fourth photoacoustic cell are both connected to the second differential amplifier.

5. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 4, characterized in that: The output terminals of the first differential amplifier and the second differential amplifier are both connected to the input terminal of the signal processor.

6. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 5, characterized in that: The light source splitting component comprises a converging mirror, a filter, a chopper, an infrared half-reflecting mirror and an infrared total-reflecting mirror. The converging mirror is arranged directly below the light source, the filter is arranged directly below the converging mirror, the chopper is arranged directly below the filter, the infrared half-reflecting mirror is arranged directly below the chopper and located at the top of the window of the second photoacoustic cell, and the infrared total-reflecting mirror is arranged on the reflected light path of the infrared half-reflecting mirror and located at the top of the window of the third photoacoustic cell.

7. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 6, characterized in that: The first sound sensor and the second sound sensor are either microphones or optical fiber sound sensors.

8. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 7, characterized in that: The first resonant cavity and the second resonant cavity have the same structure, and the ratio of the length of the resonant cavity to its cross-sectional area is greater than 10.

9. The photoacoustic cell for gas photoacoustic spectroscopy detection according to claim 8, characterized in that: The light source is an infrared light source.

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