CN215574610U

CN215574610U - Single resonant cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases

Info

Publication number: CN215574610U
Application number: CN202120681204.1U
Authority: CN
Inventors: 何赛灵; 王高旋; 蒋一鸣
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2021-04-02
Filing date: 2021-04-02
Publication date: 2022-01-18
Anticipated expiration: 2031-04-02

Abstract

The utility model discloses a single resonant cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases. The system sequentially comprises a light source module, a detection module and a processing module; the light source module is provided with a plurality of groups of light sources, each group of light sources sequentially comprises a laser driver, a distributed feedback laser and an optical fiber collimating mirror and is used for exciting gas to generate a photoacoustic effect; the detection module comprises a photoacoustic cell, a resonant cavity and a microphone, wherein the resonant cavity and the microphone are positioned in the photoacoustic cell and are used for collecting photoacoustic signals; light excited by the light source module is coupled into a path after passing through the beam splitter and enters a resonant cavity of the detection module; the processing module sequentially comprises a preamplifier, a lock-in amplifier and a data acquisition card; the data acquisition card is respectively connected with the laser driver and the computer. The utility model directly couples a plurality of laser beams without a light splitting mode, realizes the simultaneous detection of a plurality of gases, simplifies the system structure, can modulate and control the laser by only one signal without the help of a signal delay line and the like, and reduces the cost.

Description

Single resonant cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases

Technical Field

The utility model relates to the field of air pollution monitoring, in particular to a single-resonant-cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases.

Background

In recent years, various gas analysis sensors have important applications in industrial and scientific fields, such as environmental monitoring, atmospheric research, medical diagnostics, and industrial process control. Currently, multi-gas analysis is typically performed by multiple instruments, each instrument detecting a single gas individually. This method is costly and takes up a lot of space. In addition, with the continuous and rapid development of economy in China, numerous new industrial parks are built, meanwhile, hidden dangers are brought to the greatest extent, and the emission monitoring of various chemical substances in the industrial parks is important. Therefore, a need exists for a low cost gas analysis and detection system.

SUMMERY OF THE UTILITY MODEL

In order to overcome the defects of the prior art, the utility model provides a single resonant cavity photoacoustic detector for simultaneously detecting multiple gases

The spectrum system realizes the on-line monitoring of various pollution sources.

A single resonant cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases sequentially comprises a light source module, a detection module and a processing module; the light source module is provided with a plurality of groups of light sources, each group of light sources sequentially comprises a laser driver, a distributed feedback laser and an optical fiber collimating mirror and is used for exciting gas to generate a photoacoustic effect;

the detection module comprises a photoacoustic cell, a resonant cavity and a microphone, wherein the resonant cavity and the microphone are positioned in the photoacoustic cell and are used for collecting photoacoustic signals; the light excited by the light source module is coupled into one path after passing through the beam splitter and enters the resonant cavity of the detection module; the processing module sequentially comprises a preamplifier, a phase-locked amplifier and a data acquisition card; and the data acquisition card is respectively connected with the laser driver and the computer.

The resonant cavity is sealed in the photoacoustic cell, buffer cells are arranged at two ends of the resonant cavity and used for reducing and avoiding environmental noise, and the microphone is positioned in the middle of the resonant cavity and used for collecting photoacoustic signals and converting the photoacoustic signals into electric signals.

The photoacoustic cell is provided with an air inlet and an air outlet which are respectively positioned at two sides of the resonant cavity.

The current signal transmitted by the microphone is amplified by the preamplifier, enters the phase-locked amplifier to extract the photoacoustic spectrum signal, and finally enters the data acquisition card.

The utility model has the beneficial effects that:

1. multiple beams of laser are directly coupled without a light opening mode, so that simultaneous detection of multiple gases is realized, and the system structure is simplified.

2. Only one path of signal is used for modulating and controlling the laser without the help of a signal delay line and the like, so that the requirement on a signal generator is reduced, and the cost is reduced.

Drawings

FIG. 1 is a schematic diagram of a single-resonant-cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases.

The device comprises a distributed feedback laser 1, a laser driver 2, a resonant cavity 3, a microphone 4, a preamplifier 5, a lock-in amplifier 6, a data acquisition card 7, a computer 8, an optical fiber collimating mirror 9, a beam splitter 10, an air inlet 11, an air outlet 12 and a photoacoustic cell 13.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

As shown in fig. 1, a single-resonant-cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases sequentially includes a light source module, a detection module, and a processing module; the light source module is provided with a plurality of groups of light sources (two groups are shown in figure 1), and each group sequentially comprises a laser driver 2, a distributed feedback laser 1 and an optical fiber collimating mirror 9 and is used for exciting gas to generate a photoacoustic effect. The distributed feedback laser 1 tunes a diode laser with a very narrow linewidth, so that the output wavelength of the laser completely scans the absorption peak of the target gas. The distributed feedback laser 1 is then connected to a fiber collimator 9 via an optical fiber. The parallel light emitted from the fiber collimator 9 is coupled into a laser beam through the beam splitter 10 and enters the resonant cavity 3. The resonant cavity 3 is sealed in the photoacoustic cell 13, buffer cells are arranged at two ends of the resonant cavity 3 for reducing and avoiding environmental noise, and the microphone 4 is positioned in the middle of the resonant cavity 3 for collecting photoacoustic signals and converting the photoacoustic signals into electric signals. The photoacoustic cell 13 is provided with an air inlet 11 and an air outlet 12 which are respectively positioned at two sides of the resonant cavity 3.

The detection module comprises a photoacoustic cell 13, a resonant cavity 3 and a microphone 4, wherein the resonant cavity 3 and the microphone are positioned in the photoacoustic cell and are used for collecting photoacoustic signals.

The processing module comprises a preamplifier 5, a lock-in amplifier 6 and a data acquisition card 7 in sequence. The data acquisition card 7 is respectively connected with the laser driver 2 and the computer 8. The current signals transmitted by the microphone 4 are amplified by the preamplifier 5, enter the phase-locked amplifier 6 to extract photoacoustic spectrum signals, and finally enter the data acquisition card 7.

Application examples

Taking the simultaneous measurement of ammonia gas and methane as an example, the mixed gas of methane and ammonia gas enters from the gas inlet 11 and is uniformly distributed in the resonant cavity 3. The wavelength of the distributed feedback laser 1 for measuring ammonia gas was around 1512 nm and the wavelength of the distributed feedback laser 1 for measuring methane was around 1653 nm, as determined by the absorption peak positions of ammonia gas and methane.

The detection module comprises a photoacoustic cell 13, a resonant cavity 3 and a microphone 4, wherein the resonant cavity 3 and the microphone are positioned in the photoacoustic cell and are used for collecting photoacoustic signals; a data acquisition card 7 outputs a superposed signal of a sawtooth wave and a sine wave to a laser driver. The sawtooth wave is used to tune the wavelength of the laser and the sine wave is used to modulate the laser. When the tuned laser sweeps the absorption peak of the target gas in the resonant cavity 3, the photoacoustic effect is caused, and an acoustic signal is generated. And the frequency of the sound signal at this time coincides with the modulation frequency of the laser. Therefore, by changing the modulation frequency of the laser to be the same as the first longitudinal mode frequency of the resonant cavity, the sound signal with the same frequency as the first longitudinal mode frequency of the resonant cavity can be obtained, and at the moment, the sound signal generates a resonance effect in the resonant cavity, so that the sound signal is amplified. The microphone 4 located at the center of the resonant cavity 3 collects the amplified sound signal and converts it into an electrical signal.

The electric signal transmitted by the microphone 4 firstly enters the preamplifier 5 to primarily amplify the signal, and then the amplified signal enters the phase-locked amplifier 6. The digital acquisition card 7 outputs a square wave signal with the same frequency as the sine modulation signal as a reference signal of the lock-in amplifier 6, so that the lock-in amplifier 6 can extract a part of the electric signal converted by the photoacoustic signal. The final result is input into a terminal computer 8 by a digital acquisition card 7. Through the calculation of software, after one scanning period, the photoacoustic spectrum of the gas can be obtained, and the gas concentration can be inverted.

The two gases are measured simultaneously, two groups of light sources are controlled by utilizing superposition signals of sawtooth waves and sine waves, the distributed feedback type laser temperature and current are controlled, in a period, a first group of distributed feedback type lasers 1 sweep an absorption peak of a first gas firstly, at the moment, a second group of distributed feedback type lasers do not sweep an absorption peak of a second gas, and after the first group of distributed feedback type lasers sweep the absorption peak of the first gas, the wavelength of the second group of distributed feedback type lasers can sweep the absorption peak of the second gas, so that photoacoustic signals of the first gas and the second gas are obtained respectively; the processing module collects photoacoustic signals with different wavelengths together to obtain photoacoustic spectrums, and therefore the gas concentration is calculated.

For ammonia and methane, the laser scan range for ammonia was 1511.9 to 1512.3 nanometers and the scan range for methane was 1653.6 to 1654.3 nanometers by adjusting the laser driver 2. While the absorption peaks for ammonia and methane were at 1512.24 and 1653.7 nm, respectively. In the case of simultaneous scanning by both lasers, the coupled laser would sweep the methane absorption peak before the ammonia absorption peak. Therefore, only one signal is needed to control two lasers, so that photoacoustic signals of two gases are obtained in one scanning.

When two gases are detected simultaneously, if one gas A generates crosstalk to the other gas B, the concentration of the undisturbed (or least disturbed) gas A is calculated according to the photoacoustic signal of the undisturbed (or least disturbed) gas A, and the gas A is considered as the real concentration. And calculating the interference value of the gas A to the photoacoustic signal of the gas B by using the concentration of the gas A. At the moment, the measured photoacoustic of the gas B is deducted from the interference value of the gas A, so that a real photoacoustic signal of the gas B can be obtained, and a real concentration value of the gas B can be obtained. For ammonia and methane, the ammonia can interfere with the photoacoustic signal of methane, and the methane does not interfere with the signal of the ammonia. Therefore, after one-time scanning is finished, the gas concentration of the ammonia gas is inverted through the photoacoustic signal of the ammonia gas, and then the influence of the current ammonia gas concentration on the methane photoacoustic signal is calculated. After the influence brought by the photoacoustic signal of the ammonia gas is deducted from the photoacoustic signal of the methane, a real methane photoacoustic signal can be obtained, and thus the gas concentration of the methane is inverted.

It will be apparent to those skilled in the art that gases other than ammonia and methane, or two or more gases may be detected simultaneously by simple modification or modification based on the embodiments.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the utility model. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A single resonant cavity photoacoustic spectroscopy system for simultaneously detecting multiple gases, comprising: the device sequentially comprises a light source module, a detection module and a processing module; the light source module is provided with a plurality of groups of light sources, each group of light sources sequentially comprises a laser driver, a distributed feedback laser and an optical fiber collimating mirror and is used for exciting gas to generate a photoacoustic effect;

the detection module comprises a photoacoustic cell, a resonant cavity and a microphone, wherein the resonant cavity and the microphone are positioned in the photoacoustic cell and are used for collecting photoacoustic signals;

the light excited by the light source module is coupled into one path after passing through the beam splitter and enters the resonant cavity of the detection module;

the processing module sequentially comprises a preamplifier, a phase-locked amplifier and a data acquisition card;

and the data acquisition card is respectively connected with the laser driver and the computer.

2. The system of claim 1, wherein: the resonant cavity is sealed in the photoacoustic cell, buffer cells are arranged at two ends of the resonant cavity and used for reducing and avoiding environmental noise, and the microphone is positioned in the middle of the resonant cavity and used for collecting photoacoustic signals and converting the photoacoustic signals into electric signals.

3. The system of claim 2, wherein: the photoacoustic cell is provided with an air inlet and an air outlet which are respectively positioned at two sides of the resonant cavity.