CN218995141U

CN218995141U - TDLAS gas concentration monitoring system and gas absorption tank

Info

Publication number: CN218995141U
Application number: CN202220554243.XU
Authority: CN
Inventors: 商俊娟; 马俊亚; 张梦娇; 竹显伟; 张�浩; 胡建东
Original assignee: Henan Agricultural University
Current assignee: Henan Agricultural University
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2023-05-09
Anticipated expiration: 2032-03-15

Abstract

The utility model provides a TDLAS gas concentration monitoring system and a gas absorption tank, comprising a laser and a beam splitter, wherein the laser corresponds to the incident end of the beam splitter, the emergent end of the beam splitter is respectively connected with a laser frequency stabilization light path and a gas concentration monitoring light path, the incident light of the stabilization light path of the laser frequency stabilization light path corresponds to the central axis of the gas absorption tank, and the incident light of the monitoring light path of the gas concentration monitoring light path corresponds to the eccentric axis of the gas absorption tank. The beneficial effects are that: in the gas concentration monitoring system, laser is divided into two beams by a beam splitter, one beam of laser is emitted from a central shaft of a gas absorption tank, reflected by a cavity mirror, enters a photoelectric detector I by a polarization beam splitting prism, and is fed back to a laser after being processed by a feedback circuit, so that long-term stability of laser frequency is realized; the other laser beam is emitted from the eccentric shaft of the gas absorption tank, enters the photoelectric detector II after being transmitted, and then the gas concentration information is calculated by the inversion calculation circuit.

Description

TDLAS gas concentration monitoring system and gas absorption tank

Technical Field

The utility model relates to the technical field of gas concentration monitoring, in particular to a TDLAS gas concentration monitoring system and a gas absorption tank.

Background

The tunable semiconductor laser absorption spectrum (TDLAS) has the characteristics of non-contact property, high selectivity, high sensitivity, high on-line response speed, strong environmental adaptability and the like. The principle is that the output wavelength of the semiconductor laser is tuned by current and temperature, a certain absorption spectrum of the detected gas is scanned, and the concentration of the detected gas is obtained by detecting the absorption intensity of the absorption spectrum. Different atoms, ions and molecules all have their characteristic absorption lines, the kinds of the sample to be measured can be accurately distinguished through the absorption lines, and the intensity of the absorption lines can calculate the content of the gas. The light source adopted by the TDLAS technology mainly comprises an external cavity type semiconductor laser and a distributed feedback type laser. The laser is interfered by temperature, air pressure, vibration and other factors, and the center frequency of the output laser drifts along with time, which is about 90MHz per hour. If the center wavelength correction is not performed in the actual measurement system, the sequence spectrum data is overlapped, the processed spectrum line shape is widened, the fitting of the spectrum line shape is further influenced, and finally the inversion accuracy of the gas concentration is reduced.

Disclosure of Invention

The utility model provides a TDLAS gas concentration monitoring system and a gas absorption tank, which solve the problem that the laser frequency drifts along with time in the prior art, and the inversion accuracy of the gas concentration is affected.

The technical scheme of the utility model is realized as follows:

the utility model provides a TDLAS gas concentration monitoring system, includes laser instrument and beam splitter, and the laser instrument corresponds with the incident end of beam splitter, and the exit end of beam splitter is connected with laser frequency stable light path and gas concentration monitoring light path respectively, and the stable light path incident light of laser frequency stable light path corresponds with the center pin of gas absorption pond, and the monitoring light path incident light of gas concentration monitoring light path corresponds with the eccentric shaft of gas absorption pond. The incident light of the stable light path enters the gas absorption tank, and the gas absorption tank is used as a reference cavity at the moment, so that the long-term stability of the laser frequency is ensured; and the incident light of the monitoring light path enters the gas absorption tank, and the gas concentration information in the gas absorption tank is calculated through inversion of the transmission signal of the gas absorption tank.

The laser frequency stabilized light path comprises an electro-optical modulator, a polarization beam splitter prism and a photoelectric detector I, stabilized light path incident light sequentially enters a gas absorption tank through the electro-optical modulator and the polarization beam splitter prism, stabilized light path reflected light emitted by the gas absorption tank enters the photoelectric detector I through the polarization beam splitter prism, laser split by a beam splitter enters the electro-optical modulator to be subjected to phase modulation to form stabilized light path incident light, the stabilized light path incident light enters the gas absorption tank from the central shaft of the gas absorption tank through the polarization beam splitter prism, the stabilized light path incident light forms stabilized light path reflected light after being reflected in the gas absorption tank, the stabilized light path reflected light enters the photoelectric detector I through the polarization beam splitter prism, and then the stabilized light path reflected light is mixed with a driving signal of the electro-optical modulator through a mixer to obtain an error signal.

The output end of the photoelectric detector I is connected with the laser through a feedback circuit. The feedback circuit comprises an integrating circuit and a frequency locking circuit. The photoelectric detector I processes the error signal through the integrating circuit and the frequency locking circuit and feeds the processed error signal back to the laser, so that laser frequency stability is realized.

The gas concentration monitoring light path comprises an acousto-optic modulator and a photoelectric detector II, wherein incident light of the monitoring light path sequentially passes through the acousto-optic modulator and the gas absorption tank to enter the photoelectric detector II, and the output end of the photoelectric detector II is connected with the inversion calculation circuit. The laser emitted by the beam splitter is subjected to wavelength scanning and frequency modulation through the acousto-optic modulator, the modulated laser is emitted into the gas absorption tank from the eccentric shaft of the gas absorption tank, the transmission part refracted by the gas absorption tank is received by the photoelectric detector II, and then the gas concentration information is calculated through the inversion calculation circuit.

A gas absorption cell for TDLAS gas concentration monitoring system, includes the main part, and the both ends of main part are equipped with the concave mirror of relative placement, and the main part cooperates with the concave mirror and forms the cavity. The cavity is used as a reference cavity and a gas absorption cavity, and the two functions of laser frequency stabilization and gas concentration monitoring are realized by using one gas absorption tank, so that the complexity of the system is simplified and portability is provided under the condition that long-term laser stabilization can be ensured.

The two ends of the main body are respectively provided with an air inlet and an air outlet, the air inlet and the air outlet are communicated with the cavity, and gas enters the cavity from the air inlet and is discharged from the air outlet.

The main body is an indium steel pipe, and the length and the diameter of the indium steel pipe are 100mm. The low thermal expansion coefficient performance of the indium steel material is utilized to reduce heat radiation and improve the stability of the absorption cell.

The outer circle of the main body is provided with a horizontal step. The step is used for supporting the main body, so that the installation and the use of the gas absorption tank are facilitated.

The utility model has the beneficial effects that: in the gas concentration monitoring system, laser is divided into two beams by a beam splitter, one beam of laser is emitted from a central shaft of a gas absorption tank, reflected by a cavity mirror, enters a photoelectric detector I by a polarization beam splitting prism, and is fed back to a laser after being processed by a feedback circuit, so that long-term stability of laser frequency is realized; the other laser beam is emitted from an eccentric shaft of the gas absorption tank, enters a photoelectric detector II after being transmitted, and then is calculated by an inversion calculation circuit to obtain gas concentration information; in the gas concentration monitoring system, the gas absorption tank is used as a reference cavity and a gas absorption cavity, and the gas absorption tank is dual-purpose, so that the complexity of the system is effectively reduced, and the integration of the system is facilitated.

Drawings

In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the utility model, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic diagram of a TDLAS gas concentration monitoring system.

Fig. 2 is a cross-sectional view of a gas absorption cell.

Fig. 3 is a side view of a gas absorption cell.

In the figure: the device comprises a 1-laser, a 2-beam splitter, a 3-electro-optical modulator, a 31-stable light path incident light, a 32-stable light path reflected light, a 4-acousto-optic modulator, a 41-monitoring light path incident light, a 5-polarization beam splitter prism, a 6-photoelectric detector I, a 7-gas absorption tank, a 71-main body, a 72-cavity, a 73-concave reflector, a 74-air inlet, a 75-air outlet, a 76-horizontal step and an 8-photoelectric detector II.

Detailed Description

The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without any inventive effort, are intended to be within the scope of the utility model.

Embodiment 1, as shown in fig. 1, a TDLAS gas concentration monitoring system includes a laser 1 and a beam splitter 2, where the laser 1 corresponds to an incident end of the beam splitter 2, the laser 1 generates laser light and emits the laser light into the beam splitter 2, the beam splitter 2 divides one beam of the laser light into two beams of laser light, an outgoing end of the beam splitter 2 is connected with a laser frequency stabilization optical path and a gas concentration monitoring optical path, a stabilization optical path incident light 31 of the laser frequency stabilization optical path corresponds to a central axis of the gas absorption tank 7, and a monitoring optical path incident light 41 of the gas concentration monitoring optical path corresponds to an eccentric axis of the gas absorption tank 7. A beam of laser enters a laser frequency stabilization light path, is emitted from a central shaft of the gas absorption tank 7, measures a laser error signal through the laser frequency stabilization light path, and is fed back to the laser to ensure the stabilization of the laser frequency; the other laser beam enters a gas concentration monitoring light path and is emitted from the eccentric shaft of the gas absorption tank 7, and the gas concentration monitoring light path obtains the gas concentration through inversion calculation of the transmission part of the laser beam.

Further, the laser frequency stabilization light path includes the electro-optical modulator 3, polarization beam splitter prism 5 and photoelectric detector I6, the light 31 of the stabilization light path is through electro-optical modulator 3 and polarization beam splitter prism 5 entering gas absorption pond 7 in proper order, the light 32 of the stabilization light path reflection that gas absorption pond 7 split gets into photoelectric detector I6 through polarization beam splitter prism 5, the laser that beam splitter 2 split carries out the phase modulation through electro-optical modulator 3, then the center pin of follow gas absorption pond 7 is penetrated through polarization beam splitter prism 5, the cavity in the gas absorption pond 7 is the reference chamber this moment, the light 32 of the stabilization light path reflection is after the reflection of reference intracavity, the light 32 of the stabilization light path is received through corresponding photoelectric detector I6, then obtain the error signal after the frequency mixer mixes with the driving signal of electro-optical modulator 3.

Further, the output end of the photodetector i 6 is connected to the laser 1 through a feedback circuit. The feedback circuit comprises an integrating circuit and a frequency locking circuit. The error signal is fed back to the laser after being processed by the integrating circuit and the frequency locking circuit, so that the long-term stability of the laser is realized.

Further, the gas concentration monitoring light path comprises an acousto-optic modulator 4 and a photoelectric detector II 8, the incident light 41 of the monitoring light path sequentially passes through the acousto-optic modulator 4 and the gas absorption tank 7 and enters the photoelectric detector II 8, and the output end of the photoelectric detector II 8 is connected with the inversion calculation circuit. The monitoring light path incident light 41 split by the beam splitter 2, the monitoring light path incident light 41 is subjected to frequency shift and modulation by the acousto-optic modulator 4 and then is emitted from the eccentric axis of the gas absorption tank 7, the acousto-optic modulator 4 plays the functions of wavelength scanning and frequency modulation, the gas absorption cavity 7 is used as a gas absorption cavity at the moment, the transmission part of the monitoring light path incident light 41 after being reflected in the gas absorption cavity is received by the photoelectric detector II 8, then molecular spectrum absorption information is regulated by the lock-in amplifier, and the molecular spectrum absorption information is input into a control program for inversion calculation, so that gas concentration information is obtained.

Based on embodiment 1, as shown in fig. 2 and fig. 3, the gas absorption tank for the TDLAS gas concentration monitoring system includes a main body 71, the main body 71 is an indium steel pipe, the length and the diameter of the indium steel pipe are both 100mm, concave reflectors 73 are oppositely arranged at two ends of the main body 71, the concave reflectors 73 are two low-loss high-reflectivity reflectors, the main body 71 and the concave reflectors 73 are matched to form a cavity 72, the cavity 72 is used as a reference cavity and also used as a gas absorption cavity, and the system complexity is reduced by two purposes.

Further, both ends of the main body 71 are respectively provided with an air inlet 74 and an air outlet 75, the air inlet 74 and the air outlet 75 are both communicated with the cavity 72, the gas to be measured is introduced into the cavity 72 from the air inlet 74, and the gas is discharged from the air outlet 75 after measurement. The outer circle of the main body 71 is provided with a horizontal step 76, the horizontal step 76 is arranged along the axis of the main body 71, and the horizontal step 76 provides supporting force when the main body 71 is placed, so that the gas absorption tank 7 is convenient to install and use.

The foregoing description of the preferred embodiments of the utility model is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the utility model.

Claims

1. The utility model provides a TDLAS gas concentration monitoring system, includes laser instrument (1) and beam splitter (2), its characterized in that, laser instrument (1) corresponds with the incident end of beam splitter (2), and the exit end of beam splitter (2) is connected with laser frequency stable light path and gas concentration monitoring light path respectively, and the stable light path incident light (31) of laser frequency stable light path corresponds with the center pin of gas absorption pond (7), and the monitoring light path incident light (41) of gas concentration monitoring light path corresponds with the eccentric shaft of gas absorption pond (7).

2. The TDLAS gas concentration monitoring system according to claim 1, wherein the laser frequency stabilization light path comprises an electro-optical modulator (3), a polarization beam splitter prism (5) and a photodetector i (6), incident light (31) of the stabilization light path sequentially passes through the electro-optical modulator (3) and the polarization beam splitter prism (5) to enter the gas absorption tank (7), and reflected light (32) of the stabilization light path emitted by the gas absorption tank (7) passes through the polarization beam splitter prism (5) to enter the photodetector i (6).

3. TDLAS gas concentration monitoring system according to claim 2, characterized in that the output of the photodetector i (6) is connected to the laser (1) via a feedback circuit.

4. The TDLAS gas concentration monitoring system of claim 3, wherein the feedback circuit comprises an integrating circuit and a frequency-locking circuit.

5. The TDLAS gas concentration monitoring system according to any one of claims 1 to 4, wherein the gas concentration monitoring light path includes an acousto-optic modulator (4) and a photoelectric detector ii (8), incident light (41) of the monitoring light path sequentially passes through the acousto-optic modulator (4) and the gas absorption cell (7) to enter the photoelectric detector ii (8), and an output end of the photoelectric detector ii (8) is connected with the inversion calculation circuit.

6. A gas absorption cell for a TDLAS gas concentration monitoring system according to any one of claims 1 to 5, comprising a main body (71), concave reflectors (73) being arranged opposite each other at both ends of the main body (71), the main body (71) and the concave reflectors (73) cooperating to form a cavity (72).

7. The gas absorption cell as recited in claim 6, wherein both ends of the main body (71) are provided with a gas inlet (74) and a gas outlet (75), respectively, and both the gas inlet (74) and the gas outlet (75) are communicated with the cavity (72).

8. A gas absorption cell according to claim 6, wherein the body (71) is an indium steel tube, and the length and diameter of the indium steel tube are each 100mm.

9. A gas absorption cell according to claim 8, wherein the outer circumference of the body (71) is provided with a horizontal step (76).