CN116242783A - Photoacoustic spectrum measurement system capable of being used for eliminating cross influence - Google Patents
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Abstract
A photoacoustic spectrum measurement system capable of eliminating cross influence relates to the technical field of power equipment detection. Comprises a converging mirror, an infrared window, a chopper, an infrared filter and a photoacoustic cell which are sequentially arranged along an optical path. The infrared window is connected with the converging lens in a sealing way to form a sealed air cavity capable of sealing air; the mixed gas with certain concentration is sealed in a sealed air cavity between the converging mirror and the infrared window, and the converging mirror is also included. After the light source passes through the high-concentration mixed gas, certain light energy can be absorbed by the mixed gas, so that the aim of weakening other gas signals which possibly generate cross interference besides the wavelength corresponding to the gas to be detected is fulfilled. Light converged by the light source enters the gas pool after passing through the filter of the gas to be detected, and the generated photoacoustic signal is received by the microphone to realize signal acquisition.
Description
Technical Field
The present invention relates to electrical devices, and more particularly to a photoacoustic spectrometry system that can be used to eliminate cross-talk effects.
Background
With rapid development and technical progress of the power industry, large-capacity high-voltage power generation and supply oil equipment is gradually increased, and important means for maintenance and supervision of transformers, turbines and the like in the power equipment are still supervision and analysis of the power oil. The power oil technical supervision is an important technical supervision work of various power generation and supply units, and has an important role in guaranteeing the safety and economic operation of power production. In the accident cause tracking analysis of a plurality of high-voltage power equipment, the measurement and analysis of the insulating oil are more sensitive, quantized and accurate than other test methods.
Thus, there is an increasing need for simple, fast, convenient and accurate analytical instruments or systems. The detection of early faults inside oil-filled electrical equipment, particularly a power transformer, ensures the safe and reliable operation of the equipment, realizes the conversion of the periodic maintenance mode of the equipment into real-time monitoring and preventive detection or maintenance, and is beneficial to reducing the occurrence of serious power accidents.
The transformer oil can decompose some valuable gases such as CH4, C2H6, C2H4, C2H2, CO and CO2 for judging the fault type under the action of heat and electricity during long-term operation and after faults occur. Analysis of the decomposed gases in the oil is one of the most convenient and effective measures for judging the early latent faults of the oil immersed power transformer. The online analysis system used at present adopts the technical principle of gas chromatography, namely laboratory instruments are simply miniaturized and modified, and the online analysis system mainly has the following defects from the actual measurement condition in the online gas chromatography system in use at present:
1. the detection precision is not enough, the repeatability is poor, and the actual working requirements cannot be met;
2. the method requires standard gas, carrier gas and the like, and has large maintenance quantity in the later period and high long-term operation cost;
3. the gas chromatography technology has complex pipelines and more components, and the stability and reliability of long-term operation of the instrument are insufficient.
The photoacoustic spectroscopy technology is a spectroscopy technology for detecting the concentration of the absorbed gas based on the photoacoustic effect, and can effectively avoid the defects of the photoacoustic spectroscopy technology in a linear analysis system for the dissolved gas in the oil. Photoacoustic spectroscopy is a spectroscopic technique that detects the volume fraction of an absorber based on the photoacoustic effect. Compared with a gas chromatograph, the technology has the advantages of no consumption, rapid measurement, simple operation and the like. In addition, the size of the light energy absorbed by the gas can be directly measured, and the sensitivity is much higher than that of the Fourier infrared spectrum under the same gas cell length.
Photoacoustic spectroscopy is the analysis of the photoacoustic effect of gas molecules, which is produced by the absorption of light of a specific wavelength by a gas molecule. The gas absorbs light energy to cause temperature rise, and when the gas is placed in a closed container, the temperature rise correspondingly causes the pressure of the gas to rise. If the pulse light source irradiates the closed gas, the pressure wave with the same frequency as the pulse light source can be detected by using a sensitive microphone. However, if the photoacoustic effect is applied to the actual detection, two preconditions must be satisfied. Firstly, determining the specific molecular absorption spectrum of each gas, so that the infrared light source can be subjected to wavelength modulation to excite a specific gas molecule; and secondly, determining the proportional relation between the pressure wave intensity generated after the gas absorbs energy and the gas concentration. Therefore, by selecting the appropriate wavelength in combination with detecting the intensity of the pressure wave, it is possible to verify not only the presence or absence of a certain gas, but also the concentration thereof. Qualitative and quantitative analysis can be made even for certain mixtures or compounds. The transformer oil has more gas components and wide absorption position distribution, and the infrared thermal radiation light source is matched with different optical filters to excite the gas to be detected to generate photoacoustic signals.
The basic structure of the currently adopted photoacoustic spectrum measuring instrument is that a heat radiation light source with a convergence function passes through a chopper with a certain frequency to form a pulse light source, then passes through an optical filter with a certain specific center wavelength to enter a photoacoustic cell, and after the light energy is absorbed by gas to be measured in the photoacoustic cell, periodic sound pressure is generated and collected by a microphone for analysis. How to convert broadband radiation of a thermal light source into infrared light of a specific wavelength is key to photoacoustic spectrometry for measuring a specific gas concentration. The parameters of the optical filter are determined by comprehensively considering the spectral distribution of the light source and the gas absorption characteristic spectrum, so that the photoacoustic signal of the gas to be detected is improved as much as possible, and meanwhile, the absorption of other gases is considered so as not to generate cross interference. However, in actual measurement, there is an obvious intersection between absorption spectrums of different gases, so that when the absorption of the gas to be measured is widened by using a plurality of absorption lines, the influence of signal cross interference caused by excitation of other gas absorption lines must be considered, so that the signal interference between different gases needs to be effectively reduced in the measurement process for improving the accuracy of gas detection concentration.
At present, the photoacoustic spectrometry technology only depends on a single optical filter to select the wavelength, but all optical filters have certain bandwidth, so that interference of photoacoustic signals of different gases is easily caused, and meanwhile, the higher the cut-off depth of the optical filter is, the more expensive the cut-off depth of the optical filter is. In addition, there is no narrow-band filter for middle-far infrared absorption, and when the kinds of measured gas are relatively large, only the existing reflection and interference filters can be used.
Disclosure of Invention
The invention aims at the problems and provides a photoacoustic spectrometry system which can be used for eliminating cross influence and reducing interference of other gases on the basis of not changing a gas signal to be tested.
The technical scheme of the invention is as follows:
a photoacoustic spectrometry system operable to eliminate cross-over effects, comprising a thermal light source, further comprising:
the front end of the converging mirror is of an arc-shaped structure and is provided with a light source fixing position extending into the cavity of the converging mirror, and a luminous head of a hot light source enters the converging mirror and is fixed;
the infrared unit is detachably and fixedly arranged at the tail end of the converging mirror; the infrared unit comprises a metal tube and a pair of infrared windows; the pair of infrared windows are respectively and fixedly arranged at the pipe orifice of the metal pipe in a sealing way, and a sealing air cavity is formed in the metal pipe; the metal pipe is provided with an air inlet communicated with the sealed air cavity;
a chopper by which the continuously emitted light source is formed into a pulse light source of a certain period, thereby generating a periodic sound signal in the photoacoustic cell;
the transmission peak of the infrared filter corresponds to the absorption peak of the gas to be detected;
and the photoacoustic cell is provided with a microphone for collecting the sound signals generated in the photoacoustic cell, and the sound signals are transmitted to the signal amplifying, collecting and processing system through the microphone.
Specifically, the mixed gas in the closed air cavity is the mixed gas except the gas to be detected in the mixed gas.
Specifically, the converging mirror is internally provided with a medium-infrared wavelength high reflection surface.
Specifically, the metal pipe is provided with an air outlet for exhausting air.
Specifically, the transmittance of the light source after passing through the mixed gas in the closed air cavity is as follows:T= 
；
where N is the number of particles per unit volume of gas,
l is the total length from the converging mirror to the infrared window, which is the absorption cross section of the gas molecules.
Specifically, the central wavelength of the infrared filter is a certain absorption peak of the gas to be detected.
The invention seals mixed gas with certain concentration in the airtight air cavity between the converging lens and the infrared window, and the converging lens is also included. After the light source passes through the high-concentration mixed gas, certain light energy can be absorbed by the mixed gas, so that the aim of weakening other gas signals which possibly generate cross interference besides the wavelength corresponding to the gas to be detected is fulfilled. Light converged by the light source enters the gas pool after passing through the filter of the gas to be detected, and the generated photoacoustic signal is received by the microphone to realize signal acquisition.
The closed air cavity has a certain length, after the light source passes through the section of high-concentration mixed gas, the required wave band of the gas to be detected can be reserved, and other required wave bands are restrained, so that the cut-off depth of the corresponding wave bands of other gases is increased, and finally, the cross interference in the gas measurement process is effectively reduced, and particularly, the condition that the concentration of the other gases is very high and the concentration of the gas to be detected is relatively low is achieved. Through the photoacoustic spectrometry technology, the interference of other mixed gas signals can be greatly reduced in the process of measuring low-concentration gas to be measured.
Drawings
Figure 1 is a schematic diagram of the principle of the invention,
FIG. 2 is a schematic illustration of the location of the air inlet and air outlet;
in the figure, 1 is a light source fixing position, 2 is a converging mirror, 3 is an infrared window, and 4 is a chopper; the infrared filter 5, the photoacoustic cell 6, the microphone 7, the signal amplification and acquisition processing system 8, the gas inlet 91 and the gas outlet 92.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.
In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "vertical", "horizontal", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the system or element to be referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The following describes the present invention with reference to fig. 1 and 2;
a photoacoustic spectrometry system operable to eliminate cross-over effects, comprising a thermal light source, further comprising:
the front end of the converging mirror is of an arc-shaped structure and is used for converging a light source (the concave mirror plays a role in converging, the original divergence angle of divergent light is reduced), so that the light source is emitted out of the converging mirror in parallel to enter the closed air cavity, a light source fixing position extending into the cavity of the converging mirror is arranged, and a light emitting head of a hot light source enters the converging mirror and is fixed;
the infrared unit is detachably (can be in threaded connection) fixedly arranged at the tail end of the converging mirror; the infrared unit comprises a metal tube and a pair of infrared windows; the pair of infrared windows are respectively and fixedly arranged at the pipe orifice of the metal pipe in a sealing way, and a sealing air cavity is formed in the metal pipe; the metal pipe is provided with an air inlet communicated with the sealed air cavity; the invention is provided with the air outlet on the basis of arranging the air inlet; corresponding mixed gas is filled through the air inlet, and the mixed gas with different components can be repeatedly filled for a plurality of times, so that the requirements of a plurality of different tests and the elimination of system errors are ensured while the optical system elements are not dismounted or moved.
The chopper is used for shielding and passing through the light source, so that the continuously emitted light source forms a pulse light source with a certain period, and a periodic sound signal is generated in the photoacoustic cell, thereby being convenient for a data acquisition system to acquire the signal more accurately;
the transmission peak of the infrared filter corresponds to the absorption peak of the gas to be detected; the infrared filter only transmits light with the absorption peak wavelength of the gas to be detected and cuts off light with other wavelengths; after passing through the gas in the closed air cavity, the gas sequentially enters the chopper 4 and the infrared filter 5, so that the accurate measurement of the low-concentration gas to be measured can be realized;
and the photoacoustic cell is provided with a microphone for collecting the sound signals generated in the photoacoustic cell, and the sound signals are transmitted to the signal amplifying, collecting and processing system through the microphone.
And the mixed gas in the closed air cavity is the mixed gas except the gas to be detected.
The types of the mixed gas are determined by the gas to be detected and the gas in the use environment, for example, three gases 1, 2 and 3 are mixed in the environment, but the gas to be detected is 2, in order to generate a light source with the wavelength corresponding to the absorption peak of the gas 2, the high-concentration 1 gas and 3 gases are filled into the closed air cavity, when the light source passes through the closed air cavity, the light energy except the wavelength corresponding to the absorption peak of the two influencing gases can be effectively absorbed, and only the wavelength corresponding to the gas to be detected is left in the rest light sources, so that the cross influence of the 1 gas and the 3 gas on the measurement result of the gas to be detected is effectively reduced.
The cross-influence refers to: in measuring the gas 2 to be measured, the gas of the gas 1 and 3 is theoretically incapable of generating absorption and signals for the light entering the photoacoustic cell, and if the gas 1 and 3 also generate signals in measuring the gas 2 to be measured, the cross influence is called. This requires that light affecting the 1 and 3 bands of gas be treated and absorbed in advance, so that the high concentration 1 and 3 gas is filled in advance in the closed gas chamber, and light in the optical band corresponding to the absorption peaks of the 1 and 3 gas is attenuated.
The high-concentration mixed gas except the gas to be measured in the mixed gas is filled in the sealed air cavity, and according to the transmittance formula of the material, the higher the concentration of the mixed gas is, the better the absorption effect is, the lower the energy of light penetrating through the mixed gas is, the smaller the measurement interference of the gas to be measured is, and the better the measurement effect is. After the light source passes through the closed air cavity and the optical filter corresponding to the gas to be measured, light mainly with the absorption wavelength corresponding to the gas to be measured enters the photoacoustic cell 6, and the optical power of all wavelengths of other gases is effectively weakened, so that sound signals generated in the photoacoustic cell 6 are mainly generated by the gas to be measured, signals generated by other gases are much smaller than those of the traditional photoacoustic spectrometer, and high-precision measurement of the gas to be measured is effectively performed.
Further defined, the converging mirror is internally provided with a medium-infrared wavelength high reflection surface.
Further defined, the metal tube is provided with an air outlet for exhausting air.
Further defined, the transmittance of the light source after passing through the mixed gas in the closed air cavity is as follows:T= 
；
where N is the number of particles per unit volume of gas,
and L is the total length from the converging mirror to the infrared window, and the cut-off degree of the light wave band corresponding to other mixed gases is controlled by changing the concentration of the gas and the length of the sealing device.
Further defined, the central wavelength of the infrared filter is a certain absorption peak of the gas to be detected.
Further defined, the inner diameter of the converging mirror is equal to the inner diameter of the closed air cavity, such that the parallel light source enters the closed air cavity completely.
The measuring steps of the scheme are as follows:
1) Converging the thermal light source 1 into a beam of nearly parallel light through the converging mirror 2;
2) The mixed gas except the gas to be detected is filled in the sealed space, and a beam of nearly parallel light is emitted from the infrared filter 5 after passing through the mixed gas in the sealed air cavity;
3) The converged light source generates light modulated at a certain frequency after passing through the chopper 4; the frequency is selected taking into account both the magnitude of the photoacoustic signal and the response of the microphone 7, which are competing relationships, the lower the frequency is, the stronger the photoacoustic signal is generated, but the smaller the response of the microphone 7 is, so that the operating frequency of the chopper 4 is selected to be between 20-40 Hz.
4) The frequency modulated light passes through a filter with a specific center wavelength (corresponding to the absorption peak of the gas to be detected);
5) The frequency light source after passing through the optical filter enters a photoacoustic cell 6 to generate a photoacoustic signal, and the photoacoustic signal is acquired through an acquisition system;
6) And processing the acquired signals to obtain the concentration of the gas to be detected.
Example 1
The photoacoustic cell 6 is filled with CO and CO 2 The mixed gas needs to be accurately measured in experiments. The thermal light source 1 passes through a closed air cavity shown in figure 2, and CO can be filled in the closed air cavity 2 The gas passes through the infrared window 3 by the light source of the closed air cavity, then passes through the chopper 4 to obtain a pulse light source with a certain frequency, in order to measure CO, the absorption wavelength (4720 nm) of CO is selected as the central transmission wavelength of the interference filter 5, the average value of the cut-off depths of other wave bands of the filter is about 3, and after passing through the filter, the light source enters the photoacoustic cell 6 to detect the content of CO. Finally, sound signals are generated in the photoacoustic cell 6, the sound signals are converted into voltage signals after passing through a microphone, the voltage signals are amplified and collected by a data collection card, and the content of CO in the mixed gas is obtained through the processing of the collected voltage signals.
However, CO 2 Has extremely strong absorption between the wave bands of 4.17 mu m to 4.40 mu m and 13.8 mu m to 16.3 mu m. Even though the CO filter is almost cut off in this band, the average cut-off transmittance of the filter is only 0.1%, and there is still a very small amount of light sources of the corresponding band transmitted into the photoacoustic cell. When the photoacoustic cell is filled with CO 2 When mixed with CO, the CO absorbs light energy to generate sound signals, and the CO 2 Yet absorb a very small amount of light energy to produce an acoustic signal because of the CO 2 Particularly strong, and because the CO interference filter cannot completely filter the light source of the CO2 absorption band.
To verify CO 2 The gas passes through the interference filter 5 of CO (i.e. the transmittance at 4720nm is highest, CO 2 If an average transmittance of 0.1% in the absorption peak region produces an acoustic signal, the sealing device is not filled with CO 2 The gas, using only a single CO filter, found high concentration CO 2 Has a relatively large influence on CO measurement, and 5000ppm of CO 2 The magnitude of the signal generated by the CO of about 200ppm produced, it is evident that the monolithic CO filter does not suppress CO well 2 The effect on the CO signal results in an acoustic signal in the measurement result even if no CO gas is present in the photoacoustic cell.
In this embodiment, the total length of the seal is 20 cm, filled with 90% CO 2 After the gas, 10000ppm of CO was found 2 The resulting signal is on the order of the error range, with the signal being almost zero. The photoacoustic spectrometry technology designed by the invention can be used for effectively inhibiting the wavelengths of all gas absorption bands except the gas to be tested.
The invention discloses a photoacoustic spectrometry technology capable of eliminating cross influence. In the mixed gas of the known kind, the concentration of the gas to be measured can be measured with high accuracy. The scheme designs a gas sealing cavity in the space between the condenser and the optical filter, and seals mixed gas with certain concentration during measurement. After the light source passes through the section of high-concentration mixed gas, the required wave band of the gas to be measured can be reserved, other required light source wave bands are restrained, and the light source enters the photoacoustic cell 6, so that the cut-off depth of the corresponding wave bands of other gases is increased, and finally, the cross interference in the gas measurement process is effectively reduced.
The invention skillfully designs a photoacoustic spectrum measurement technology capable of eliminating cross influence, and compared with the existing photoacoustic spectrum technology, the photoacoustic spectrum measurement technology has the following advantages:
1. the experimental device space is effectively utilized, a wavelength light source required by other mixed gases is skillfully formed, and the cut-off efficiency of the original photoacoustic spectrometry system is greatly improved.
2. The measurement technique does not change the optical power of the gas to be measured entering the photoacoustic cell 6.
3. The measuring system can replace the corresponding gas types and concentrations according to the actual measurement requirements, so that different measurement requirements are met, and the manufacturing cost of the expensive optical filter is saved.
The measuring method can be widely applied to the fields of spectrum measurement, infrared high-precision measurement technology and the like, and by using the method, the accuracy of a test result can be ensured, the interference caused by other mixed gases can be effectively eliminated, and in addition, the device of the technology has low processing requirements, and is convenient and flexible.
For the purposes of this disclosure, the following points are also described:
(1) The drawings of the embodiments disclosed in the present application relate only to the structures related to the embodiments disclosed in the present application, and other structures can refer to common designs;
(2) The embodiments disclosed herein and features of the embodiments may be combined with each other to arrive at new embodiments without conflict;
the above is only a specific embodiment disclosed in the present application, but the protection scope of the present disclosure is not limited thereto, and the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (6)
1. A photoacoustic spectrometry system for eliminating cross-talk effects comprising a thermal light source, further comprising, in order along an optical path:
the front end of the converging mirror is of an arc-shaped structure and is provided with a light source fixing position extending into the cavity of the converging mirror, and a luminous head of a hot light source enters the converging mirror and is fixed;
the infrared unit is detachably and fixedly arranged at the tail end of the converging mirror; the infrared unit comprises a metal tube and a pair of infrared windows; the pair of infrared windows are respectively and fixedly arranged at the pipe orifice of the metal pipe in a sealing way, and a sealing air cavity is formed in the metal pipe; the metal pipe is provided with an air inlet communicated with the sealed air cavity;
a chopper by which the continuously emitted light source is formed into a pulse light source of a certain period, thereby generating a periodic sound signal in the photoacoustic cell;
the transmission peak of the infrared filter corresponds to the absorption peak of the gas to be detected;
and the photoacoustic cell is provided with a microphone for collecting the sound signals generated in the photoacoustic cell, and the sound signals are transmitted to the signal amplifying, collecting and processing system through the microphone.
2. The photoacoustic spectrometry system of claim 1, wherein the mixed gas provided in the closed air chamber is a mixed gas other than the gas to be measured.
3. A photoacoustic spectrometry system for eliminating cross-talk according to claim 1 wherein the converging mirror inner surface is a mid-infrared wavelength highly reflective surface.
4. A photoacoustic spectrometry system for eliminating cross-talk according to claim 4, wherein the metal tube is provided with an air outlet for exhausting air.
5. A photoacoustic spectrometry system for eliminating cross-talk according to claim 1 wherein the transmittance of the light source through the gas mixture in the closed gas chamber is:T= 
；
where N is the number of particles per unit volume of gas,
l is the total length from the converging mirror to the infrared window, which is the absorption cross section of the gas molecules.
6. A photoacoustic spectrometry system according to claim 1, wherein the central wavelength of the infrared filter is a certain absorption peak of the gas to be measured.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310254264.9A CN116242783A (en) | 2023-03-16 | 2023-03-16 | Photoacoustic spectrum measurement system capable of being used for eliminating cross influence |
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