CN111238677B - Method for measuring gas temperature based on single-spectral-line TDLAS - Google Patents
Method for measuring gas temperature based on single-spectral-line TDLAS Download PDFInfo
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- CN111238677B CN111238677B CN201811432210.2A CN201811432210A CN111238677B CN 111238677 B CN111238677 B CN 111238677B CN 201811432210 A CN201811432210 A CN 201811432210A CN 111238677 B CN111238677 B CN 111238677B
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- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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Abstract
The invention discloses a method for measuring gas temperature based on single-spectral-line TDLAS, which is applied to a system for measuring gas temperature by using single-spectral-line TDLAS. Compared with the prior art, the invention can be used for measuring the gas temperature by only one diode laser, does not need to use a high-precision standard tool to accurately calibrate the wavelength of the absorption spectrum, and is particularly suitable for the condition that the distribution intervals between spectral lines are far under the low-pressure condition, such as a hydrogen fluoride chemical laser, a deuterium fluoride chemical laser and the like.
Description
Technical Field
The invention belongs to the technical field of spectral measurement, and particularly relates to a method for measuring gas temperature by using an optical method, which is mainly used for measuring the gas temperature under the condition of low air pressure, is particularly suitable for the condition that the distribution intervals among all absorption spectral lines of target molecules are far, and can realize the purpose of measuring the gas temperature by using only one diode laser.
Background
Gas temperature measurement techniques can be largely classified into two categories, contact and non-contact. The contact type temperature measurement technology mainly comprises a thermocouple, a thermal resistor and the like, and can obviously reduce the service life of temperature measurement equipment under the condition that the temperature to be measured is higher or the gas to be measured is corrosive. The non-contact temperature measurement technology mainly comprises an optical temperature measurement technology, an acoustic temperature measurement technology, a CCD (charge coupled device) imaging temperature measurement technology and the like which are emerging in recent years, and the non-contact temperature measurement technology has the greatest advantages of not disturbing a temperature field to be measured, not being influenced by corrosive gas and having a wide temperature measurement range.
Optical temperature measurement techniques can be further classified into spontaneous emission spectroscopy and absorption spectroscopy. For a high-temperature object which can be approximately radiated by a black body, the temperature distribution of the high-temperature object can be obtained by utilizing the infrared radiation spectral intensity distribution of the high-temperature object, such as an infrared thermal imager and the like. For gas substances in a thermodynamically nonequilibrium state, such as gases emitting light by chemical reaction, the gas temperature can also be obtained according to the boltzmann's law of distribution based on the intensity distribution of vibrational lines or rotational lines of spontaneous emission spectrum of excited species therein. For gases in the ground state condition that do not themselves emit light, the gas temperature must be measured using absorption spectroscopy, most commonly tunable diode absorption spectroscopy (TDLAS).
In measuring gas temperature using TDLAS techniques, the most commonly used is the double absorption line method, which has the core principle of selecting two suitable gas absorption lines, making the ratio of their line intensities a sensitive function of temperature, and measuring the gas temperature by measuring the ratio of the line intensities. However, since most tunable diode lasers have a narrow wavelength tuning range of only ± 1nm or several nm, two independent tunable diode lasers (including laser controllers) must be used for simultaneous measurement when the two spectral lines are far apart, which results in high cost of the measuring instrument. In addition, when two lasers are used for measurement at the same time, time division multiplexing or wavelength division multiplexing technology must be used, so that the experimental scheme is complex.
From the viewpoint of cost performance, when measuring the gas temperature by using the TDLAS technique, sometimes a single absorption spectrum method (the applicable range is under the low pressure condition) is used, and the basic principle is that under the low pressure condition, the spectral broadening of the molecular absorption spectrum is mainly based on doppler broadening, and the spectral width of the doppler broadening is temperatureFunction:
the gas temperature can be measured by measuring the line width Δ v of the absorption line. The method has the advantages of simple use, good robustness and low cost, and has the disadvantages that a high-precision standard tool is required to carry out time-domain frequency-domain transformation and wavelength calibration on the abscissa of the absorption spectrum. This is because the abscissa of the TDLAS direct absorption spectrum is generally the number of sampling points at time (seconds) or equal time intervals, and the line width in the formula must be converted to the number of wave (cm) s-1) Can be used to calculate the gas temperature T.
In view of the above, in order to reduce the manufacturing cost, and achieve the purpose of using only one tunable diode laser to measure the gas temperature, and at the same time, not using a high-precision standard to perform time-domain frequency-domain transformation or wavelength calibration on the absorption spectrum, we invented a new method for measuring the gas temperature based on single-spectral TDLAS.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a gas temperature measuring method based on single-spectral-line TDLAS under the condition of low air pressure, does not need to use a high-precision standard tool to carry out time-domain frequency-domain transformation or wavelength calibration on an absorption spectrum, is particularly suitable for the condition that the distribution intervals among molecular absorption spectral lines are long, such as a hydrogen fluoride chemical laser, a deuterium fluoride chemical laser and the like, and forms a set of feasible method.
The invention provides a method for measuring gas temperature based on single-spectral line TDLAS, which is applied to a system for measuring gas temperature by using single-spectral line TDLAS and comprises the following steps:
dividing light emitted by a tunable diode laser into two beams, wherein one beam passes through a standard gas cell, the other beam passes through a gas area to be detected, and after being received by two photoelectric detectors respectively, the two beams of light are used for transmitting an amplified electric signal to an oscilloscope or a data acquisition card;
step two, adjusting the temperature of the standard gas pool to respectively obtain two temperatures T1And T2Direct absorption spectrum S of a conditioned standard gas cell1And S2The abscissa unit is time (second) or equivalent time (number of sampling points), and the ordinate unit is signal intensity (volt) of the photoelectric detector, and calibration parameters k and b are obtained after data analysis and processing, and the method specifically comprises the following steps:
1) direct absorption spectrum S1And S2Processing to make the ordinate unit of the absorbance A;
2) fitting the formula A ═ A with the spectrum0+a exp(-(t-t0)2/2W2) For the processed absorption spectrum S1And S2Fitting is carried out to respectively obtain spectral width parameters W related to the abscissa1And W2(ii) a In the spectrum fitting formula, t is the spectrum abscissa (time), A is the spectrum ordinate (absorbance), A is0、a、t0And W is a fitting parameter;
3) using a calibration formula
For temperature parameter T1、T2And a spectral width parameter W1And W2Calculating to obtain calibration parameters k and b;
step three, measuring the direct absorption spectrum S of the adjustable diode laser after passing through the gas area to be measured, obtaining the spectral width parameter W after the data analysis processing in the step two, and then utilizing the calibration parameters k and b and a calibration formula
Calculating to obtain the temperature T of the gas to be measured;
when the invention carries out parameter calibration by adjusting the temperature of the standard gas pool, two temperatures T need to be adjusted1And T2；
Spectral width parameter W, W of the present invention1And W2The unit of (a) is time (seconds) or equivalent time (number of sampling points);
the range of the standard gas pool pressure and the pressure of the gas area to be measured is 50-2000 Pa.
The invention has the beneficial effects that:
1. compared with the traditional TDLAS temperature measuring device, the gas temperature measuring device can measure the gas temperature by only using one tunable diode laser, thereby greatly reducing the manufacturing cost of the instrument;
2. the absorption spectrum measured by the oscilloscope is directly analyzed to obtain the gas temperature, a high-precision standard tool is not needed for wavelength calibration, time domain and frequency domain transformation is not needed, and the complexity of data analysis is reduced.
The invention has the characteristics of low manufacturing cost, simple operation, good robustness and the like, is suitable for measuring the gas temperature under the low-pressure condition, and is particularly suitable for the condition that spectral lines are distributed at far intervals under the low-pressure condition, such as a hydrogen fluoride chemical laser, a deuterium fluoride chemical laser and the like.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required in the description of the embodiments will be briefly introduced below. It is to be understood that the drawings in the following description are illustrative of some, but not all embodiments of the invention. It will be clear to a person skilled in the art that other figures can also be obtained from these figures without inventive work.
Fig. 1 is a flow chart illustrating a method for measuring a gas temperature based on a single-line TDLAS according to the present invention.
Fig. 2 shows the original absorption spectrum of the gas to be measured in the optical cavity of the HF chemical laser according to the present invention, where the abscissa is time (sec) and the ordinate is the signal intensity (v) of the photodetector.
FIG. 3 is a schematic view of the analysis and processing of the original absorption spectrum of the gas to be measured in the optical cavity of the HF chemical laser according to the present invention. The blue curve shown in fig. 3 is the experimentally measured raw absorption spectrum. (1) And (2) represents the two-sided non-absorbed fraction, and as a baseline, the baseline may be line-fitted using the formula I ═ at + c, to obtain parameters a and c of the line fitting. Substituting the abscissa data t into the formula I as at + c to obtain the light intensity before absorption, which is denoted as I0(the red curve shown in FIG. 3 is I0). Chinese character 'Jing' is a Chinese characterFormula A ═ ln (I)0The absorbance A was obtained after the operation of/I).
FIG. 4 is a spectrum of the present invention after data processing, with time t (sec) on the abscissa and absorbance A on the ordinate.
FIG. 5 is a fitting result of absorption spectra of temperature measurement according to the present invention, with time on the abscissa and absorbance on the ordinate. Fitting the formula A ═ A with the spectrum0+a exp(-(t-t0)2/2W2) After fitting, obtaining each fitting parameter as A0＝0.00184，a＝0.38374，t0＝1.97124×10-5s，W＝3.35468×10-6s, the spectral width parameter W is 3.35468 × 10-6s。
FIG. 6 shows the calibration result of the standard gas cell and the measurement result of the gas to be measured according to the present invention. Obtaining a calibration parameter k which is 6.956 multiplied by 10 according to the measurement result of the standard gas cell6And b is-4.154. Then according to the measured result of the gas to be measured (the spectrum width W is 3.35468 multiplied by 10)-6s), the temperature T of the gas to be measured in the optical cavity of the HF chemical laser is 368K.
Detailed Description
The technical solution of the method for measuring gas temperature based on single-spectral TDLAS according to the present invention will be described in further detail with reference to the accompanying drawings in the embodiments of the present invention. It is to be understood that the embodiments described herein are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the scope of the present invention.
Fig. 1 shows a specific flowchart of the method for measuring gas temperature based on single-spectral TDLAS according to the present invention, which comprises the following specific implementation steps:
step one, dividing the same laser beam into two laser beams.
Firstly, a signal generator provides sawtooth waves for a diode laser for continuously scanning laser wavelength; laser emitted by the diode laser is divided into two parts by a beam splitter which is divided into two parts, one part is received by a photoelectric detector after passing through an HF standard gas pool, and then an electric signal is sent to an oscilloscope; the other part of the gas to be measured penetrates through an optical cavity area of the HF chemical laser and is received by the photoelectric detector, and then the electric signal is sent to the oscilloscope; the oscilloscope is used for storing original direct absorption spectra of the gas to be measured in the HF standard gas pool and the HF chemical laser cavity area. A typical raw direct absorption spectrum is given in fig. 2.
And step two, obtaining calibration parameters by using a standard gas pool.
Before measuring the temperature of the gas to be measured, calibration parameters k and b are firstly obtained by using a standard gas pool. Adjusting the temperature of the standard gas pool to respectively obtain two temperatures T1298K and T2Original direct absorption spectrum S of standard gas cell under 405K condition1And S2A typical raw direct absorption spectrum can be referred to fig. 2.
The calibration parameters k and b are obtained after the following data analysis processing steps.
The specific method of the data analysis processing steps is as follows:
1) as shown in FIG. 3, with an absorption spectrum S1For example, when spectral data processing is performed, a straight line is fitted to a baseline by using the formula I ═ at + c with the unabsorbed portions (1) and (2) on both sides of the absorption line as the baseline, where I is the photodetector signal intensity (volt), t is the time (second), and a and c are fitting parameters; finally, parameters a-47.4928 and c-0.0928 of straight line fitting are obtained. Substituting the abscissa data (i.e., time t) into equation I0When the intensity of light before non-absorption is obtained, 47.4928t +0.0928, the intensity is denoted as I0(the red curve shown in FIG. 3 is I0) (ii) a The absorbed light intensity is taken as I (I is the blue curve shown in fig. 3), and is represented by formula a ═ ln (I)0The absorbance A was obtained after the operation of/I). The absorption spectrum after the treatment still has time on the abscissa and absorbance a on the ordinate, as shown in fig. 4. In a similar manner to that described above,can be measured by measuring the absorption spectrum S2And (5) carrying out conversion treatment to obtain an absorption spectrum with the ordinate as absorbance A.
2) As shown in FIG. 5, with an absorption spectrum S1For example, after the ordinate is the absorbance a, the spectrum is directly fitted to the formula a ═ a0+a exp(-(t-t0)2/2W2) Fitting is carried out to obtain each fitting parameter as A0＝0.00162，a＝0.39268，t0＝1.98462×10-5s，W＝3.08098×10-6s。
Note that in the spectrum fitting formula a ═ a0+a exp(-(t-t0)2/2W2) In the formula, t is the spectrum abscissa (time), A is the spectrum ordinate (absorbance), and A is0、a、t0And W is a fitting parameter; wherein only the fitting parameter W is needed for the next step we are going on to calculate (named spectral width parameter), other parameters are less important.
In the absorption spectrum S1The obtained fitting parameter W is noted as spectral width parameter W1＝3.08098×10-6s。
Similarly, the absorption spectrum S can be measured by2Processing to obtain each fitting parameter A0＝0.00127，a＝0.41389，t0＝2.00473×10-5s，W＝3.4931410-6s to obtain a spectral width parameter W2＝3.4931410-6s。
3) As shown in FIG. 6, using a calibration formula
For the two sets of data obtained (W)1＝3.08098×10-6，T1＝298)、(W2＝3.49314×10-6，T2405), the calibration parameter k can be easily obtained 6.956 × 106And b-4.154.
And step three, measuring the temperature of the gas to be measured by using the calibration parameters.
Measuring the direct absorption spectrum S of the tunable diode laser after passing through the gas region to be measured to obtain dataAfter analysis processing, each fitting parameter is obtained as A0＝0.00184，a＝0.38374，t0＝1.97124×10-5s，W＝3.35468×10- 6s, so that the spectral width parameter W is 3.35468 × 10-6s and using a calibration formula
And calculating to obtain the temperature T of the gas to be measured which is 368K.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (4)
1. A gas temperature measuring method based on single-spectral line TDLAS is applied to a gas temperature measuring system based on single-spectral line TDLAS, and is characterized by comprising the following steps:
dividing light emitted by a tunable diode laser into two beams, wherein one beam passes through a standard gas cell, the other beam passes through a gas area to be detected, and after being received by two photoelectric detectors respectively, the two beams of light are used for transmitting an amplified electric signal to an oscilloscope or a data acquisition card;
step two, adjusting the temperature of the standard gas pool to respectively obtain two temperatures T1And T2Direct absorption spectrum S of a conditioned standard gas cell1And S2The method comprises the following steps of obtaining calibration parameters k and b after data analysis and processing, wherein the abscissa of the method is time or equivalent time, the unit of the time is second, the unit of the equivalent time is the number of sampling points, the ordinate of the method is signal intensity of a photoelectric detector, and the unit of the signal intensity of the photoelectric detector is volt, and the specific steps are as follows:
1) direct absorption spectrum S1And S2Processing the mixture so that the unit of ordinate thereof becomes absorbanceA；
2) Using a spectral fitting formula
For the processed absorption spectrum S1And S2Fitting to obtain spectral width parameters related to the abscissaW 1AndW 2(ii) a In the formula of spectral fit, timetAs the abscissa of the spectrum, absorbanceAIs the ordinate of the spectrum of the light,
as fitting parameters, fitting parameters are setWNamed spectral width parameter;
3) using a calibration formula
To temperature parameterT 1、T 2And spectral width parameterW 1AndW 2calculating to obtain calibration parameters k and b;
step three, measuring the direct absorption spectrum S of the adjustable diode laser after passing through the gas area to be measured, and obtaining the spectral width parameter after the data analysis processing in the step two
Then using the calibration parameters k and b to pass through the calibration formula
Calculating to obtain the temperature of the gas to be measuredT。
2. The method for measuring the gas temperature based on the single-line TDLAS as claimed in claim 1, wherein: when the parameter calibration is carried out by adjusting the temperature of the standard gas pool, two temperatures T need to be adjusted1And T2。
3. The method for measuring the gas temperature based on the single-line TDLAS as claimed in claim 1, wherein: the spectral width parameter W, W1And W2In seconds or number of sample points.
4. The method for measuring the gas temperature based on the single-line TDLAS as claimed in claim 1, wherein: the range of the pressure of the standard gas pool and the pressure of the gas area to be measured is 50-2000 Pa.
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