CN103308186A - Method for measuring temperature in vacuum environment based on wavelength modulation spectrum technology - Google Patents

Abstract

The invention discloses a method for measuring a temperature in a vacuum environment based on a wavelength modulation spectrum technology, and belongs to the technical field of tunable laser diode absorption spectroscopy. According to the method, a laser is modulated by utilizing a high-frequency sine wave, a low-frequency triangular wave and a low-frequency square wave based on the wavelength modulation spectrum technology, so that selected two temperature measurement spectral lines appear at a high level position and a low level position respectively; spectral line scanning is realized by the triangular wave; the second harmonic signal ratio of the two spectral lines is obtained by experimental measurement; the rotational temperature of gas molecules is determined by comparing the second harmonic signal ratio with a theoretical calculating value; and the rotational temperature and a translational temperature (the classical thermodynamic temperature) are kept balance all the time, so that the temperature of gas can be measured. By the method, the problems of surface material analysis and temperature traceability of a current contact temperature sensor applied in the vacuum environment are solved.

Description

Based on thermometry under the vacuum environment of Wavelength modulation spectroscopy technology

Technical field

The present invention relates to thermometry under a kind of vacuum environment, particularly measure temperature under the vacuum environment based on the method for quadratic harmonics in the Wavelength modulation spectroscopy technology.

Background technology

Along with the development of China's Models For Space Science And Technology, vacuum environment is tested, particularly spacecraft thermal vacuum test becomes an extremely important test checking job, and wherein the temperature survey under the vacuum environment becomes the crucial measuring technology of above-mentioned research.But up to the present, traditional contact type temperature sensor is still adopted in the measurement of temperature basically in the spacecraft thermal vacuum test, such as T-shaped thermopair, the PT100 platinum resistance, MF51 thermistor etc., but heat transfer type changes under vacuum environment, this moment is to workpiece, what sensor played the intensification effect mainly is radiation, and sensor exists the surface to resolve phenomenon under vacuum environment, therefore adopt the temperature sensor measurement vacuum environment temperature of demarcating under the normal pressure to exist many uncertain factors, find that such as the Chinese Academy of Space Technology branched temperature sensor is measured same objective measurement in ground level heat vacuum environment simulation test under atmospheric pressure environment approaching, but measurement result differs larger under vacuum environment, and maximum can arrive 2 ℃.For this reason, development advanced, temperature measurement technology has great civilian and military application background accurately, can provide effective technological approaches and project data for solving spacecraft thermal vacuum test.

TDLAS (Tunable Diode Laser Absorption Spectroscopy) is that grew up in recent years, advanced, the direct gas parameter detection technique of measurement gas molecule rotation temperature (keeping balance with classical thermodynamics temperature " translation temperature " moment), this technology is utilized the laser of narrowband scanning gas molecule characteristic absorpting spectruming line of tunable wave length, then the laser intensity after being absorbed by gas molecule by analysis obtains gas temperature to be measured, therefore has the advantages such as high wavelength selectivity, high sensitivity, system's versatility.TDLAS has formed two kinds of main measuring methods as leading take direct absorption spectroscopy techniques and Wavelength modulation spectroscopy technology since setting up.Directly absorption spectroscopy techniques is by the direct match gas absorption of the ratio of incident intensity and transmitted light intensity rate function, and then by absorptivity function measurement gas temperature, but directly be absorbed in factors such as easily being subject to particle concentration, laser intensity fluctuation in the measurement impact and can't Accurate Curve-fitting gas absorption rate function, and then cause thermometric error.And Wavelength modulation spectroscopy technology (Wavelength Modulation Spectroscopy, WMS) in measuring process by echo signal is carried out high frequency modulated, but not echo signal is not owing to having to be removed through being modulated in the follow-up harmonic wave testing process, therefore can effectively reduce the interference of background signal in the measuring system, greatly improve temperature measurement accuracy and sensitivity, be particularly useful for the on-line measurement of gas temperature under rugged surroundings or the weak acceptance condition.

Summary of the invention

There are the problems such as surfacing parsing, temperature traceability in order to solve traditional contact type temperature sensor measurement vacuum environment temperature, the objective of the invention is to set up based on thermometry under the vacuum environment of Wavelength modulation spectroscopy technology.

Technical scheme of the present invention is as follows: a kind of based on thermometry under the vacuum environment of Wavelength modulation spectroscopy technology, it is characterized in that the method comprises the steps:

1) determine the measurement gas medium, select two characteristic spectral lines pair of this gas medium from the HITRAN spectra database, its centre frequency is respectively ν ₀₁And ν ₀₂

2) take semiconductor laser with tunable as light source, regulate temperature and the electric current of laser controller, make the output frequency of semiconductor laser with tunable be stabilized in frequency ν ₀The place,

And demarcate and monitor with wavemeter;

The high_frequency sine wave that the low frequency triangular wave of the low-frequency square-wave that 3) the first signal generator is produced, the generation of secondary signal generator and lock-in amplifier produce is inputted laser controller after superposeing through totalizer, drives the laser of semiconductor laser with tunable generation respectively at frequency ν ₀₁And ν ₀₂Scanning and modulation occur in the place, and to make centre frequency be ν ₀₁With centre frequency be ν ₀₂Two spectral lines appear at respectively high level place and the low level place of square wave;

4) the measurement gas medium is filled with in the vacuum chamber, by pressure transducer vacuum chamber pressure is measured; The diaphotoscope that sees through vacuum chamber one end after the laser alignment with scanning and modulation arrives vacuum chamber other end catoptron, received by photodetector after the reflection, the photodetector output signal is connected to digital oscilloscope and shows and input lock-in amplifier and carry out the second harmonic signal detection;

5) second harmonic signal of lock-in amplifier being exported is input to computer data acquisition and treatment system after gathering by data collecting card, and this computer data acquisition and treatment system is handled as follows data:

A. calculate second harmonic peakedness ratio RR and temperature T function curve according to following formula;

S in the formula _2f-peak-1And S _2f-peak-2Be respectively two second harmonic peak values that characteristic spectral line is right,

With

Be respectively two light intensity that characteristic spectral line is right,

With Be respectively two linear functions that characteristic spectral line is right, S ₁(T) and S ₂(T) be respectively two line strengths that characteristic spectral line is right, its size is decided by environment temperature T, θ ∈ [π, π];

B. utilize software program to obtain the right separately centre frequency place second harmonic peak value of two characteristic spectral lines in the step 1), and calculate peak value ratio RR;

C. obtain the vacuum environment temperature T according to second harmonic peak value ratio RR and temperature T function curve.

The inventive method is selected the absorption line of two gas molecules of the same race based on the Wavelength modulation spectroscopy technology, obtains the second harmonic signal of two spectral lines, determines temperature under the vacuum environment by the peakedness ratio of the two harmonic signal.Other method has following advantage relatively: the method can be eliminated the impact of pressure in measuring process, and temperature survey under the vacuum environment is carried out in the restriction that therefore can not be stressed, and measuring error is little, and precision is high.

Description of drawings

Fig. 1 is temperature measurement system structure principle chart under the vacuum environment of the present invention.

Fig. 2 is that experimental example of the present invention carries out temperature measurement system structure principle chart under the vacuum environment in calibration cell.

Fig. 3 is for C ₂H ₂The second harmonic peak value ratio that obtains of two absorption lines and the function curve between the temperature.

Fig. 4 is temperature measurement system software flow pattern under the vacuum environment of the present invention.

Fig. 5 is the experimental example experimental result, and the calibration cell temperature drops to-20 ℃ by-10 ℃ in the experimentation.

Among the figure: 1-first signal generator 1; 2-secondary signal generator 2; 3-lock-in amplifier; 4-totalizer; 5-laser controller; 6-semiconductor laser with tunable; 7-wavemeter; 8-vacuum chamber; 9-diaphotoscope; 10-catoptron; 11-photodetector; 12-pressure transducer; 13-digital oscilloscope; 14-data collecting card; 15-computer data acquisition and treatment system; 16-calibration cell.

Embodiment

The present invention is further illustrated below in conjunction with accompanying drawing.

The invention provides a kind ofly based on temperature online measuring method under the vacuum environment of Wavelength modulation spectroscopy technology, the method has comprised following steps:

1) determine the measurement gas medium, select two characteristic spectral lines pair of this gas medium from the HITRAN spectra database, its centre frequency is respectively ν ₀₁And ν ₀₂

2) take semiconductor laser with tunable 6 as light source, regulate temperature and the electric current of laser controller 5, make the output frequency of semiconductor laser with tunable 6 be stabilized in frequency ν ₀The place,

And demarcate and monitor with wavemeter 7;

3) input laser controller 5 after the low frequency triangular wave that the low-frequency square-wave that first signal generator 1 is produced, secondary signal generator 2 produce and the high_frequency sine wave of lock-in amplifier 3 generations superpose through totalizer 4 drives the laser of semiconductor laser with tunable 6 generations respectively at frequency ν ₀₁And ν ₀₂Scanning and modulation occur in the place, and to make centre frequency be ν ₀₁With centre frequency be ν ₀₂Two spectral lines appear at respectively high level place and low level place, laser instantaneous frequency ν and the laser intensity I of square wave ₀Represent with formula (1):

$\left\{\begin{array}{c}v=\stackrel{\&OverBar;}{v}+a\cos \left(\mathrm{\&omega;t}\right)\\ I_0={\stackrel{\&OverBar;}{I}}_0+{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1\cos (\mathrm{\&omega;t}+{\mathrm{\&psi;}}_1)\end{array}\right.---\left(1\right)$

In the formula:

With

Be the average sweep frequency of laser and light intensity; A is the frequency modulation (PFM) amplitude, and its unit is cm ^-1ω is the angular frequency of modulation signal; Δ I ₁Linear modulation amplitude for laser intensity; ψ ₁Be the phase differential between laser intensity modulation and the frequency modulation (PFM);

4) the measurement gas medium is filled with in the vacuum chamber 8, is measured by 12 pairs of vacuum chamber pressure of pressure transducer; The diaphotoscope 9 that sees through vacuum chamber 8 one ends after the laser alignment with scanning and modulation arrives vacuum chamber other end catoptron 10, receives transmitted light intensity I by photodetector 11 after the reflection _tWith incident intensity I ₀Ratio with formula (2) expression:

In the formula: P is the gas stagnation pressure, and its unit is atm; S (T) is the line strength of absorption line, and its unit is cm ^-2Atm ^-1, its size is only relevant with gas temperature T; X is the volumetric concentration of gas to be measured; L is the transmission range of laser in gas medium, and its unit is cm; Be absorption line shape function and satisfied

Bring into the instantaneous light intensity of laser in the formula (1) in the formula (2) and carry out Fourier expansion, the instantaneous light intensity expression that can obtain transmission laser is with formula (3) expression:

$I_t=F_{00}+\underset{k=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}[{\mathrm{<figure-callout\; id="1"\; label="F\; k"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">F</figure-callout>}}_k\&CenterDot;\cos \left(\mathrm{k\&omega;t}\right)+{\mathrm{<figure-callout\; id="2"\; label="F\; k"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">F</figure-callout>}}_k\&CenterDot;\sin \left(\mathrm{k\&omega;t}\right)]---\left(3\right)$

Coefficient F in the formula ₀₀, F ₁₁, F ₁₂, F ₂₁, F ₂₂, F _K1, F _K2Expression formula represents with formula (4):

$\left\{\begin{array}{c}{F}_{00}={\stackrel{\&OverBar;}{I}}_0{A}_0+\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1}{2}{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">A</figure-callout>}}_1\cos {\mathrm{\&psi;}}_1\\ F_{11}={\stackrel{\&OverBar;}{I}}_0{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">A</figure-callout>}}_1+{\mathrm{\&Delta;I}}_1(A_0+\frac{{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">A</figure-callout>}}_2}{2})\cos {\mathrm{\&psi;}}_1\\ {\mathrm{<figure-callout\; id="12"\; label="F"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">F</figure-callout>}}_{12}={\mathrm{\&Delta;I}}_1(-A_0+\frac{{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">A</figure-callout>}}_2}{2})\sin {\mathrm{\&psi;}}_1\\ F_{21}={\stackrel{\&OverBar;}{I}}_0{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">A</figure-callout>}}_2+\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1}{2}({\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">A</figure-callout>}}_1+A_3)\cos {\mathrm{\&psi;}}_1\\ F_{22}=\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1}{2}(-{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">A</figure-callout>}}_1+A_3)\sin {\mathrm{\&psi;}}_1\\ {\mathrm{<figure-callout\; id="1"\; label="F\; k"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">F</figure-callout>}}_k={\stackrel{\&OverBar;}{I}}_0{A}_k+\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1}{2}(A_{k-1}+A_{k+1})\cos {\mathrm{\&psi;}}_1\\ {\mathrm{<figure-callout\; id="2"\; label="F\; k"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">F</figure-callout>}}_k=\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="I"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_1}{2}(-A_{k-1}+A_{k+1})\sin {\mathrm{\&psi;}}_1,k=\mathrm{3,4}\&CenterDot;\&CenterDot;\&CenterDot;\end{array}---\left(4\right)\right.$

Coefficient A _kExpression formula with formula (5) expression:

Photodetector 11 output signals are connected to digital oscilloscope 13 and show and input lock-in amplifier 3 and carry out second harmonic signal and detect the second harmonic signal S that lock-in amplifier 3 detects _2fRepresent with formula (6):

$S_{2f}=G\&CenterDot;[{\stackrel{\&OverBar;}{I}}_0{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA00003148379000011.png,HDA00003148379000012.png"\; state="\{\{state\}\}">A</figure-callout>}}_2+\frac{{\mathrm{\&Delta;I}}_1}{2}({\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA00003148379000021.png"\; state="\{\{state\}\}">A</figure-callout>}}_1+A_3)\cos \left({\mathrm{\&psi;}}_1\right)]---\left(6\right)$

G is the photoelectricity enlargement factor in the formula, at core frequency place, A ₁=A ₃=0, so the second harmonic signal peak value S of core frequency place _2f-peakRepresent with formula (7):

In the formula, θ ∈ [π, π]; Very low at pressure, and absorptivity is less than 0.1 o'clock, formula (7) but formulate (8):

By formula (8) as can be known, when two spectral line second harmonic peak values are compared, can eliminate the photoelectricity amplification coefficient, absorb light path, gas stagnation pressure and concentration as influencing factor, centre frequency is ν ₀₁The second harmonic peak value S that obtains of spectral line _2f-peak-1With centre frequency be ν ₀₂The second harmonic peak value S that obtains of spectral line _2f-peak-2Between ratio R R with formula (9) expression:

In the formula

That centre frequency is ν ₀₁The spectral line light intensity,

That centre frequency is ν ₀₂The spectral line light intensity, the ratio of the two is the constant of determining;

5) after the second harmonic signal of lock-in amplifier 3 being exported gathers by data collecting card 14, be input to computer data acquisition and treatment system 15, at first calculate second harmonic peak value ratio RR and temperature T function curve according to formula (9), then obtain two characteristic spectral lines to centre frequency place second harmonic peak value separately according to the data that collect, and calculate peak value ratio RR, obtain the vacuum environment temperature T according to second harmonic peak value ratio RR and temperature T function curve at last.

Experimental example:

1) with C ₂H ₂As the temperature survey medium, be filled with in the vacuum chamber 8, vacuum chamber 8 is put into calibration cell 16, allow calibration cell 16 temperature automatically drop to-20 ℃ from-10 ℃, compare with the First class standard platinum resistance, select two characteristic spectral lines pair from the HITRAN spectra database, its centre frequency is respectively 6558.7925cm ^-1And 6558.9156cm ^-1

2) take semiconductor laser with tunable 6 as light source, regulate temperature and the electric current of laser controller 5, make the output frequency of semiconductor laser with tunable 6 be stabilized in frequency 6558.8541cm ^-1Locate, and demarcate and monitor with wavemeter 7;

The 5kHz high_frequency sine wave that the 20Hz low frequency triangular wave of the 0.1Hz low-frequency square-wave that 3) first signal generator 1 is produced, 2 generations of secondary signal generator and lock-in amplifier 3 produce is inputted laser controller after superposeing through totalizer 4, drives the laser of semiconductor laser with tunable 6 generations respectively at frequency 6558.7925cm ^-1And 6558.9156cm ^-1Scanning and modulation occur in the place, and to make centre frequency be 6558.7925cm ^-1With centre frequency be 6558.9156cm ^-1Two spectral lines appear at respectively high level place and the low level place of square wave;

4) the measurement gas medium is filled with in the vacuum chamber 8, is measured by 12 pairs of vacuum chamber pressure of pressure transducer; The diaphotoscope 9 that sees through vacuum chamber 8 one ends after the laser alignment with scanning and modulation arrives vacuum chamber other end catoptron 10, received by photodetector 11 after the reflection, photodetector 11 output signals are connected to digital oscilloscope 13 and show and input lock-in amplifier 3 and carry out the second harmonic signal detection;

5) second harmonic signal of lock-in amplifier 3 output is gathered by data collecting card 14 after, being input to computer data acquisition and treatment system 15, to obtain centre frequency be 6558.7925cm ^-1Second harmonic peak value S _2f-peak-1With centre frequency be 6558.9156cm ^-1Second harmonic peak value S _2f-peak-2Ratio RR, according to the relation of ratio R R and temperature T, can obtain temperature T, measurement result as shown in Figure 5, the C that measures of " ★ " expression TDLAS wherein ₂H ₂Gas temperature, and "●" represents the calibration cell temperature that the First class standard platinum resistance measures.In measuring process, gaseous tension increases to 85Pa uniformly by 10Pa, it verifies that mainly TDLAS is not subjected to the impact (it is 0.167Pa/min that the control vacuum system makes its leak rate) of gas stagnation pressure when thermometric, gas temperature changes to-20 ℃ by-10 ℃, and does not wait in tens of minutes-10 ℃ ,-20 ℃ two temperature spots stops.Measurement result shows: the calibration cell temperature that the gas temperature that TDLAS measures and First class standard platinum resistance measure is consistent with each other, and is not subjected to the impact of gas stagnation pressure.

Claims (1)

1. one kind based on thermometry under the vacuum environment of Wavelength modulation spectroscopy technology, it is characterized in that the method comprises the steps:

1) determine the measurement gas medium, select two characteristic spectral lines pair of this gas medium from the HITRAN spectra database, its centre frequency is respectively ν ₀₁And ν ₀₂

2) take semiconductor laser with tunable (6) as light source, regulate temperature and the electric current of laser controller (5), make the output frequency of semiconductor laser with tunable (6) be stabilized in frequency ν ₀The place,

And demarcate and monitor with wavemeter (7);

3) input laser controller (5) after high_frequency sine wave process totalizer (4) stack that the low frequency triangular wave that the low-frequency square-wave that first signal generator (1) is produced, secondary signal generator (2) produce and lock-in amplifier (3) produce drives the laser of semiconductor laser with tunable (6) generation respectively at frequency ν ₀₁And ν ₀₂Scanning and modulation occur in the place, and to make centre frequency be ν ₀₁With centre frequency be ν ₀₂Two spectral lines appear at respectively high level place and the low level place of square wave;

4) the measurement gas medium is filled with in the vacuum chamber (8), by pressure transducer (12) vacuum chamber pressure is measured; The diaphotoscope (9) that sees through vacuum chamber (8) one ends after the laser alignment with scanning and modulation arrives vacuum chamber other end catoptron (10), received by photodetector (11) after the reflection, photodetector (11) output signal is connected to digital oscilloscope (13) and shows and input lock-in amplifier (3) and carry out the second harmonic signal detection;

5) second harmonic signal of lock-in amplifier (3) being exported is input to computer data acquisition and treatment system (15) after gathering by data collecting card (14), and this computer data acquisition and treatment system is handled as follows data:

A. calculate second harmonic peakedness ratio RR and temperature T function curve according to following formula;

S in the formula _2f-peak-1And S _2f-peak-2Be respectively two second harmonic peak values that characteristic spectral line is right;

With

Be respectively two light intensity that characteristic spectral line is right;

With

Be respectively two linear functions that characteristic spectral line is right, S ₁(T) and S ₂(T) be respectively two line strengths that characteristic spectral line is right, its size is decided by environment temperature T, θ ∈ [π, π];

B. utilize software program to obtain the right separately centre frequency place second harmonic peak value of two characteristic spectral lines in the step 1), and calculate peak value ratio RR;

C. obtain the vacuum environment temperature T according to second harmonic peak value ratio RR and temperature T function curve.

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