CN108008146B - A kind of method and apparatus improving gas flow rate measurement accuracy - Google Patents
A kind of method and apparatus improving gas flow rate measurement accuracy Download PDFInfo
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- CN108008146B CN108008146B CN201711075096.8A CN201711075096A CN108008146B CN 108008146 B CN108008146 B CN 108008146B CN 201711075096 A CN201711075096 A CN 201711075096A CN 108008146 B CN108008146 B CN 108008146B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
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Abstract
The invention belongs to high-speed gas concentration, the field of measuring technique of flow velocity, disclose a kind of method and apparatus for improving gas velocity measurement precision.This method utilizes Wavelength modulation spectroscopy (WMS) technology, two even harmonics signals (nf and mf are demodulated simultaneously with lock-in amplifier, n, m=2,4,6 ... and n > m), the narrow and sharp peak-to-peak signal of high s/n ratio is obtained with mf normalization nf (WMS-nf/mf), gas flow rate is calculated by the Doppler frequency shift at narrow peak, Measurement Resolution and precision can be improved.The device of the invention is made of tunable laser, photodetector and lock-in amplifier etc..The work step of device is: two beam laser and airflow direction be angled to intersect and is slanted through airflow field, shoot laser is received and converted to electric signal by two detectors respectively, it is demodulated to obtain WMS-nf/mf signal by lock-in amplifier, the flow velocity of gas is calculated by the Doppler frequency shift of two signals.
Description
Technical field
The invention belongs to the flow velocitys of high-speed gas, measurement of concetration technical field, are related to tunable diode laser and absorb light
The method and apparatus of spectral technology implement this programme by the spectral line to be measured to object gas, in measurement gas concentration and flow velocity
Meanwhile the Measurement Resolution and precision of flow velocity can be improved.
Background technique
For High Speed Flow Field, as aerospace engine nozzle at, the measurement of gas flow rate is extremely important.And it is traditional
Speed-measuring method such as Pitot tube, hot-wire anemometer etc., belong to contact type measurement, be not only easy to interfere combustion process, and
And rugged environment also will affect the reliability of its service life and measurement result.Tunable diode laser absorption spectroscopy (Tunable
Diode Laser Absorption Spectroscopy, TDLAS) technology, utilize the narrow linewidth and wavelength of semiconductor laser
The characteristics such as tuning, quickly scan absorption line, it can be achieved that measurement while to temperature, pressure, constituents ratio.TDLAS
In conjunction with laser doppler technique, quick, the on-line measurement to high-speed flow flow velocity can be further realized, is a kind of suitable for disliking
The contactless flow-speed measurement method of bad environment.
Measurement of the TDLAS for High Speed Flow Field starts from the nineties in last century.Basic scheme is based on direct absorption spectrum
(DAS) technology or Wavelength modulation spectroscopy second harmonic (WMS-2f) Detection Techniques, laser, which is divided into two-way relative gas velocity, is in
Intersect incidence by flow field, determines flow velocity using the Doppler frequency shift of DAS signal or WMS-2f signal.In both schemes,
Doppler frequency shift is determined that peak width is narrower, and the judgement for absorbing peak position is more accurate, i.e. flow velocity resolution ratio by the spacing of two absorption peaks
It is related with breadth of spectrum line.Therefore, it is limited by line width and sample rate, the resolution ratio of speed is not often high, with common aqueous vapor position
At the 1398nm for Absorption Line, the half of absorption line is high, and half-breadth is about 0.1cm-1, can extrapolate when laser beam and air-flow
When the angle at 45 ° of direction, velocity resolution is about 59.40m/s.If the flow velocity of measurand is lower than 59.40m/s, measurement accuracy
It can be reduced with accuracy, not be able to satisfy the demand of low speed measurement and a wide range of flow velocity measurement.
Therefore the present invention is proposed on the theoretical research foundation of forefathers based on the double higher hamonic wave detections of Wavelength modulation spectroscopy
Scheme improves detection accuracy to a certain extent, and the concentration of component of gas is measured while measuring flow velocity.
Summary of the invention
The present invention is directed to overcome the deficiencies of the prior art and provide a kind of method and dress for improving TDLAS flow velocity measurement accuracy
It sets.Based on methods and apparatus of the present invention, while two different even harmonics signals of Wavelength modulation spectroscopy are acquired, improved
The measurement gas flow rate precision and detection sensitivity of TDLAS system, this method and device can be used for high-speed flow it is online, it is in situ,
Monitoring application in real time.
In order to achieve the above objectives, the technical scheme is that the method for improving gas flow rate measurement accuracy, feature exist
In passing through lock-in amplifier and demodulate two even higher hamonic wave signal (nf and mf simultaneously using Wavelength modulation spectroscopy (WMS) technology
Signal, n, m=2,4,6... and n > m), obtain the narrow of two high s/n ratios using mf normalization nf signal (WMS-nf/mf) and
The peak-to-peak signal of point, the Doppler frequency shift by observing the two narrow peaks are finally inversed by high gas flow rate.
Angle theta between gas flow rate and frequency shift (FS) Δ υ, laser transmission direction and air-flow velocity direction and there is no
The centre frequency υ of gaseous absorption line when frequency displacement0It is related:
Wherein, c is the light velocity, VgasFor air-flow velocity, unit: ms-1；Δ υ is frequency shift (FS), υ0For there is no frequency displacements
When gaseous absorption line centre frequency, unit: Hz；Angle of the θ between laser transmission direction and air-flow velocity direction, it is single
Position: °.
Since each even-order harmonic component of Wavelength modulation spectroscopy reduces with the increase of overtone order, thus it is common to use
WMS-4f/2f (i.e. n=4, m=2) signal, obtains the narrow and sharp peak-to-peak signal of two high s/n ratios, its usual peak width is than straight
Narrow 5 times of absorption spectrum signal or more are connect, determines Doppler frequency shift, to improve measurement accuracy and resolution ratio.
The device of TDLAS measurement accuracy is improved based on higher hamonic wave detection 4f/2f, comprising: laser controller, semiconductor swash
Light device, signal generator, photodetector, digital servo-control module, etalon, A/D converter, computer or embedded processing
Device, collimation lens etc..Laser controller controls semiconductor laser laser, via laser beam splitter one dividing into three, wherein
A branch of to carry out Wavelength calibration by etalon, in addition two beams converge to photodetector by collimation lens after tested air-flow and connect
Row photoelectric conversion is taken in, the electric signal after conversion enters digital lock-in amplifier, while the higher hamonic wave for being 4f and 2f by frequency
It is demodulated, finally three road signals is passed to and carries out the processing of data in computer or processor, analyzes, displays and saves.
Compared with prior art, technical characterstic of the invention and effect:
The ratio between double higher hamonic waves that the present invention uses detecting strategy, improve to a certain extent flow velocity measurement resolution ratio and
Precision.
Detailed description of the invention
Fig. 1 is the TDLAS block diagram using the carry out gas detection of the method for the present invention
1 laser controller
2 semiconductor lasers
3 beam splitters
4 etalons
5 A/D converters
6 tested air-flows
7,10 photoelectric detection module
8,11 digital servo-control amplification module
9 computers or embeded processor
12 signal generating modules
Fig. 2 is the Frequency Shift (embodiment 1) using 4f/2f obtained by this method
Fig. 3 is the Frequency Shift (embodiment 2) using 6f/2f obtained by this method
Specific embodiment
The present invention is a kind of method and apparatus for improving gas flow rate measurement accuracy, and the theoretical basis based on forefathers utilizes
Wavelength modulation spectroscopy (WMS) technology demodulates two even higher hamonic wave signal (nf and mf signal, n, m by lock-in amplifier simultaneously
=2,4,6... and n > m), believed using the narrow and sharp peak that mf normalization nf signal (WMS-nf/mf) obtains two high s/n ratios
Number, the precision and resolution ratio of gas flow rate measurement can be improved in the Doppler frequency shift by observing the two narrow peaks.
The technical scheme is that
Based on the method that WMS-nf/mf improves TDLAS measurement accuracy, detection gas are to the absorption line of laser to including dense
The measurement of the parameter of gas including degree, pressure, temperature and flow velocity, characterized in that since laser passes through high-speed flow Shi Qi
It is important to flow direction, Doppler frequency shift can be generated when so receiving laser, have the Doppler frequency shift size of two absorption lines, i.e.,
Can at inverting high-speed flow flow velocity.
Angle theta between gas flow rate and frequency shift (FS) Δ υ, laser transmission direction and air-flow velocity direction and there is no
The centre frequency υ of gaseous absorption line when frequency displacement0It is related:
Wherein, c is the light velocity, VgasFor air-flow velocity, unit: ms-1；Δ υ is frequency shift (FS), υ0For there is no frequency displacements
When gaseous absorption line centre frequency, unit: Hz；Angle of the θ between laser transmission direction and air-flow velocity direction, unit: °
With reference to the accompanying drawing with the specific experiment specific embodiment that the present invention will be described in detail:
Using 760nm laser as light source, with O2For object gas, O is chosen2Spectral line at 760.445nm be to
Spectral line is surveyed, tested air-flow is the air stream of flowing, is analyzed below specific experiment.
Embodiment 1:(760nm laser, Vgas=100m/s, 4f/2f)
Below for analyzing oxygen molecule in the absorption line at 760.445nm, explanation calculates gas stream with this programme
The measurement method of speed.The absorption line that our Selection Center wavelength are 760.445nm in this embodiment, with θ1=45 °, θ2=
135 ° intersect oblique incidence influent stream speed be 100m/s air flow field, enable n=4, m=2, that is, allow two digital lock-in amplifiers simultaneously
Demodulation obtains WMS-4f/2f signal.
| λ0, nm | λ1, nm | λ2, nm | θ1 | θ2 |
| 760.445 | 760.44518 | 760.44482 | 45° | 135° |
T=296K, P=1atm.
Air-flow velocity:
Using above-mentioned formula, obtaining air-flow velocity is Vgas=100.44m/s, relative error 0.44%.Compared to only use
WMS-2f measures (relative error about 4.0%), and error reduces an order of magnitude.
Embodiment 2:(760nm laser, Vgas=100m/s)
Below for analyzing oxygen molecule in the absorption line at 760.445nm, explanation calculates gas stream with this programme
The measurement method of speed.The absorption line that our Selection Center wavelength are 760.445nm in this embodiment, with θ1=45 °, θ2=
135 ° intersect oblique incidence influent stream speed be 100m/s oxygen flow field, enable n=6, m=2, that is, allow two digital lock-in amplifiers simultaneously
Demodulation obtains WMS-4f/2f signal.
| λ0, nm | λ1, nm | λ2, nm | θ1 | θ2 |
| 760.445 | 760.44518 | 760.44482 | 45° | 135° |
T=296K, P=1atm.
Air-flow velocity: Vgas=λ0Δυ/(Cosθ1-Cosθ2)
Using above-mentioned formula, obtaining air-flow velocity is Vgas=101.24m/s, relative error 1.24%.
The flow velocity for resulting in gas in experiment, effectively increases Measurement Resolution and precision.
Claims (3)
1. a kind of method for improving gas flow rate measurement accuracy, which is characterized in that utilize Wavelength modulation spectroscopy WMS technology, pass through
Lock-in amplifier demodulates two even higher hamonic wave signal nf and mf signals, n, m=2 simultaneously, and 4,6... and n > m utilizes mf normalizing
Change nf signal WMS-nf/mf and obtain the narrow and sharp peak-to-peak signal of two high s/n ratios, by the Doppler for observing the two narrow peaks
Frequency displacement can be improved the precision and resolution ratio of gas flow rate measurement；
Include: based on the WMS-nf/mf method for improving TDLAS measurement accuracy
Measurement of the detection gas to the absorption line of laser to the parameter of the gas including concentration, pressure, temperature and flow velocity,
Due to laser pass through high-speed flow when it is important in airflow direction, so receive laser when can generate Doppler frequency shift, have two
The Doppler frequency shift size of absorption line, can be finally inversed by high-speed flow flow velocity；
The air-flow velocity: Vgas=λ0Δυ/(cosθ1-cosθ2),
Wherein, c is the light velocity, VgasFor air-flow velocity, unit: ms-1；Δ υ is frequency shift (FS), λ0For center wavelength；λ1And λ2For
The absorption line wavelength of two generation Doppler frequency shifts；θ1It is λ for wavelength1Absorption line and air-flow velocity direction between folder
Angle；θ2It is λ for wavelength2Absorption line and air-flow velocity direction between angle, unit: °.
2. a kind of method for improving gas flow rate measurement accuracy as described in claim 1, characterized in that due to wavelength modulation light
It composes each even-order harmonic component to reduce with the increase of overtone order, thus it is common to use WMS-4f/2f signal, obtains two height
The narrow and sharp peak-to-peak signal of signal-to-noise ratio, its usual peak width determine Doppler's frequency than narrow 5 times of direct absorption spectrum signal or more
It moves, to improve measurement accuracy and resolution ratio.
3. a kind of detect the device for improving flow velocity measurement accuracy based on higher hamonic wave, characterized in that include: laser controller, can
Tunable semiconductor lasers, signal generator, photodetector, digital servo-control module, etalon, computer or embedded processing
Device, light collimating lenses；Laser controller controls laser needed for semiconductor laser goes out to test, and divides via laser beam splitter one
Be three, wherein a branch of be used for Wavelength calibration by etalon, in addition two beams with airflow direction is angled intersects oblique inject
Airflow field, two beam shoot lasers are converted to electric signal into two digital lock-in amplifiers, often by two detector receptions respectively
A digital lock-in amplifier demodulates obtain WMS-nf/mf signal simultaneously, and three road signals are finally passed to computer or embedded place
Device is managed, the processing, analysis and preservation of data are carried out；
Using Wavelength modulation spectroscopy WMS technology, two idol higher hamonic wave signal nf and mf letters are demodulated simultaneously by lock-in amplifier
Number, n, m=2,4,6... and n > m obtain the narrow and sharp of two high s/n ratios using mf normalization nf signal WMS-nf/mf
Peak-to-peak signal, the Doppler frequency shift by observing the two narrow peaks can be improved the precision and resolution ratio of gas flow rate measurement；
Include: based on the WMS-nf/mf method for improving TDLAS measurement accuracy
Measurement of the detection gas to the absorption line of laser to the parameter of the gas including concentration, pressure, temperature and flow velocity,
Due to laser pass through high-speed flow when it is important in airflow direction, so receive laser when can generate Doppler frequency shift, have two
The Doppler frequency shift size of absorption line, can be finally inversed by high-speed flow flow velocity；
The air-flow velocity: Vgas=λ0Δυ/(cosθ1-cosθ2),
Wherein, c is the light velocity, VgasFor air-flow velocity, unit: ms-1；Δ υ is frequency shift (FS), λ0For center wavelength；λ1And λ2For
The absorption line wavelength of two generation Doppler frequency shifts；θ1It is λ for wavelength1Absorption line and air-flow velocity direction between folder
Angle；θ2It is λ for wavelength2Absorption line and air-flow velocity direction between angle, unit: °.
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| CN110361359B (en) * | 2019-07-16 | 2020-11-24 | 清华大学 | Absorption rate function reproduction method based on even harmonic |
| CN110596040A (en) * | 2019-09-10 | 2019-12-20 | 上海东富龙科技股份有限公司 | Gas detection device, system and method based on TDLAS technology |
| CN111751484A (en) * | 2020-04-13 | 2020-10-09 | 中国科学院力学研究所 | Solid-liquid rocket engine fuel burning rate measuring system |
| CN112378616B (en) * | 2020-11-16 | 2021-12-10 | 中国科学技术大学 | High-speed flow field multi-parameter measurement system and method based on wavelength modulation absorption spectrum |
| CN113280996B (en) * | 2021-04-25 | 2023-02-03 | 中国航天空气动力技术研究院 | Method for measuring speed of free flow of high-enthalpy flow field |
| CN114814286B (en) * | 2022-02-25 | 2023-06-02 | 上海理工大学 | Online low-pressure system flow velocity testing device and method |
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| CN100590419C (en) * | 2006-10-17 | 2010-02-17 | 中国科学院安徽光学精密机械研究所 | New nodal real time gas concentration monitoring method and sensor |
| CN104126106B (en) * | 2011-12-20 | 2016-11-09 | 小利兰·斯坦福大学托管委员会 | A kind of method of the calibration-free scanning wavelength modulated spectrum for gas sensing |
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