Multi-component gas online test method and device
Technical field
The present invention relates to a kind of gas-detecting device and method.Particularly relate to a kind of gas sample that need not to gather, the scene of directly applying to relates to the online constituent analysis of multiple gaseous state composition in the air and real-time detection, the analysis of measurement of concetration, based on the multi-component gas online test method and the device of near infrared tuning laser spectrum.
Background technology
Air quality is concerning the ecologic equilibrium and human beings'health and development.In a large amount of industrial gaseous waste of all kinds of industrial and mining enterprises discharging to ecologic environment with human health threatens big and the big waste gas of discharge capacity mainly contains: oxides of nitrogen (NOx), sulphuric dioxide (SO
2), phosphorus (P), carbon monoxide (CO), halogenated hydrocarbons, volatile organic matter toxic gases such as (VOCs).
In the present ambient air quality monitoring of China, monitoring project is many with SO
2, NOx, O
3, CO, THC (THC) and suspended particulates (PM10) etc. are main.And to monitoring and the control aspect of VOCs, corresponding regulations, standard and corresponding monitoring method still remain further perfect.In view of VOCs pollutant subject under discussion is attracted attention and the trend of environment ozone pollution gradually, confirm the kind and the concentration of its discharging, obtain related data with online robotization continuous monitoring equipment, control its discharging, have very important significance and urgency, its market outlook are wide, and economic results in society are remarkable.
The research of the on-line monitoring of VOCs at home and abroad is subjected to paying close attention to widely in the air, has multiple (potential) method can be applied to the monitoring of VOCs.
As GC/FID or GC/MS analytic approach, gather tested gas sample, carry out pre-service, enrichment, separate with gas chromatograph (GC) after, detect as detecting device with ionic flame burning (FID) or mass spectrometer (MS) etc. again.This method is the most accurate to the qualitative and quantitative of the kind of monitored thing component, can obtain ppb magnitude (10
-9), be the Current Standard method.Its shortcoming is: send lab analysis behind the spot sampling, do not have the ageing and movability of analysis, and sampling and testing process complexity; Adopt the method for sampling of " point " simultaneously, can only provide the instantaneous value of a point, data represented property is relatively poor.Still can't satisfy at present the needs of real-time robotization continuous monitoring.
Portable field detecting instrument and for example: adopt the photoionization detection technique, by minipump specific organic volatile compound suction photoionization sensing chamber, by vacuum UV lamp gas molecule is carried out ionization, under the polarized electric field effect, ion and electronics clash into to pole plate, thus the weak current that formation can be detected.Photoionization detector (PID) can detectable concentration from ppm (10
-6) to the VOCs of ppb magnitude, the scene that can be applied to VOCs in air, soil, mud and the water is detected.The industrial safety hygienic conditions that the portable field detecting instrument is used for higher pollution concentration more detect, and add that relatively poor, the detectable gaseous species of its precision is few, and are not suitable for the low concentration VOCs analysis or the long-term continuous monitoring use of Atmospheric composition.
SnO2 gas sensor array for another example is used for escaping gas in the environment-identification, as propane, and methyl alcohol, ethyl, benzene, dimethylbenzene, ethane etc.Analog result shows that can there be under the noise conditions object gas that picks out of success in this system.Adopt the artificial neural network processing procedure that better noise permission is not only arranged, and can detect object gas with sensor still less.But the sensitivity of gas sensor array method is low, and the detectable gas kind is few; That is that all right is ripe in the VOCs context of detection, still awaits the progress of material technology aspect.
Also have fourier infrared line spectrum (FTIR) analytical technology, comprise open Fourier infrared spectrograph (Open-PathFTIR), passive type Fourier infrared spectrograph (Passive FTIR).FTIR utilizes Michelson interferometer, converts interferogram to infrared spectrogram by Fourier transform, obtains the spectral information of gas componant, and spectral analysis is carried out in the match of absorption spectrum and laboratory reference spectrum, can measure simultaneously multiple components.The sensitivity of FITR system is low, cost an arm and a leg, and interference gas such as water, carbon dioxide are big to the influence of measurement result; In addition, Fourier transform calculates consuming time, and the detection system that has needs cooling; Equipment volume is huge.
Tunable laser absorption spectrum (TDLAS) technology: based on tunable diode laser, temperature or injection current by the control diode laser, can export the fine setting of optical maser wavelength, (2~30um) carry out open laser long-range measures at middle infrared.The shortcoming of TDLAS is that tuning range has limited detectable gaseous species, and laser instrument and the detecting device in middle-infrared band needs the price of liquid nitrogen refrigerating, optical element, stability to await development of science and technology in addition.At present, at home and abroad TDLAS is used for the monitoring to automobile and motorcycle exhaust emissions, gas, methane etc. more, and it is less to carry out trace VOCs Study of Monitoring.
Because the most content of VOCs in the environment is very low, belong to trace and trace scope, also there is not ripe VOCs continuous monitor system product at present in the world, yet there is not the limit value of the formal VOCs of official concentration.
The absorption in near-infrared spectra (wavelength is in the 780-2500nm scope) district mainly is because the frequency multiplication (vibrational state is in one or several transition between energy level of being separated by) of molecular vibration or sum of fundamental frequencies (transition takes place the energy inter-stage of two kinds of vibrational states of molecule simultaneously) absorption causes.Near infrared spectrum mainly is that the compound that contains key groups such as C-H, O-H, N-H absorbs and the sum of fundamental frequencies absorption in the frequency multiplication of mid infrared region fundamental vibration.The inorganics sample that contains the organism of H key group and combine with it is along with the variation of component content, and its near infrared light spectrum signature also will change thereupon.According to the variation characteristic of spectrum, can be in the hope of the content of tested composition.Sensitivity, precision, accuracy and reliability that near-infrared spectrum technique and combining of chemometrics method have greatly been improved quantitative test are used widely in fields such as pharmacy, agricultural, oil; Compare with the mid-infrared light spectral coverage, detecting device has higher sensitivity and response speed; The radiation efficiency of light source is higher; It is little that its optical element more stablizes, is subjected to working environment to influence, low price; Need not sample and prepare, be applicable to field quick detection and real-time online analysis, have quick, non-destruction, advantage such as efficient.
Summary of the invention
Technical matters to be solved by this invention is, the characteristic absorption of a kind of tuning range by expanding semiconductor laser to cover multiple gases is provided, in the dynamic process of thermal tuning, detect with improve measuring speed, high-frequency signal detect improve the sensitivity that detects, with the method for linear identification in conjunction with the multivariate modeling, thereby realize the multiple gases composition fast, multi-component gas online test method and the device that detect simultaneously based on interior cavity semiconductor laser.
The technical solution adopted in the present invention is: a kind of multi-component gas online test method, be airborne multiple gases to be carried out constituent analysis and concentration detection by near infrared tuning laser spectrum, adopt a plurality of semiconductor lasers, cover different wavelength coverages respectively, laser to a plurality of semiconductor lasers is modulated, internal temperature by semiconductor cooler control semiconductor laser, in the variation of temperature process, measure, needed accurate wavelength is calculated by real-time temperature value measured and injection current, the method that combines based on modulation spectrum and multivariate modeling realizes constituent analysis and the measurement of concetration to multiple gases, at first open many optical path pool are placed measure field, detect then; Described detection includes following steps:
Provide the laser driver of high-frequency current modulation signal to carry out electric current tuning by the injection current noise spectra of semiconductor lasers of control semiconductor laser by modulation signal generator;
Temperature detection/controller changes temperature and carries out thermal tuning with noise spectra of semiconductor lasers by the internal temperature of the thermoelectric refrigerating unit control laser instrument of semiconductor laser inside;
Semiconductor laser is after the double modulation of excess temperature and electric current, optical maser wavelength has obtained tuning, emitting laser tell after by the fiber-to-fiber coupling mechanism a part of laser again through Optical Fiber Transmission to open many optical path pool, at open many optical path pool inner laser repeatedly reflection takes place, emitting laser arrives balance receiver through Optical Fiber Transmission again after the absorption of tested gas;
Also send into balance receiver through another part laser that fiber coupler is told through optical fiber;
The signal that balance receiver is picked up is sent into lock-in amplifier after prime amplifier amplifies, send into computing machine again after A/D converter is digital signal with analog signal conversion and handle;
Described multivariate modeling is that the method for multiple harmonic The data partial least square method (PLS) that computing machine is obtained is set up Quantitative Analysis Model, and modeling process is: the multiple harmonic data X and the measured physical quantity y of spectrum are extracted major component matrix T=[t
1, t
2..., t
f] and U=[u
1, u
2..., u
f], the requirement that PLS decomposes is: make t
1And u
1Covariance reach maximum:
Major component matrix T and U are done linear regression, and b is the correlation coefficient matrix
U=Tb+e
b=(T
TT)
-1T
TU
Spectrum X for unknown sample
Un, obtain predicted value: y
Un=X
UnB.
The present invention can adopt a plurality of semiconductor lasers, and with a kind of mode of operation in time-division and the frequency division, the method that combines based on modulation spectrum and multivariate modeling realizes constituent analysis and the measurement of concetration to multiple gases.
The wave band that is used for the light of measurement gas composition of the present invention can comprise: the near infrared region of the multiple-frequency vibration of multi-component gas molecule and sum of fundamental frequencies vibration, wavelength is from 800nm to 2500nm.
Detect a plurality of harmonic componentss of modulation spectrum simultaneously, f, 2f, 3f ..., nf, the multiple harmonic of absorption spectra is carried out fusion treatment.
The signal that described balance receiver is picked up is after prime amplifier amplifies, form a plurality of signalling channels by a plurality of lock-in amplifiers, receive a plurality of harmonic componentss of absorption spectra respectively, a plurality of harmonic datas are carried out A/D respectively be converted to digital signal and be sent to computing machine.
In computing machine, adopt the method for Fourier transform to carry out spectrum analysis, different harmonic componentss is separated.
Pick-up unit wherein, include: the modulation signal generator of Lian Jieing, laser driver, laser spectrum light path, signal conditioning circuit, computing machine successively, wherein, computing machine also connects modulation signal generator, and computing machine also is connected with the laser spectrum light path by temperature detection/controller.
Described laser spectrum light path includes: a plurality of semiconductor lasers, fiber coupler, open many optical path pool and balanced type photelectric receiver, wherein, the input end of semiconductor laser connects laser driver, output terminal links to each other with fiber coupler by optical fiber, an output terminal of fiber coupler connects open many optical path pool by optical fiber, another output terminal of the output terminal of open many optical path pool and fiber coupler is connected the balanced type photelectric receiver by optical fiber respectively, and the output of balanced type photelectric receiver connects signal conditioning circuit.
Described signal conditioning circuit includes prime amplifier, a plurality of lock-in amplifier and the A/D converter that connects successively, wherein, the input end of prime amplifier connects the balanced type photelectric receiver in the laser spectrum light path, lock-in amplifier also connects modulation signal generator, and A/D converter connects computing machine.
Described signal conditioning circuit includes prime amplifier and A/D converter, and wherein, the input end of prime amplifier connects the balanced type photelectric receiver in the laser spectrum light path, and A/D converter connects computing machine.
Multi-component gas online test method of the present invention and device are a kind of dynamic testing method and device, by expand the tuning range of semiconductor laser based on the dual tuned mode of temperature, electric current, with the characteristic absorption of coverage goal gas as much as possible; By the detection of dynamic in the adjustment process of temperature, calculate accurate wavelength by real-time temperature value measured and injection current, accuracy control over temperature is converted into the accurate measurement of temperature, can reduces in the detection the high-precision requirement of temperature and improve measuring speed; Injection current to laser instrument carries out high frequency modulated, can effectively reduce various The noise by detecting modulation spectrum, improves the signal to noise ratio (S/N ratio) of signal; The linear identification of absorption spectra improves the sensitivity that detects and the specificity of detection in conjunction with the method for multivariate modeling, and then detects when realizing the multiple gases composition.
Description of drawings
Fig. 1 is that the structure of detection system first embodiment of the present invention is formed synoptic diagram;
Fig. 2 is that the structure of detection system second embodiment of the present invention is formed synoptic diagram.
Wherein:
1: modulation signal generator 2: laser driver
3,4,5: semiconductor laser 6: fiber coupler
7,8: optical fiber 9: be temperature detection/controller
10: be open many optical path pool 10: be the balanced type photelectric receiver
12: prime amplifier 13,14,15: lock-in amplifier
16: be A/D converter 17: computing machine
18: printer 19: real-time clock
20: display
Embodiment
Below in conjunction with drawings and Examples multi-component gas online test method of the present invention and device are made a detailed description.
Multi-component gas online test method of the present invention, be airborne multiple gases to be carried out constituent analysis and concentration detection by near infrared tuning laser spectrum, adopt a plurality of semiconductor lasers, cover different wavelength coverages respectively, laser to a plurality of semiconductor lasers is modulated, internal temperature by semiconductor cooler control semiconductor laser, in the variation of temperature process, measure, needed accurate wavelength is calculated by real-time temperature value measured and injection current, the method that combines based on modulation spectrum and multivariate modeling realizes constituent analysis and the measurement of concetration to multiple gases, at first open many optical path pool 10 are placed measure field, detect then; Described detection includes following steps::
When beginning to measure, startup provides the laser driver 2 of high-frequency current modulation signal to carry out electric current tuning by the injection current noise spectra of semiconductor lasers 3,4,5 of control semiconductor laser 3,4,5 by modulation signal generator 1 to the thermal tuning of laser instrument simultaneously; Temperature detection/controller 9 changes temperature and carries out thermal tuning with noise spectra of semiconductor lasers 3,4,5 by the internal temperature of the thermoelectric refrigerating unit control laser instrument of semiconductor laser 3,4,5 inside;
Semiconductor laser 3,4,5 is after the double modulation of excess temperature and electric current, optical maser wavelength has obtained tuning, emitting laser through optical fiber 7 tell behind the fiber coupler 6 a part of laser again through optical fiber coupling (or transmission) to open many optical path pool 10, at open many optical path pool 10 inner lasers repeatedly reflection takes place, emitting laser is transferred to balance receiver 11 through optical fiber 8 again after the absorption of tested gas; Also send into balance receiver 11 through another part laser that fiber coupler 6 is told through optical fiber 8;
The signal that balance receiver 11 is picked up is sent into lock-in amplifier 13,14,15 after prime amplifier 12 amplifies, send into computing machine 17 again after A/D converter 16 is digital signal with analog signal conversion and handle.
The present invention adopts a plurality of semiconductor lasers, and with a kind of mode of operation in time-division and the frequency division, the method that combines based on modulation spectrum and multivariate modeling realizes constituent analysis and the measurement of concetration to multiple gases.The wave band that is used for the light of measurement gas composition comprises: the near infrared region of the multiple-frequency vibration of multi-component gas molecule and sum of fundamental frequencies vibration, wavelength is from 800nm to 2500nm.
The present invention detects a plurality of harmonic componentss of modulation spectrum simultaneously, f, 2f, 3f ..., nf, the multiple harmonic of absorption spectra is carried out fusion treatment.
The signal that described balance receiver 11 is picked up is after prime amplifier 12 amplifies, form a plurality of signalling channels by a plurality of lock-in amplifiers 13,14,15, receive a plurality of harmonic componentss of absorption spectra respectively, a plurality of harmonic datas are carried out A/D respectively be converted to digital signal and be sent to computing machine 17.In computing machine 17, adopt the method for Fourier transform to carry out spectrum analysis, different harmonic componentss is separated.
The multiple harmonic of tested gas is data from the all-order derivative of its absorption spectra, the characteristic information such as composition, concentration that promptly in the each harmonic data, all includes gas, what the multiple harmonic of tested gas absorption spectrum obtained is a kind of high frequency, narrow band signal, can effectively suppress the influence of the absorption etc. of system drifting, outside electromagnetic interference, circuit noise and coexistence chaff interference; And the high signal of order is better to the inhibition ability of low-frequency disturbance.Reduce very soon yet the amplitude of signal increases with order, make that signal to noise ratio (S/N ratio) reduces along with order increases.
Even-order harmonic (2f, 4f, 6f ...) maximal value in the center of gaseous absorption line, and its line style is all with this center line symmetry; The center of gaseous absorption line and odd harmonic (f, 3f, 5f ...) 0 correspondence, n rank odd harmonic maximal value is worth a little corresponding to the rate of change of (n-1) order harmonics most.The each harmonic of absorption spectra has reflected the linear of spectrum in essence, and its data have comprised information such as the concentration, temperature, pressure, dissimilar noises of tested gas.
Method to the multiple harmonic The data partial least square method (PLS) obtained is set up Quantitative Analysis Model, and the multiple harmonic data X and the measured physical quantity y (concentration, temperature, pressure etc.) of spectrum extracted major component matrix T=[t
1, t
2..., t
f] and U=[u
1, u
2..., u
f], the requirement that PLS decomposes is: make t
1And u
1Covariance reach maximum:
Major component matrix T and U are done linear regression, and b is the correlation coefficient matrix
U=Tb+e (1)
b=(T
TT)
-1T
TU (2)
Spectrum X for unknown sample
Un, obtain predicted value: y
Un=X
UnB (3)
The low order spectrum harmonic data (as 2 rank) that records is carried out pre-service and standardization, eliminate of the influence of instrument response function measurement data.Standardized data are compressed pre-service, and the several features point wavelength that obtains selecting based on the spectroscopic data of these unique point wavelength, is used partial least square method and is set up the quantitative forecast model.Its input quantity X is the spectroscopic data (X of each characteristic wavelength
λ 1, X
λ 2, X
λ 3...), its output quantity y is the kind and the concentration information (C of tested gas to be measured
1, C
2, C
3...).Modeling process is same as described above.
As shown in Figure 1, multi-component gas on-line measuring device of the present invention, include: Chuan Lian modulation signal generator 1, laser driver 2, laser spectrum light path 21, signal conditioning circuit 22, computing machine 17 successively, wherein, computing machine 17 also connects modulation signal generator 1, and computing machine 17 also is connected with laser spectrum light path 21 by temperature detection/controller 9.Computing machine 17 also is connected with printer (18), real-time clock (19), display (20).
Described laser spectrum light path 21 includes: as a plurality of semiconductor lasers 3 of light source, 4,5, fiber coupler 6, open many optical path pool 10 and balanced type photelectric receiver 11, wherein, semiconductor laser 3,4,5 input end connects laser driver 2, output terminal links to each other with fiber coupler 6 by optical fiber 7, an output terminal of fiber coupler 6 connects open many optical path pool 10 by optical fiber 8, another output terminal of the output terminal of open many optical path pool 10 and fiber coupler 6 is connected balanced type photelectric receiver 11 by optical fiber 8 respectively, is used to eliminate semiconductor laser 3,4,5 noise and other common-mode noise.The output of balanced type photelectric receiver 11 connects signal conditioning circuit 22.
Power drive by laser driver 2 injection currents of laser instrument 3,4,5, realize that the high-frequency current of laser is tuning; Temperature detection/controller 9 is by thermoelectric refrigerating unit (the Thermoelectric Cooler of semiconductor laser 3,4,5 inside, TEC) control the internal temperature of laser instrument 3,4,5, and pass through the internal temperature of thermistor (NTC) the Laser Measurement device 3,4,5 of semiconductor laser 3,4,5 inside.
Above-mentioned light source also can using gases laser instrument or dye laser, uses the wavelength coverage of the different laser instrument of N emission wavelength with coverage goal gas.
Described signal conditioning circuit 22 includes prime amplifier 12, a plurality of lock-in amplifier 13,14,15 and the A/D converter 16 of polyphone successively, wherein, the input end of prime amplifier 12 connects the balanced type photelectric receiver 11 in the laser spectrum light path 21, lock-in amplifier 13,14,15 also connects modulation signal generator 1, and A/D converter 16 connects computing machine 17.The output signal of 12 pairs of balanced type photelectric receivers 11 of prime amplifier is amplified, the output signal of prime amplifier 12 is sent to a plurality of lock-in amplifiers 13,14,15, the output of modulation signal generator 1 also inputs to these lock-in amplifiers 13,14,15 respectively, and make the centre frequency of these lock-in amplifiers 13,14,15 be set to f, 2f, 3f......nf respectively, the demodulated output signal of lock-in amplifier is sent to multi-channel a/d converter 16 respectively, thereby analog quantity is converted to digital signal.
The signal that computing machine 17 (embedded or PC computing machine) collects carries out digital filtering, calculates the predicted value of object gas composition with reference to being stored in calibration curve in its storer, and the object gas concentration value that calculates shown that on display 20 simultaneous computer is also controlled and managed laser driver 2, modulation signal generator 1, temperature detection/controller 9, display 20.The data processing of carrying out in computing machine is to carry out digital filtering, gross error rejecting, temperature compensation, background deduction pre-service.
As shown in Figure 2, described signal conditioning circuit 22 can also be: include prime amplifier 12 and A/D converter 16, wherein, the input end of prime amplifier 12 connects the balanced type photelectric receiver 11 in the laser spectrum light path 21, and A/D converter 16 connects computing machine 17.
Do not use the lock-in amplifier 13,14,15 of hardware at present embodiment, is digital signal and be to use high-speed a/d converter with analog signal conversion, by software phase-sensitive detection method the each harmonic composition is extracted, carry out method same as the previously described embodiments again and handle.
In example of the present invention, select for use:
The model of laser driver is: MAX3735;
The model of semiconductor laser is: QDFBSS-1600, QDFBLD-1460;
Fiber coupler is: 3 * 1;
The model of balanced type photelectric receiver is: 1817-FC;
The model of prime amplifier is: AMT-07;
The model of A/D converter is: AD7714.