CN104237135B - CO gas detecting systems and method based on quartz tuning fork strengthened optoacoustic spectroscopy - Google Patents
CO gas detecting systems and method based on quartz tuning fork strengthened optoacoustic spectroscopy Download PDFInfo
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- CN104237135B CN104237135B CN201410566870.5A CN201410566870A CN104237135B CN 104237135 B CN104237135 B CN 104237135B CN 201410566870 A CN201410566870 A CN 201410566870A CN 104237135 B CN104237135 B CN 104237135B
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Abstract
CO gas detecting systems and method based on quartz tuning fork strengthened optoacoustic spectroscopy, are related to a kind of CO gas detecting systems and method.It is in order to the accuracy of detection for solving existing CO gases optoacoustic spectroscopy detection technique it is not high the problem of.Current controling signal is sent to laser controller by data processing module by function generator, temperature control parameter is sent to laser controller simultaneously, laser controller driving laser transmitting near-infrared laser, is incided in air chamber after collimation, focusing；Gas absorbs luminous energy and is converted to heat energy, and then is converted to sound pressure signal, and the quartz tuning-fork being installed in air chamber converts acoustic signals into electric signal；The electric signal of quartz tuning-fork is input to the Measurement channel input of lock-in amplifier after conversion, amplification, and the reference signal of lock-in amplifier associative function generator carries out second-harmonic detection, and then inverting CO gas concentrations to be measured.The present invention is applied to the detection of CO gases.
Description
Technical field
The present invention relates to a kind of CO gas detecting systems and method.
Background technology
The CO gases of underground coal mine are both inflammable and explosive and toxic gas, if leakage or aggregation cannot be sent out in time
It is existing, not only it is also easy to produce blast, causes fire, and also pollution environment even results in pernicious poisoning.CO gases can be effectively anti-
The overheat and ageing process of solid insulating material in operation power transformer are reflected, by the detection to CO gases, oil can be forecast
Paper insulated inside transformer Hidden fault and development, realize early diagnosis.Initial Stage of Fire, CO gases can be as a kind of special
Levy gas to determine whether combustible combustion, and then realize fire alarm and monitoring.
The detection of CO gases is widely used in modern production life, and particularly many occasions need to carry out trace CO gases
Detection, conventional CO detection methods can be divided into metal oxide method, electrochemical process and spectral absorption method etc..Catalyst combustion type CO gases
Detection means output signal is linear with gas volume fraction, is suitable for the monitoring of higher gas volume fraction, selection
Property is poor, big by air speed influence.Metal-oxide semiconductor (MOS) CO gas-detecting devices are to low volume fraction gas signal exporting change
Greatly, sensitivity is high, and service life is high, response speed block, and selectivity is not good.Field effect transistor cast CO gas-detecting devices are stable
Property good, high temperature resistant, resistance to strong acid, poor sensitivity, selectivity it is poor.Comparatively, the CO gases based on spectrum theory are detected
Method has the following advantages：Realize noncontact online auto monitoring；Instrumental sensitivity is high, as long as selecting suitable spectral band, just
The precision of object gas ppm magnitudes can be realized；Because measurement result only reflects the concentration average level in a region, its result
It is representative.
T unable filter (Tunable Diode Laser Absorption
Spectroscopy, TDLAS) its essence is a kind of absorption spectroscopy techniques, utilizes the narrow linewidth and wavelength of semiconductor laser to adjust
Humorous characteristic, changes laser output wavelength by changing temperature and electric current, under test gas absworption peak is scanned, by analyzing gas
Gas concentration is determined to the absorption of light.
Cavity ring down spectroscopy technology (Cavity ring down spectroscopy, CRDS) is the hair eighties in last century
A kind of direct absorption spectroscopy techniques of high sensitivity that exhibition is got up, current cavity ring down spectroscopy technology has been widely used in explosive
The fields such as gas detection, atmospheric monitoring.
FFIR technology (Fourier Transform infrared spectroscopy, TFIR)
It is the Main Means of atmosphere environment supervision.The infrared conversion spectrum technology of Fourier can shine according to molecule in specific wavelength infrared ray
Absorbing state under penetrating recognizes, quantifies material composition.By using open light path design, light can be made under test gas
Effective optical path lengthening is to 1km.FTIR technologies have the high good, sensitivity of selectivity, high resolution, the response time is fast, do not consume load
The advantages of gas.Agriculturally, generally believe that the infrared conversion instrument of open light path Fourier is for measuring ammonia in agricultural industry
The effective tool of concentration, is increasingly used widely in air quality context of detection.
Differential optical absorption spectrum (Differential Optical Absorption Spectroscopy, DOAS) is made
Have been widely recognized and apply in the range of European Union for a kind of atmospheric monitoring technology.In the evolution of DOAS technologies,
External numerous scholars in terms of DOAS system configurations, detection device, inversion algorithm successively to being improved, perfect DOAS skills
Art.At present, DOAS system researches production is concentrated mainly on the developed countries such as Sweden, Germany, the U.S., France and Russia.
Direct absorption spectrometry requires that light path is longer, requires strict to optical path pool design, manufacture, electrical noise and light source power
The influence of fluctuations monitoring limit, the ambient noise that environment is brought is difficult to eliminate.
Optoacoustic spectroscopy (photoacoustic spectroscopy, PAS) originates from 1880, and Bell is reported first
Optoacoustic effect, subsequent Viegerov completes spectrochemical analysis for gases first.But it is due to detection technique limitation, until 20th century
Just, with the development of laser technology and promoting the use of for high sensitivity microphone, optoacoustic spectroscopy is just able to high speed development.Light
Acousto-optic spectral technology is that, by modulation of source to object gas absorption region, optoacoustic pool gas Absorption modulation light is simultaneously excited to high energy
State, energy is converted into molecular kinetic energy during radiationless transition to lower state, causes temperature to produce cyclically-varying, progressively
A cycle pressure change is formed, voice signal is further produced, and the sound signal frequencies are identical with modulating light frequency.Sound
Message number can be caught by highly sensitive microphone, and its intensity is directly proportional to gas concentration in photoacoustic cell.In order to improve system detectio
Sensitivity and antijamming capability, generally use wavelength-modulation technique harmonic detection technique.
But at present, the accuracy of detection of existing CO gases optoacoustic spectroscopy detection technique is not high.
The content of the invention
The present invention be in order to the accuracy of detection for solving existing CO gases optoacoustic spectroscopy detection technique it is not high the problem of, so as to carry
For a kind of CO gas detecting systems and method based on quartz tuning fork strengthened optoacoustic spectroscopy.
CO gas detecting systems based on quartz tuning fork strengthened optoacoustic spectroscopy, including data processing module, laser
Source module and photoacoustic signal detection module,
Data processing module includes preamplifier 9, the first lock-in amplifier 10, the second lock-in amplifier 13, data and adopted
Truck 1 and computer 14；
Laser light source module includes function generator 2, laser controller 3, laser 4, fiber optic collimator bag 5 and condenser lens
6；
Photoacoustic signal detection module includes air chamber 7, quartz tuning-fork 8, reference gas chamber 11 and photodetector 12；The quartz
Tuning fork 8 is located in air chamber 7, filled with CO gases in the air chamber 7；Filled with CO gases in reference gas chamber 11；
Data collecting card 1 connects the current controling signal input of current controling signal output end and function generator 2,
First electrical signal of function generator 2 is connected with the electric signal input end of laser controller 3；Data collecting card 1
Temperature control signals output end is connected with the temperature control signals input of laser controller 3；
The driving output laser of laser 4 of laser controller 3, the laser is incident to poly- after being collimated through fiber optic collimator bag 5
Focus lens 6, and line focus lens 6 are focused in air chamber 7, and excite CO gases to produce sound pressure signal, the laser is passed through after air chamber 7
It is incident to reference gas chamber 11；
Quartz tuning-fork 8 receives sound pressure signal and is simultaneously converted to electric signal, the electrical signal of the quartz tuning-fork 8 with it is preposition
The electric signal input end connection of amplifier 9；The output end of the preamplifier 9 and the first telecommunications of the first lock-in amplifier 10
The connection of number input；Second electric signal of the reference signal input and function generator 2 of first lock-in amplifier 10 is defeated
Go out end connection；The output end of first lock-in amplifier 10 is connected with the first data signal input of data collecting card 1；
Photodetector 12 is used to detect the laser signal in reference gas chamber 11 and is converted to electric signal, believes as measurement
Number；The measurement signal output end of the photodetector 12 is connected with the first electric signal input end of the second lock-in amplifier 13；
The second electrical signal connection of the reference signal input and function generator 2 of second lock-in amplifier 13；It is described
The output end of second lock-in amplifier 13 is connected with the second data signal input of data collecting card 1；
Data collecting card 1 is communicated with computer 14.
The CO gas detection methods of quartz tuning fork strengthened optoacoustic spectroscopy based on said system, it is by following steps
Realize：
Computer 14 sends control signals to information acquisition card 1, and current controling signal is passed through function by information acquisition card 1
Generator 2 is sent to laser controller 3, while temperature control parameter is sent into laser controller 3, laser controller
The 3 driving transmitting near-infrared lasers of laser 4, are incided in air chamber 7 after the collimation of fiber optic collimator bag 5 and condenser lens 6 are focused on；
The luminous energy that CO gases in air chamber 7 absorb near-infrared laser is converted to heat energy, and then is converted to sound pressure signal, in air chamber 7
Quartz tuning-fork 8 convert acoustic signals into electric signal；
By the electric signal of quartz tuning-fork 8 after conversion, amplification, the Measurement channel for being input to a lock-in amplifier 10 is defeated
Enter end, the reference signal of the associative function generator 2 of lock-in amplifier 10 carries out second-harmonic detection, and then inverting obtains CO to be measured
Gas concentration.
It also comprises the following steps：
Be filled with the reference gas chamber 11 after air chamber 7 with CO gas concentrations identical CO gases in air chamber, using position
The laser signal absorbed in the detection of photodetector 12 after reference gas chamber 11 by gas, and the laser signal is converted to
Electric signal；
No. two lock-in amplifiers 13 receive the electric signal, while the high_frequency sine wave that access is sent from function generator 2,
And then feedback control is carried out, the optical maser wavelength that will deviate from is locked in Absorption Line as frequency discrimination signal using harmonic signal
Center, realizes laser frequency stabilization.
The beneficial effects of the invention are as follows：One, the present invention is substituted traditional using quartz tuning fork strengthened sound pressure detection device
Microphone, improves the quality factor q of sound pressure detection device, and the sensitivity of optoacoustic spectroscopy CO gas detecting systems is improved into 2-3
Individual magnitude；
2nd, the present invention substitutes traditional microphone using quartz tuning fork strengthened sound pressure detection device, improves modulation letter
Number frequency f, enhance system environment resistant low frequency noises ability；
3rd, the quartz tuning fork strengthened acoustic pressure detection device of present invention design, the use of resonatron improves sound pressure signal
Detection sensitivity, it is suppressed that interference of the environment with frequency noise；
4th, present invention design laser frequency stabilization backfeed loop, harmonic signal is as frequency discrimination signal, by filters center
Wavelength locking is in one absorption peak position of CO gases, it is to avoid the laser ripple that detection is caused due to factors such as environment temperatures for a long time
Long drift.
Brief description of the drawings
Fig. 1 is the present invention based on quartz tuning fork strengthened trace gas detection system structural representation；
Fig. 2 is quartz tuning fork strengthened sound pressure detection device structural representation；
The stable measurement result schematic diagram that Fig. 3 is measured for a long time for the present invention；
Embodiment
Embodiment one, the CO gas detecting systems based on quartz tuning fork strengthened optoacoustic spectroscopy, including number
According to processing module, laser light source module and photoacoustic signal detection module,
Data processing module includes preamplifier 9, the first lock-in amplifier 10, the second lock-in amplifier 13, data and adopted
Truck 1 and computer 14；
Laser light source module includes function generator 2, laser controller 3, laser 4, fiber optic collimator bag 5 and condenser lens
6；
Photoacoustic signal detection module includes air chamber 7, quartz tuning-fork 8, reference gas chamber 11 and photodetector 12；The quartz
Tuning fork 8 is located in air chamber 7, filled with CO gases in the air chamber 7；Filled with CO gases in reference gas chamber 11；
Data collecting card 1 connects the current controling signal input of current controling signal output end and function generator 2,
First electrical signal of function generator 2 is connected with the electric signal input end of laser controller 3；Data collecting card 1
Temperature control signals output end is connected with the temperature control signals input of laser controller 3；
The driving output laser of laser 4 of laser controller 3, the laser is incident to poly- after being collimated through fiber optic collimator bag 5
Focus lens 6, and line focus lens 6 are focused in air chamber 7, and excite CO gases to produce sound pressure signal, the laser is passed through after air chamber 7
It is incident to reference gas chamber 11；
Quartz tuning-fork 8 receives sound pressure signal and is simultaneously converted to electric signal, the electrical signal of the quartz tuning-fork 8 with it is preposition
The electric signal input end connection of amplifier 9；The output end of the preamplifier 9 and the first telecommunications of the first lock-in amplifier 10
The connection of number input；Second electric signal of the reference signal input and function generator 2 of first lock-in amplifier 10 is defeated
Go out end connection；The output end of first lock-in amplifier 10 is connected with the first data signal input of data collecting card 1；
Photodetector 12 is used to detect the laser signal in reference gas chamber 11 and is converted to electric signal, believes as measurement
Number；The measurement signal output end of the photodetector 12 is connected with the first electric signal input end of the second lock-in amplifier 13；
The second electrical signal connection of the reference signal input and function generator 2 of second lock-in amplifier 13；It is described
The output end of second lock-in amplifier 13 is connected with the second data signal input of data collecting card 1；
Data collecting card 1 is communicated with computer 14.
Operation principle：In optoacoustic spectroscopy, the optoacoustic detected using quartz tuning fork strengthened optoacoustic spectroscopy is believed
Number it can be expressed as：
S（P）=KI α Q (P) ε (P)
Wherein：K is system constants, and I is laser power, and α (absorbs with test gas and cut for the absorption coefficient of under test gas
Face and concentration dependent amount), ε (P) is acousto-optic conversion efficiency, and Q (P) is the quality factor of tuning fork.The quality factor q reflection of tuning fork
The size for the damping that the loss or vibration of vibrational energy are subject to, it is however generally that the quality factor of quartz tuning-fork are up to 104Magnitude.
Because quartz tuning-fork has very high Q values, therefore adaptation enhanced photo acoustic spectral technique can provide higher detectivity.
The characteristic of quartz tuning-fork shows that the sound wave produced between being raised one's arm two can make quartz tuning-fork two raise one's arm generation symmetrically
Vibration, can just produce effective piezoelectric signal.In general environment, the frequency of noise is generally less than 32KHz, i.e. wavelength and is more than
3cm, and quartz tuning-fork two the distance between is raised one's arm as 0.3mm or so, much smaller than the wavelength of noise, the frequency of even noise connects
Nearly quartz tuning-fork intrinsic frequency, two vibrations raised one's arm of quartz tuning-fork are equidirectional caused by noise from distant place, will not be produced
Effective piezoelectric signal, therefore quartz tuning-fork can realize and environment acoustic pressure noise is immunized.
The photoacoustic signal that optoacoustic effect is produced has a feature, is exactly the size of acoustical signal and modulating frequency is inversely proportional pass
System, so modulating frequency is typically located at 1-4KHz scopes by traditional optoacoustic spectroscopy, and quartz tuning-fork working frequency is：
32.768KHz, this has cut down photoacoustic signal.Therefore the present invention uses design structure as shown in Figure 2, adds at quartz tuning-fork two ends
Upper resonatron, can effectively improve photoacoustic signal.Internal diameter is an important parameter of resonatron, works as resonatron, when in resonatron
When footpath is much smaller than wavelength, the transmission mode of sound wave can approximately regard one-dimensional resonatron as.Resonance bore D scope is：
Wherein：V is the velocity of sound, and f is the frequency of sound wave, and η is Viscosity Factor of Gas, and ρ is the density of gas.Resonance bore can
The scope is selected to be：0.36mm ＜ D ＜ 6.1mm.
Standing wave is formed in resonatron, the length of resonatron is equal to the integral multiple of half-wavelength, according to wavelength and frequency relation
Understand：
Wherein：N is natural number, and V is the velocity of sound, and L is resonance length of tube, and Δ l is correction of the resonance length of tube in openend,
Typically take 0.6D.The resonatron being open for two ends, when n takes it is strange when, the center of resonatron is the antinode of pressure wave, can
So that quartz tuning-fork is put into this position, you can obtain stronger voice signal.When the frequency of quartz tuning-fork：f0=
32.768KHz when, L=4.408mm.
Data processing module output current control signal produces tens Hz low frequency to function generator 2, function generator 2
Sawtooth waveforms and the high_frequency sine wave that frequency is f, the low frequency sawtooth wave output terminal and high frequency sinusoidal wave output terminal of function generator 2 are all
Two current modulated inputs of laser controller 3 are connect, the inside of laser controller 3 is driven containing add circuit and electric current
Dynamic circuit, the laser diode input of the driving current output termination laser 4 of laser controller 3；Data processing
Module also output temperature control signal is connect in a temperature modulation signal input part of laser controller 3, laser controller 3
Contain TEC drive circuits and thermistor interface circuit, the TEC inputs of the output termination laser 4 of laser controller 3 in portion
End, the input of laser controller 3 also connects the thermistor output end of laser 4, for the temperature of detection laser, feedback
Control the temperature of laser；Laser light source module realizes the tune of laser output wavelength by controlling the temperature and electric current of laser 4
The modulation of system and laser emission frequency.It is 1565.98nm, laser control that CO gases, which may be selected, to absorb the corresponding wavelength in peak position
The temperature modulation of device 3 and current-modulation collective effect processed, adjust laser 4 in the way of length scanning so that the output of laser 4 swashs
The centre wavelength of light is 1565.98nm.Current controling signal is adjusted, the set of frequency of high_frequency sine wave is f, and modulation obtains laser
The tranmitting frequency f of the output laser of device 4 is quartz tuning-fork resonant frequency f0Half, i.e.,：F=f0/2。
The described gas detecting system based on quartz tuning fork strengthened optoacoustic spectroscopy, the current-modulation of laser 4 frequency
Rate is the high frequency sinusoidal wave frequency rate f that function generator 2 is exported, and the frequency of quartz tuning-fork 8 is f0, it is typically set at f=f0/2.Cause
This needs the frequency f to quartz tuning-fork 80Calibrated, to ensure the reference signal of lock-in amplifier 10 and lock-in amplifier 13
Meet harmonic detecting requirement.In the calibration mode, a pin of quartz tuning-fork 8 is used as measurement end, another pin
It is coupled with a sine wave.While the frequency of sine wave is scanned, the excitation current of quartz crystal oscillator is also measured, by finding
The corresponding scan frequency of maximum excitation electric current carrys out determiner resonant frequency f0。
The laser modulated passes through fiber optic collimator bag 5, condenser lens 6, incides in air chamber 7.Under test gas is by optical signal
Sound pressure signal is converted to, sound pressure signal intensity is directly proportional under test gas concentration.Sound pressure signal is converted to piezoelectricity by quartz tuning-fork 8
Current signal, piezoelectric current signal intensity is directly proportional to sound pressure signal intensity.Because quartz tuning-fork two is raised one's arm in resonatron
Heart position, can eliminate the interference from extraneous same frequency signal.During measurement, the pin ground connection of quartz tuning-fork 8, another
Pin connects the input of preamplifier 9, and preamplifier is mutual impedance preamplifier, current signal can be converted into voltage
Signal, and signal is amplified.The measurement signal input of the output termination lock-in amplifier 10 of preamplifier, lock-in amplifier
The high frequency sinusoidal wave output terminal of 10 reference signal input termination function generator.Lock-in amplifier 10 carries out second harmonic inspection
Survey, be finally inversed by under test gas CO concentration.
Contain the under test gas of identical CO concentration in reference gas chamber 11 after air chamber 7, after reference gas chamber 11
The laser signal that the detection of photodetector 12 absorbs by gas, and convert optical signals to electric signal.Photodetector 12
The measurement signal input of output termination lock-in amplifier 13, the reference signal input termination function generator of lock-in amplifier 13
High frequency sinusoidal wave output terminal.Lock-in amplifier 13 carries out triple-frequency harmonics demodulation, and the output terminating data of lock-in amplifier 13 is adopted
The input of truck 1.Using the zero passage dot characteristics of odd harmonic, using harmonic signal as frequency discrimination signal, according to certain
Feedback control algorithm, the optical maser wavelength that will deviate from is locked in Absorption Line center, realizes laser frequency stabilization.
Embodiment two, according to embodiment one based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that fiber optic collimator bag 5, condenser lens 6 are located in same light path.
Embodiment three, according to embodiment two based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that reference gas chamber 7 is rectangular parallelepiped structure；
Laser light incident window 71 and laser emitting window 72, laser light incident are respectively arranged with its left side wall and right side wall
The upper end of window 71 and the upper end of laser emitting window 72 to air chamber it is tilted set, and with vertical direction angulation
It is 5 °~7 °；Incidence window 71 and exit window 72 are in the light path described in claim 2；
The upper and lower surface of reference gas chamber 7 has air inlet 73 and gas outlet 74.
Embodiment four, according to embodiment three based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that reference gas chamber 7 is cuboid, then the long 15mm of the optical path direction of reference gas chamber 7, vertical light
The wide 15mm in road direction, high 12mm.
Embodiment five, according to embodiment four based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that laser 4 is semiconductor laser with tunable, the laser is internally integrated TEC systems
Cooler and thermistor.
Embodiment six, according to embodiment one based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that quartz tuning-fork 8 includes quartz crystal oscillator 81 and double resonance pipe 82；The quartz crystal oscillator 81
It is that frequency is 32.768KHz, sloughs the pole structure of vacuum shell；
Double resonance pipe 82 is symmetrically distributed in quartz crystal oscillator both sides, and the double resonance pipe 82 is cut close to the side of quartz crystal oscillator 81
The distance between plane is raised one's arm for 100 microns with 81 liang of quartz crystal oscillator in face.
Embodiment seven, according to embodiment six based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that 81 liang of quartz crystal oscillator, which is raised one's arm, to be centrally located in the focus of condenser lens 6.
Embodiment eight, according to embodiment seven based on quartz tuning fork strengthened optoacoustic spectroscopy
The differences of CO gas detecting systems be that preamplifier 9 is mutual impedance preamplifier.
The CO gases of embodiment nine, quartz tuning fork strengthened optoacoustic spectroscopy based on embodiment one
Detection method, it is realized by following steps：
Computer 14 sends control signals to information acquisition card 1, and current controling signal is passed through function by information acquisition card 1
Generator 2 is sent to laser controller 3, while temperature control parameter is sent into laser controller 3, laser controller
The 3 driving transmitting near-infrared lasers of laser 4, are incided in air chamber 7 after the collimation of fiber optic collimator bag 5 and condenser lens 6 are focused on；
The luminous energy that CO gases in air chamber 7 absorb near-infrared laser is converted to heat energy, and then is converted to sound pressure signal, in air chamber 7
Quartz tuning-fork 8 convert acoustic signals into electric signal；
By the electric signal of quartz tuning-fork 8 after conversion, amplification, the Measurement channel for being input to a lock-in amplifier 10 is defeated
Enter end, the reference signal of the associative function generator 2 of lock-in amplifier 10 carries out second-harmonic detection, and then inverting obtains CO to be measured
Gas concentration.
It also comprises the following steps：
Be filled with the reference gas chamber 11 after air chamber 7 with CO gas concentrations identical CO gases in air chamber, using position
The laser signal absorbed in the detection of photodetector 12 after reference gas chamber 11 by gas, and the laser signal is converted to
Electric signal；
No. two lock-in amplifiers 13 receive the electric signal, while the high_frequency sine wave that access is sent from function generator 2,
And then carry out feedback control as frequency discrimination signal using harmonic signal, the centre wavelength of laser 4 is locked in be measured
One absorption peak position of CO gases, centre wavelength can be 1565.98nm.
The described gas detecting system based on quartz tuning fork strengthened optoacoustic spectroscopy, the output of laser 4 laser, light
Fibre collimation bag 5, condenser lens 6, the laser light incident window 71 of air chamber 7, laser emitting window 72, reference gas chamber 11, photodetection
12 are sequentially placed in same light path.It is the pillar quartz crystal oscillator that 32.768KHz sloughs vacuum shell that quartz tuning-fork 8, which includes frequency,
81, the two of quartz crystal oscillator 81, which raises one's arm, is centrally located at the focal position of described condenser lens, obtains the ceiling capacity of laser excitation；
Also include double resonance pipe 82, the unilateral a length of 4mm of resonatron, resonance bore is 0.55mm, quartz crystal oscillator two is raised one's arm
The antinode of standing wave is formed positioned at resonatron, sound pressure signal quality is improved；Resonatron 82 is close to the lateral section of quartz crystal oscillator one and stone
English crystal oscillator 81 raise one's arm plane distance be 100 microns, distance cross conference influence standing wave formation.
The incidence window 71 of air chamber 7 and exit window 72, equal upper end are set to air chamber is tilted, with angle alleged by vertical direction
Degree is 5~7 °, and such setting avoids laser from interfering phenomenon.
The described gas detecting system based on quartz tuning fork strengthened optoacoustic spectroscopy, laser diode current modulating frequency
The high frequency sinusoidal wave frequency rate f exported for function generator, the frequency of quartz tuning-fork 8 is f0, it is typically set at f=f0/2.In system
Before measurement, to the frequency f of quartz tuning-fork 80Calibrated.In the calibration mode, a pin of quartz tuning-fork 8 is used as measurement
End is used, and another pin is coupled with a sine wave.While the frequency of sine wave is scanned, the excitation current of quartz crystal oscillator
Also it is measured, by finding the corresponding scan frequency of maximum excitation electric current come determiner resonant frequency f0。
In measurement mode, the modulating frequency of laser is set to the half of quartz tuning-fork intrinsic frequency, i.e.,：f0/ 2, stone
One pin ground connection of English tuning fork, another pin carries out second harmonic as end of probe, the signal of generation by data processing module
Demodulation.Data processing module output current control signal is to function generator 2, and function generator 2 produces tens Hz low frequency saw
Tooth ripple and the high_frequency sine wave that frequency is f, the two of which input of the output termination laser controller 3 of function generator 2, swash
Add circuit and current driving circuit are contained in the inside of light device controller 3, and an output of laser controller 3 connects laser 4
Laser diode input；Data processing module also exports one of input that warm control signal connects laser controller 3,
TEC drive circuits and thermistor interface circuit are contained in the inside of laser controller 3, and the output termination of laser controller 3 swashs
The TEC inputs of light device 4, the input of laser controller 3 also connects the thermistor output end of laser 4, sharp for detecting
The temperature of light device, the temperature of feedback control laser；Laser light source module is realized and swashed by controlling the temperature and electric current of laser 4
The modulation of light device output wavelength and the modulation of laser emission frequency.The corresponding wavelength in CO gases absorption peak position, which may be selected, is
1565.98nm, laser temperature modulation and laser diode current modulate collective effect, and laser is adjusted in the way of length scanning,
So that the centre wavelength of laser output laser is 1565.98nm.Adjust current controling signal, the set of frequency of high_frequency sine wave
For f, the tranmitting frequency f that modulation obtains laser output laser is quartz tuning-fork resonant frequency f0Half, i.e.,：F=f0/2。
The laser modulated is output to fiber optic collimator bag 5, the laser transmitted in optical fiber is changed into directional light, through over-focusing
Mirror is focused on, and is incided in air chamber 7 so that laser energy converges to 81 liang of centers of raising one's arm of quartz crystal oscillator of quartz tuning-fork 8.Treat
Survey gas to absorb luminous energy and be converted to heat energy, absorb luminous energy and be directly proportional to gas concentration, in the case of given volume, heat energy turns
Sound pressure signal is changed to, therefore sound pressure signal intensity is directly proportional under test gas concentration.Sound pressure signal is converted to electricity by quartz tuning-fork 8
Signal, because quartz tuning-fork two is raised one's arm positioned at resonatron center, can eliminate the interference from extraneous same frequency signal.Survey
During amount, the pin ground connection of quartz tuning-fork 8, another pin connects the input of preamplifier 9, and preamplifier is mutual resistance
Anti- preamplifier, is converted to voltage signal, and signal is amplified by quartz tuning-fork piezoelectric current signal.Preamplifier it is defeated
Go out to terminate the measurement signal input of lock-in amplifier 10, the reference signal input termination function generator of lock-in amplifier 10
High frequency sinusoidal wave output terminal.Lock-in amplifier 10 carries out second-harmonic detection, need to be according to calibrating gas to system during primary detection
Demarcated, measurement multi-group data carries out curve fitting, and calibrated system can carry out gas detection, and lock-in amplifier 10 is defeated
The second harmonic signal gone out and gas concentration are proportional.
System also includes the feedback control loop of laser frequency stabilization, containing identical in the reference gas chamber 11 after air chamber 7
The under test gas of concentration, the laser signal that the detection of photodetector 12 after reference gas chamber 11 absorbs by gas, and will
Optical signal is converted to electric signal.The measurement signal input of the output termination lock-in amplifier 13 of photodetector 12, lock is mutually put
The high frequency sinusoidal wave output terminal of the reference signal input termination function generator of big device 13.Lock-in amplifier 13 carries out triple-frequency harmonics
Demodulation, the input of the output termination data collecting card 1 of lock-in amplifier 13.Using the zero passage dot characteristics of odd harmonic, use
Harmonic signal is as frequency discrimination signal, and according to certain feedback control algorithm, the optical maser wavelength that will deviate from is locked in Absorption Line
Center, the centre wavelength of selection can be 1565.98nm, realize laser frequency stabilization.
During concrete application, the present invention carries out the frequency calibration of quartz tuning-fork 8, when measuring first, by calibrating gas to being
System is demarcated；After system calibrating, in measurement mode, gas concentration measure loop and laser frequency stabilization feedback control loop are same
When work, good portability, stability is high, and strong antijamming capability can be monitored on-line for a long time.
Claims (4)
1. the CO gas detecting systems based on quartz tuning fork strengthened optoacoustic spectroscopy, including data processing module, lasing light emitter
Module and photoacoustic signal detection module, it is characterized in that：
Data processing module includes preamplifier (9), the first lock-in amplifier (10), the second lock-in amplifier (13), data
Capture card (1) and computer (14)；Preamplifier (9) is mutual impedance preamplifier；
Laser light source module includes function generator (2), laser controller (3), laser (4), fiber optic collimator bag (5) and focused on
Lens (6)；Fiber optic collimator bag (5), condenser lens (6) are located in same light path；Laser (4) is tunable semiconductor laser
Device, the laser is internally integrated TEC refrigerators and thermistor；Contain add circuit and electric current inside laser controller (3)
Drive circuit, the laser diode input of the driving current output termination laser (4) of laser controller (3)；Number
A temperature modulation signal input part of laser controller (3), laser are connect according to processing module also output temperature control signal
Contain TEC drive circuits and thermistor interface circuit, the output termination laser of laser controller (3) inside controller (3)
The TEC inputs of device (4), the input of laser controller (3) also connects the thermistor output end of laser (4), for examining
Survey the temperature of laser, the temperature of feedback control laser；Laser light source module by controlling the temperature and electric current of laser (4),
Realize the modulation of laser output wavelength and the modulation of laser emission frequency；
Photoacoustic signal detection module includes air chamber (7), quartz tuning-fork (8), reference gas chamber (11) and photodetector (12)；It is described
Quartz tuning-fork (8) is located in air chamber (7), filled with CO gases in the air chamber (7)；Filled with CO gases in reference gas chamber (11)；Stone
English tuning fork (8) includes quartz crystal oscillator (81) and double resonance pipe (82)；The quartz crystal oscillator (81) is that frequency is 32.768KHz, taken off
Remove the pole structure of vacuum shell；Double resonance pipe (82) is symmetrically distributed in quartz crystal oscillator both sides, and the double resonance pipe (82) is close
The lateral section of quartz crystal oscillator (81) one and quartz crystal oscillator (81) two the distance between plane of raising one's arm are 100 microns, quartz crystal oscillator (81)
Two, which raise one's arm, is centrally located in the focus of condenser lens (6)；Air chamber (7) is rectangular parallelepiped structure；Divide on its left side wall and right side wall
Laser light incident window (71) and laser emitting window (72), the upper end of laser light incident window (71) and laser exit window are not provided with
The upper end of mouth (72) is set to air chamber is tilted, and is 5 °~7 ° with vertical direction angulation；Incidence window
(71) it is located at exit window (72) with fiber optic collimator bag (5), condenser lens (6) in same light path；The upper surface of air chamber (7) and
Lower surface has air inlet (73) and gas outlet (74)；
Data collecting card (1) connects the current controling signal input of current controling signal output end and function generator (2),
First electrical signal of function generator (2) is connected with the electric signal input end of laser controller (3)；Data collecting card
(1) temperature control signals output end is connected with the temperature control signals input of laser controller (3)；
Laser controller (3) driving laser (4) output laser, the laser is incident to after being collimated through fiber optic collimator bag (5)
Condenser lens (6), and line focus lens (6) are focused in air chamber (7), and excite CO gases to produce sound pressure signal, the laser is worn
Cross and reference gas chamber (11) is incident to after air chamber (7)；
Quartz tuning-fork (8) receives sound pressure signal and is simultaneously converted to electric signal, the electrical signal of the quartz tuning-fork (8) with it is preposition
The electric signal input end connection of amplifier (9)；The of the output end of the preamplifier (9) and the first lock-in amplifier (10)
One electric signal input end is connected；The of the reference signal input and function generator (2) of first lock-in amplifier (10)
Two electrical signals are connected；The output end of first lock-in amplifier (10) is believed with the first data of data collecting card (1)
The connection of number input；
Photodetector (12) is used to detect the laser signal in reference gas chamber (11) and be converted to electric signal, believes as measurement
Number；The measurement signal output end of the photodetector (12) connects with the first electric signal input end of the second lock-in amplifier (13)
Connect；Second electrical signal of the reference signal input and function generator (2) of second lock-in amplifier (13) connects
Connect；The output end of second lock-in amplifier (13) is connected with the second data signal input of data collecting card (1)；
Data collecting card (1) is communicated with computer (14).
2. the CO gas detecting systems according to claim 1 based on quartz tuning fork strengthened optoacoustic spectroscopy, it is special
Levy and be, air chamber (7) is cuboid, then air chamber (7) the long 15mm of optical path direction, the wide 15mm in vertical optical path direction, high 12mm.
3. the CO gas detecting systems according to claim 1 based on quartz tuning fork strengthened optoacoustic spectroscopy, it is special
Levy and be that quartz crystal oscillator (81) two is raised one's arm and be centrally located in the focus of condenser lens (6).
4. the CO gas detection methods of the quartz tuning fork strengthened optoacoustic spectroscopy based on claim 1, it is characterized in that：It by
Following steps are realized：
Computer (14) sends control signals to information acquisition card (1), and current controling signal is passed through letter by information acquisition card (1)
Number generator (2) is sent to laser controller (3), while temperature control parameter is sent into laser controller (3), laser
Device controller (3) driving laser (4) transmitting near-infrared laser, is focused on by fiber optic collimator bag (5) collimation and condenser lens (6)
After incide in air chamber (7)；The luminous energy that CO gases in air chamber (7) absorb near-infrared laser is converted to heat energy, and then is converted to
Sound pressure signal, the quartz tuning-fork (8) in air chamber (7) converts acoustic signals into electric signal；
By the electric signal of quartz tuning-fork (8) after conversion, amplification, the Measurement channel for being input to a lock-in amplifier (10) is defeated
Enter end, the reference signal of lock-in amplifier (10) associative function generator (2) carries out second-harmonic detection, and then inverting is treated
Survey CO gas concentrations；
The described CO gas detection methods based on quartz tuning fork strengthened optoacoustic spectroscopy, also comprise the following steps：
Be filled with reference gas chamber (11) after air chamber (7) with CO gas concentrations identical CO gases in air chamber, using position
The laser signal absorbed in photodetector (12) detection after reference gas chamber (11) by gas, and the laser signal is turned
It is changed to electric signal；
No. two lock-in amplifiers (13) receive the electric signal, while the high_frequency sine wave that access is sent from function generator (2),
And then feedback control is carried out, the optical maser wavelength that will deviate from is locked in Absorption Line as frequency discrimination signal using harmonic signal
Center, realizes laser frequency stabilization.
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