CN103163087B - Method of adopting photoacoustic spectrometry method to detect concentration of sulfuryl fluoride residual gas - Google Patents
Method of adopting photoacoustic spectrometry method to detect concentration of sulfuryl fluoride residual gas Download PDFInfo
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- CN103163087B CN103163087B CN201310041226.1A CN201310041226A CN103163087B CN 103163087 B CN103163087 B CN 103163087B CN 201310041226 A CN201310041226 A CN 201310041226A CN 103163087 B CN103163087 B CN 103163087B
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Abstract
The invention discloses a method of adopting a photoacoustic spectrometry method to detect concentration of sulfuryl fluoride residual gas. The method includes the following steps: monochromatic light with adjustable strength is obtained through adoption of a non-interference thermal radiation source and through light chopping of a chopper and filtering of an optical filter; adjustable spectrum is irradiated on trace sulfuryl fluoride gas in a photoacoustic cell, and molecules of the sulfuryl fluoride gas absorb electromagnetic radiation, are excited to jump to a higher-level excited state and then return the ground state through stretching vibration and deformation vibration; the temperature of the gas is raised through vibration, the gas releases heat energy, the released heat energy can enable the molecules of the sulfuryl fluoride gas to generate periodic heating according to modulation frequency of the light so as to generate periodic pressure fluctuation; and the pressure fluctuation is detected through adoption of a silicon micro microphone with the vibration sensitiveness of smaller than 1dB, signals are amplified through a conversion circuit to obtain photoacoustic signals, the photoacoustic signals are converted into electric signals through a periphery circuit, the electric signals are amplified through a lock-in amplifier in the periphery circuit and sent into a data acquisition circuit, and finally the concentration of sulfuryl fluoride residual gas is obtained through calculation.
Description
Technical field
The invention belongs to trace gas detection technical field, be specifically related to a kind of method utilizing photocaustic spectroscopy to detect Determination of Trace Sulfur acyl fluorides gas concentration, be applicable to the detection that such as inspection and quarantine fumigating gas is residual.
Background technology
Vikane, molecular formula SO
2f
2, be colourless, odorless under normal temperature and pressure.The features such as vikane has that diffusion permeability is strong, broad spectrum disinfestation, dosage are economized, residual quantity is low, desinsection speed fast, the loose gas time is short, low temperature is easy to use, do not affect germination percentage and toxicity is lower, therefore be widely used in warehouse, freighter, container and buildings, reservoir dam, termite control and gardens to survive the winter the control of insect, the tree moth dryness insect that lives, such as, in customs inspection quarantine field, vikane as fumigant, for the control to harmful organism, crops and secondary product stifling etc.
But residual sulfuryl fluoride gas has certain toxic action to human body, if vikane content is more than 0.02g/m in atmosphere
3, human body can cause nervous centralis impaired after sucking, and causes convulsions, even can cause breath stopped and death time serious.Therefore, we strictly will monitor sulfuryl fluoride gas concentration that is residual, trace, to ensure personal safety.
Meanwhile, vikane is also a kind of potent greenhouse gases, the serious greenhouse effect that can cause environment, and people need to monitor the vikane of trace, prevent the pollution of the environment.
For the detection of micro-sulfuryl fluoride gas, China's standard main definitions three kinds of detection methods: vapor-phase chromatography, thermal conductivity method and infrared detection method.
Aforesaid chromatographic ultimate principle sample gas is injected in chromatographic column analyze.Gas sample containing vikane is carried down by inert carrier gas, slowly by arriving detecting device after chromatographic column, needs the temperature controlling chromatographic column therebetween, so that gas sample is separated out time difference by classes of compounds during chromatographic column and reaches the object be separated it.Subsequently, its concentration value is obtained by after the parameter such as time, area of the compound obtained by detecting device precipitation collection of illustrative plates and this compound concentration known spectral contrast.This method is the method that domestic experimental determination vikane is conventional, its advantage be highly sensitive, antijamming capability good.Shortcoming be can not Site Detection, analysis time long, bulky, need to rely on and pass into carrier gas continuously.
Aforesaid thermal conductivity method is the characteristic based on gas with various with different thermal conductivity, and the change according to thermal conductivity detects gas concentration.Thermal conductivity method core is thermal conductivity sensor, is integrated with a resistive heater in thermal conductivity sensor inside.When sulfuryl fluoride gas flows through resistance wire, because sulfuryl fluoride gas has certain thermal conductivity, heat to a certain degree can be taken away, cause wire temperature to change.The heat that the sulfuryl fluoride gas of variable concentrations is taken away can be different, can cause wire temperature that different changes occurs, and by detecting wire temperature situation of change, thus obtains concentration value corresponding to sulfuryl fluoride gas.The advantage of this detection method is highly sensitive; Shortcoming is poor anti jamming capability, and sensor is short for serviceable life, needs frequent calibrating instrument.
Aforesaid Infrared Detection Method utilizes sulfuryl fluoride gas to carry out measurement of concetration in the light absorption of mid infrared region (6.82 ~ 9 μm), when a branch of constant infrared light of 6.82 ~ 9 μm passes through the medium containing sulfuryl fluoride gas, the energy of light is absorbed by sulfuryl fluoride gas, luminous flux is attenuated, measure the luminous energy attenuated, the concentration of sulfuryl fluoride gas can be obtained.The application of this method is comparatively general, but when measuring such as, because mid infrared region also exists the absorption spectra of other gases, moisture, carbon dioxide etc., cause the accuracy of detection of vikane and lower limit to be interfered, cannot detect the concentration of micro-sulfuryl fluoride gas in this way very well.
In view of above-mentioned prior art, be necessary to be explored more preferably to the detection method of sulfuryl fluoride gas residual concentration, for this reason, the present invention has done a large amount of and useful research, and technical scheme described below produces under this background.
Summary of the invention
A kind of photocaustic spectroscopy is the object of the present invention is to provide to detect the method for sulfuryl fluoride gas residual concentration.Photocaustic spectroscopy is the novel spectral technique based on optoacoustic effect, and be different from traditional infrared spectrum technology, light signal is effectively converted into acoustical signal by it, and obtains final gas concentration by the detection computations of accurate microphone to voice signal.Due to the special optical structure of optoacoustic spectroscopy and the specific calculations process in signals collecting, signal processing, make the method energy highly effective gathering faint light acoustical signal, and effectively reject the interference of background signal, be highly suitable for trace gas concentration detection field, and the noiseless detection in complex environment.
The object of the invention is to have come like this: a kind of device utilizing photocaustic spectroscopy to detect sulfuryl fluoride gas residual concentration, comprises light source, chopper, optical filter, photoacoustic cell, microphone and infrared moisture sensor; Wherein light source connects chopper, is arranged on photoacoustic cell side with optical filter; Infrared moisture sensor is arranged on the opposite side of photoacoustic cell; Microphone is arranged on the bottom of photoacoustic cell, and light source sends light source and is transmitted into chopper, cuts light by chopper, forms light modulated; Light modulated is irradiated to after on optical filter, and forming arrowband can modulated spectrum, is irradiated into photoacoustic cell.
Utilize photocaustic spectroscopy to detect a method for sulfuryl fluoride gas residual concentration, said method comprising the steps of:
Step 1, light source adopt non-interfering infrared source, cut light and optical filter optical filtering, obtain the monochromatic light that intensity can be modulated by chopper;
Step 2, can modulate spectral illumination sealing photoacoustic cell in micro-sulfuryl fluoride gas on, be excited after the electromagnetic radiation of sulfuryl fluoride gas molecule absorption, transit to the excited state of higher level, and get back to ground state by stretching vibration and deformation vibration;
Step 3, vibrations cause the rising of gas temperature, and discharge heat energy, and the heat energy of release makes vikane molecule produce periodic heat by the modulating frequency of light, thus produces periodic pressure fluctuation;
Step 4, pressure surge adopt vibration sensing degree to be less than the micro-microphone detection of silicon of <1dB, and obtain photoacoustic signal by change-over circuit amplifying signal, photoacoustic signal converts electric signal to by peripheral circuit, send into data acquisition circuit by after the lock-in amplifier amplification signal in peripheral circuit again, finally calculate vikane residual concentration.
In a specific embodiment of the present invention, described non-interfering heat radiation light source works in 850 degrees Celsius, to obtain larger infrared power density.
In another specific embodiment of the present invention, described optical filter 3 for wave number be 860, centre wavelength is the narrow band pass filter of 11.6 microns, because the absorption line intensity of steam only between wave number 800 to 900 is very low, this narrow band pass filter effectively can shield the undesired signal that steam produces for sulfuryl fluoride gas Concentration Testing.
In another specific embodiment of the present invention, described microphone is the micro-formula microphone of silicon.
Compared with prior art, advantage of the present invention is: provide a kind of method that photocaustic spectroscopy detects sulfuryl fluoride gas residual concentration.Photocaustic spectroscopy is that light signal is effectively converted into acoustical signal, and obtains final gas concentration by the detection computations of accurate microphone to voice signal.Due to the special optical structure of optoacoustic spectroscopy and the specific calculations process in signals collecting, signal processing, make the method energy highly effective gathering faint light acoustical signal, and effectively reject the interference of background signal, be highly suitable for trace gas concentration detection field, and the noiseless detection in complex environment.
Accompanying drawing explanation
Fig. 1 is the present invention's blackbody radiation light source used spectral radiance at different temperatures.
Fig. 2 is the structural representation of equipment therefor of the present invention.
Fig. 3 is steam and the absorption spectrogram of sulfuryl fluoride gas in 400 to 1700 wave-number ranges.
Embodiment:
With non-interfering infrared source as light source 1, coordinate narrow band pass filter and the mechanical chopper of centre wavelength 11.6 microns, 860 wave numbers, obtaining the monochromatic light exposure that intensity can modulate enters in the photoacoustic cell 4 of sealing, be excited after gas molecules sorb electromagnetic radiation in photoacoustic cell 4, transit to the excited state of higher level.The electronic state of molecule, vibrations and rotary state are all quantized.Usually, gas molecule can get back to ground state by emitting fluorescence or vibrations, and vibrations cause the rising of gas temperature, and transferring energy, be referred to as radiationless relaxation phenomena.The prerequisite that this Non-radiative relaxation processes produced by vibration is occurred is, relaxation time much faster than lifetime of excited state.Attenuation is 10 in the usual time of visible ray
-7s is 10 at 10um place
-2s.For producing radiationless decay, the relation of relaxation time and pressure very close (die-away time t and pressure be inversely proportional to) and can under atmospheric pressure produce great changes (10
-3– 10
-8s).
Radiation source is modulated to the acoustic frequency making Temperature cycling change, causes the cyclical variation of pressure, this change can produce voice signal, and in gas detect, this voice signal is detected by highly sensitive microphone.
Utilizing photoacoustic spectrum sensor to detect vikane residual concentration is exactly based on this optoacoustic effect, this photoacoustic spectrum sensor as shown in Figure 2, comprise: light source 1, chopper 2, optical filter 3, photoacoustic cell 4, microphone 5, infrared moisture sensor 6 and peripheral circuit, wherein light source 1 connects chopper 2; Photoacoustic cell 4 side is embedded in optical filter 3; Infrared moisture sensor 6 is embedded in the opposite side of photoacoustic cell 4; Microphone 5 is embedded in the bottom of photoacoustic cell 4.
Light source 1 of the present invention uses non-interfering infrared source, and non-interfering infrared source sends broad spectrum light source, after broad spectrum light source is transmitted into chopper 2, cuts light by chopper 2, forms light modulated, after on the optical filter 3 that this light modulated is irradiated to 11.6 microns, optical source wavelength scope is filtered, forming wave number is 860, centre wavelength be the monochromatic light exposure that can modulate of the intensity of 11.6 microns enter sealing photoacoustic cell 4 in sulfuryl fluoride gas on, be excited after the electromagnetic radiation of sulfuryl fluoride gas molecule absorption, transit to the excited state of higher level, and get back to ground state by vibrations, vibrations cause the rising of gas temperature, and discharge heat energy, the heat energy of release makes vikane molecule produce periodic heat by the modulating frequency of light, thus produce periodic pressure fluctuation, this pressure surge can detect with sensitive microphone 5, and obtain photoacoustic signal by change-over circuit amplifying signal, photoacoustic signal converts electric signal to by peripheral circuit, data acquisition circuit is sent into again by after the lock-in amplifier amplification signal in peripheral circuit, the quantitative test of vikane residual concentration is completed finally by formula (1) formula (2) formula (3) formulae discovery, the detection of vikane concentration is completed with this.
The non-interfering infrared source that the present invention adopts, is operated in 850 degree.The continuous spectrum that IR thermal emitter generally has close to blackbody radiation distributes, as shown in Figure 1.Be characterized in utilizing emitted light spectrum width, easy to use in conjunction with narrow band pass filter, working stability is reliable.When light beam is modulated with audio frequency (tens hertz to a few KHz), air pressure is just modulated with same frequency and form sound wave, for the amplitude A of the photoacoustic signal be operated under low frequency non-resonant behavior
0(w)
Be expressed as:
Be wherein the absorption coefficient of gas, Pa is the dividing potential drop of gas, and v is the specific heat ratio of gas, and v=Cp/Cv, w is the modulating frequency of light, and T is for disappearing the excitation life-span, and I is beam intensity, and wherein r is the radial distance of photon; W is spot radius, and V is the volume of photoacoustic cell 4, and i is imaginary unit.For specific gas, the factors such as modulating frequency of the amplitude of photoacoustic signal and the light intensity of exciting light and spectral characteristic, photoacoustic cell 4 structure and light is relevant.
For optical filter 3, we select wave number 860, centre wavelength to be the narrow band pass filter of 11.6 microns.As Fig. 3 vikane absorbs the absorption spectrogram of spectrogram and steam, the Absorption Line of sulfuryl fluoride gas has relatively high intensity and density in wave number 500 to 550,800 to 900,1250 to 1300,1450 to 1550 base band.And the absorption line intensity of steam only between wave number 800 to 900 is very low, so we select wave number to be 860, centre wavelength is the undesired signal that the narrow band pass filter of 11.6 microns effectively can shield steam and produces for sulfuryl fluoride gas Concentration Testing.
For photoacoustic cell 4, the present invention uses disresonance cylindrical structure, when gas weak absorbing, can think that light intensity I is evenly distributed in photoacoustic cell 4, i.e. I (r, w)=I (w).The power arranging light beam is again W, then I=Wl/V, and wherein l is the length of photoacoustic cell 4, and V is volume.Can draw after space integral is carried out to the light intensity in formula (1):
As can be seen from formula (2) formula, the xsect reducing photoacoustic cell 4 cavity is conducive to obtaining higher photoacoustic signal amplitude.But the size due to photoacoustic cell 4 also depends on the installation site of microphone 5, more need to consider the effect of light beam coupling and the collimation adjustment difficulty of light beam.Transverse heat transfer effect also can be made to decline and the excitation life-span T that causes disappearing increases if the volume of photoacoustic cell 4 is too small, result makes photoacoustic signal reduce.The present invention gets photoacoustic cell 4 internal diameter 15 mm in the present system, and length is 50 mm, to reduce because window absorbs the coherent noise produced.
For microphone 5, the present invention selects the micro-microphone of silicon.Because traditional capacitor microphone is without any power supply rejection ability, very little mains fluctuations just will cause intermittent noise.And in Machine Design, conventional condenser microphone can not only detect voice signal, can also detect mechanical vibration, and finally vibration is converted to low frequency sound signals, like this, when this type of microphone is placed in vibration environment, vibrates and will become the dominant noise source of audio system.The present invention use the micro-microphone of silicon be utilize silicon thin film to detect acoustic pressure, it can on chip an integrated analog to digital converter, formed have numeral export microphone.Compared with traditional capacitor microphone, silicon micro-microphone sound pressure level is high, and chip internal generally has pre-amplification circuit, and therefore sensitivity is very high; Its Hz-KHz is wide, generally at 100 ~ 10KHZ; And distortion is little, total harmonic distortion <1% (at 1KHZ, 500mV p-p); Vibration sensing degree is less than <1dB.In addition, the micro-microphone of silicon also has excellent electromagnetism interference characteristic, and humidity environment and temperature shock.We are by micro-for this silicon microphonic acoustic-electric conversion coefficient S
mw () substitutes into the amplitude A that can obtain photoacoustic signal in formula (2)
m(w):
Formula can be found out in (3), and the modulating frequency lower photoacoustic signal amplitude of light beam is larger, but for general microphone, during w < 100 H z, acousto-electric-index S
mw () just has obvious decline, when modulating frequency is too low in addition, 1/ f noise of electronic amplification system also obviously increases.Because tested concentration C is the intrinsic standoff ratio of gas, C=Pa/P
0, this formula is substituted into formula (3) finally tested gas concentration can be calculated.
In sum, technical scheme provided by the invention has the good and strong point that device volume is little of high sensitivity, wide dynamic range, high stability, shielding interference.Photocaustic spectroscopy surveys the principle of vikane without the need to adding any chemical substance, and this inventive method is once dispatched from the factory after demarcation calibration, optical texture is stablized, and without the need to doing secondary or repeatedly calibrating, it also avoid the shortcoming of electrical conductivity method.Compare with non-dispersion infrared analytic approach, light signal is effectively converted into acoustical signal by it, and obtains final gas concentration by the detection computations of accurate microphone to voice signal.Due to the special optical structure of optoacoustic spectroscopy and the specific calculations process in signals collecting, signal processing, make the method energy highly effective gathering faint light acoustical signal, and effectively reject the interference of background signal, be highly suitable for trace gas concentration detection field, and the noiseless detection in complex environment.
Claims (3)
1. utilize photocaustic spectroscopy to detect a method for sulfuryl fluoride gas residual concentration, said method comprising the steps of:
Step 1, light source (1) adopt non-interfering infrared source, light and optical filter (3) optical filtering is cut by chopper (2), obtain the monochromatic light that intensity can be modulated, wherein, optical filter (3) for wave number be 860, centre wavelength is the narrow band pass filter of 11.6 microns, and described non-interfering heat radiation light source works in 850 degrees Celsius;
Step 2, can modulate spectral illumination sealing photoacoustic cell (4) in micro-sulfuryl fluoride gas on, be excited after the electromagnetic radiation of sulfuryl fluoride gas molecule absorption, transit to the excited state of higher level, and get back to ground state by stretching vibration and deformation vibration;
Step 3, vibrations cause the rising of gas temperature, and discharge heat energy, and the heat energy of release makes vikane molecule produce periodic heat by the modulating frequency of light, thus produces periodic pressure fluctuation;
Step 4, pressure surge adopt vibration sensing degree to be less than the micro-microphone detection of silicon of <1dB, and obtain photoacoustic signal by change-over circuit amplifying signal, photoacoustic signal converts electric signal to by peripheral circuit, send into data acquisition circuit by after the lock-in amplifier amplification signal in peripheral circuit again, finally calculate vikane residual concentration.
2. the method utilizing photocaustic spectroscopy to detect sulfuryl fluoride gas residual concentration according to claim 1, is characterized in that described photoacoustic cell (4) uses disresonance cylindrical structure.
3. the method utilizing photocaustic spectroscopy to detect sulfuryl fluoride gas residual concentration according to claim 1, is characterized in that the residual concentration of the sulfuryl fluoride gas described in step 4 passes through formula
Obtain, in formula,
for the amplitude of photoacoustic signal,
for the absorption coefficient of gas, Pa is the dividing potential drop of gas,
for the specific heat ratio of gas,
for the modulating frequency of light,
for disappearing the excitation life-span, I is beam intensity, and W is spot radius, and V is the volume of photoacoustic cell (4), and i is imaginary unit,
for acousto-electric-index.
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| CN103954578A (en) * | 2014-05-14 | 2014-07-30 | 江苏舒茨测控设备有限公司 | Photoacoustic spectrum detection device for detecting residual concentration of sulfuryl fluoride gas |
| CN106769973A (en) * | 2017-03-03 | 2017-05-31 | 江苏舒茨测控设备股份有限公司 | Ammonia gas detection means and method are detected using photocaustic spectroscopy |
| CN109490215A (en) * | 2019-01-03 | 2019-03-19 | 江苏舒茨测控设备股份有限公司 | Utilize the system and method for photocaustic spectroscopy detection methyl bromide gas concentration |
| CN117517240B (en) * | 2024-01-08 | 2024-03-19 | 新仟意能源科技(成都)集团有限责任公司 | Light hydrocarbon component on-line detection method and system based on infrared light |
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| US4051371A (en) * | 1976-04-26 | 1977-09-27 | Massachusetts Institute Of Technology | Opto-acoustic spectroscopy employing amplitude and wavelength modulation |
| KR100493154B1 (en) * | 2002-03-20 | 2005-06-03 | 삼성전자주식회사 | Apparatus of non-invasive measurement of bio-fluid concentration by using photoacoustic spectroscopy |
| CN1928531A (en) * | 2006-09-12 | 2007-03-14 | 西南科技大学 | Method for detecting methane gas concentration with opto-acoustic spectroscopic method |
| CN101936879B (en) * | 2010-07-28 | 2011-11-30 | 山东大学 | Photoacoustic spectroscopy gas detecting system based on Mach-Zehnder interferometer |
| CN102226752A (en) * | 2011-04-08 | 2011-10-26 | 常熟舒茨电子科技发展有限公司 | Method for detecting concentration of sulfur dioxide by using photoacoustic spectrometry |
| CN102495017A (en) * | 2011-11-09 | 2012-06-13 | 山东惠工电气股份有限公司 | Detecting instrument of sulfur hexafluoride gas decomposition products |
| CN102661918A (en) * | 2012-05-28 | 2012-09-12 | 中国科学院电工研究所 | Off-resonance photoacoustic spectrometric detection and analysis device |
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