CN102062722B - Laser program-controlled gas concentration detection system and detection method - Google Patents
Laser program-controlled gas concentration detection system and detection method Download PDFInfo
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- CN102062722B CN102062722B CN200910237838A CN200910237838A CN102062722B CN 102062722 B CN102062722 B CN 102062722B CN 200910237838 A CN200910237838 A CN 200910237838A CN 200910237838 A CN200910237838 A CN 200910237838A CN 102062722 B CN102062722 B CN 102062722B
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Abstract
A laser program-controlled gas concentration detection system comprises a program-controlled processor, a program-controlled current source, a cylindrical air chamber, a long wavelength laser, a photoelectric detector, a micro-current detector, a signal generator and a lock-in amplifier, wherein the program-controlled current source communicates with the program-controlled processor through a cable; the center of one end of the cylindrical air chamber is provided with a flange device; one end of the long wavelength laser transfers light in the flange of the cylindrical air chamber through an optical fiber, the other end is connected with the program-controlled current source; the photoelectric detector is arranged on the other end of the cylindrical air chamber; the micro-current detector collects the current signals of the photoelectric detector and communicates with the program-controlled processor; the signal generator adds modulation signals on the program-controlled current source and communicates with the program-controlled processor; and the lock-in amplifier collects the signals of the photoelectric detector and communicates with the program-controlled processor.
Description
Technical field
The present invention relates to Fibre Optical Sensor, optoelectronic areas.Be applied to the evil gas detection, atmospheric humidity detects, and other all be applied to that gas concentration detects, the field of gas characteristic sensing.
Background technology
In gas sensing, gas concentration measurement field, methods such as widespread use capacitive transducer and galvanochemistry are carried out the measurement of concentration.Yet capacitance sensing and electrochemical method come with some shortcomings in gas detection.When measuring, steam has the wet slow problem of moving back as carrying out with capacitive transducer; And can damage gas composition with electrochemical method itself.And, use photoelectric technology based on the high-precision gas concentration detector of Fibre Optical Sensor, have that response speed is fast, measuring accuracy is high, gas composition is destroyed advantages such as little.
According to the Beer law, when wavelength is that λ, intensity are I
0Certain gas through finite concentration C of beam of laser (λ), and after being the segment distance of L through length.Light intensity I that receives (λ) and initial light intensity I
0Relation (λ) is I (λ)=I
0(λ) exp (α CL).Wherein α is the absorption coefficient of the light of λ to wavelength for this kind gas.When λ just was in strong absorption peak of this gaseous spectrum, α was very big, and the light of this wavelength is obvious by this gas absorption.Through the light intensity of passing the light behind the gas is analyzed, just can calculate the concentration of this gas.
Under the very little situation of the concentration of gas,, utilize phase lock amplifying technology that the harmonic wave of the light that passes gas is detected, and the data that obtain are handled through load-modulate signal on laser instrument.Can accurately detect small concentration.
Through using programmable current source, waveform generator, the laser instrument of specific wavelength, photodetector on a large scale, program control multimeter, the gas detecting system that devices such as lock-in amplifier are built.Can laser wavelength accurately be locked on the absorption peak of gas to be measured through computer program control.And can under the measurement environment of high concentration and low concentration, switch the measuring method of selecting: under high concentration, switch to the direct method of measurement, under low concentration, switch to the harmonic measure method.And through gathering the data on program control multimeter and the lock-in amplifier, the concentration of real-time follow-up detected gas.
Summary of the invention
As a kind of new gas concentration test macro; The present invention adopts the method for Fibre Optical Sensor, utilize wavelength and seized gas absorption spectrum coupling long wavelength laser as detection source, through detecting light through behind the gas to be measured; Light intensity weaken degree, obtain the concentration of gas to be measured.
The present invention adopts programme controlled method to seek the absorption peak and the locked laser wavelength of this gas.Through the data that programmed control processor processes current detecting meter or lock-in amplifier transmit, kinetic measurement gas concentration.And Dynamic Selection detection method: when being judged to be high concentration, select the direct method of measurement; When being judged to be low concentration, select to improve the harmonic wave probe method of precision.
For achieving the above object, the invention provides a kind of program control gas concentration detection system, comprising:
One programmed control processor;
One programmable current source, this programmable current source can the output DC source or on the direct supply of output the overlapped high-frequency signal, this programmable current source is through line and the communication of programmed control processor, this programmable current source is supplied power to long wavelength laser;
One cylindricality air chamber, the chamber of this cylindricality air chamber are open structure, and with environmental gas UNICOM, the center of an end of this cylindricality air chamber is equipped with flange apparatus;
One long wavelength laser, an end of this long wavelength laser advances optically-coupled in the flange of cylindricality air chamber through optical fiber, and the other end of this long wavelength laser is connected with programmable current source;
One photodetector, this photodetector is installed in the other end of cylindricality air chamber, the laser alignment that the position that this photodetector is installed should be coupled into the flange place;
One little current detecting meter, this little current detecting meter is gathered the current signal on the photodetection meter, this little current detecting meter and the communication of programmed control processor;
One signal generator, this signal generator is carried in modulation signal on the programmable current source, this signal generator and the communication of programmed control processor;
One lock-in amplifier, this lock-in amplifier is gathered signal, this lock-in amplifier and the programming controller communication on the photodetection meter.
Wherein this programmed control processor is a computing machine or is processor chips.
Wherein programmable current source is a current source circuit.
Wherein little current detecting is counted an AD sampling A circuit.
Wherein signal generator is a sinusoidal signal generation chip circuit.
Wherein lock-in amplifier is a digital PLL circuit.
Wherein the wavelength of long wavelength laser is selected to decide according to the absorption spectra of gas to be measured, and its wavelength is the wavelength at the strong absorption peak place of selection gas to be measured.
The present invention provides a kind of detection method of program control gas concentration detection system, and this detection method adopts detection system as claimed in claim 1, comprises the steps:
Step 1: shutdown signal generator; Pass through programmable current source; At the linear zone of long wavelength laser work, continuous stepping output current from low to high, the position of the low ebb through detecting the photocurrent that detects on little current detecting meter; Calculate wavelength locking, make programmable current source at this position output DC stream;
Step 2: the programmed control processor receives the signal that little current detecting meter transmits continuously, obtains the concentration C of gas through the direct method of measurement;
Step 3:, return step 2 when the value that the calculates time more than or equal to a comparison value;
Step 4: when the value that the calculates time less than a comparison value; The opening signal generator; For programmable current source adds modulation signal; Detect the harmonic components of the signal that photodetector detects with lock-in amplifier, the second harmonic composition that calculates photocurrent through the harmonic measure method becomes the ratio of branch with first harmonic, calculate gas concentration C;
Step 5: when the second harmonic composition becomes value that the ratio of branch calculates less than a comparison value with first harmonic when, return step 4;
Step 6: when calculating the second harmonic composition becomes branch with first harmonic the value of ratio more than or equal to a comparison value, the shutdown signal generator returns step 2.
Wherein the formula of direct method of measurement concentration C calculating is I (λ)=I
0(λ) exp (α CL), wherein I (λ) is detected photocurrent, I
0Photocurrent when (λ) absorbing for nothing, α is an absorption intensity, and L is cylindricality air chamber 3 length, and C is a gas concentration to be measured.
Parameter I wherein
0(λ), α, k all can the method through calibration obtain before the formal application of system, and be cured in the programmed control processor.
Wherein signal generator is added in the 10%-15% that the modulation current amplitude on the programmable current source is the direct current amplitude of programmable current source output; Frequency is a few k KHzs, and can be according to concrete effect adjustment, after confirming; This parameter no longer becomes, and is solidificated in the programmed control processor as preset parameter.
The invention has the beneficial effects as follows: adopt Fibre Optical Sensor to carry out the method for gas concentration measurement, can effectively improve the reaction time of measurement, carry out data real-time collection and with the real-time calculating of concentration.Compare with traditional capacitance type sensor, lag time shortens greatly.
Traditional sensors exist to receive saturated, deficiency such as measurement of factor under the low concentration.The present invention both can be under the high concentration gaseous environment measures the accurate concentration of supersaturated gas through the direct method of measurement; Again can be under the light concentration gas environment; Through for laser instrument adds modulated current signal,, effectively improve the measuring accuracy under the low concentration through the harmonic measure method.
Although the wavelength of the long laser instrument of choosing is corresponding with gas absorption to be measured peak, to different working temperatures and working current, the output wavelength of laser instrument still has small variations.The present invention adopts programmed control to sweep the anti-method of electric current automatically, can the output wavelength of laser instrument accurately be locked on the absorption peak of gas to be measured.With the accuracy of measuring after guaranteeing.
The present invention can be according to the processing to data; Be in high concentration or low concentration when dynamically judging gas concentration, and dynamic height according to concentration, through programmed control; Under high concentration, select the direct method of measurement, under low concentration, select for use the harmonic measure method to improve precision.
Description of drawings
For further specifying technology contents of the present invention, below in conjunction with accompanying drawing the present invention is described further, wherein:
Fig. 1 is the overall system structure figure of the program control laser gas concentration of the present invention detector.
Fig. 2 is the system construction drawing when choosing the direct method of measurement and initial lock wavelength.
Fig. 3 is " bright dipping power-current " curve and " photocurrent-wavelength " curve when carrying out the initial current step-scan.
Fig. 4 is the system construction drawing when choosing the harmonic measure method.
Fig. 5 is a laser gas concentration detector system workflow diagram.
Embodiment
The invention provides the system of a cover gas concentration measurement.This system is based on photoelectron technology, the light through analyzing specific wavelength through behind the gas by the amount of gas absorption, calculate the concentration of gas.
As shown in Figure 1, comprising: a programmed control processor 1, this programmed control are sentenced device 1 can be a computing machine, also can be processor chips.One programmable current source 2, this current source can be by programmed control processor 1 control output particular current signal.One air chamber 3, its chamber is long to be L, this chamber is open structure; With environmental gas UNICOM; The center of one end of this air chamber 3 is equipped with flange apparatus, is used for coupled fiber, and photodetector 5 is installed at other end center; The laser alignment that the position that photodetector is installed should be coupled into the flange place, the detection wavelength coverage of photodetector 5 should cover the Wavelength of Laser that coupling is come in.One long wavelength laser 4, wavelength is by the gas decision of required detection, and wavelength should be by the wavelength at the strong absorption peak place of probe gas.In general, the strong absorption peak of gas molecule is all at infrared band, is long wavelength laser so we select.This long wavelength laser 4 should be the band refrigerator can temperature control laser instrument.One little current detecting meter 6, this little current detecting meter 6 should both can detect the small electric flow valuve, can image data be transferred to programmed control processor 1 again.Signal generator 7 can produce sinusoidal tiny signal, and this signal can be added on the programmable current source 2, makes programmable current source on the basis of output DC current, and an AC signal superposes.Lock-in amplifier 8 is used for locking photocurrent and has the signal with signal generator 7 added frequency same frequencys, and add the signal of frequency two frequencys multiplication.
Programmed control processor 1 and programmable current source 2 are connected by circuit, carry out programmed control and data transmission.Programmed control processor 1 and little current detecting meter 6 are connected through circuit, carry out programmed control and data acquisition; Programmable current source 2 is given long wavelength laser 4 loading current signals through circuit; Long wavelength laser 4 links to each other with air chamber 3 through optical fiber; Photodetector 5 is transferred to photocurrent on little gallon meter 6 through circuit; Signal generator 7 is connected with programmable current source 2 through circuit, is used for sinusoidal current signal is loaded into DC current; Connect programmed control processor 1 through circuit image data from the lock-in amplifier 8; Programmed control processor 1 links to each other with signal generator 14 through circuit, and signal generator 14 is carried out programmed control; Photodetector 5 is transferred on the lock-in amplifier 8 through the photocurrent that circuit will contain harmonic components.
In system shown in the present, programmed control processor 1, programmable current source 2, little current detecting meter 6, signal generator 7, lock-in amplifier 8 both can be an instrument independently, can be again chip or the signal conditioning circuit that can realize function of the same race.
Among the present invention, the operation wavelength of the laser instrument of choosing should be the wavelength at strong absorption peak place of the gas of required detection.Water vapor concentration is an example in the atmosphere to detect, and chooses the long wavelength laser of 1854nm, and the gas detection process is carried out according to the following steps.It is basic identical to detect other gas concentration methods, just selects corresponding laser instrument.
The detection method of a kind of program control gas concentration detection system of the present invention, this detection method adopts foregoing detection system, comprises the steps:
With long wavelength laser 4 temperature controls at 25 ℃.Make programmed control processor 1 control programmable current source 2 at the ascending stepping output DC stream of the linear zone of long wavelength laser 4 work; Each stepped intervals 2 seconds; The current value that each stepping increases is 2 minimum steps that can reach of this programmable current source; The power of the photocurrent that the phototransformation that receives with current detecting meter 6 detection photodetectors 5 becomes; And give programmed control processor 1 with detected data back because the change of working current can make the output light wavelength of long wavelength laser 4 that small variation is arranged, the process of stepping output current make laser instrument output power is linear increase in; Output wavelength is the absorption peak of inswept required detected gas slowly also; Owing to itself just contain certain moisture in the air chamber 3, when the wavelength of long wavelength laser 4 outputs just was the strong absorption peak of water vapor, light was passing through air chamber 3 backs by a large amount of absorptions.Like this, as shown in Figure 3: Fig. 3 (a) increases the output power linearity of laser instrument for the working current that stepping increases laser instrument; Fig. 3 (b) detects the intensity of detected photocurrent on the meter 6 for its current corresponding.
Shown in Fig. 3 (b), this figure has a sharp-pointed low ebb.When this low ebb was output light wavelength just for the absorption peak of steam, light was caused by water vapor absorption in air chamber 3.Calculate the working current of the corresponding laser instrument in low ebb place through programmed control processor 1.Make programmable current source 2 at this position output DC stream, make the wavelength of long wavelength laser 4 outputs be the absorption peak of water vapor just.It is wavelength locking.
Because direct measuring method satisfies Beer law I (λ)=I
0(λ) exp (α CL).Through the water vapour environment of given two concentration known, detect I
0Change (λ), calibration obtains α and I
0Value (λ).
When obtaining measuring termination signal, through programmed control processor 1 shutdown signal generator 7 successively, programmable current source 2, lock-in amplifier 8 and current detecting meter 6.
The formula that direct method of measurement concentration C is calculated is I (λ)=I
0(λ) exp (α CL), wherein I (λ) is detected photocurrent, I
0Photocurrent when (λ) absorbing for nothing, α is an absorption intensity, and L is cylindricality air chamber 3 length, and C is a gas concentration to be measured.
Parameter I wherein
0(λ), α, k all can the method through calibration obtain before the formal application of system, and be cured in the programmed control processor 1.
Above gas detection step is to be example to measure water vapor, but native system is not limited only to measure water vapor concentration.Native system and above-mentioned measuring process are applicable to the measurement of concetration of most of gas, only need to select the laser instrument of operation wavelength at the strong absorption peak of tested gas place, all can be by the accurate concentration of measuring tested gas of above-mentioned steps.
Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (2)
1. the detection method of the program control gas concentration detection system of laser, the program control gas concentration detection system of this laser comprises:
One programmed control processor;
One programmable current source, this programmable current source can the output DC source or on the direct supply of output the overlapped high-frequency signal, this programmable current source is through line and the communication of programmed control processor, this programmable current source is supplied power to long wavelength laser;
One cylindricality air chamber, the chamber of this cylindricality air chamber are open structure, and with environmental gas UNICOM, the center of an end of this cylindricality air chamber is equipped with flange apparatus;
One long wavelength laser, an end of this long wavelength laser advances optically-coupled in the flange of cylindricality air chamber through optical fiber, and the other end of this long wavelength laser is connected with programmable current source;
One photodetector, this photodetector is installed in the other end of cylindricality air chamber, the laser alignment that the position that this photodetector is installed should be coupled into the flange place;
One little current detecting meter, this little current detecting meter is gathered the current signal on the photodetection meter, this little current detecting meter and the communication of programmed control processor;
One signal generator, this signal generator is carried in modulation signal on the programmable current source, this signal generator and the communication of programmed control processor;
One lock-in amplifier, this lock-in amplifier is gathered the signal on the photodetection meter, this lock-in amplifier and programming controller communication;
Wherein this programmed control processor is a computing machine or is processor chips;
Wherein programmable current source is a current source circuit;
The detection method of the program control gas concentration detection system of this laser comprises the steps:
Step 1: shutdown signal generator; Pass through programmable current source; At the linear zone of long wavelength laser work, continuous stepping output current from low to high, the position of the low ebb through detecting the photocurrent that detects on little current detecting meter; Calculate wavelength locking, make programmable current source at this position output DC stream;
Step 2: the programmed control processor receives the signal that little current detecting meter transmits continuously, obtains the concentration C of gas through the direct method of measurement;
Step 3:, return step 2 when the value that the calculates time more than or equal to a comparison value;
Step 4: when the value that the calculates time less than a comparison value; The opening signal generator; For programmable current source adds modulation signal; Detect the harmonic components of the signal that photodetector detects with lock-in amplifier, the second harmonic composition that calculates photocurrent through the harmonic measure method becomes the ratio of branch with first harmonic, calculate gas concentration C;
Step 5: when the second harmonic composition becomes value that the ratio of branch calculates less than a comparison value with first harmonic when, return step 4;
Step 6: when calculating the second harmonic composition becomes branch with first harmonic the value of ratio more than or equal to a comparison value, the shutdown signal generator returns step 2.
2. the detection method of the program control gas concentration detection system of laser according to claim 1, wherein the formula of direct method of measurement concentration C calculating is I (λ)=I
0(λ) exp (α CL), wherein I (λ) is detected photocurrent, I
0Photocurrent when (λ) absorbing for nothing, α is an absorption intensity, and L is cylindricality air chamber (a 3) length, and C is a gas concentration to be measured.
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| CN102353649A (en) * | 2011-06-30 | 2012-02-15 | 中国科学院长春光学精密机械与物理研究所 | Method for remotely measuring ethanol gas concentration based on binary spectrum analysis technology |
| CN102359951A (en) * | 2011-06-30 | 2012-02-22 | 中国科学院长春光学精密机械与物理研究所 | Remote sensing quick laser automatic predetection device for drunk driving |
| CN103940776A (en) * | 2013-01-22 | 2014-07-23 | 中国科学院电工研究所 | Humidity detection device and humidity detection method using humidity detection device |
| CN103994975B (en) * | 2014-06-19 | 2016-09-28 | 山西大学 | A kind of gas detection method based on this locality demodulation modulation optical signal technologies and device |
| JPWO2016047170A1 (en) * | 2014-09-22 | 2017-04-27 | 株式会社東芝 | Exhalation diagnostic device |
| CN105136740A (en) * | 2015-10-26 | 2015-12-09 | 中国人民解放军军事医学科学院卫生装备研究所 | Temperature and humidify monitoring system based on TDLAS |
| CN108306171A (en) * | 2018-03-04 | 2018-07-20 | 南京理工大学 | Optical fiber laser monitoring and protecting device and guard method |
| CN111829980B (en) * | 2020-07-23 | 2021-08-10 | 安徽农业大学 | Linear nonlinear correction detection system and method based on harmonic technology |
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