CN103472030A - Novel method used for driving direct-current regulation and phase locking of micro water vapor detection - Google Patents

Abstract

The invention provides a novel method used for driving direct-current regulation and phase locking of micro water vapor detection, and belongs to the technical field of optical fiber sensing detection. Wavelength modulation is conducted on a laser, and signals pass through gas-absorption peaks and non-absorption positions are detected through the phase locking technology and are processed. An achieving system comprises a temperature controlling and driving module of the laser, a DFB laser, a gas chamber, a photoelectric detector, a current-voltage conversion module, a phase locking module and a single chip microcomputer. According to the novel method, the phase locking module is used, direct-current regulation is conducted on driving signals of the laser before phase locking, so that phase locking results become direct-current signals, the non-absorption positions are found conveniently and processed in an average mode, the signal to noise ratio can be greatly improved, and information of gas concentration is effectively extracted. In addition, the system further has the advantages of being small in size, simple in structure, low in cost and the like.

Description

A kind of driving DC adjustment detected for the minor amount of water steam phase-locked new method

Technical field

The invention belongs to Fibre Optical Sensor Detection Techniques field, is a kind ofly to use phase-locked, laser instrument direct current adjustment simultaneously and measure the new method that averaging carries out the detection of minor amount of water steam.

Background technology

Detecting water vapor concentration all has very important significance in a lot of fields.In rock gas, the existence of water can cause the pipeline water blocking, causes pipeline ice blockage, and corroded pipeline, equipment and instrument affect the accuracy of gas metering, causes very big harm to safety in production and the use of rock gas.In transformer oil, the more, the corrosion speed of aging, the apparatus insulated aging and metal parts of oil itself is faster for water cut, and the content of monitoring water content in oil is very necessary.In the electrical equipments such as high-voltage switch gear, SF6 can with water generation chemical reaction, cause apparatus insulated hydraulic performance decline, but also can be to environment.Therefore, on-line monitoring water vapour content in SF6 carried out accurately and timely is extremely important.The trace gas detection method of nowadays using has dew point method, electrolytic process, capacitance-resistance method etc.Utilize the detection system ubiquity of these method designs reaction slowly, serviceable life is short, and low precision and cost are very high.Therefore, certainly separate the problems referred to above in the urgent need to a kind of simple detection method.

The second-harmonic detection method of mentioning in the Xu Zhen of Northcentral University paper that peak is write " research of gas density second-harmonic detection correlation technique " is to utilize first harmonic to be modulated laser instrument, behind the gas absorption peak laser signal carry the signal of a large amount of frequencies, utilize phase-locked module to carry out the secondary frequency harmonics under the secondary reference signal is auxiliary and survey the signal that can obtain the secondary singal of air inclusion concentration information and filter other frequency contents.This method can significantly improve signal to noise ratio (S/N ratio), but, due to the restriction that is subject to integrator in phase-locked module, wave filter equiband and design parameter, make phase-locked waveform easily change even lopsided, so detection accuracy is restricted.

Summary of the invention

For defect and the deficiency that overcomes prior art, the invention provides the new method of a kind of high precision, the detection of high stability minor amount of water steam.

The technical scheme of the inventive method is as follows:

A kind of driving DC adjustment detected for the minor amount of water steam phase-locked new method, by following measuring system, realized, this system comprises temperature control and the driver module of laser instrument, Distributed Feedback Laser, air chamber, photodetector, the current/voltage modular converter, phase-locked module, single-chip microcomputer, wherein the temperature control of laser instrument is connected with Distributed Feedback Laser with driver module, before Distributed Feedback Laser is positioned at air chamber, photodetector is placed in the air chamber back, the photodetector output terminal is connected to the input end of current/voltage modular converter, the output terminal of current/voltage modular converter is connected with phase-locked module, phase-locked module is connected with single-chip microcomputer, the temperature control of laser instrument and driver module are responsible for the temperature of Distributed Feedback Laser and are controlled, the modulation signal of Distributed Feedback Laser is provided, providing respectively that to be positioned at water vapor absorption peak place wavelength be that 1368.597nm and 1368.41nm(are without absorption place) the direct current biasing signal of wavelength is for the selection of Distributed Feedback Laser output center wavelength, reference signal is provided to phase-locked module simultaneously, Output of laser is received through water vapor absorption peak place with without the laser of absorption place wavelength by photodetector after air chamber, the current/voltage modular converter is converted to voltage signal for the photocurrent by the photodetector conversion, phase-locked module is chosen with reference signal frequency with signal frequently for the voltage signal from conversion, because the fixing therefore phase-locked result of the selection of centre wavelength is direct current signal, single-chip microcomputer detects average rear output display to phase-locked result, and the method step is as follows:

1) control driving and temperature control module and produce the primary modulation signal for the Distributed Feedback Laser driving, and the generation frequency is twice in the secondary reference signal of primary modulation ripple for phase-locked module frequency-selecting, simultaneously, by Single-chip Controlling, drive signal for generation of making Distributed Feedback Laser output light wavelength center respectively at water vapor absorption peak place with without the direct current signal of the position of absorption place, be respectively used to detect absorption intensity and selection of datum when absorbing;

2) connect light path, laser output is received by photodetector after connecting the air chamber of gas to be measured, is converted to driving signal and is contained accordingly the voltage signal that water vapour absorbs by the electric current and voltage modular converter afterwards;

3) electric current and voltage modular converter output terminal connects phase-locked module, to the result after conversion, carry out phase-locked, obtain the direct current harmonic signal with secondary reference signal same frequency, respectively to through the water vapor absorption peak with without absorbing direct current signal that place obtains, subtracting each other the water vapor concentration information that obtains after average.

The phase-locked principle that the present invention adopts is as described in the Xu Zhen of Northcentral University paper that peak is write " research of gas density second-harmonic detection correlation technique ", and under an atmospheric pressure, the absorption linearity of water vapor can be meaned by lorentzian curve usually:

$\mathrm{\α}\left(v\right)=\frac{{\mathrm{\α}}_0}{1+{\left(\frac{v-{\mathrm{\υ}}_{.0}}{\mathrm{\γ}}\right)}^2}---\left(1\right)$

The absorption coefficient that α in formula (ν) is the υ place for gas in light frequency, α ₀for the absorption coefficient of water vapor in the absorption peak center, γ is Absorption Line plate width.Regulate temperature and the direct drive electric current of laser instrument, making optical maser wavelength is a certain absorption peak place that fixes on water vapor.Then, on the driving current signal of laser instrument, the sinusoidal signal of stack appropriate frequency and amplitude, modulated the wavelength of laser instrument, and it is changed by sinusoidal rule at the absorption peak place, has:

v＝υ _c+Δυ·sinωt (2)

ν wherein _cfor the laser instrument centre frequency, Δ ν is the frequency modulation (PFM) amplitude, and the absorption coefficient expression formula can be expressed as:

$\mathrm{\α}\left(\mathrm{\υ}\right)=\frac{{\mathrm{\α}}_0}{1+{\left(\frac{{\mathrm{\υ}}_C-{\mathrm{\υ}}_0+\mathrm{\Δ}\·\sin \mathrm{\ωt}}{\mathrm{\γ}}\right)}^2}---\left(3\right)$

Due to laser instrument light intensity also corresponding the modulation, so formula is:

I(υ)=I ₀(υ)(1+η.sinωt)[1-α(υ)CL] (4)

In formula, L is the light path that light passes through gas to be measured, the volumetric concentration that C is gas to be measured.Laser wavelength is stabilized in to the absorbent core place, ν is arranged _c=ν ₀, the definition degree of modulation

(3) formula can turn to:

$\mathrm{\α}\left(\mathrm{\υ}\right)=\frac{{\mathrm{\α}}_0}{1+x^2\·{\sin }^2\left(\mathrm{\ωt}\right)}---\left(5\right)$

(5) formula is launched to Fourier series, and known except DC component, it is the strongest in each harmonic only having even-order harmonic and second harmonic signal:

α(υ)＝α ₀[k ₀-k ₂·sin(2ωt)+k ₄·sin(4ωt)-...] (6)

Formula also deformable is:

I(υ)=I ₀(υ)(1+ηsinωt)[1-α ₀CL(k ₀-k ₂.sin(2ωt)+k ₄.sin(4ωt)-...)] (7)

Can see by formula the concentration information that the amplitude of even-order harmonic component contains gas to be measured.Utilize the signal of other frequencies of target signal filter of phaselock technique locking second harmonic frequency, the amplitude that detects the second harmonic frequency signal can draw water vapor concentration.

Generally phase-lockedly for detection of gas, use overlapped high-frequency modulation signal on the low frequency sweep signal more, because scanning different times absorption peak is also different through the position of modulating wave, cause the amplitude of corresponding frequencies harmonic wave also changing, so phase-locked result is not desirable mathematic(al) representation but contains the multi-frequency composition, therefore to wave filter, require very high; In addition, for different sweep frequencies, from the matching used integrator of phase-locked module and wave filter, also need to select different parameters, make the measurement result of overall system and dirigibility be restricted.The present invention removes the low frequency sweep signal, adopts the center of DC control laser instrument output light wavelength.Choose respectively that the absorption peak center is modulated sinusoidally and without the position of absorption peak, conveniently choose basis zero point, and acquired results is direct current signal, facilitate filtering and make average result more stable.

The accompanying drawing explanation

Fig. 1 is the system construction drawing of realizing of the present invention.

Wherein: 1, the temperature control of laser instrument and driver module, 2, Distributed Feedback Laser, 3, air chamber, 4, photodetector, 5, the current/voltage modular converter, 6, phase-locked module, 7, single-chip microcomputer, 8, the primary modulation ripple drives signal and direct current signal, 9, the second harmonic reference signal.

Fig. 2 is that wavelength of the present invention is selected schematic diagram.

In figure, curve is the spectrogram that water vapor absorbs, wherein: wherein: the wavelength-1368.597nm at the water vapor absorption peak place that (1) is chosen, the wavelength-1368.41nm without absorption place that (2) are chosen.

Embodiment

Below in conjunction with drawings and Examples, the present invention will be further described, but be not limited to this.

Embodiment:

As shown in Figure 1, a kind of driving DC adjustment detected for the minor amount of water steam phase-locked new method, by following measuring system, realized, this system comprises temperature control and the driver module 1 of laser instrument, Distributed Feedback Laser 2, air chamber 3, photodetector 4, current/voltage modular converter 5, phase-locked module 6, single-chip microcomputer 7, wherein the temperature control of laser instrument is connected with Distributed Feedback Laser 2 with driver module 1, before Distributed Feedback Laser 2 is positioned at air chamber 3, photodetector 4 is placed in air chamber 3 back, photodetector 4 output terminals are connected to the input end of current/voltage modular converter 5, the output terminal of current/voltage modular converter 5 is connected with phase-locked module 6, phase-locked module 6 is connected with single-chip microcomputer 7, the temperature control of laser instrument and driver module 1 are responsible for the temperature of Distributed Feedback Laser 2 and are controlled, the modulation signal of Distributed Feedback Laser 2 is provided, providing respectively and be positioned at water vapor absorption peak place wavelength (as water vapor 1368.597nm) and 1368.41nm(without absorption place) the direct current biasing signal of wavelength is for the selection of Distributed Feedback Laser 2 output center wavelengths, reference signal is provided to phase-locked module 6 simultaneously, Output of laser is received through water vapor absorption peak places with without the laser of absorption place wavelength by photodetector 4 after air chamber, current/voltage modular converter 5 is converted to voltage signal for the photocurrent by photodetector 4 conversions, phase-locked module 6 is chosen with reference signal frequency with signal frequently for the voltage signal from conversion, because the fixing therefore phase-locked result of the selection of centre wavelength is direct current signal, single-chip microcomputer 7 detects average rear output display to phase-locked result, and the method step is as follows:

1) control driving and temperature control module and produce the primary modulation signal for the Distributed Feedback Laser driving, and the generation frequency is twice in the secondary reference signal of primary modulation ripple for phase-locked module frequency-selecting, simultaneously, by Single-chip Controlling, drive signal for generation of making Distributed Feedback Laser output light wavelength center respectively at water vapor absorption peak place with without the direct current signal of the position of absorption place, be respectively used to detect absorption intensity and selection of datum when absorbing;

2) connect light path, laser output is received by photodetector after connecting the air chamber of gas to be measured, is converted to driving signal and is contained accordingly the voltage signal that water vapour absorbs by the electric current and voltage modular converter afterwards;

3) electric current and voltage modular converter output terminal connects phase-locked module, to the result after conversion, carry out phase-locked, obtain the direct current harmonic signal with secondary reference signal same frequency, respectively to through the water vapor absorption peak with without absorbing direct current signal that place obtains, subtracting each other the water vapor concentration information that obtains after average.

Claims (1)

1. the driving DC adjustment detected for the minor amount of water steam phase-locked new method, by following measuring system, realized, this system comprises temperature control and the driver module of laser instrument, Distributed Feedback Laser, air chamber, photodetector, the current/voltage modular converter, phase-locked module, single-chip microcomputer, wherein the temperature control of laser instrument is connected with Distributed Feedback Laser with driver module, before Distributed Feedback Laser is positioned at air chamber, photodetector is placed in the air chamber back, the photodetector output terminal is connected to the input end of current/voltage modular converter, the output terminal of current/voltage modular converter is connected with phase-locked module, phase-locked module is connected with single-chip microcomputer, the temperature control of laser instrument and driver module are responsible for the temperature of Distributed Feedback Laser and are controlled, the modulation signal of Distributed Feedback Laser is provided, provide respectively that to be positioned at water vapor absorption peak place wavelength be the selection of the direct current biasing signal of 1368.597nm and 1368.41nm wavelength for the Distributed Feedback Laser output center wavelength, reference signal is provided to phase-locked module simultaneously, Output of laser is received through water vapor absorption peak place with without the laser of absorption place wavelength by photodetector after air chamber, the current/voltage modular converter is converted to voltage signal for the photocurrent by the photodetector conversion, phase-locked module is chosen with reference signal frequency with signal frequently for the voltage signal from conversion, because the fixing therefore phase-locked result of the selection of centre wavelength is direct current signal, single-chip microcomputer detects average rear output display to phase-locked result, and the method step is as follows:

1) control driving and temperature control module and produce the primary modulation signal for the Distributed Feedback Laser driving, and the generation frequency is twice in the secondary reference signal of primary modulation ripple for phase-locked module frequency-selecting, simultaneously, by Single-chip Controlling, drive signal for generation of making Distributed Feedback Laser output light wavelength center respectively at water vapor absorption peak place with without the direct current signal of the position of absorption place, be respectively used to detect absorption intensity and selection of datum when absorbing;

2) connect light path, laser output is received by photodetector after connecting the air chamber of gas to be measured, is converted to driving signal and is contained accordingly the voltage signal that water vapour absorbs by the electric current and voltage modular converter afterwards;

3) electric current and voltage modular converter output terminal connects phase-locked module, to the result after conversion, carry out phase-locked, obtain the direct current harmonic signal with secondary reference signal same frequency, respectively to through the water vapor absorption peak with without absorbing direct current signal that place obtains, subtracting each other the water vapor concentration information that obtains after average.

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