CN105424632A - Micro water steam concentration detection method with self-controlled measuring range - Google Patents

Abstract

The invention discloses a micro water steam concentration detection method with a self-controlled measuring range, and belongs to the field of gas sensor system detection. The system comprises a single chip microcomputer, a laser temperature controlling and driving module, a DFB laser, a gas chamber, a photoelectric detector, a current-voltage conversion module, a lock phase amplifier, a high precision reference voltage generator, a subtractor, a gain control module, and a signal collecting module. The measuring range selecting module of multipath fixed parameter of a conventional secondary harmonic method micro water steam detection system is modified to obtain the provided system; after the lock phase amplifier obtains the harmonic amplitude containing concentration information, the gain control module is used to control the harmonic gain, at the same time, through the information exchange between the gain control module and the signal collecting module, the measuring range self control can be realized; and finally the water steam concentration of a gas to be detected can be calculated according to the harmonic amplitude and the gain value. The provided method breaks the limitation of concentration measuring range on circuit detection, enlarges the detected concentration range, effectively improves the signal/noise ratio, and is beneficial for extracting gas concentration information.

Description

A kind of micro water vapor detectable concentration method of range automatic control

Technical field

Gas sensing system detection field of the present invention is a kind of new method simultaneously using high-accuracy voltage reference, direct current adjustment and Single-chip Controlling to gather trace amounts of water vapor concentration information.

Background technology

Water is the important substance that we depend on for existence, detects water vapor concentration all significant in a lot of field.Such as extra-high voltage electric transmission and transformation system equipment medium gas SF ₆in containing moisture time, can generate toxicity and the very strong chemical substance of corrosivity, etching insulative equipment, even blasts.At food-processing industry, the liquid water content in packaging bag exceeds standard, and directly can affect food quality.In transformer oil, water cut is more, and oil itself is aging, apparatus insulated aging and metal parts corrosion speed is faster; In rock gas, the existence of water can cause pipeline water blocking, and corroded pipeline, instrument and equipment affect the accuracy of gas metering, cause high risks to the safety in production of rock gas and use.And fiber gas sensor because its good stability, measuring accuracy are high, electromagnetism interference, on-line checkingi, the advantages such as non-electric detection can be realized obtain applying more and more widely in the measurement of trace gas concentration.

Nowadays be the method for quadratic harmonics for the most effective method of measurement micro water vapor, the one belonging to fiber gas sensor is effectively applied, and the method measuring accuracy is high, good stability, and antijamming capability is strong.In order to the water vapor concentration adapting to more wide region is measured, improve system signal noise ratio further, in different concentration ranges simultaneously, need to arrange the different circuit parameter selective circuit of measuring range of multichannel, this makes circuit lengthy and jumbled, the wasting of resources, and can introduce more multicircuit noise.Therefore, the problems referred to above are solved in the urgent need to the simple and easy effective detection method of one.

Harbin Engineering University Zhang Keke to write the second-harmonic detection method mentioned in paper " spectral absorption formula fiber-optic fiber gas etection theory and technical research " be utilize first harmonic to modulate laser instrument, behind gas absorption peak, laser signal carries the signal of a large amount of frequency, utilizes lock-in amplifier under secondary reference signal is assisted, carry out secondary frequency Harmonic Detection and can obtain the secondary singal of air inclusion concentration information and filter the signal of other frequency contents.The amplitude of the second harmonic signal finally detected is relevant with water vapor concentration, and along with water vapor concentration increases, harmonic amplitude presents linear increase.If do not take corresponding measure, in the moisture concentration of wide region detects, the harmonic amplitude had under the concentration range of part exceeds acquisition range.Therefore must carry out different circuit parameter process to the water vapor under variable concentrations, circuit can be caused so complicated, conversion trouble, and easily introduce other circuit noises, therefore detect ease and be restricted.

Summary of the invention

In order to overcome defect and the deficiency of prior art, the invention provides a kind of micro water vapor detectable concentration method of range automatic control, the method can more simple and convenient and accurately effectively carry out the detection of water vapor concentration.

The technical scheme of the inventive method is as follows:

A kind of micro water vapor detectable concentration method of range automatic control, realized by following measuring system, this system comprises Chip Microcomputer A, single-chip microcomputer B, temperature control driver module, Distributed Feedback Laser, air chamber, photodetector, current/voltage modular converter, lock-in amplifier, precision voltage reference generator, subtracter, gain control module and signal acquisition module, temperature control driver module comprises temperature control module and driver module, Chip Microcomputer A connects driver module, temperature control driver module is connected with Distributed Feedback Laser, before Distributed Feedback Laser is positioned at air chamber, photodetector is placed after air chamber, photodetector output terminal is connected to the input end of current/voltage modular converter, current/voltage modular converter output terminal is connected with lock-in amplifier, Chip Microcomputer A connects the reference signal input end of lock-in amplifier, for lock-in amplifier provides reference signal, lock-in amplifier is connected with the normal phase input end of subtracter, the second harmonic obtained by lock-in amplifier demodulation can send into the normal phase input end of subtracter, precision voltage reference generator is connected with the negative input of subtracter, gain control module is connected between the output terminal of subtracter and negative input to form negative feedback connected mode, gain control module is connected with single-chip microcomputer B respectively with signal acquisition module simultaneously, to control the backfeed loop of harmonic amplitude gain, signal acquisition module often gathers an amplitude, single-chip microcomputer B ride gain control module once adjusts, simultaneously the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, the method step is as follows:

1) connected by above-mentioned each parts, switch on power, debugging light path and circuit can normally work; Open air chamber valve, by gas inject air chamber to be measured, inflate 20 minutes, guarantee in air chamber without other gas residue;

2) Chip Microcomputer A produces the sweep signal of primary modulation Signal averaging low frequency as drive singal, input queued switches module, driver module drives the luminescence of Distributed Feedback Laser, temperature control module controls laser. operating temperature simultaneously, Chip Microcomputer A also produces the reference signal input end that a frequency is twice in the secondary reference signal input lock-in amplifier of primary modulation ripple, for lock-in amplifier frequency-selecting, before formal measurement, oscillograph is connected on respectively driver module output terminal and lock-in amplifier reference signal input end, check drive singal and reference signal whether normal;

3) the laser input air chamber that laser instrument sends produces and absorbs, light signal after absorption arrives photodetector through optical fiber, light signal is converted into current signal by photodetector, by current/voltage modular converter, signal is changed into the voltage signal carrying aqueous vapor information, current/voltage modular converter output terminal connects lock-in amplifier input end, lock-in amplifier carries out phase-locked process for this voltage signal and reference signal, obtains the second harmonic signal comprising moisture concentration information;

4) for ensureing that second harmonic signal is in the collectable scope of signal acquisition module, the harmonic signal to lock-in amplifier exports is needed to carry out DC offset voltage adjustment, lock-in amplifier output terminal connects the normal phase input end of subtracter, the negative input that precision voltage reference generator connects subtracter provides high-accuracy stable voltage for subtracter, by the voltage swing regulating precision voltage reference generator to produce, adjustment participates in the DC voltage size of subtracter computing, reaches the object of adjustment harmonic signal DC offset voltage;

5) input end of the second harmonic signal entering signal acquisition module exported by subtracter, signal acquisition module carries out amplitude collection to second harmonic, just the harmonic amplitude carrying moisture concentration information can be obtained, signal acquisition module is connected with single-chip microcomputer B, input single-chip microcomputer B after harmonic amplitude is exported by signal acquisition module, the program of pre-set ride gain in single-chip microcomputer B, and specify harmonic amplitude scope, the harmonic amplitude of collection and setting range are made comparisons by single-chip microcomputer B, if harmonic amplitude is within setting range, then do not need adjustment; If harmonic amplitude is greater than setting range maximal value, gain control module can control to reduce yield value, and harmonics reduces, and amplitude declines; If harmonic amplitude is less than setting range minimum value, gain control module can control to increase yield value, and harmonics increases, and amplitude becomes large; Entering signal acquisition module is again incited somebody to action by adjusted harmonic wave, repeat said process, often through once adjusting, the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, by the data of display, originally will reduce by harmonic amplitude, and then obtain water vapor concentration;

6) moisture concentration of gas to be measured detects complete, powered-down.

The present invention adopt Cleaning Principle as Harbin Engineering University Zhang Keke write as described in paper " spectral absorption fiber-optic fiber gas etection theory and technical research ", at one atm, the absorption of water vapor linearly can be represented by lorentzian curve, at infrared band, the absorption coefficient of water vapor is less, and the output intensity of normal atmosphere pressure can be expressed as:

I(v)＝I ₀(v)[1-α(v)CL](1)

In formula α (υ) for gas be the absorption coefficient at υ place in light frequency, L is the light path of light by gas to be measured, and C is the volumetric concentration of gas to be measured.Regulate temperature and the direct driving current of laser instrument, make optical maser wavelength be a certain absorption peak place fixing on water vapor.Then, the driving current signal of laser instrument superposes the sinusoidal signal of appropriate frequency and amplitude, modulate the wavelength of laser instrument, make it change by sinusoidal rule at absorption peak place, laser instrument instantaneous output is:

(t)＝v _c+Δνcosωt(2)

In formula, Δ ν is modulation amplitude, and ω is modulation angular frequency, ν _cfor filters center frequency.Laser wavelength is stabilized in absorbent core place, namely has ν _c=ν ₀, normalized frequency skew x can utilize line half-width γ and instantaneous frequency ν to represent

$x=\frac{v-v_0}{\mathrm{\γ}}=x_0+m\cos \mathrm{\ω}t---\left(3\right)$

In formula: x ₀=(ν _c-ν ₀)/γ; M=Δ ν/γ is wavelength-modulated coefficient.After gas absorption, the output signal detected is

S(x)＝I(x)＝I(x ₀+mcosωt)(4)

Fourier expansion is carried out to (4), direct current and 1 can be obtained, 2, the expression formula of 3 subharmonic, for warbled lorentzian curve, in the even harmonics signal amplitude at the centre frequency place of Absorption Line, contain the concentration information of gas to be measured, can be used for measure gas concentrations.Water vapor concentration is larger, and harmonic amplitude can be higher.But the maximum amplitude of each even harmonics signal reduces with the increase of overtone order, only have even-order harmonic and second harmonic signal is the strongest in each harmonic, second harmonic expression formula is as follows

$S_2\left(x\right)=I_0{\mathrm{\α}}_0\[\frac{-4}{m^2}+\frac{\sqrt{2}}{m^2}\frac{(r+1-x^2)\sqrt{r+x}+2\left|x\right|\sqrt{r-x}}{r}\]---\left(5\right)$

In formula: X=1-x ²+ m ²;

Utilize phaselock technique to lock the signal of other frequencies of target signal filter of second harmonic frequency, detect second harmonic, if now secondary harmonic amplitude is A.Because the second harmonic signal demodulated is without direct current biasing, add DC reference voltage, second harmonic is adjusted in the collectable scope of signal acquisition module, and DC reference voltage does not change secondary harmonic amplitude, suppose that direct current adjustment reference voltage is M, output voltage is now

S′ ₂(x)＝S ₂(x)+M(6)

Now second harmonic S ' ₂x () amplitude is still A, in the concentration range of different range, secondary harmonic amplitude be made in same scope, need to carry out enlargement factor adjustment, and suppose that signal intensity p doubly, then now output signal is

S″ ₂(x)＝p[S ₂(x)+M](7)

The secondary harmonic amplitude collected is pA, in the signal processing, secondary harmonic amplitude is reduced by permanent circuit parameters relationship, can obtain water vapor concentration information.

In traditional micro water vapor detection system, second harmonic measurement range selection part is realized by the discharge circuit of different amplification, and measurement range selection scope is little, and setting parameter is complicated, troublesome poeration, and circuit is lengthy and jumbled, and noise is large.The present invention adds gain control module, as the part of harmonic signal gain factor adjustment, by Single-chip Controlling, by the backfeed loop of signal acquisition module-single-chip microcomputer-gain control module formation control harmonics, real-time monitoring secondary harmonic amplitude, simultaneously adjust yield value rapidly, make harmonic amplitude in the acquisition range of setting, final water vapor concentration information is by adopting secondary harmonic amplitude and yield value determine jointly.The method breaks traditions the restriction of circuit measurement range selection, no matter moisture concentration size, gain regulation module all by harmonic amplitude adjustment in acquisition range, expand moisture concentration measurement range.This circuit system is more succinctly stablized, and Signal-to-Noise effectively improves, and the performance boost for micro water vapor Concentration Testing has very great help.

Accompanying drawing explanation

Fig. 1 of the present inventionly realizes system construction drawing.

Wherein: 1, Chip Microcomputer A, 2, temperature control driver module, 3, Distributed Feedback Laser, 4, air chamber, 5, photodetector, 6, current/voltage modular converter, 7, lock-in amplifier, 8, subtracter, 9, gain control module, 10, precision voltage reference generator, 11, signal acquisition module, 12, single-chip microcomputer B, 13, the reference signal of lock-in amplifier, 14, drive singal.

Fig. 2 is that the drive singal that single-chip microcomputer sends is transferred to driver module with drive laser luminescence, and this waveform is obtained in low frequency trapezoidal wave sweep signal by high_frequency sine wave Signal averaging.

Fig. 3 detects the harmonic signal obtained, and the amplitude of harmonic signal also has the information of moisture concentration, therefore gathers harmonic amplitude and just can obtain moisture concentration.

Embodiment

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

Embodiment:

As shown in Figure 1, a kind of micro water vapor detectable concentration method of range automatic control, realized by following measuring system, this system comprises Chip Microcomputer A, B, temperature control driver module 2, Distributed Feedback Laser 3, air chamber 4, photodetector 5, current/voltage modular converter 6, lock-in amplifier 7, subtracter 8, gain control module 9, precision voltage reference generator 10 and signal acquisition module 11, temperature control driver module 2 comprises temperature control module and driver module, Chip Microcomputer A connects driver module, temperature control driver module is connected with Distributed Feedback Laser 3, before Distributed Feedback Laser 3 is positioned at air chamber 4, air chamber 4 places photodetector 5 below, photodetector 5 output terminal is connected to the input end of current/voltage modular converter 6, current/voltage modular converter 6 output terminal is connected with lock-in amplifier 7, Chip Microcomputer A connects the reference signal input end of lock-in amplifier 7, for lock-in amplifier 7 provides reference signal, lock-in amplifier 7 is connected with the normal phase input end of subtracter 8, the second harmonic obtained by lock-in amplifier 7 demodulation can send into the normal phase input end of subtracter 8, precision voltage reference generator 10 is connected with the negative input of subtracter 8, gain control module 9 is connected between the output terminal of subtracter 8 and negative input to form negative feedback connected mode, gain control module 9 is connected with single-chip microcomputer B respectively with signal acquisition module 11 simultaneously, to control the backfeed loop of harmonic amplitude gain, signal acquisition module often gathers an amplitude, single-chip microcomputer B ride gain control module once adjusts, simultaneously the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, the method step is as follows:

1) connected by above-mentioned each parts, switch on power, debugging light path and circuit can normally work; Open air chamber valve, by gas inject air chamber to be measured, inflate 20 minutes, guarantee in air chamber without other gas residue;

2) Chip Microcomputer A produces the sweep signal of primary modulation Signal averaging low frequency as drive singal, input queued switches module, driver module drives the luminescence of Distributed Feedback Laser, temperature control module controls laser. operating temperature simultaneously, Chip Microcomputer A also produces the reference signal input end that a frequency is twice in the secondary reference signal input lock-in amplifier of primary modulation ripple, for lock-in amplifier frequency-selecting.Before formal measurement, oscillograph is connected on respectively driver module output terminal and lock-in amplifier reference signal input end, check drive singal and reference signal whether normal;

3) the laser input air chamber that laser instrument sends produces and absorbs, light signal after absorption arrives photodetector through optical fiber, light signal is converted into current signal, by current/voltage modular converter, signal is changed into the voltage signal carrying aqueous vapor information, current/voltage modular converter output terminal connects lock-in amplifier input end, lock-in amplifier carries out phase-locked process for this voltage signal and reference signal, obtains the second harmonic signal comprising moisture concentration information;

4) for ensureing that second harmonic signal is in the collectable scope of signal acquisition module, the harmonic signal to lock-in amplifier exports is needed to carry out DC offset voltage adjustment, lock-in amplifier output terminal connects the normal phase input end of subtracter, the negative input that precision voltage reference generator connects subtracter provides high-accuracy stable voltage for subtracter, by the voltage swing regulating precision voltage reference generator to produce, adjustment participates in the DC voltage size of subtracter computing, reaches the object of adjustment harmonic signal DC offset voltage;

5) input end of the second harmonic signal entering signal acquisition module exported by subtracter, signal acquisition module carries out amplitude collection to second harmonic, just the harmonic amplitude carrying moisture concentration information can be obtained, signal acquisition module is connected with single-chip microcomputer B, input single-chip microcomputer B after harmonic amplitude is exported by signal acquisition module, the program of pre-set ride gain in single-chip microcomputer B, and specify harmonic amplitude scope, the harmonic amplitude of collection and setting range are made comparisons by single-chip microcomputer B, if harmonic amplitude is within setting range, then do not need adjustment; If harmonic amplitude is greater than setting range maximal value, gain control module can control to reduce yield value, and harmonics reduces, and amplitude declines; If harmonic amplitude is less than setting range minimum value, gain control module can control to increase yield value, and harmonics increases, and amplitude becomes large; Entering signal acquisition module is again incited somebody to action by adjusted harmonic wave, repeat said process, often through once adjusting, the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, by the data of display, originally will reduce by harmonic amplitude, and then obtain water vapor concentration;

6) moisture concentration of gas to be measured detects complete, powered-down.

Claims (1)

1. the micro water vapor detectable concentration method of a range automatic control, realized by following measuring system, this system comprises Chip Microcomputer A, single-chip microcomputer B, temperature control driver module, Distributed Feedback Laser, air chamber, photodetector, current/voltage modular converter, lock-in amplifier, precision voltage reference generator, subtracter, gain control module and signal acquisition module, temperature control driver module comprises temperature control module and driver module, Chip Microcomputer A connects driver module, temperature control driver module is connected with Distributed Feedback Laser, before Distributed Feedback Laser is positioned at air chamber, photodetector is placed after air chamber, photodetector output terminal is connected to the input end of current/voltage modular converter, current/voltage modular converter output terminal is connected with lock-in amplifier, Chip Microcomputer A connects the reference signal input end of lock-in amplifier, for lock-in amplifier provides reference signal, lock-in amplifier is connected with the normal phase input end of subtracter, the second harmonic obtained by lock-in amplifier demodulation can send into the normal phase input end of subtracter, precision voltage reference generator is connected with the negative input of subtracter, gain control module is connected between the output terminal of subtracter and negative input to form negative feedback connected mode, gain control module is connected with single-chip microcomputer B respectively with signal acquisition module simultaneously, to control the backfeed loop of harmonic amplitude gain, signal acquisition module often gathers an amplitude, single-chip microcomputer B ride gain control module once adjusts, simultaneously the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, the method step is as follows:

1) connected by above-mentioned each parts, switch on power, debugging light path and circuit can normally work; Open air chamber valve, by gas inject air chamber to be measured, inflate 20 minutes, guarantee in air chamber without other gas residue;

2) Chip Microcomputer A produces the sweep signal of primary modulation Signal averaging low frequency as drive singal, input queued switches module, driver module drives the luminescence of Distributed Feedback Laser, temperature control module controls laser. operating temperature simultaneously, Chip Microcomputer A also produces the reference signal input end that a frequency is twice in the secondary reference signal input lock-in amplifier of primary modulation ripple, for lock-in amplifier frequency-selecting, before formal measurement, oscillograph is connected on respectively driver module output terminal and lock-in amplifier reference signal input end, check drive singal and reference signal whether normal;

3) the laser input air chamber that laser instrument sends produces and absorbs, light signal after absorption arrives photodetector through optical fiber, light signal is converted into current signal by photodetector, by current/voltage modular converter, signal is changed into the voltage signal carrying aqueous vapor information, current/voltage modular converter output terminal connects lock-in amplifier input end, lock-in amplifier carries out phase-locked process for this voltage signal and reference signal, obtains the second harmonic signal comprising moisture concentration information;

4) for ensureing that second harmonic signal is in the collectable scope of signal acquisition module, the harmonic signal to lock-in amplifier exports is needed to carry out DC offset voltage adjustment, lock-in amplifier output terminal connects the normal phase input end of subtracter, the negative input that precision voltage reference generator connects subtracter provides high-accuracy stable voltage for subtracter, by the voltage swing regulating precision voltage reference generator to produce, adjustment participates in the DC voltage size of subtracter computing, reaches the object of adjustment harmonic signal DC offset voltage;

5) input end of the second harmonic signal entering signal acquisition module exported by subtracter, signal acquisition module carries out amplitude collection to second harmonic, just the harmonic amplitude carrying moisture concentration information can be obtained, signal acquisition module is connected with single-chip microcomputer B, input single-chip microcomputer B after harmonic amplitude is exported by signal acquisition module, the program of pre-set ride gain in single-chip microcomputer B, and specify harmonic amplitude scope, the harmonic amplitude of collection and setting range are made comparisons by single-chip microcomputer B, if harmonic amplitude is within setting range, then do not need adjustment; If harmonic amplitude is greater than setting range maximal value, gain control module can control to reduce yield value, and harmonics reduces, and amplitude declines; If harmonic amplitude is less than setting range minimum value, gain control module can control to increase yield value, and harmonics increases, and amplitude becomes large; Entering signal acquisition module is again incited somebody to action by adjusted harmonic wave, repeat said process, often through once adjusting, the data of the yield value of the harmonic amplitude collected and adjustment are inputted computer by serial ports by single-chip microcomputer B, and in computer, show preservation, by the data of display, originally will reduce by harmonic amplitude, and then obtain water vapor concentration;

6) moisture concentration of gas to be measured detects complete, powered-down.