CN204359684U - A kind of high-precision gas concentration detection apparatus - Google Patents

Abstract

The utility model discloses a kind of high-precision gas concentration detection apparatus, comprise laser beam emitting device and photoelectric detector, described laser beam emitting device comprises drive circuit for laser and laser instrument, the input end of described drive circuit for laser is connected with totalizer, described photoelectric detector is connected with detection filter unit and data processing unit, described detection filter unit comprises the current-voltage conversion circuit be connected in turn, bandwidth-limited circuit and pre-amplification circuit, the output terminal of described bandwidth-limited circuit wherein a road in turn with pre-amplification circuit, lock-in amplify circuit is connected with the first low-pass filter circuit, an other road is connected with RMS-DC converter circuit and the second low-pass filter circuit in turn, described first low-pass filter circuit is connected with data processing unit respectively with the output terminal of the second low-pass filter circuit.This gas concentration detection apparatus can the concentration of accurate measurement gas, and eliminate the impact that circuit and transmittance change produce gas concentration measurement, and accuracy of detection is improved.

Description

A kind of high-precision gas concentration detection apparatus

Technical field

The utility model belongs to Gas Thickness Detecting Technology field, specifically, relates to a kind of high-precision gas concentration detection apparatus.

Background technology

Spectroscopic gas analytical technology carrys out back analysis gas concentration by measurement gas transmittance, therefore wants the tested gas concentration of Measurement accuracy, the transmittance of necessary accurately measurement gas.The factors such as the pollution of dust, form and laser power attenuation change all can make measurement gas transmittance change, the impact eliminating transmittance need find one when transmittance changes, synchronous with absorbing second harmonic peak-to-peak value, to change in proportion factor of influence, is divided by and eliminates transmittance to absorb harmonic peaks peak value and this factor and change impact on the instrument linearity.How finding factor of influence that is synchronous with absorbing harmonic peaks peak value, that change in proportion, becoming key of the present utility model.Theoretically, there is multiple factor to select, but have very large uncertainty due to the result that affects of the factor such as device, circuit on the selected factor.

The detection method of current more employing is that the input current and working temperature by controlling laser instrument makes laser frequency scan the absorption line of tested gas, in frequency sweeping ranges, can measure and obtain second harmonic signal amplitude and DC component signal, concentration due to gas is decided by the ratio of the second harmonic signal of transmitted light intensity and DC component signal, and the two ratio is:

$S_{\mathrm{out}}\∝\frac{({2V}_{\mathrm{PP}\max }-V_{\mathrm{PP}\min 1}-V_{\mathrm{PP}\min 2})\·k}{(V_{\mathrm{DC}2}-V_{\mathrm{DC}1})\·k}=\frac{{2V}_{\mathrm{PP}\max }-V_{\mathrm{PP}\min 1}-V_{\mathrm{PP}\min 2}}{V_{\mathrm{DC}2}-V_{\mathrm{DC}1}}$

In formula: k represents that dust in light path, form pollute and the influence coefficient to two paths of signals such as laser power attenuation change; V _dC1and V _dC2be respectively the DC component signal corresponding to two valleies of second harmonic.Above-mentioned formula is defaulted as when the dust in laser delivery optics, form pollution and laser power decay produce light intensity attenuation, two signals can equal proportion decline, also namely influence coefficient k value is identical, dust no matter in which kind of situation in laser delivery optics, form pollute and laser power the is decayed light intensity attenuation caused, the ratio of second harmonic signal and DC component signal remains unchanged.If measure two signals, and utilize this ratio to carry out analytical gas concentration, then dust, form pollutes and the factor such as laser power change can be eliminated for the impact of the measurement result of instrument.But when environment temperature, air pressure change, the width of absorption line can change, and the second harmonic line style of absorption signal also can correspondingly change, show as the change of the direct current component value corresponding to two valleies of second harmonic, also, now utilize the concentration of the ratio measurement gas of second harmonic signal and DC component signal to produce measured deviation, also, when environment temperature, air pressure change, the width of absorption line can change, to k ₁and k ₂impact be different, according to the current computing method thinking both equal proportions changes, result of calculation will produce relatively large deviation.

Utility model content

The affected factor of existing gas concentration detection method is many, the coarse technical matters of testing result in order to solve for the utility model, provides a kind of high-precision gas concentration detection apparatus, can solve the problem.

In order to solve the problems of the technologies described above, the utility model is achieved by the following technical solutions:

A kind of high-precision gas concentration detection apparatus, comprise laser beam emitting device and photoelectric detector, described laser beam emitting device comprises drive circuit for laser and laser instrument, the input end of described drive circuit for laser is connected with totalizer, described photoelectric detector is connected with detection filter unit and data processing unit, described detection filter unit comprises the current-voltage conversion circuit be connected in turn, bandwidth-limited circuit and pre-amplification circuit, the output terminal of described bandwidth-limited circuit wherein a road in turn with pre-amplification circuit, lock-in amplify circuit is connected with the first low-pass filter circuit, an other road is connected with RMS-DC converter circuit and the second low-pass filter circuit in turn, described first low-pass filter circuit is connected with data processing unit respectively with the output terminal of the second low-pass filter circuit.

Further, between described current-voltage conversion circuit and bandwidth-limited circuit, automatic gain control circuit is connected with.

Further, an other input end of described lock-in amplify circuit is connected with phase shift frequency multiplier circuit, for receiving high_frequency sine wave modulation signal.

Further again, described data processing unit comprises A/D change-over circuit, and described first low-pass filter circuit is connected with the input end of described A/D change-over circuit respectively with the output terminal of the second low-pass filter circuit.

Further, between described current-voltage conversion circuit and bandwidth-limited circuit, automatic gain control circuit is connected with.

Compared with prior art, advantage of the present utility model and good effect are: high-precision gas concentration detection method of the present utility model, the ratio that make use of second harmonic signal and sinusoidal wave effective value exports as system, for calculating gas concentration, high_frequency sine wave modulation signal is all derived from the sinusoidal wave effective value through tested gas owing to absorbing harmonic peaks peak value, the influenced Complete Synchronization of institute on year-on-year basis, transmittance decay excessive in, light decay is consistent with the impact of sinusoidal wave effective value on absorption harmonic peaks peak value, therefore this method can eliminate the impact that transmittance change produces gas concentration measurement, accuracy of detection is improved.

After reading the detailed description of the utility model embodiment by reference to the accompanying drawings, other features of the present utility model and advantage will become clearly.

Accompanying drawing explanation

In order to be illustrated more clearly in the utility model embodiment or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only embodiments more of the present utility model, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is a kind of embodiment block scheme of the high-precision gas concentration detection apparatus that the utility model proposes;

Fig. 2 is the system light path basic comprising figure of the high-precision gas concentration detection apparatus that the utility model proposes.

Embodiment

Below in conjunction with the accompanying drawing in the utility model embodiment, be clearly and completely described the technical scheme in the utility model embodiment, obviously, described embodiment is only the utility model part embodiment, instead of whole embodiments.Based on the embodiment in the utility model, those of ordinary skill in the art are not making the every other embodiment obtained under creative work prerequisite, all belong to the scope of the utility model protection.

Embodiment one, present embodiments provide a kind of high-precision gas concentration detection apparatus, as shown in Figure 1, comprise laser beam emitting device and photoelectric detector, described laser beam emitting device comprises drive circuit for laser and laser instrument, the input end of described drive circuit for laser is connected with totalizer, described photoelectric detector is connected with detection filter unit and data processing unit, described detection filter unit comprises the current-voltage conversion circuit be connected in turn, bandwidth-limited circuit and pre-amplification circuit, the output terminal of described bandwidth-limited circuit wherein a road in turn with pre-amplification circuit, lock-in amplify circuit is connected with the first low-pass filter circuit, an other road is connected with RMS-DC converter circuit and the second low-pass filter circuit in turn, described first low-pass filter circuit is connected with data processing unit respectively with the output terminal of the second low-pass filter circuit.

Wherein, as shown in Figure 1 and Figure 2, the step adopting the pick-up unit of the raising tuning laser gas concentration accuracy of detection of the present embodiment to carry out gas concentration detection is:

S1, amplifier totalizer are applied to drive circuit for laser after low frequency triangular voltage sweep signal, high_frequency sine wave modulation signal and direct current signal being added, and the electric current as drive circuit for laser inputs;

S2, laser drive circuit drive laser Emission Lasers signal, through the tested gas in air chamber;

S3, photoelectric detector receive the laser signal of output after associated gas in air chamber absorbs and carry out Photoelectric Detection, are converted to voltage signal and input to detection filter unit;

After voltage signal after conversion is carried out bandpass filtering treatment by S4, detection filter unit the signal that exports wherein a road successively after enlarge leadingly, lock-in amplify and low-pass filtering treatment, obtain second harmonic signal, an other road obtains effective value signal through RMS-DC converter circuit, and this effective value signal is carried out low-pass filtering treatment and exports;

S5, data processing unit receive second harmonic signal and effective value signal, and carry out A/D conversion, and sampling calculates its crest value V _ppmax, trough value V _ppmin, and effective value V _rMS, described effective value V _rMSfor effective value signal is at the effective value of crest sampling instant place of second harmonic signal;

S6, data processing unit calculate gas concentration X to be measured, wherein,

$X\∝\frac{V_{\mathrm{pp}\max }-V_{\mathrm{pp}\min }}{V_{\mathrm{RMS}}}.$

The pick-up unit of the raising tuning laser gas concentration accuracy of detection of the present embodiment, according to Beer-Lambert law and modulation spectroscopy, under specified temp, pressure, the amplitude of harmonic signal is directly proportional to the concentration of gas to be measured, by a series of hardware circuit, detection signal is processed, finally calculates the concentration measuring gas to be measured.By adopting RMS-DC converter circuit counting sinusoidal wave effective value correction gas concentration result, owing to absorbing harmonic peaks peak value and the sinusoidal wave effective value V through tested gas _rMSall derive from high frequency modulated sine wave, suffered by be no matter the factors such as laser intensity change, circuit dark current affect Complete Synchronization on year-on-year basis, both ratio and laser intensity, transmittance are decayed, and all it doesn't matter for size, therefore, gas concentration in prior art can be solved and detect the technical matters of the impact of Stimulated Light intensity, circuit, dark current etc.

Wherein, described RMS-DC converter circuit can adopt RMS-DC converter chip to realize.

As a preferred embodiment, between described current-voltage conversion circuit and bandwidth-limited circuit, be connected with automatic gain control circuit.Owing to changing when laser power, dust, the factor such as form pollution be when causing the luminous power received to change, automatic growth control can adjust enlargement factor automatically, make the signal amplitude that receives basicly stable, this step is a kind of coarse adjustment for eliminating the transmittance change that the factor such as dust, form pollution causes.

An other input end of described lock-in amplify circuit is connected with phase shift frequency multiplier circuit, for receiving high_frequency sine wave modulation signal.Input in the current signal of drive circuit for laser and include high_frequency sine wave modulation signal, by measuring-signal being moved in the frequency away from low-frequency noise to the modulation of laser instrument, this frequency band that is amplified in of signal completes, namely lock-in amplify step is carry out demodulation restoring signal by lock-in amplify circuit, reduces the impact of noise and interference.Therefore, in order to ensure the correct recovery of signal, the reference signal inputted in lock-in amplify step is two frequency-doubled signals of high_frequency sine wave modulation signal.

Described data processing unit comprises A/D change-over circuit, and described first low-pass filter circuit is connected with the input end of described A/D change-over circuit respectively with the output terminal of the second low-pass filter circuit.A/D change-over circuit calculates its crest value V for sampling _ppmax, trough value V _ppmin, and effective value V _rMS.

Certainly; above-mentioned explanation is not to restriction of the present utility model; the utility model is also not limited in above-mentioned citing, the change that those skilled in the art make in essential scope of the present utility model, remodeling, interpolation or replacement, also should belong to protection domain of the present utility model.

Claims (4)

1. a high-precision gas concentration detection apparatus, it is characterized in that, comprise laser beam emitting device and photoelectric detector, described laser beam emitting device comprises drive circuit for laser and laser instrument, the input end of described drive circuit for laser is connected with totalizer, described photoelectric detector is connected with detection filter unit and data processing unit, described detection filter unit comprises the current-voltage conversion circuit be connected in turn, bandwidth-limited circuit and pre-amplification circuit, the output terminal of described bandwidth-limited circuit wherein a road in turn with pre-amplification circuit, lock-in amplify circuit is connected with the first low-pass filter circuit, an other road is connected with RMS-DC converter circuit and the second low-pass filter circuit in turn, described first low-pass filter circuit is connected with data processing unit respectively with the output terminal of the second low-pass filter circuit.

2. pick-up unit according to claim 1, is characterized in that, between described current-voltage conversion circuit and bandwidth-limited circuit, be connected with automatic gain control circuit.

3. pick-up unit according to claim 1, is characterized in that, an other input end of described lock-in amplify circuit is connected with phase shift frequency multiplier circuit, for receiving high_frequency sine wave modulation signal.

4. the pick-up unit according to any one of claim 1-3, it is characterized in that, described data processing unit comprises A/D change-over circuit, and described first low-pass filter circuit is connected with the input end of described A/D change-over circuit respectively with the output terminal of the second low-pass filter circuit.