CN103411923B - A kind of normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology - Google Patents

Abstract

The invention provides a kind of normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology, comprise the following steps: utilize optical fiber splitter that laser is divided into two-way, a road is through gas to be measured, and for generation of measuring-signal, another road is through N ₂the path of purification, for generation of reference signal, described measuring-signal and reference signal are gathered by Multi-path synchronous sampled data capture card; Described measuring-signal and reference signal are normalized, through linear function transformation, between the amplitude transformation of described measuring-signal and reference signal to [0,1]; Utilize the measuring-signal after normalization and reference signal to calculate the absorption signal of gas, deducted by the oblique varying signal irrelevant with absorption, what stay is the part that reflection absorbs.Effect of the present invention effectively to suppress the fluctuating institute reasons for its use noise of laser intensity on the impact of measurement result, and effectively improve measuring accuracy, the lower limit of the low measurement of a step-down of going forward side by side, is with a wide range of applications.

Description

A kind of normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology

Technical field

The present invention relates to a kind of noise-reduction method of tunable laser spectroscopy technology, be specifically related to a kind of normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology.

Background technology

Tunable diode laser absorption spectrometry technology utilizes narrow-linewidth laser to scan the absorption line of gas molecule to be measured, by analyzing the concentration and the temperature that are obtained gas to be measured by the laser intensity after gas molecules sorb to be measured.Compare with thermometry with traditional gas concentration, tunable diode laser absorption spectrometry technology tool has the following advantages: non-cpntact measurement, and laser obtains absorption information through gas to be measured, measuring process to gas flowfield to be measured without any interference; Measuring speed is fast, and the response time can reach ms level; Measuring system realizes simple, and fibre optical transmission and coupling scheme make it easily adapt to measurement environment and miniaturization; Measurement selectivity is strong, measures the interference not by other gas compositions and change thereof.Therefore, tunable laser spectroscopy technology is widely used in the field such as combustion diagnosis and environmental monitoring.Such as, patent " uses the hot gas temperature of tunable diode laser to measure " in combustion gas turbine (application number: 201110278846.8) invented a kind of burning gases measurement mechanism be arranged in combustion gas turbine based on tunable diode laser absorption spectrometry technology, for accurately measuring ignition temperature in combustion gas turbine or other hot gas temperature; Patent " tunable diode laser absorption spectroscopy temperature real-time detector " (application number: 201010583531.X) has invented a kind of temperature monitor based on tunable diode laser absorption spectrometry technology, utilize infrared laser beam to pass temperature province to be measured, utilize the characteristic absorpting spectruming line of steam in this region to obtain the temperature in region to be measured in real time; Patent " optical texture of laser absorption spectrum atmospheric methane concentration on-line computing model " (patent No.: ZL200520071347.1) utilizes tunable laser spectroscopy technology to combine with long path cell technology to form the on-Line Monitor Device of methane content in air.

When adopting concentration and the temperature of tunable diode laser absorption spectrometry commercial measurement gas, the fluctuating of laser intensity is the one of the main reasons of production background noise.When the absorption of gas to incident light is less, measurement result is more easily subject to the interference of ground unrest, and then causes larger measuring error, limits detection sensitivity.Paper " tuning semiconductor laser absorption spectrum autobalanced detection technique study " (number: 0253-2239 (2007) 02-0350-4) have studied the auto-balanced detection circuit with electron gain compensation mechanism, the output signal of self-equilibrating circuit by article.But the output signal of self-equilibrating circuit has log characteristic, directly can not reflect the concentration of gas to be measured, need by calibration and retrieving concentration determination fit equation, and calculate the concentration of gas.Because the change of temperature can change absorption signal, therefore, for the situation of different temperatures, need to re-start demarcation to instrument, this limits the practical application of the method to a certain extent.

Adopt two-path tunable laser absorption spectrum technology, a road is the measuring beam through gas to be measured, and another road is through N ₂the path reference beam of purification, the fluctuating institute production background noise of laser intensity can be reflected in the measuring-signal that two-way light beam obtains simultaneously, the signal that two-way light beam obtains is normalized, the oblique varying signal irrelevant with absorption can be deducted, what stay is the part that reflection absorbs, and effectively suppresses the fluctuating institute reasons for its use noise of laser intensity on the impact of measurement result.In addition, owing to not carrying out nonlinear transformation to measuring-signal in signal processing, therefore, the absorption signal obtained after calculating can be directly used in the calculating of temperature and gas concentration.

Summary of the invention

In order to Background suppression noise is effectively on the impact of measurement result, improve measurement sensistivity, the measurement lower limit of the low tunable diode laser absorption spectrometry technology of a step-down of going forward side by side, the invention provides a kind of normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology.

The technical solution adopted in the present invention is as follows:

Step one, utilizes optical fiber splitter that laser is divided into two-way, and a road through gas to be measured, by a photoelectric detector, produces measuring-signal V after collimating mirror collimation exports _meas, N is passed in another road after collimating mirror collimation exports ₂the path of purification, by another photoelectric detector, produces reference signal V _ref, described measuring-signal and reference signal are gathered by Multi-path synchronous sampled data capture card, and are transferred in computing machine;

Step 2, to described measuring-signal V _measwith described reference signal V _refbe normalized, through linear function transformation, between the amplitude transformation of described measuring-signal and reference signal to [0,1],

$V_{\mathrm{meas}-\mathrm{norm}}=\frac{V_{\mathrm{meas}}-\min \left(V_{\mathrm{meas}}\right)}{\max \left(V_{\mathrm{meas}}\right)-\min \left(V_{\mathrm{meas}}\right)}---\left(1\right)$

$V_{\mathrm{ref}-\mathrm{norm}}=\frac{V_{\mathrm{ref}}-\min \left(V_{\mathrm{ref}}\right)}{\max \left(V_{\mathrm{ref}}\right)-\min \left(V_{\mathrm{ref}}\right)}---\left(2\right)$

Wherein V _meas-normrepresent the measuring-signal after normalization, V _ref-normrepresent the reference signal after normalization, min (V) and max (V) represents minimum value and the maximal value of signal V respectively;

Step 3, calculates the absorption signal α of gas,

$\mathrm{\α}=\frac{V_{\mathrm{ref}-\mathrm{norm}}-V_{\mathrm{meas}-\mathrm{norm}}}{V_{\mathrm{ref}-\mathrm{norm}}}---\left(3\right)$

Effect of the present invention: the normalization noise-reduction method of employing two-path tunable laser absorption spectrum technology of the present invention, by the normalized to measuring-signal and reference signal, the oblique varying signal irrelevant with absorption is deducted, what stay is the part that reflection absorbs, and effectively suppress the fluctuating institute reasons for its use noise of laser intensity on the impact of measurement result, improve the sensitivity of measuring system.

Accompanying drawing explanation

Fig. 1 is the measuring system of the normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology.

Fig. 2 is measuring-signal V _measwith reference signal V _ref.

Fig. 3 is the measuring-signal V after normalization _meas-normwith the reference signal V after normalization _ref-norm.

Fig. 4 is the absorption signal α adopting the normalization noise-reduction method of two-path tunable laser absorption spectrum technology to obtain _normwith the absorption signal α adopting traditional direct absorption process to obtain _dAScontrast.

Fig. 5 is the absorption signal α adopting for 1000 times traditional direct absorption process to obtain _dASmean value α _averwith α _norm, α _dAScontrast.

In Fig. 1: 1-signal generator; 2-laser controller; 3-laser instrument; 4-1 × 2 optical fiber splitter; The output channel one of 5-optical fiber splitter; The output channel two of 6-optical fiber splitter; 7-fiber optic collimator mirror; 8-gas to be measured; 9-N ₂the path of purification; 10-photodetector; 11-Multi-path synchronous sampled data capture card; 12-computing machine.

Embodiment

In the present embodiment, with H ₂the centre frequency of O is 7185.6cm ^-1spectral line to H in air ₂o is absorbed as example, utilizes the normalization noise-reduction method of described two-path tunable laser absorption spectrum technology to obtain described centre frequency for 7185.6cm ^-1the absorption signal of spectral line, work as H ₂when the absorption of O to incident light is less, compared with traditional direct absorption process, the fluctuating institute reasons for its use noise that the normalization noise-reduction method of described two-path tunable laser absorption spectrum technology can suppress laser intensity to rise and fall effectively is on the impact of measurement result, effectively improve measuring accuracy, the lower limit of the low measurement of a step-down of going forward side by side.

Below in conjunction with accompanying drawing, the present invention is further illustrated:

As shown in Figure 1, system comprises signal generator, laser controller, laser instrument, optical fiber splitter, fiber optic collimator mirror (two), photodetector (two), synchronously sampled data capture card and computing machine to the measuring system of the normalization noise-reduction method of employing two-path tunable laser absorption spectrum technology of the present invention.Wherein, described laser controller regulates laser frequency and power by change temperature and electric current.Centered by described laser instrument, frequency is 7185.6cm ^-1distributed feedback type semiconductor laser, exemplary power 20mW, laser linewidth is less than 10MHz.Described fiber optic collimator mirror output beam diameter is 0.75mm.Effective light-sensitive surface diameter of described photodetector is 1mm, and light signal is converted to electric signal by described photodetector.Described Multi-path synchronous sampled data capture card carries out synchronous acquisition to multiple signals, and is transferred to described Computer Storage.

By demarcating, step one, determines that described centre frequency is 7185.6cm ^-1the design temperature of described laser controller corresponding to spectral line, by described signal generator output frequency for the output current of laser controller described in the triangular modulation of 500Hz changes the frequency of described laser instrument.The laser coupled exported by laser instrument is in 1 × 2 optical fiber splitter, and the fiber outlet of optical fiber splitter is described fiber optic collimator mirror.Laser in the output channel one of described optical fiber splitter through air, by described photoelectric detector, produces measuring-signal V after described fiber optic collimator mirror collimation _meas; Laser in the output channel two of optical fiber splitter passes through N after described fiber optic collimator mirror collimation ₂the path of purification, namely not through air, by photoelectric detector described in another, produces reference signal V _ref.Described measuring-signal V _measwith described reference signal V _refas shown in Figure 2.

Step 2, to described measuring-signal V _measwith described reference signal V _refbe normalized, through linear function transformation, by described measuring-signal V _measwith reference signal V _refamplitude transformation between [0,1],

$V_{\mathrm{meas}-\mathrm{norm}}=\frac{V_{\mathrm{meas}}-\min \left(V_{\mathrm{meas}}\right)}{\max \left(V_{\mathrm{meas}}\right)-\min \left(V_{\mathrm{meas}}\right)}---\left(1\right)$

$V_{\mathrm{ref}-\mathrm{norm}}=\frac{V_{\mathrm{ref}}-\min \left(V_{\mathrm{ref}}\right)}{\max \left(V_{\mathrm{ref}}\right)-\min \left(V_{\mathrm{ref}}\right)}---\left(2\right)$

Wherein V _meas-normrepresent the measuring-signal after normalization, V _ref-normrepresent the reference signal after normalization, min (V) and max (V) represents minimum value and the maximal value of signal V respectively, described measuring-signal V _measwith described reference signal V _refnormalization result as shown in Figure 3;

Step 3, calculates the absorption signal α of gas _norm, the oblique varying signal irrelevant with absorption is deducted, and suppresses the fluctuating institute reasons for its use noise of laser intensity on the impact of measurement result.

${\mathrm{\α}}_{\mathrm{norm}}=\frac{V_{\mathrm{ref}-\mathrm{norm}}-V_{\mathrm{meas}-\mathrm{norm}}}{V_{\mathrm{ref}-\mathrm{norm}}}---\left(3\right)$

By the absorption signal α adopting the normalization noise-reduction method of two-path tunable laser absorption spectrum technology to obtain _normthe absorption signal α obtained with traditional direct absorption process _dAScontrast, as shown in Figure 4, described absorption signal α _normflatness be obviously better than α _dASflatness.In order to verify the correctness of the normalization noise-reduction method adopting two-path tunable laser absorption spectrum technology further, by described α _norm, α _dASthe absorption signal α obtained with 1000 described traditional direct absorption processes _dASmean value α _avercompare, as shown in Figure 5, α _averwith α _normdegree of agreement be better than α _averwith α _dASdegree of agreement.In sum, compared with described traditional direct absorption process, adopt the normalization noise-reduction method of two-path tunable laser absorption spectrum technology effectively on the impact of measurement result, the precision measured can be improved, the lower limit of the low measurement of a step-down of going forward side by side by Background suppression noise.

Above to the description of the present invention and embodiment thereof, being not limited thereto, is only one of embodiments of the present invention shown in accompanying drawing.When not departing from the invention aim, designing the structure similar with this technical scheme or embodiment without creation, all belonging to scope.

Claims (1)

1. adopt a normalization noise-reduction method for two-path tunable laser absorption spectrum technology, the method comprises the following steps:

Step one, changes the design temperature of laser controller, determines the centre frequency of distributed feedback type semiconductor laser; The output current of laser controller described in the triangular modulation utilizing signal generator to export, changes the frequency of described distributed feedback type semiconductor laser, scans the absorption line of gas molecule to be measured; The laser coupled exported by laser instrument is in 1 × 2 optical fiber splitter, the fiber outlet of optical fiber splitter is fiber optic collimator mirror, laser in the output channel one of described optical fiber splitter through gas to be measured, by a photoelectric detector, produces measuring-signal V after described fiber optic collimator mirror collimation _meas; Laser in the output channel two of optical fiber splitter passes through N after described fiber optic collimator mirror collimation ₂the path of purification, by another photoelectric detector, produces reference signal V _ref, described measuring-signal and reference signal are gathered by Multi-path synchronous sampled data capture card, and are transferred in computing machine;

Step 2, to described measuring-signal V _measwith described reference signal V _refbe normalized, through linear function transformation, between the amplitude transformation of described measuring-signal and reference signal to [0,1],

$V_{meas-norm}=\frac{V_{meas}-min\left(V_{meas}\right)}{\max \left(V_{meas}\right)-\min \left(V_{meas}\right)}---\left(1\right)$

$V_{ref-norm}=\frac{V_{ref}-min\left(V_{ref}\right)}{max\left(V_{ref}\right)-\min \left(V_{ref}\right)}---\left(2\right)$

Wherein V _meas-normrepresent the measuring-signal after normalization, V _ref-normrepresent the reference signal after normalization, min (V) and max (V) represents minimum value and the maximal value of signal V respectively;

Step 3, deducts the oblique varying signal irrelevant with absorption, and obtain absorption signal α, inhibit the fluctuating institute reasons for its use noise of laser intensity on the impact of measurement result, α is

$\mathrm{\α}=\frac{V_{ref-norm}-V_{meas-norm}}{V_{ref-norm}}---\left(3\right)$

Described absorption signal α is directly used in the calculating of temperature and gas concentration, improves measuring accuracy, reduces measurement lower limit.