CN1215837A - On-line near infrared multicomponent measuring method and apparatus - Google Patents

Abstract

A technique for in-line automatic detection of multiple components contained in one substance and its devices feature that a single light source, a single detector and the 4-wavelength, dual-light-path and 8-light-beam measuring method and system are used. Its advantages are low cost, optically adaptive function for automatic elimination and compensation of error caused by the change in ambient temp, light source and colour temp, power supply fluctuation and circuit drift, high and stable measurement precise, good repeatability and the function of judging, prompting and eliminating the interference of near infrared radiation.

Description

A kind of online near infrared multicomponent measuring method and instrument

The invention belongs to the photoelectricity test technical field, relate to the instrumentation in the automatic control of a kind of process, relate in particular to a kind of online near infrared material multicomponent measuring method and equipment.

In the prior art, in order to improve the quality of products, reduce energy resource consumption, the protection environment is increased economic efficiency, and in process of production certain component content in the measured object is carried out on-line monitoring and control usually.For example in metallurgy industry, measure and control the moisture in the raw material; Measure and control the content or the concentration of heterogeneity in raw material, middle product and the final products in the industry such as food, solid beverage, chemical fertilizer, chemical.Therefore this kind instrument is the crucial instrument during process is controlled automatically.This kind instrument generally is to utilize material composition the absorption intensity of near infrared spectrum district specific wavelength radiation energy to be measured the content or the concentration of material composition.Existing near infrared Fourier transform spectrometer, near infrared light grating spectrograph, near infrared prism spectrometer and the near infrared acoustooptic modulation spectrometer etc. that use in the present prior art.In above-mentioned this quasi-instrument, though can both be in the mensuration that realizes in varying degrees material composition or concentration, near infrared light grating spectrograph and near infrared prism spectrometer are because sweep time is long, and measuring speed can not be used for on-line measurement slowly; Though the measuring speed of near infrared Fourier transform spectrometer and near infrared acoustooptic modulation spectrometer can satisfy the requirement of on-line measurement, has very high measuring accuracy as Laboratory Instruments, it costs an arm and a leg, and is not easy to apply on commercial production.

Japan's " instrumentation technology " magazine (1996.06) discloses the IRM series moisture meter that a kind of Japanese thousand wild Co., Ltd. (CHINOCorporation) produce, and this instrument is a kind of composition of energy measurement moisture only, and other compositions that can not measurement of species.The moisture meter of IRM series adopts the measuring principle on three-wavelength monochromatic light road, and it is made up of near-infrared light source illumination section, monochromator part, photoelectricity receiving unit, signal processing and computer system.For the reflectivity of eliminating measured object, distance, quality (surface state, color, component etc.) change and the influence of external interference factor, except the characteristic absorption wavelength of selecting moisture, select in addition not constituted three wavelength that instrument uses near this wavelength by two wavelength of moisture absorption.The radiation energy of these three wavelength is projected the measured object surface, utilize photodetector PbS to convert electric signal to, adopt scale operation, eliminated the influence of above-mentioned factor through the radiation energy that the measured object surface diffuse reflectance is returned.But because vulcanized lead (PbS) detector has the shortcoming of thermal effect; The transmitance of interference filter element centre wavelength is the function of temperature, so system must have temperature compensation or internal reference function, could allow the variation of instrument operating ambient temperature.And the shortcoming of this moisture meter is to eliminate or to compensate the measuring error that causes because of variation of ambient temperature automatically, but also exists because power-supply fluctuation, optical element is aging and factor such as interference causes the defectives such as variation of measurement result.

At the deficiencies in the prior art and defective, purpose of the present invention and task are to provide a kind of online near infrared multicomponent measuring method and instrument that meets optics self-adaptation principle for industrial automation, it can not only be eliminated automatically or compensate because of variation of ambient temperature and power-supply fluctuation, optical element is aging and factor such as interference causes measuring error, has the advantage of high precision, high stability; But also it is lower to have a cost, is convenient to the characteristics of promotion and application in commercial production.

The present invention is achieved by the following technical solutions: it comprises the near-infrared light source illuminator, the chopper wheel of interference filter element is housed, photodetector, signal processing system that the signal of photodetector output is handled and coupled computer system, it is characterized in that adopting the measuring method of four wavelength double light paths, eight light beams, this measuring method is: will measure the light signal of light path generation and the light signal of reference path generation respectively and project successively on the same photodetector.In the one-period that chopper wheel rotates, this photodetector alternately receives four modulated light signals that produce from four modulated light signals measuring that light path produces and reference path by the time partitioning scheme, and it is converted to eight electric signal respectively.To above-mentioned eight electric signal amplify, filtering, phase-locked amplification, demodulation, be to be sent to computing machine after the digital signal via A/D converter with analog signal conversion, calculate the concentration of measured object composition by being stored in calculation procedure in the computer storage then.

Realize a kind of online near infrared multicomponent measuring instrument of said method, it comprises by a near-infrared light source and with this light source and is installed in the illuminator that spherical reflector, the collimation lens on the same optical axis, the chopper wheel that interference filter element is housed, plane mirror, condenser are formed; The measurement light path of forming by imaging object lens, photodetector and measured object; Signal processing that the signal of photodetector output is handled and coupled computer system, it is characterized in that also comprising a reference path, this reference path by with above-mentioned light source at first plane mirror on the same surface level and be installed in second plane mirror of this catoptron vertical direction with collimation lens and the catoptron of second plane mirror on same optical axis and form; Also comprise the process of measurement and the calculation procedure that are stored in the computer memory.

Because material composition has absorption to the near infrared wave radiation energy of specific wavelength, its endergonic intensity is relevant with the concentration or the content of composition, and this measuring instrument is determined its component content or concentration by the intensity of measurement features wavelength absorption energy just.

Accompanying drawing 1 is the optical system synoptic diagram.

Accompanying drawing 2 is the A-A cut-open view of Fig. 1.

Accompanying drawing 3 is reticle configuration synoptic diagram.

Accompanying drawing 4 is the A-A cut-open view of Fig. 3.

Accompanying drawing 5 is signal processing system synoptic diagram.

Accompanying drawing 6 is measuring-signal synoptic diagram.

Accompanying drawing 7 is microcomputer system synoptic diagram.

Accompanying drawing 8 is calculation procedure FB(flow block).

Describe measuring principle of the present invention, method and specific embodiments in detail below in conjunction with accompanying drawing: because material composition has absorption to the near infrared wave radiation energy of specific wavelength, its endergonic intensity is relevant with the concentration or the content of composition, and this measuring method and instrument are determined its component content or concentration by the intensity of measurement features wavelength absorption energy just.

As shown in Figure 1, this instrument adopts the measuring principle of four wavelength double light paths, 8 light beams.One the tunnel for measuring light path, and another road is a reference path.By infrared light supply 8 and be installed in spherical reflector 7, the collimation lens 9 on the same optical axis, the chopper wheel 18 that interference filter element is housed, plane mirror 14, condenser 16 with this light source and form illumination path, form by imaging object lens 1, photodetector 3 and measured object 17 and measure light path.Reference path by with above-mentioned light source 8 at first plane mirror 6 on the same surface level and be installed in second plane mirror 5 of this catoptron vertical direction with collimation lens 4 and the catoptron 2 of second plane mirror 5 on same optical axis and form.During measurement, the near-infrared radiation that measuring light route infrared light supply 8 sends, through spherical reflector 7 reflection back imaging at light source 8 places, afterwards through collimation lens 9 with after being installed in interference filter element 10～13 (interference filter element adopts 4) on the chopper wheel 18, three-wavelength (measurement wavelength X _m, reference wavelength λ ₁With reference wavelength λ ₂) monochromatic near-infrared radiation ripple and the near-infrared radiation of all band λ through catoptron 14, condenser 16, cover glass 15 project on the measured object 17 successively, are converged on vulcanized lead (PbS) detector 3 by imaging object lens 1 via the irreflexive radiated wave of measured object.The near-infrared radiation that reference path is sent by infrared light supply 8, through plane mirror 6,5 and collimation lens 4 and after being installed in interference filter element 10～13 on the same chopper wheel 18, three wavelength (are measured wavelength X _m, reference wavelength λ ₁With reference wavelength λ ₂) monochromatic near-infrared radiation ripple and the near-infrared radiation of all band λ directly project successively on same vulcanized lead (PbS) detector 3 via catoptron 2.Detector 3 receives from the signal of measuring light path and reference path in proper order by the time partitioning scheme, and as shown in Figure 6, the phase receives 8 different signals weekly.Adopt this optical system, by to collection, the data processing of 8 photosignals with calculate the content or the concentration of the multiple composition of measured object.

If I _{λ m}, I _{λ 1}, I _{λ 2}, I _λWavelength X is measured in expression respectively _m, reference wavelength λ ₁, reference wavelength λ ₂Reflex to the photocurrent that photodetector 3 is exported with all band λ through measuring light path.I _{A λ m}, I _{A λ 1}, I _{A λ 2}, I _{A λ}Represent to be incident upon the photocurrent of photodetector 3 outputs respectively via reference path, then:

I _λm=I _st _λmr _λm(1-α _λmC)E _λmT _λm (1)

I _λ1=I _st _λ1r _λ1(1-α _λ1C)E _λ1T _λ1 (2)

I _λ2=I _st _λ2r _λ2(1-α _λ2C)E _λ2T _λ2 (3)

I _λ=I _st _λr _λ(1-α _λC)E _λT _λ (4)

I _aλm=k ₁I _st _λmE _λmT _λm (5)

I _aλ1=k ₁I _st _λ1E _λ1T _λ1 (6)

I _aλ2=k ₁I _st _λ2E _λ2T _λ2 (7)

I _aλ=k ₁I _st _λE _λT _λ (8)

In the formula: I _sThe luminous intensity of-light source;

t _{λ m}, t _{λ 1}, t _{λ 2}, t _λThe transmitance of-respective wavelength filter plate;

r _{λ m}, r _{λ 1}, r _{λ 2}, r _λ-measured object is to the reflectivity of respective wavelength;

α _{λ m}, α _{λ 1}, α _{λ 2}, α _λ-measured object composition is to the absorption coefficient of respective wavelength;

The content or the concentration of C-measured object composition;

E _{λ m}, E _{λ 1}, E _{λ 2}, E _λ-detector is to the photoelectric transformation efficiency of respective wavelength;

T _{λ m}, T _{λ 1}, T _{λ 2}, T _λ-detector is to the temperature coefficient of respective wavelength;

k ₁-reference light path and the scale-up factor of measuring the light path luminous flux.Order $E=k\frac{\frac{I_{\mathrm{\λ}1}}{I_{\mathrm{a\λ}1}}+\frac{I_{\mathrm{\λ}2}}{I_{\mathrm{a\λ}2}}}{\frac{I_{\mathrm{\λm}}}{I_{\mathrm{a\λm}}}}---\left(9\right)$

K-scale-up factor in the formula.With formula (1)～(3), (4)～(6) substitution formula (9) is because four signals of the measurement light path that detector receives and four signals in the reference path are all from same light source, through identical interference filter element, received amplification by same detector, obtain through arrangement $E=k\frac{(r_{\mathrm{\λ}1}+r_{\mathrm{\λ}2})-(r_{\mathrm{\λ}1}{\mathrm{\α}}_{\mathrm{\λ}1}+r_{\mathrm{\λ}2}{\mathrm{\α}}_{\mathrm{\λ}2})C}{r_{\mathrm{\λm}}(1-{\mathrm{\α}}_{\mathrm{\λm}}C)}---\left(10\right)$

This formula explanation signal intensity is only relevant with surface reflectivity, absorption coefficient and the concentration of measured object.

As seen this measuring method drift, light source ages and the light source color temperature that can eliminate devices such as electronic circuit automatically change in time and eliminate automatically since the aging and variation of ambient temperature of interference filter element to the influence of measurement result.

Because the variation of measured object quality (surface state, color, constituent etc.) causes the variation of measured object surface dichroism, causes r _{λ m}, r _{λ 1}, r _{λ 2}Change, thereby cause measuring error.Because this variation causes that measuring baseline tilts, and measures wavelength X by correct selection _m, reference wavelength λ ₁And λ ₂, can eliminate the influence of this error.As-kind of special case, make λ ₁And λ ₂Be positioned at λ _mBoth sides, and make λ _m-λ ₁=λ ₂-λ _mIn such cases, α _{λ 1}=α _{λ 2}, become r respectively because the measured object quality changes the reflection coefficient that causes _{λ 1}+ Δ and r _{λ 2}-Δ, so signal intensity E is constant.

Only when the concentration of composition in the measured object changed, signal intensity E changed in the formula (10).Therefore can reflect the variation of measured object constituent concentration exactly.

The computing formula of measured object constituent concentration is

Y=aX ³+ bX ²X=LgE in+cX+d (11) formula; (12)

A, b, c, d-undetermined coefficient.

Remove and measure wavelength X _m, reference wavelength λ ₁And λ ₂Increase in the native system measuring all band signal I of light path outward, _λAll band signal I with reference light path _{A λ}Measurement, the order $E_{}$ ${}_1=k_2\frac{I_{\mathrm{\λ}}}{I_{\mathrm{a\λ}}}=\frac{r_{\mathrm{\λ}}(1-{\mathrm{\α}}_{\mathrm{\λ}}C)}{K_1}---\left(13\right)$ When intensity is I ₀Extraneous near-infrared radiation measured object surface the time, intensity I _λIncrease, and I _{A λ}Constant, at this moment $E_{}$ ${}_1=K_2\frac{I_{\mathrm{\λ}}}{I_{\mathrm{a\λ}}}=\frac{r_{\mathrm{\λ}}(1-{\mathrm{\α}}_{\mathrm{\λ}}C)}{k_1}(1+\frac{I_a}{I_s})---\left(14\right)$ E ₁With I ₀Increase and increase, therefore can be used to judge the interference that has or not extraneous near-infrared radiation.If this occurs, the measurement result of this moment is unreliable, sends alerting signal, gets rid of the influence of disturbing.

Therefore this system can real-Time Compensation light source ages and the centre wavelength transmitance of the drift of the variation of colour temperature, power-supply fluctuation, electronic circuit, interference filter element change with the signal that the drift of temperature etc. causes with the drift of temperature, detector signal, the variation of measure signal intensity is only changed with the variation of constituent concentration, and promptly system has the adaptive function of optics.Measurement data is stable, good reproducibility, precision height.In addition system to external world the disturbing effect of near-infrared radiation also can discern and point out eliminating at any time.

Accompanying drawing 3 is reticle configuration synoptic diagram.Chopper wheel 18 is driven by motor 23, with 1000 rev/mins speed rotation.Interference filter element 10～13 is housed on the chopper wheel, and its center sees through wavelength and is respectively λ _m, λ ₁λ ₂And λ, wherein λ _mBe the absorbing wavelength of tested composition, λ ₁And λ ₂For not absorbing or absorb few wavelength.Make λ generally speaking _m-λ ₁=λ ₂-λ _m, λ is a band pass filter, seeing through wavelength is 0.8～2.6 μ m.19,20 is light emitting diode, and 21,22 is photoelectric receiving tube.In phase weekly, photoelectric receiving tube 21 receives 24 synchronizing signals, as the speed lockin signal of motor, by the 30 control motor uniform rotation of speed phase locking unit.Simultaneously, 8 signals producing behind three frequency division of 24 synchronizing signals are used for sampled signal.In phase weekly, photoelectric receiving tube receives 1 signal as reset signal, samples in order to control cycle.Photodetector 3 alternately receives the light signal of measuring light path and reference light path by the time partitioning scheme, receives 8 light signals in one-period, as shown in Figure 6.

Accompanying drawing 5 is signal processing system synoptic diagram.The task that signal processing system will be finished is to convert electric signal to via detector 3 and it is amplified by the light signal after absorption of sample, the scattering with without the light signal of sample.Signal by detector output amplifies through prime amplifier 24, and the output signal after the amplification is input to bandpass filter 25.The synchronizing signal that another route photoelectric receiving tube 21 produces is input to phase shifter 29 through after the bandpass filter 28.Amplify through low-pass filter 27 filtering again after multiplier 26 multiplies each other by the signal of phase shifter 29 outputs and the output signal of bandpass filter 25, obtain and the proportional phase sensitive detection direct current signal output of measured signal amplitude.

If signal V _s(t)=V _sCos (ω _sT+ θ _s) (15) reference signal is $V_R\left(t\right)=\frac{4}{\mathrm{\π}}\underset{n=0}{\overset{\∝}{\mathrm{\Σ}}}\frac{1}{2n+1}\cos \left[(2n+1)({\mathrm{\ω}}_{R}t+{\mathrm{\θ}}_R)\right]---\left(16\right)$ The two back of multiplying each other: $V_0\left(t\right)=\underset{n=0}{\overset{\∝}{\mathrm{\Σ}}}\frac{2V_s}{2n+1}\cos \left\{\right[{\mathrm{\ω}}_s\±(2n+1){\mathrm{\ω}}_R]t+[{\mathrm{\θ}}_s\±(2n+1){\mathrm{\θ}}_R\left]\right\}---\left(17\right)$ Work as ω _S=ω _RThe time, V ₀(t) produce a DC quantity in $\frac{2V_s}{\mathrm{\π}}\cos ({\mathrm{\θ}}_s-{\mathrm{\θ}}_R)$ , other are of ac, through after the low-pass filtering, and only remaining flip-flop.Thereby phase sensitive detection is output as $V_0\left(t\right)=\frac{2V_s}{\mathrm{\π}}\cos ({\mathrm{\θ}}_s-{\mathrm{\θ}}_R)---\left(18\right)$ Adjust two phase difference between signals (θ _S-θ _R), make it to equal 0, then V ₀(t) maximum output 2V is arranged _s/ π, this value has reflected the amplitude of signal linearly.

Spectral detection belongs to feeble signal to be handled, and total system comprises that phase-locked amplification, the locking of modulating motor speed etc. partly form.Through the signal V after the phase-locked amplification ₀(t) input to single-chip microcomputer via A/D converter, follow procedure calculates the concentration of material composition.

Fig. 7 is the microcomputer system block diagram.Microcomputer system is made of 80C198 single-chip microcomputer 32 and PC 31.Single-chip microcomputer is finished data acquisition, data processing, calculating and control function.Be connected with PC by RS-422 serial data communication mouth, send data to PC, single-chip microcomputer and a whole set of instrument are carried out telemanagement and control by PC.

When needs are controlled production run, be converted to 4～20mA electric signal by the constituent concentration value that calculates via Digital To Analog Convert DA1230, control signal as manipulater, realization is controlled the concentration of tested composition, thereby make controller be implemented in line traffic control to production run, to improve the quality of products, economical with materials reduces energy resource consumption.

The present invention compared with prior art has the following advantages and useful effect: because the present invention adopts Measuring method and the corresponding system thereof of two light path 8 light beams of four wavelength, not only realized material many The detection of composition or concentration, and the energy real-Time Compensation is because variation, the power supply ripple of light source ages and colour temperature The drift of moving, electronic circuit, the center wavelength transmitance of interference filter element are with drift and the spy of temperature Survey the device signal with the signal intensity that the drift of temperature etc. causes, make the variation of measure signal intensity only with one-tenth The variation of branch concentration and changing, namely system has optics self adaptation function. So measurement data is stable, Repeatability is good, precision is high. In addition system to external world the interference effect of near-infrared radiation also can at any time differentiate And prompting is got rid of. The present invention both had been applicable to the many of the solid materials such as powdery, graininess, sheet and fiber Plant constituent concentration and detect, also be applicable to the detection of slurry shape, paste and liquid material Multiple components concentration. In industry such as food, beverage, smelting, light industry, pottery, tobacco, medicine, papermaking, timber processing In be widely used. Measured constituent concentration and the thickness of material are irrelevant, and particularly suitable is in material The online contactless continuous measuring of composition.

Claims (4)

1, a kind of online near infrared material multicomponent measuring method, it comprises the near-infrared light source illuminator, the chopper wheel of interference filter element is housed, photodetector, signal processing system that the signal of photodetector output is handled and coupled computer system, it is characterized in that adopting the measuring method of four wavelength double light paths, eight light beams, its measuring process is as follows:

A. will measure the light signal of light path generation and the light signal of reference path generation respectively projects on the same photodetector successively;

B. in the one-period of chopper wheel, this photodetector alternately receives four modulated light signals that produce from four modulated light signals measuring that light path produces and reference path by the time partitioning scheme, and it is converted to eight electric signal respectively;

C. to above-mentioned eight electric signal amplify, filtering, phase-locked amplification, demodulation, be to be sent to computing machine after the digital signal via A/D converter with analog signal conversion;

D. calculate the concentration of measured object composition by being stored in calculation procedure in the computer storage.

2. according to the described a kind of online near infrared material multicomponent measuring method of claim 1, it is characterized in that the digital signal of computing machine with the measured object constituent concentration, via the D/A converter conversion, become 4～20mA electric signal output that the concentration of measured object composition is controlled.

3. one kind is adopted online near infrared multicomponent measuring instrument as claimed in claim 1, it comprises by a near-infrared light source and with this light source and is installed in spherical reflector on the same optical axis, collimation lens, the chopper wheel of interference filter element is housed, plane mirror, the illumination path that condenser is formed, by the imaging object lens, the measurement light path that photodetector and measured object are formed, signal processing that the signal of photodetector output is handled and coupled computer system, it is characterized in that also comprising a reference path, this reference path by with above-mentioned light source first plane mirror on the same surface level and be installed in this catoptron vertical direction on second plane mirror and form with the collimation lens and the catoptron of second plane mirror on same optical axis.

4. according to the described a kind of online near infrared multicomponent measuring instrument of claim 3, it is characterized in that adopting on the chopper wheel 4 interference filter elements.

Images