CN103471641B - A kind of temperature drift auto-correction method of current vortex sensor - Google Patents

Abstract

The invention provides a kind of temperature drift auto-correction method of current vortex sensor, the method is the equivalent inductance and the resistance that adopt certain impedance measuring circuit to obtain detecting coil simultaneously, utilize the relation of its inductance and electrical resistance temperature and measured change, eliminate the impact of temperature variation, extract actual measured change information.The eddy current sensor signals modulate circuit that the present invention is made up of impedance measurement module (4) and correction calculation module (5), achieves while the measured information of acquisition, automatic calibration, eliminates the impact of temperature variation.The present invention carries out temperature drift and corrects and do not increase extra probe, coil or temperature sensor, and temperature drift calibration result is remarkable, and have applied widely, structure simple, be easy to the plurality of advantages such as realization.Adopt the present invention to carry out temperature drift automatic calibration to monocoil electric vortex displacement sensor probe, its temperature drift coefficient generally can be reduced to less than 5nm/ DEG C from 500nm/ DEG C.

Description

A kind of temperature drift auto-correction method of current vortex sensor

Technical field

The present invention relates to current vortex sensor field, particularly relate to a kind of auto-correction method of Temperature Drift of Eddy Current Transducers.

Background technology

Eddy current displacement sensor adopts the inductive coil applying high frequency pumping to produce inductive loop in target conductor, distance change between detecting coil and measured target is converted to the change of inductive coil impedance (comprising inductance and resistance), signal conditioning circuit obtains displacement information by the change of measuring detecting coil parameter.Current vortex sensor is widely applied to the displacement of various industry spot and experimental study, vibration, angle and speed, or thickness, resistivity and temperature survey.Due to current vortex sensor self, the many advantages such as it is high that it has stability, and environmental pollution is insensitive, and operating temperature range is wide, and frequency response is wide, low price.For high-resolution displacement/vibration survey, because its price is low, affected by environment little, ratio capacitance formula displacement transducer has more advantage.

But due to the temperature coefficient of resistivity of detecting coil and target conductor very large, therefore the temperature coefficient of current vortex sensor is also very large, and this directly limit it measures occasion application at some accurate displacements.Therefore it is very important for correcting the temperature drift of current vortex sensor or compensate.

Current main compensation (correction) measure mainly contains: 1, increase differential compensation coil, such method adds volume and the complicacy of probe, also versatility is not possessed, temperature compensation can not be carried out to the different detections of a target, except compensating coil, also need, to differential winding, suitable sensor conductor face is also installed.2, the noninductive coil increasing noninductive same resistance value carrys out temperature sensor change and affords redress, the temperature drift that the temperature variation that this method can only eliminate detecting coil resistance itself causes, to the temperature drift of inductance, and the drift that the temperature drift of the resistivity of target conductor causes can not compensate.3. adopt temperature element to carry out measuring tempeature, realize the correction of temperature drift, although this method is feasible, but due to the temperature of the different parts of sensor inconsistent, need a lot of temperature element, and the temperature element increased adds a lot of lead-in wire, not only increases the complexity of Circuits System, also make the number of leads of the critical components such as probe add a lot, reduce the portability of sensor.In addition on the one hand, this temperature compensation does not possess versatility.4, the low resistance temperature drift alloy material coiling detecting coil adopting some precious metals to manufacture, this sonde configuration is the same with ordinary ultrasonic probe, but expensive.Although this method reduces the temperature drift of detecting coil itself, the also temperature drift that causes of uncontrollable target conductor, thoroughly can not eliminate the temperature drift of probe-goal systems, still there is very large temperature drift in such current vortex sensor.

Summary of the invention

The object of this invention is to provide a kind of auto-correction method of temperature drift of current vortex sensor, eliminate probe and the target temperature change impact measured on accurate displacement/vibration etc., the information of the measure physical quantities of acquisition reality.

The present invention is achieved through the following technical solutions:

A temperature drift auto-correction method for current vortex sensor, the method is passed through by the detection of a target, current vortex sensor probe, concentric cable, and the system of impedance measurement module and correction calculation module composition realizes, and implementation procedure comprises following steps:

Step 1), choose a general current vortex sensor probe comprising a detecting coil, or make the current vortex sensor probe that comprises a detecting coil; Current vortex sensor probe is connected to impedance measuring circuit by concentric cable, and the output terminal of impedance measuring circuit is connected to correction calculation circuit;

Step 2), design and produce an impedance measuring circuit, can record two independent parameters of detecting coil impedance: the information of resistance R and the information of inductance L, the information of resistance R and the information of inductance L of the detecting coil that impedance measuring circuit records use magnitude of voltage U respectively _land U _rrepresent;

Step 3), utilize existing current vortex sensor temperature coefficient measuring system and sensitivity measure system, record U _land U _ras follows with the relation equation of measured x and temperature T:

$\left\{\begin{array}{c}{U}_L=f_L(x,T)\\ U_R=f_R(x,T)\end{array}\right.---\left(1\right)$

Step 4), solve an equation (1) obtain measured x and T and measured value U _land U _robtain relational expression as follows:

$\left\{\begin{array}{c}x=g_L(U_L,U_R)\\ T=g_R(U_L,U_R)\end{array}\right.---\left(2\right)$

Step 5), the operation relation arranging correction calculation module make it consistent with the operation relation in expression formula (2), then it exports U _xnamely the measured x after representative correction, then measurement result is not acted upon by temperature changes, and can also obtain the information of temperature variation simultaneously.

Further, described impedance measuring circuit (4) can record two independent parameters of detecting coil (6) impedance simultaneously.Specifically utilize the complex impedance metering circuit that bridge diagram, differential amplifier (15) and the orthogonal lock-in amplifier of two-way (16) are formed, the real part of detecting coil (6) impedance and resistance R and imaginary part and inductance L can be recorded simultaneously, or record amplitude Z and the phase place A of impedance simultaneously.

Further, it is characterized in that, described correction calculation circuit is the ratio adding circuit be made up of gain adjustable amplifier and totalizer, or the computing module be made up of data acquisition and the IC that possesses complex digital calculation function.

Further, the probe of described current vortex sensor is air core coil probe, does not comprise magnetic core.

Further, the detection of a target material of described current vortex sensor is non-ferromagnetic conductive material.

Further, the drift that the temperature variation that the method corrects detecting coil and target conductor simultaneously causes, and do not need temperature element.

Further, the method is also applicable to have a measured eddy current sensor.

Further, described measured eddy current sensor is eddy current displacement sensor, and it is measured as displacement or vibration x; Or be current vortex film thickness measuring sensor, it is measured as conducting film thickness h; Or be current vortex sensor for measuring resistivity, it is measured as the electricalresistivityρ of metal material.

Further, less at range, when temperature variation is little, the relation of inductance L and resistance R and displacement x and temperature T can be thought linear, can describe by direct linear relation.

Principle of the present invention is: the present invention adopts demodulator circuit to measure resistance and inductance two parameters of detecting coil respectively, also can be amplitude and the phasing degree of impedance, or other two parameters that independently can represent coil impedance.The inductance of detecting coil and resistance are the function of displacement, and all vary with temperature again, be the function of temperature, therefore its inductance and resistance can regard the binary function of displacement x and temperature T as simultaneously.Record the inductance of detecting coil and the resistance value variation relation with displacement and temperature respectively.For the current vortex sensor of wide range, or the situation that range of temperature is larger, adopt polynomial expression to describe this relation.And for high-resolution small-range, precise displacement sensor, its operating ambient temperature variation range is little, in the temperature range of its whole measurement displacement range and work, inductance and resistance change are very little, therefore direct linear relationship can describe, record corresponding sensitivity coefficient.Because resistance and inductance have different sensitivity coefficients to displacement and temperature, therefore we can list two equations of resistance and inductance and displacement and temperature relation.Utilize this two equations, just can solve displacement x and temperature T two unknown quantitys.In actual measurement, according to the result of solving an equation in previous step, the relation of displacement x and temperature T and resistance R and inductance L can be obtained.As long as therefore set the parameter of correction calculation circuit (5), R and the L value that impedance measurement module records can be utilized, calculate the displacement measurement x of not temperature influence in real time, the information of temperature variation can also be obtained simultaneously.The resistance R of detecting coil and inductance L are all the functions of displacement and temperature, this relation for same group of probe and target, be unique, determine, and this relation has repeatability.The present invention is just based on this point, and the auto-compensation achieving eddy current sensor temperature drift corrects.

The present invention is compared with several temperature compensations described in background technology:

1, to have versatility good in the present invention, and structure is simple, does not increase extra hardware, does not change the structure of probe, do not need temperature element, only realized the automatic calibration of temperature drift by signal processing circuit.

2, the present invention intactly solves the temperature drift that probe coil and measured target cause.And mostly only eliminate the temperature drift of coil itself unlike said method, and the drift that measured target temperature variation causes cannot be reduced.

3, the present invention is creatively by measuring two parameters of inductive coil simultaneously, and utilize two parameters to the different sensitivity coefficients of displacement and temperature variation, obtain real displacement information, make the temperature drift of eddy displacement sensor can be low to moderate less than 5nm/ DEG C.

Accompanying drawing explanation

Fig. 1 is the eddy current sensor temperature drift corrective system schematic diagram that the present invention uses;

Fig. 2 is the sonde configuration of eddy current sensor;

Fig. 3 is the circuit structure of signal excitation and impedance measurement module;

Fig. 4 is the inductance of eddy current sensor detecting coil and the variation relation of electrical resistance displacement;

Fig. 5 (a) for inductance signal at different temperature with the relation curve of displacement; (b) for resistance signal at different temperature with the relation curve of displacement;

Fig. 6 is the circuit structure of correction calculation module: (a) analog operational circuit (b) digital operational circuit;

Fig. 7 (a) is for inductance and resistance signal are with the variation relation of displacement; B relation that () is inductance and resistance signal variation with temperature;

Fig. 8 (a) is for correcting the relation exported with displacement; B () is for correcting the relation exported with temperature;

Fig. 9 (a) is the temperature drift of the eddy current displacement sensor before correction; B () is for adopting the temperature drift of the eddy current displacement sensor after the inventive method correction;

When Figure 10 is impedance measurement, complex impedance makes the schematic diagram of Orthogonal Decomposition at corresponding coordinate system.

Description of reference numerals is as follows:

1: the detection of a target; 2: current vortex sensor is popped one's head in; 3: concentric cable; 4: impedance measurement module; 5: correction calculation module; 6: detecting coil; 7: coil protect shell; 8: probing shell; 9: epoxide-resin glue; 10: reference coil; 11: precision resistance; 12: signal source; 13: power amplifier; 14: phase shifter; 15: differential amplifier; 16: lock-in amplifier; 17: gain adjustable amplifier; 18: totalizer; 19: data acquisition (ADC); 20: digital signal processor (DSP).

Embodiment

Below to adopt the eddy current displacement sensor of bearing calibration of the present invention specifically to introduce embodiments of the present invention.

As shown in Figure 1, based on eddy current displacement sensor system of the present invention primarily of the detection of a target 1, current vortex sensor probe 2, concentric cable 3, impedance measurement module 4 and correction calculation module 5 form.The signal demodulating circuit part of the temperature drift self-correcting current vortex sensor of the present embodiment is primarily of signal source 12, and impedance measurement module 4 and correction calculation module 5 form.

First current vortex sensor probe 2 is made, as shown in Figure 2.Adopt the copper enameled wire of certain diameter on quartz glass tube, turn to detecting coil 6, detecting coil can turn to the shape of individual layer helix, also multilayer short solenoid type can be turned to, the number of turns is chosen and is wanted appropriate, coiling is as far as possible accurate, when ensureing that inductance is maximum, reduce wire resistor and stray capacitance as far as possible.The detecting coil 6 that coiling is good carries out sealing with DP460 epoxide-resin glue to be fixed, and screen layer and the inner core of two the end of a thread respectively with concentric cable 3 of coil weld together.The stainless-steel tube choosing appropriate length and diameter is fixed together through the quartz glass substrate glue of concentric cable 3 and detecting coil 6, forms probing shell 8.The axis that as far as possible ensures detecting coil and stainless-steel tube axis is it is noted that point-blank time bonding.In addition, the front end face of stainless-steel tube and the distance of coil are greater than the diameter of coil, thus avoid the electromagnetic field of coil to produce eddy current loss on stainless-steel tube.Next, coil protect gets up as coil protect shell 7 by the plexi-glass tubular of the suitable size of design processing, thus avoids detecting coil 6 in use procedure occur wearing and tearing and destroy.Epoxide-resin glue 9 is adopted to be filled with a sealing between probing shell 8 and detecting coil 6, coil protect shell 7.Finally epoxide-resin glue 9 is all used to fill, fix, seal in all gaps between probing shell 8 and concentric cable 3.Other one section of corresponding joint of welding of concentric cable 3, to be connected with signal conditioning circuit part.The length of concentric cable is with more short better when satisfied measurement needs.

Be illustrated in figure 3 a kind of embodiment of the impedance measurement module of detecting coil.Current vortex sensor will work, and needs the AC signal applying high frequency to encourage.When real work, our selecting frequency and the higher sine wave signal of range stability are as signal source 12, and the frequency of signal source is 1MHz.Due to eddy current sensor work time, need larger electric current to encourage, therefore also need a power amplifier 13 pairs of signal sources to carry out Current amplifier, so that as excitation signal energizes alternating current bridge.This alternating current bridge is primarily of detecting coil 6, and reference coil 10 and two precision resistances 11 are formed as sampling resistor.The parameter of bridge diagram element needs meticulously to select, so that circuit meets bridge balance condition.Two precision resistances 11 adopt 0.1% precision, the superhigh precision that temperature coefficient is less than 5ppm/ DEG C, the resistance of ultra-low temperature drift, and resistance is identical.For making this alternating current bridge balance, the parameter of detecting coil 6 and reference coil 10 need meet condition below:

$\left\{\begin{array}{c}{Z}_d=Z_r\\ {\mathrm{\φ}}_d={\mathrm{\φ}}_r\end{array}\right.$ Or $\left\{\begin{array}{c}{L}_d=L_r\\ R_d=R_r\end{array}\right.---\left(3\right)$

Subscript d in formula and r represents the parameter of detecting coil 6 and reference coil 10 respectively, and φ is the phase place of impedance.

First, the distance x of the equilibrium position between detecting coil and target be chosen ₀, then select suitable component parameters, make alternating current bridge in this position balance.Under normal circumstances, the equiva lent impedance Z of eddy current probe _effcan represent with following formula:

Z _eff＝[R _c+R _e(x,ρ,μ,f)]+jω[L _c+L _e(x,ρ,μ,f)](4)

In above formula, R _cand L _cbe respectively resistance and the inductance of coil itself.R _eand L _ebe respectively the impedance variation because the eddy current on the detection of a target causes.The impedance that this eddy current causes and probe target distance are from x, and the electricalresistivityρ of target conductor, magnetic permeability μ, frequency of operation f is relevant.The eddy current sensor probe that the present invention is used, adopt the AC signal excitation of fixed frequency, the detection of a target is non-ferromagnetic conductive material, relative permeability μ _r=1.For the detection of a target of commaterial, its electricalresistivityρ only changes with temperature.The resistance R of coil itself _cand inductance L _calso have certain temperature coefficient, change with temperature, therefore the equiva lent impedance of eddy current probe can be expressed as the function of displacement x and temperature T, as shown in the formula:

Z _eff＝[R _c(T)+R _e(x,T)]+jω[L _c(T)+L _e(x,T)]＝R(x,T)+jωL(x,T)(5)

As can be seen here, the real part R of detecting coil impedance is the function of displacement and temperature, and imaginary part L is also the function of displacement and temperature.It should be noted that, magnetic permeability due to ferrimagnet also affects impedance and the probe target transmission characteristic of coil, and the variation relation of magnetic permeability and temperature is usually all very complicated, and be not constant relation, can along with ferromagnetic environment, the magnetization etc. and changing, therefore be particularly limited to, the present invention the probe of current vortex sensor that is suitable for be air core coil, the material of the detection of a target is the conductive material of nonferromagnetic, its relative permeability is all 1, and does not change with temperature and other environmental factor.The real part R of detecting coil impedance and imaginary part L is the function of displacement and temperature, this relation for same group of probe and target, be unique, determine, and this relation has repeatability, can not arbitrarily change.This is the theoretical foundation that the present invention is achieved.

When not considering temperature variation, adopt high-precision electric impedance analyzer can record the resistance of eddy current probe and inductance with displacement variation relation as shown in Figure 4.As shown in Figure 4, the relation of the resistance of detecting coil and inductance and displacement is all nonlinear, is less than inside the very little scope of of probe radius sensitiveer in distance.Select suitable distance x ₀as probe and the equilibrium position of target, herein, alternating current bridge reaches balance.In general, equilibrium distance should be enough little, to improve the sensitivity of sensor to greatest extent, also will ensure that sensor can not collide with target in whole measurement range simultaneously.For most high resolving power eddy current displacement sensor, x ₀the 0.05-0.2 that can get probe radius r doubly, gets x in this example ₀=0.1r.Next, reference coil be made, make alternating current bridge reach balance.Equilibrium position place is recorded with electric impedance analyzer, at the operating frequencies, the equivalent resistance of probe and inductance.The resistance of the reference coil made is all consistent with probe with inductance, and electric bridge just can reach balance.First choose the constantan enameled wire of suitable diameter and length, make its resistance consistent with probe equivalent resistance.Then constantan enameled wire is wound on quartz glass bar, the direction of adjustment coiling and tightness degree, makes its inductance consistent with probe equivalent inductance, then use epoxide-resin glue fixing seal, be welded on signal conditioning circuit plate.The temperature coefficient of resistivity of constantan is very little, adds good packaging technology, and inductance and the resistance of the reference coil so made are all very stable, and the temperature coefficient of its resistance and inductance can reach less than 20ppm/ DEG C.

Impedance measurement module is primarily of differential amplifier 15, and phase shifter 14 and two lock-in amplifiers 16 form.The output signal of alternating current bridge is amplified by differential amplifier, then carries out demodulation by the lock-in amplifier that two-way is orthogonal respectively, thus obtains the resistance U of detecting coil _rwith inductance signal U _l.In general, the relation of the inductance of detecting coil and resistance and displacement is nonlinear, and as shown in Figure 4, and this resistance and inductance also vary with temperature.In actual measurement, in order to the convenience calculated, the funtcional relationship in formula (4) represents with following formula usually:

$\left\{\begin{array}{c}{U}_L=U_L(x,T)={\mathrm{\Σ}}_{i=0}^n{\mathrm{\Σ}}_{j=0}^m{p}_{\mathrm{ij}}{x}^i{T}^j\\ U_R=U_R(x,T)={\mathrm{\Σ}}_{i=0}^n{\mathrm{\Σ}}_{j=0}^m{q}_{\mathrm{ij}}{x}^i{T}^j\end{array}\right.---\left(6\right)$

In formula, n and m is the exponent number of the fitting of a polynomial chosen.P _ijand q _ijpolynomial coefficient, only relevant with the feature of concrete sensor.In theory, after perfect measurement goes out these coefficients, we can obtain the calculation expression of displacement x and temperature T.

$\left\{\begin{array}{c}x=x(U_L,U_R)={\mathrm{\Σ}}_{i=0}^n{\mathrm{\Σ}}_{j=0}^m{a}_{\mathrm{ij}}{U}_L^i{U}_R^j\\ T=T(U_L,U_R)={\mathrm{\Σ}}_{i=0}^n{\mathrm{\Σ}}_{j=0}^m{b}_{\mathrm{ij}}{U}_L^i{U}_R^j\end{array}\right.---\left(7\right)$

In fact, due to U _rand U _lbe all the binary polynomial function of x and T, want the coefficient in complete measure equation (6), and the coefficient calculated in x and T acquisition formula (7) of solving an equation, may realize hardly.In systems in practice, we adopt following method to calculate best displacement x and the calculation expression of temperature T.Temperature is not the amount that we are concerned about, is therefore only described to accurately calculate displacement x as far as possible herein.

Experimental provision is put in temperature control box, at m group temperature, measures U respectively _rand U _lwith the relation curve of displacement x as shown in Figure 5.Wherein temperature range [T ₁, T ₂] temperature range for allowing during working sensor, [x ₀-a, x ₀+ a] be the range of displacement measurement of sensor, the range of sensor is 2a.Because displacement x can be write as U _rand U _lpolynomial form:

$x=x(U_L,U_R)={\mathrm{\Σ}}_{i=0}^n{\mathrm{\Σ}}_{j=0}^m{a}_{\mathrm{ij}}{U}_L^i{U}_R^j---\left(8\right)$

Curve at each temperature of Fig. 5 is got n data point, substitute in formula 8, can calculate and use coefficient a accordingly _ijthe shift value represented.Adopt least square fitting, make the coefficient a that the error sum of squares of the shift value calculated by formula (8) is minimum _ijbe the multinomial coefficient in updating formula (8).

Correction calculation circuit 5 is set, makes its parameter consistent with coefficient in formula (8), the information of actual tested displacement can be obtained.This computing not only eliminates the temperature drift of sensor, but also corrects the nonlinearity erron of its displacement measurement.In the system of reality, n and m gets suitable value can ensure good correction accuracy, n and m gets too large, will increase the computation complexity of system, the real-time response of influential system.Calculate for such polynomial revise, correction calculation module should adopt digital operational circuit as shown in Figure 6 (b).By the computing formula in good DSP or MCU of programming, utilize the U that ADC collects _rand U _ldata, can directly calculate corresponding displacement x export.Same method, also can be used for accounting temperature information.

For the high-resolution position displacement sensor of most of real work, its range all very little (being only tens microns), when work, range of temperature also little (several degrees Celsius to tens degrees Celsius, this is for high-accuracy displacement measurement, is a necessary condition), in whole measurement range, inductance L and the resistance R variable quantity of detecting coil are all very little, and therefore the variation relation of inductance L and resistance R and displacement x and temperature T can be thought linear.Formula (6) above can be simplified to following form:

$\left\{\begin{array}{c}{U}_L=k_{11}x+K_{12}T+C_L\\ U_R=K_{21}x+K_{22}T+C_R\end{array}\right.---\left(9\right)$

K in formula _ijthe sensitivity coefficient being inductance and resistance to displacement and temperature, C _land C _rconstant, only relevant with equalized temperature working point with the displacement that system is chosen, can not consider.Solving an equation, (9) can to obtain the expression formula of displacement x and temperature T as follows:

$\left\{\begin{array}{c}x=K_1{U}_L+K_2{U}_R+x_0\\ T=K_3{U}_L+K_4{U}_R+T_0\end{array}\right.---\left(10\right)$

K in formula _ithe correction equation coefficient calculated, x ₀and T ₀for displacement balance point and the equalized temperature point of system, be constant for the system set, do not affect measurement result.

Concerning sensing system, we in isoperibol, in the shorter time, can apply the displacement of a linear change, record U _land U _rto the variation relation of displacement as shown in Fig. 7 (a), corresponding sensitivity coefficient K can be obtained thus ₁₁and K ₂₁.Because Measuring Time is enough little, adds and be in isoperibol, the drift therefore caused by factors such as temperature is negligible, and measurement can be satisfied the demand.After the displacement x of then fixation of sensor probe and target, system is put into a temperature control box, applying temperature variation, utilizes temperature element to record the temperature variation of whole process, and with U in data collecting card and the whole process of computer recording _land U _rchange.Whole process, temperature variation is relatively slower, thus ensures all parts thermally equivalent of sensor, and temperature unanimously changes.The U recorded _land U _rwith the variation relation of temperature T as shown in Fig. 7 (b), corresponding temperature coefficient K can be obtained thus ₁₂and K ₂₂.Bring equation (9) into, the correction calculation coefficient that can obtain in formula (10) of solving an equation.

For the situation of this linear operation, can directly adopt simple analog computing circuit as shown in Figure 6 (a) to realize, it is made up of the amplifier 17 of two adjustable gain and a totalizer 18.Regulate two-way gain adjustable amplifier 17, make its enlargement factor be respectively K ₁and K ₂, the output of totalizer is actual displacement information U _x, this result is not acted upon by temperature changes.Adopt same correction calculation module, corresponding coefficient is set, also can obtain the change information U of temperature _t.U _xand U _twith displacement and temperature variation relation as shown in Figure 7.

So far, a Low Drift Temperature based on temperature drift automatic correcting method, high-resolution eddy current displacement sensor has just been made.In order to check the validity of the method, we measure in the process of temperature variation 5 DEG C, the drift that sensor exports.(a) and (b) of Fig. 8 sets forth and adopt the method to correct front and back, the output shift of sensor.As seen from Figure 9, before correction, the drift of sensor is approximately 500nm/ DEG C, and after adopting our bearing calibration, coefficient of deviation only has about 2nm/ DEG C, reduces more than 200 times.The sensor made based on the present invention is for the resolution of Subnano-class, and there is so low temperature drift coefficient, in a lot of application scenario, condenser type or laser interference formula displacement transducer can be replaced, measure in application at accurate displacement and there is very wide prospect.

Description is above only that one of the present invention is comparatively simple, the good embodiment of effect.Illustrated temperature compensation is except being used in eddy current displacement sensor, can also be applied to any except temperature variation, only have the current vortex sensor that measured, as electric vortex sensor measuring conducting film thickness, measure the occasions such as conductor resistance rate.The present invention is the convenience described, and has been described in detail for eddy current displacement sensor, and other current vortex sensor hereinafter will do concise and to the point describing, and detailed embodiment, can with reference to the situation of eddy current displacement sensor above.

The relational expression of the equiva lent impedance of the detecting coil of the general current vortex sensor that formula (4) describes, for the situation measuring conductor resistance rate with current vortex sensor probe, the distance x of probe and target is fixed value, frequency of operation f is fixed value, the detection of a target is nonferromugnetic material, its relative permeability is 1, is also fixed value.Therefore the impedance of detecting coil can be write as following form:

Z _eff＝[R _c+R _e(ρ)]+jω[L _c+L _e(ρ)]（11）

Due to the detection of a target resistivity obviously and temperature correlation, the resistivity that we record is the resistivity under current target temperature, and this measurement result also can be subject to the impact of the inductance of probe itself and the temperature coefficient of resistance.In order to obtain specified temp T ₀the electricalresistivityρ of lower target ₀, formula above can be write as following form:

Z _eff＝[R _c(T)+R _e(ρ(T))]+jω[L _c+L _e(ρ(T))]（12）

Resistivity due to the detection of a target is material and temperature funtion, and its resistivity can be expressed as following form:

ρ(T)＝ρ ₀+f _ρ(T)(13)

F in above formula _ρfor the resistivity of this material and the funtcional relationship of temperature, therefore the detection of a target is at temperature T ₀under electricalresistivityρ ₀the amount relevant with temperature when measuring.Therefore, the equiva lent impedance of detecting coil can be write as following form:

Z _eff＝[R _c(T)+R _e(ρ ₀,T)]+jω[L _c(T)+L _e(ρ ₀,T)]＝R(ρ ₀,T)+jωL(ρ ₀,T)(14)

As can be seen here, the resistance of detecting coil and inductance are all the binary functions of detection of a target resistivity and temperature, adopt and displacement measurement in temperature drift correct same method, get final product the impact of the temperature variation in corrected resistivity measurement, obtain accurately under specified temp, the resistivity actual value of certain material.

For the situation of conducting film thickness measure, if the thickness of conductive film is less than the skin depth under current vortex sensor frequency of operation, so the thickness of conducting film is also an amount relevant with detecting coil impedance.Now, the equiva lent impedance of the detecting coil of current vortex sensor can be write as following form:

Z _eff＝[R _c+R _e(ρ,f,μ,t,x)]+jω[L _c+L _e(ρ,f,μ,t,x)](15)

When conducting film thickness measure, probe and target distance are fixed values, frequency of operation is also fixed value, the relative permeability of nonferromugnetic material is 1, it is fixed value, the resistivity of the detection of a target is the function of temperature, and the resistance of detecting coil and inductance are also the functions of temperature, and therefore formula (15) can be write as following form:

Z _eff＝[R _c(T)+R _e(t,T)]+jω[L _c(T)+L _e(t,T)]＝R(t,T)+jωL(t,T)（16）

As can be seen here, the resistance R of detecting coil and inductance L are all the functions of conducting film thickness t and temperature T, copy the temperature drift bearing calibration in displacement measurement, record resistance and inductance value by impedance measurement module simultaneously, and utilize the coefficient demarcated in advance, real film thickness can be calculated, and be not acted upon by temperature changes.The method can also be applied in the on-line monitoring system of the production line of some conductive films, by analyzing the resistance and inductance value that record, we can be real-time know, whether the temperature of the conducting film of production line and thickness meet production standard, any one parameter generation ANOMALOUS VARIATIONS, can monitor, and distinguish.

Similar with mentioned above three kinds of situations, in addition to temperature, only have the current vortex sensor that is measured, the inventive method can be adopted to carry out temperature drift correction, just do not repeat one by one, during enforcement at this, all can refer to the method, determine concrete temperature drift corrective action.

About the problem of impedance measurement, need slightly to remark additionally.In complex plane xoy as shown in Figure 10, impedance namely can be expressed as real part R and imaginary part ω L and, also uniquely can be determined by amplitude Z and phasing degree A, therefore the impedance measurement module in the present invention can measure real part and imaginary part, also amplitude and phase place can be measured, the temperature drift do not affected below corrects, and just corresponding coefficient there occurs change.Further, the two paths of signals that impedance measuring circuit records, neither amplitude and phase place, neither real part and imaginary part, do not affect the application of the inventive method yet.As in the coordinate system x ' oy ' in Figure 10, this impedance can resolve into Z ₁and Z ₂two coordinate components.Although Z ₁and Z ₂all neither the real part of this complex impedance or imaginary part, neither its amplitude or phase place, but Z ₁and Z ₂remain two amounts that can be used for complete this resistance value of expression, relevant relation can be expressed as follows:

$\tilde{Z}=R+\mathrm{\ωLj}=\left|Z\right|\∠A=Z_1{i}^{\text{'}}+Z_2{j}^{\text{'}}=(x_1+y_{1}j)i^{\text{'}}+(x_2+y_{2}j)j^{\text{'}}---\left(20\right)$

The vector of unit length of i ', j in formula ' be respectively x ' oy ' coordinate system two coordinate axis; x ₁, y ₁z respectively ₁component in xoy coordinate system two coordinate axis; x ₂, y ₂z respectively ₂component in xoy coordinate system two coordinate axis.As can be seen here, impedance circuit measure two amount Z ₁and Z ₂, be just equivalent to complex impedance to make Orthogonal Decomposition at corresponding coordinate system, in essence with real part and the imaginary part representation of impedance, and amplitude phase place representation is of equal value.Therefore, in the actual enforcement of the inventive method, impedance measurement module specifically measures which two amounts are unimportant, and this can affect corresponding sensitivity coefficient, can not impact bearing calibration and measurement result itself.In actual applications, can according to circumstances design corresponding impedance measuring circuit, if its can measure two independently can the amount of complete representation detecting coil impedance, just can meet this bearing calibration the thought that is suitable for.

Advantage and concrete improvement of bearing calibration of the present invention can also be:

This bearing calibration the probe that is suitable for adopt the electric vortex displacement sensor probe of conventional single coil, without the need to increasing any extra compensating coil.This bearing calibration is without any need for temperature-measuring element or temperature sensor.The coil resistance that this bearing calibration is obtained by two-way restituted signal and inductance signal realize.This bearing calibration does not need feedback element, the same with common eddy current sensor, and the impedance variation directly by measuring detecting coil obtains measured information.This bearing calibration not only compensate for the temperature drift of coil itself, comprises the temperature drift that target conductor causes and have also been obtained correction.This bearing calibration, can also correction of Nonlinear error while Tc drift.

The not disclosed in detail part of the present invention belongs to the known technology of this area.

Although be described the illustrative embodiment of the present invention above; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.

Claims (9)

1. the temperature drift auto-correction method of a current vortex sensor, the method is by popped one's head in by the detection of a target (1), current vortex sensor (2), concentric cable (3), the system that impedance measurement module (4) and correction calculation module (5) form realizes, and it is characterized in that implementation procedure comprises following steps:

Step 1), choose general current vortex sensor probe (2) comprising a detecting coil, or make current vortex sensor probe (2) that comprises a detecting coil; Current vortex sensor probe (2) is connected to impedance measurement module (4) by concentric cable (3), and the two-way of impedance measurement module (4) exports the input as correction calculation module (5);

Step 2), design and produce an impedance measurement module (4), can record two independent parameters of detecting coil (6) impedance: the information of resistance R and the information of inductance L, the information of resistance R and the information of inductance L of the inductive coil that impedance measurement module (4) records use magnitude of voltage U respectively _rand U _lrepresent;

Step 3), utilize existing current vortex sensor temperature coefficient measuring system and sensitivity measure system, record U _land U _ras follows with the relation equation of measured x and temperature T:

Step 4), solve an equation (1) obtain measured x and T and measured value U _land U _robtain relational expression as follows:

Step 5), the operation relation that arranges correction calculation module (5) makes it consistent with the operation relation in expression formula (2), then it exports U _xnamely the measured x after representative correction, then measurement result is not acted upon by temperature changes, and can also obtain the information of temperature variation simultaneously.

2. the temperature drift auto-correction method of a kind of current vortex sensor according to claim 1, it is characterized in that, described impedance measurement module (4) can record two independent parameters of detecting coil (6) impedance simultaneously, specifically utilize the complex impedance metering circuit that bridge diagram, differential amplifier (15) and the orthogonal lock-in amplifier of two-way (16) are formed, record the real part of detecting coil (6) impedance and resistance R and imaginary part and inductance L simultaneously, or record amplitude Z and the phase place A of impedance simultaneously.

3. the temperature drift auto-correction method of a kind of current vortex sensor according to claim 1, it is characterized in that, described correction calculation module (5) is the analog operational circuit be made up of gain adjustable amplifier (17) and totalizer (18), or the digital operational circuit be made up of data acquisition (19) and the microprocessor (20) that possesses complex digital calculation function.

4. the temperature drift auto-correction method of the current vortex sensor according to claim 1 or 2 or 3, is characterized in that, the probe of described current vortex sensor is air core coil probe, does not comprise magnetic core.

5. the temperature drift auto-correction method of current vortex sensor according to claim 1 and 2, is characterized in that, the measured target material of described current vortex sensor is non-ferromagnetic conductive material.

6. the temperature drift auto-correction method of current vortex sensor according to claim 1 and 2, is characterized in that, the drift that the temperature variation that the method corrects detecting coil and target conductor simultaneously causes, and without any need for temperature-measuring element.

7. the temperature drift auto-correction method of current vortex sensor according to claim 1, is characterized in that, the method is also applicable to have a measured eddy current sensor.

8. the temperature drift auto-correction method of current vortex sensor according to claim 7, is characterized in that, described eddy current sensor is eddy current displacement sensor, and it is measured as displacement or vibration x; Or be current vortex film thickness measuring sensor, it is measured as conducting film thickness h; Or be current vortex sensor for measuring resistivity, it is measured as the electricalresistivityρ of metal material.

9. the temperature drift auto-correction method of current vortex sensor according to claim 1, it is characterized in that, less at range, when temperature variation is little, the relation of inductance L and resistance R and displacement x and temperature T is thought linear, can describe by direct linear relation.