CN103471641A - Method for automatically correcting temperature drift of electrical vortex sensor - Google Patents

Abstract

The invention provides a method for automatically correcting temperature drift of an electrical vortex sensor. According to the method, a certain impedance measuring circuit is utilized to obtain the equivalent inductance and the resistance of a detection coil, the relationship, changing along with temperature and measurement, of the inductance and the resistance of the detection coil is utilized to remove the influence of temperature changes and extract actual measured change information. According to the method, signals of the vortex sensor composed of an impedance measuring module (4) and a rectification calculating module (5) is used for conditioning the circuit, so that to-be-measured information is obtained, rectification is conducted automatically, and the influence of temperature changes is removed at the same time. According to the method, when temperature drift is rectified, no extra probes or coils or temperature sensors are further arranged, and temperature drift rectification effect is remarkable. Moreover, the method has the advantages of being wide in application range, simple in structure, easy to implement and the like. When the method is used for automatically rectifying the temperature drift of a probe of the electrical vortex sensor, temperature drift coefficients can generally be reduced to below 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 the current vortex sensor field, relate in particular to a kind of auto-correction method of Temperature Drift of Eddy Current Transducers.

Background technology

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

Yet because the temperature coefficient of resistivity of detecting coil and target conductor is very large, so the temperature coefficient of current vortex sensor is also very large, this has directly limited it and has measured the application of occasion at some accurate displacements.Therefore it is very important the temperature drift of current vortex sensor being proofreaied and correct or compensated.

Current main compensation (correction) measure mainly contains: 1, increase the differential compensation coil, such method has increased volume and the complicacy of probe, do not possess versatility yet, can not carry out temperature compensation to the different detections of a target, except compensating coil, also need, to differential winding, suitable sensor conductor face also is installed.2, the noninductive coil that increases noninductive same resistance value comes the temperature sensor variation to afford redress, this method can only be eliminated the temperature drift that the temperature variation of 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 measure temperature, realize the correction of temperature drift, although this method is feasible, yet because the temperature of the different parts of sensor is inconsistent, need a lot of temperature elements, and the temperature element increased increases a lot of lead-in wires, not only increased the complexity of Circuits System, also make the number of leads of the critical components such as probe increase a lot, reduced the portability of sensor.On the one hand, this temperature compensation does not possess versatility in addition.4, adopt the low resistance temperature of some precious metal manufactures to float alloy material coiling detecting coil, this sonde configuration is the same with ordinary ultrasonic probe, but expensive.Although this method has reduced the temperature drift of detecting coil itself, the temperature drift that also uncontrollable target conductor causes, can not thoroughly eliminate the temperature drift of probe-goal systems, and still there is very large temperature drift in such current vortex sensor.

Summary of the invention

The auto-correction method that the purpose of this invention is to provide a kind of temperature drift of current vortex sensor, eliminate probe and target temperature and change accurate displacement/measured impacts such as vibration, obtains the information of actual measure physical quantities.

The present invention is achieved through the following technical solutions:

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

Step 1), choose the general current vortex sensor that comprises a detecting coil probe, or make a current vortex sensor probe that comprises a detecting coil; The current vortex sensor probe is connected to impedance measuring circuit by concentric cable, and the output terminal of impedance measuring circuit is connected to the 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 the resistance R of the detecting coil that impedance measuring circuit records and the information of inductance L are used respectively magnitude of voltage U _land U _rmean;

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 that the correction calculation module is set make it consistent with the operation relation in expression formula (2), its output U _xmeasured x after i.e. representative is proofreaied and correct, 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.The complex impedance metering circuit of specifically utilizing bridge diagram, differential amplifier (15) and two-way quadrature lock-in amplifier (16) to form, the real part that can simultaneously record detecting coil (6) impedance is that resistance R and imaginary part are inductance L, or records 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 consisted of gain adjustable amplifier and totalizer, or by data acquisition with possess the computing module that the IC of complex digital calculation function forms.

Further, the probe of described current vortex sensor is the 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 method has been proofreaied and correct the drift that the temperature variation of detecting coil and target conductor causes simultaneously, and does not need temperature element.

Further, the method also is 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 the conducting film thickness h; Or be the current vortex sensor for measuring resistivity, it is measured as the electricalresistivityρ of metal material.

Further, less at range, in the little situation of temperature variation, the relation of inductance L and resistance R and displacement x and temperature T can be thought linear, can directly with linear relation, describe.

Principle of the present invention is: the present invention adopts demodulator circuit to measure respectively resistance and two parameters of inductance of detecting coil, can be also 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, all varies with temperature again simultaneously, and be the function of temperature, so its inductance and resistance can be regarded the binary function of displacement x and temperature T as.Record respectively the inductance of detecting coil and the resistance value variation relation with displacement and temperature.For the current vortex sensor of wide range, or the larger situation of range of temperature, 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 can directly by linear relationship, describe, and record corresponding sensitivity coefficient.Because resistance and inductance have different sensitivity coefficients to displacement and temperature, so we can list two equations of resistance and inductance and displacement and temperature relation.Utilize this two equations, just can solve two unknown quantitys of displacement x and temperature T.In actual measurement, according to the result of solving an equation in previous step, can obtain the relation of displacement x and temperature T and resistance R and inductance L.As long as therefore set the parameter of correction calculation circuit (5), the R that can utilize the impedance measurement module to record and L value, calculate the not displacement measurement x of temperature influence in real time, can also obtain the information of temperature variation simultaneously.The resistance R of detecting coil and inductance L are all the functions of displacement and temperature, and this relation, for same group of probe and target, be unique, definite, and this relation has repeatability.The present invention just is being based on this point, has realized that the auto-compensation of eddy current sensor temperature drift is proofreaied and correct.

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

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

2, the present invention has intactly solved the temperature drift that probe coil and measured target cause.And mostly only got rid of the temperature drift of coil itself unlike said method, and can't reduce the drift that the measured target temperature variation causes.

3, the present invention is creatively by measure two parameters of inductive coil simultaneously, and utilize the different sensitivity coefficients of two parameters to displacement and temperature variation, obtain real displacement information, made the temperature drift of eddy displacement sensor can be low to moderate below 5nm/ ℃.

The accompanying drawing explanation

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

The sonde configuration that Fig. 2 is eddy current sensor;

The circuit structure that Fig. 3 is signal excitation and impedance measurement module;

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

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

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

Fig. 7 (a) is inductance and the resistance signal variation relation with displacement; (b) be the relation of inductance and resistance signal variation with temperature;

Fig. 8 (a) is for proofreading and correct the relation of output and displacement; (b) for proofreading and correct the relation of output and temperature;

Fig. 9 (a) is the temperature drift of the eddy current displacement sensor before proofreading and correct; (b) for adopting the temperature drift of the eddy current displacement sensor after the inventive method is proofreaied and correct;

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

Description of reference numerals is as follows:

1: the detection of a target; 2: the current vortex sensor probe; 3: concentric cable; 4: the impedance measurement module; 5: the correction calculation module; 6: detecting coil; 7: the 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

The eddy current displacement sensor that adopts bearing calibration of the present invention of below take is specifically introduced embodiments of the present invention as example.

As shown in Figure 1, based on eddy current displacement sensor system of the present invention, mainly by the detection of a target 1, current vortex sensor pops one's head in 2, concentric cable 3, and 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 mainly by signal source 12, and impedance measurement module 4 and correction calculation module 5 form.

At first make current vortex sensor probe 2, as shown in Figure 2.Adopt the copper enameled wire of certain diameter to turn to detecting coil 6 on quartz glass tube, detecting coil can turn to the shape of individual layer helix, also can turn to the short solenoid type of multilayer, the number of turns is chosen and is wanted appropriate, coiling is as far as possible accurate, in the situation that guarantee the inductance maximum, reduce wire resistor and stray capacitance as far as possible.The detecting coil 6 use DP460 epoxide-resin glues that coiling is good seal fixing, and screen layer and the inner core of respectively with concentric cable 3 of two the end of a thread of coil weld together.The stainless-steel tube of choosing appropriate length and diameter is fixed together with glue through the quartz glass substrate of concentric cable 3 and detecting coil 6, forms probing shell 8.It is noted that the axis that as far as possible guarantees detecting coil and stainless-steel tube axis in the time of bonding point-blank.In addition, the distance of the front end face of stainless-steel tube and coil is greater than the diameter of coil, thereby avoids the electromagnetic field of coil to produce eddy current loss on stainless-steel tube.Next, the plexi-glass tubular of the suitable size of design processing gets up coil protect as coil protect shell 7, thereby avoids detecting coil 6 in use procedure wearing and tearing occur and destroy.Between probing shell 8 and detecting coil 6, coil protect shell 7, adopt epoxide-resin glue 9 to fill sealing.Finally the gapped epoxide-resin glue 9 of all using of the institute between probing shell 8 and concentric cable 3 is filled, fixes, sealed.Other one section corresponding joint of welding of concentric cable 3, in order to partly be connected with signal conditioning circuit.The length of concentric cable is with more short better in the situation that meets the measurement needs.

Be illustrated in figure 3 a kind of embodiment of the impedance measurement module of detecting coil.Current vortex sensor will be worked, and the AC signal that need to apply high frequency is encouraged.When real work, the higher sine wave signal of our selecting frequency and range stability is as signal source 12, and the frequency of signal source is 1MHz.While working due to eddy current sensor, need larger electric current to be encouraged, therefore also need 13 pairs of signal sources of a power amplifier to carry out the electric current amplification, so that as the excitation signal energizes alternating current bridge.This alternating current bridge is mainly by detecting coil 6, and reference coil 10 and two precision resistances 11 form as sampling resistor.The parameter of bridge diagram element needs meticulously to select, so that circuit meets the bridge balance condition.Two precision resistances 11 adopt 0.1% precision, the superhigh precision that temperature coefficient is less than 5ppm/ ℃, and 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 following condition:

$\left\{\begin{array}{c}{Z}_d=Z_r\\ {\mathrm{\φ}}_d={\mathrm{\φ}}_r\end{array}\right.$ 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 mean respectively the parameter of detecting coil 6 and reference coil 10, the phase place that φ is impedance.

At first, choose equilibrium position between detecting coil and target apart from x ₀, then select suitable component parameters, make alternating current bridge in this position balance.Generally, the equiva lent impedance Z of eddy current probe _effcan mean 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 caused due to the eddy current on the detection of a target.The impedance that this eddy current causes with the probe target distance from x, 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, and 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 _ccertain temperature coefficient is also arranged, change with temperature, so 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, because the magnetic permeability of 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 not constant relation, can be along with ferromagnetic environment, the magnetization etc. and changing, therefore be particularly limited, the probe of the current vortex sensor that the present invention is applicable is air core coil, the conductive material that the material of the detection of a target is nonferromagnetic, its relative permeability is all 1, and with temperature and other environmental factor, does not change.The real part R of detecting coil impedance and imaginary part L are the functions of displacement and temperature, and this relation, for same group of probe and target, is unique, definite, and this relation has repeatability, can arbitrarily not 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 the variation relation of displacement 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, and a very little scope the inside that is less than probe radius in distance is sensitiveer.It is suitable for x to select ₀as the equilibrium position of probe and target, herein, alternating current bridge reaches balance.In general, equilibrium distance should be enough little, in order to improve to greatest extent the sensitivity of sensor, also will guarantee that sensor can not collide with target in whole measurement range simultaneously.For most high resolving power eddy current displacement sensor, x ₀can get the 0.05-0.2 of probe radius r doubly, get x in this example ₀=0.1r.Next, make reference coil, make alternating current bridge reach balance.Record the place, equilibrium position with electric impedance analyzer, under frequency of operation, the equivalent resistance of probe and inductance.The resistance of the reference coil of making is all consistent with probe with inductance, and electric bridge just can reach balance.At first choose the constantan enameled wire of suitable diameter and length, make its resistance consistent with the probe equivalent resistance.Then the constantan enameled wire is wound on quartz glass bar, adjusts direction and the tightness degree of coiling, make its inductance consistent with the probe equivalent inductance, then use the epoxide-resin glue fixing seal, be welded on the 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 of so making are all very stable, and the temperature coefficient of its resistance and inductance can reach below 20ppm/ ℃.

The impedance measurement module is mainly by differential amplifier 15, and phase shifter 14 and two lock-in amplifiers 16 form.Differential amplifier is amplified the output signal of alternating current bridge, then carries out demodulation by the lock-in amplifier of two-way quadrature respectively, thereby 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, for the convenience of calculating, the funtcional relationship in formula (4) means 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, the exponent number that n and m are 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 solve an equation and calculate the coefficient in x and T acquisition formula (7), may realize hardly.In real system, we adopt following method to calculate the calculation expression of best displacement x and temperature T.Therefore temperature is not the amount that we are concerned about, only take to accurately calculate displacement x as far as possible and describe as example herein.

Experimental provision is put in temperature control box, at m group temperature, measures respectively U _rand U _lwith the relation curve of displacement x as shown in Figure 5.Temperature range [T wherein ₁, T ₂] temperature range that allows during for 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:

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

Get n data point on curve at each temperature of Fig. 5, in substitution formula 8, can calculate the corresponding coefficient a that uses _ijthe shift value meaned.Adopt least square fitting, make the coefficient a of the error sum of squares minimum of the shift value calculated by formula (8) _ijbe the multinomial coefficient in updating formula (8).

Correction calculation circuit 5 is set, makes its parameter consistent with coefficient in formula (8), can obtain the information of actual tested displacement.The temperature drift of sensor has not only been eliminated in this computing, but also has proofreaied and correct the nonlinearity erron of its displacement measurement.In actual system, n and m get suitable value can guarantee good correction accuracy, and n and m get too large, will increase the computation complexity of system, affect the real-time response of system.For such polynomial expression correction calculation, the correction calculation module should adopt digital operational circuit as shown in Figure 6 (b).By the computing formula in the good DSP of programming or MCU, the U that utilizes ADC to collect _rand U _ldata, can directly calculate the output of corresponding displacement x.Same method, also can be used for accounting temperature information.

High-resolution position displacement sensor for most of real works, its range is very little (being only tens microns) all, in the time of work, also little (several degrees centigrade to tens degrees centigrade of range of temperature, this is a necessary condition for high-accuracy displacement measurement), in whole measurement range, the inductance L of detecting coil and resistance R variable quantity are all very little, so the variation relation of inductance L and resistance R and displacement x and temperature T can be thought linear.Top formula (6) 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 _ijinductance and the resistance sensitivity coefficient to displacement and temperature, C _land C _rbe constant, the displacement of only choosing with system is relevant with the equalized temperature working point, 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, for the system set, be constant, do not affect measurement result.

Concerning sensing system, we can in the shorter time, apply the displacement of a linear change in isoperibol, record U _land U _ras shown in Fig. 7 (a), can obtain thus corresponding sensitivity coefficient K to the variation relation of displacement ₁₁and K ₂₁.Because Measuring Time is enough little, add in isoperibol, the drift therefore caused by factors such as temperature can be ignored, and measurement can be satisfied the demand.Then after the displacement x of fixation of sensor probe and target, system is put into to a temperature control box, apply temperature variation, utilize 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 _rvariation.Whole process, temperature variation is slower, thereby guarantees all parts thermally equivalent of sensor, and temperature unanimously changes.The U recorded _land U _ras shown in Fig. 7 (b), can obtain thus corresponding temperature coefficient K with the variation relation of temperature T ₁₂and K ₂₂.Bring equation (9) into, solve an equation and can obtain the correction calculation coefficient in formula (10).

For the situation of this linear operation, can directly adopt simple analog computing circuit as shown in Figure 6 (a) to realize, it is comprised of two adjustable amplifier 17 and totalizers 18 of gain.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 the variation relation of displacement and temperature as shown in Figure 7.

So far, a Low Drift Temperature based on the 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 have measured in the process of 5 ℃ of temperature variation, the drift of sensor output.(a) of Fig. 8 and (b) provided respectively before and after employing the method proofreaies and correct the output shift of sensor.As seen from Figure 9, before correction, the drift of sensor is approximately 500nm/ ℃, and after adopting our bearing calibration, coefficient of deviation only has 2nm/ ℃ of left and right, has reduced more than 200 times.The sensor of making based on the present invention possesses the resolution of Subnano-class, and there is so low temperature drift coefficient, in a lot of application scenarios, can replace condenser type or laser interference formula displacement transducer, measure in application and there is very wide prospect at accurate displacement.

Description above is only that the present invention is a kind of simpler, and effect is embodiment preferably.Temperature compensation shown in the present is except being used in eddy current displacement sensor, can also be applied to any except temperature variation, only have a measured current vortex sensor, as electric vortex sensor measuring conducting film thickness, measure the occasions such as conductor resistance rate.The present invention is the convenience of narration, and the eddy current displacement sensor of take has been described in detail as example, and other current vortex sensor hereinafter will be done briefly to narrate, and detailed embodiment can be 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) is described, for pop one's head in to measure the situation of conductor resistance rate with current vortex sensor, the probe and target apart from x, be 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 resistivity of the detection of a target obviously and temperature correlation, the resistivity that we record is the resistivity at the current goal temperature, and this measurement result also can be subject to the impact of the temperature coefficient of the inductance of probe itself and resistance.In order to obtain specified temp T ₀the electricalresistivityρ of lower target ₀, top formula can be write as following form:

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

Because the resistivity of the detection of a target is material and temperature funtion, 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, so the detection of a target is in temperature T ₀under the electricalresistivityρ ₀it is the relevant amount of 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, same method is proofreaied and correct in temperature drift in employing and displacement measurement, get final product the impact of the temperature variation in the 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 the current vortex sensor frequency of operation, the thickness of conducting film is also an amount relevant with the detecting coil impedance so.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 the 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, so 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 the impedance measurement module simultaneously, and the prior coefficient of having demarcated of utilization, can calculate real film thickness, and not be acted upon by temperature changes.The method can also be applied in the on-line monitoring system of production line of some conductive films, the resistance recorded by analysis and inductance value, we can be real-time know, whether the temperature of the conducting film of production line and thickness meet production standard, any one parameter abnormal changes, can monitor, and distinguish.

Similar with three kinds of situations mentioned above, except temperature, only have a measured current vortex sensor, can adopt the inventive method to carry out the temperature drift correction, just not repeat one by one at this, during enforcement, all can, with reference to the method, determine concrete temperature drift corrective action.

About the problem of impedance measurement, need to slightly remark additionally.In complex plane xoy as shown in figure 10, impedance can be expressed as real part R and imaginary part ω L and, also can be come by amplitude Z and phasing degree A unique definite, therefore the impedance measurement module in the present invention can be measured real part and imaginary part, also can measure amplitude and phase place, the temperature drift that does not affect back is proofreaied and correct, and is that variation has occurred corresponding coefficient.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.In the coordinate system x ' oy ' in Figure 10, this impedance can be resolved 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:

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

I ' in formula, j ' is respectively the vector of unit length of two coordinate axis of x ' oy ' coordinate system; x ₁, y ₁respectively Z ₁component on two coordinate axis of xoy coordinate system; x ₂, y ₂respectively Z ₂component on two coordinate axis of xoy coordinate system.As can be seen here, two amount Z that impedance circuit is measured ₁and Z ₂, just be equivalent to complex impedance is made to 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, the 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 impedance of complete representation detecting coil amount, just can meet the applicable thought of this bearing calibration.

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

The applicable probe of this bearing calibration adopts the electric vortex displacement sensor probe of single coil commonly used, without 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 the two-way restituted signal and inductance signal are realized.This bearing calibration does not need feedback element, the same with common eddy current sensor, directly by the impedance variation of measuring detecting coil, obtains measured information.This bearing calibration has not only compensated the temperature drift of coil itself, comprises that the temperature drift that target conductor causes has also obtained correction.This bearing calibration, can also the correction of Nonlinear error in the Tc drift.

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

Although the above is described the illustrative embodiment of the present invention; 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 variations appended claim limit and definite the spirit and scope of the present invention in, these variations are apparent, all innovation and creation that utilize the present invention to conceive are all at the row of protection.

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, it is characterized in that implementation procedure comprises following steps:

Step 1), choose the general current vortex sensor that comprises a detecting coil probe (2), or make a 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 output of impedance measurement module (4) is as the input of 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 the resistance R of the inductive coil that impedance measuring circuit (4) records and the information of inductance L are used respectively magnitude of voltage U _rand U _lmean;

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 that correction calculation module (5) is set make it consistent with the operation relation in expression formula (2), its output U _xmeasured x after i.e. representative is proofreaied and correct, 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 measuring circuit (4) can record two independent parameters of detecting coil (6) impedance simultaneously, the complex impedance metering circuit of specifically utilizing bridge diagram, differential amplifier (15) and two-way quadrature lock-in amplifier (16) to form, the real part that can simultaneously record detecting coil (6) impedance is that resistance R and imaginary part are inductance L, or records 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 consisted of gain adjustable amplifier (17) and totalizer (18), or by data acquisition (19) with possess the digital operational circuit of microprocessor (20) formation of complex digital calculation function.

4. according to claim 1 or 2 or 3 described Temperature Drift of Eddy Current Transducers auto-correction methods, it is characterized in that, the probe of described current vortex sensor is the air core coil probe, does not comprise magnetic core.

5. Temperature Drift of Eddy Current Transducers auto-correction method 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. current vortex sensor temperature automatic drift according to claim 1 and 2 bearing calibration, is characterized in that, the method has been proofreaied and correct the drift that the temperature variation of detecting coil and target conductor causes simultaneously, and without any need for temperature-measuring element.

7. current vortex sensor temperature automatic drift according to claim 1 bearing calibration is characterized in that the method also is applicable to have a measured eddy current sensor.

8. current vortex sensor temperature automatic drift according to claim 7 bearing calibration 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 the conducting film thickness h; Or be the current vortex sensor for measuring resistivity, it is measured as the electricalresistivityρ of metal material.

9. current vortex sensor temperature automatic drift according to claim 1 bearing calibration, it is characterized in that, less at range, in the little situation of temperature variation, the relation of inductance L and resistance R and displacement x and temperature T can be thought linear, can directly with linear relation, describe.

Images