JP2911828B2 - Multi-parameter eddy current measurement system with parameter compensation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an eddy current sensor device, and more particularly to an apparatus using a single coil for simultaneously measuring a plurality of parameters of a conductive object.

[0002]

BACKGROUND OF THE INVENTION Eddy current sensors are well known in the art. These devices are used in various situations where it is desired to measure parameters such as separation or electrical resistance in a non-contact manner.
Eddy current sensors have been used to measure the displacement, electrical properties of a material, and other physical features that change the electrical properties of the material (eg, thickness and flaws).
One such application is the measurement of runout on magnetic steel rollers. in this case,
Eddy current sensor systems have been used to measure runner out on rollers, but their sensitivity to the typical permeability change in such rollers limits their accuracy. An eddy current sensor system is also used to measure the thickness of an aluminum can during molding. In the process of making the can, a carbide punch is used, and the aluminum cup is draw-formed through a series of dies to form a finished can. The centerline position of the punch affects the actual thickness of the can and, in conventional devices, may also affect the apparent thickness of the can.

[0003] Thickness sensing using eddy currents is already performed in the prior art, and some prior art devices adjust the circuit impedance so that the system is insensitive to distance. included. This system generally uses a typical three coil eddy current configuration with one driver coil and two pickup coils. The driver coil excites the material by the AC magnetic field, and the pickup coil detects a change in impedance caused by the eddy current induced in the material. Since this technology uses three coils, the manufacturing cost is relatively high, and if not operated within a limited range, errors due to lift-off (separation of the sensor from the object to be measured) can be reduced. Still sensitive. Other devices use eddy current sensors to detect cladding thickness with a single coil, but are still sensitive to errors resulting from lift-off. In order to distinguish thickness variations from other effects, devices with multiple frequencies have been developed, but the two frequencies require high cost and complicated circuitry to implement.

Other devices for measuring thickness with an eddy current device use the orthogonal impedance output of an eddy current sensor to determine lift-off from the surface of the object to be measured and compensate for the same. Lift-off errors are corrected by physically moving the sensor to a particular impedance and measuring its quadrature impedance component. However, this design has some inherent problems. For example, the servo system must physically (moving) the sensor to position it, which limits the availability of the device, such as inability to use it at high speeds, limited placement, and severe restrictions on the environment in which the device is used. There is a demand for significant inhibition. Furthermore, for proper operation, the impedance signal components (real and imaginary) must be completely orthogonal.

[0005] In general, known devices are configured such that only one parameter can be measured, usually another parameter being dependent on this parameter. For example, the apparatus and method disclosed in U.S. Pat. No. 4,290,017 discloses an oscillator with an amplifier for providing gain.
And a feedback loop connecting the input and output of the amplifier, and the level and frequency of the oscillator signal connected in the loop are adjusted according to the eddy current induced on the surface of the sample to be measured. A port ferromagnetic resonator. A variable attenuator is provided, which is connected to a feedback loop to adjust the power level of the oscillator. Also provided is an adjustable phase shifter, which changes the overall phase shift of the signal in the loop. Also provided is a probe connected to the circuit, which operates in transient mode (t
In ransition mode), it responds to the electromagnetic field generated by the eddy current. The probe comprises a ferromagnetic crystal with an outer circuit loop surrounding the crystal and an inner circuit loop surrounding the crystal orthogonal to the outer loop. This device (U.S. Pat. No. 4,290,017) is capable of measuring both magnitude and phase changes in the signal of the system and can independently measure the real and imaginary parts of the impedance of the circuit.

US Pat. No. 4,727,322 discloses a method and apparatus for measuring system parameters, such as the thickness of a workpiece, by means of eddy currents generated in the workpiece as a result of bringing the probe close to the surface. doing. The sensor in the probe measures two orthogonal components of complex impedance. In operation of the device according to US Pat. No. 4,727,322, the sensor is moved in the direction of the workpiece until one component of the impedance reaches a predetermined value and the characteristic value is measured as the value of the other component. The first component is selected during calibration as the element that is most sensitive to changes in the distance between the sensor and the measured object.

The apparatus disclosed in US Pat. No. 3,358,225 details a lift-off compensation technique for eddy current meters. The device includes an impedance bridge, which has one generator operating at a constant frequency and voltage. The device compares the impedance of an eddy current probe located in close proximity to a conductive sample with the standard impedance associated with the probe, and separates the output of the unbalanced reactive and resistive components of the impedance bridge from each other. Used to supply to. The apparatus includes a mechanism for selecting a predetermined portion of one output, combining it with the other output, providing a signal connected to a reader, and indicating the thickness of the sample under test.

An eddy current non-contact sensor is also disclosed in US Pat.
No. 3,619,805, and a eddy current surface mapping system shown in U.S. Pat. No. 4,755,753 for detecting defects in an object to be measured. U.S. Patent No.
The eddy current defect detection systems of 3,718,855 and 3,496,458 rely on a single coil in their sensing sensor probe. Another example of a single probe device is found in a device that supports eddy current probes used to scan (scan) irregular surfaces (US Pat. No. 4,644,274). This U.S. Patent No. 4,438,754
The electromagnetic system found in the signal is used to detect and remotely control the spatial relationship between the instrument and the device under test. The system is based on a magnetic device positioned opposite the instrument and the object to be measured, such that magnetic flux passes between the magnetic elements through the surface of the object to be measured.

These conventional devices generally have the disadvantage of requiring a plurality of coils and frequencies, or the inability to simultaneously measure different parameters (such as the thickness of the material or the degree of separation). Using only a single coil,
It is desirable that the eddy current device be able to measure two parameters simultaneously, and the system of the present invention aims to approach such an invention.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a measurement system for simultaneously measuring two parameters (eg, thickness and displacement) using one eddy current sensor coil operated at one fixed frequency. It is in.

It is another object of the present invention to provide a system of the above type which is relatively insensitive to changes in the electrical properties of the material.

[0012] Still another aspect of the present invention is that the output signal is located at a specific point in the system impedance plane.
(map to unique points) To provide a system of the type described above.

It is yet another object of the present invention to provide a system of the above type for orthogonalizing electrical output signals so that more than one variable can be sensed.

It is yet another object of the present invention to provide an apparatus of the type described above which can measure temperature and can use this as a correction factor for other measured parameters.

Still another aspect of the present invention is that a single sensor can measure in a limited space, in a harsh environment, with a relatively simple electronic device, and still maintain good sensitivity to measurement parameters. An apparatus of the type described above is provided.

According to the present invention, a method for measuring physical parameter characteristics (parameters include material, thickness, temperature, magnetic permeability, and conductivity) of an object to be measured includes an electric component characterized by system electric parameters. And providing an excitation circuit having an excitation circuit impedance defined by the system electrical parameters.

The method also includes providing a sensor having an electrical coil of a preselected diameter. The coil is located at a selected separation distance from the measured object. An excitation signal of one preselected angular frequency is generated in the coil, and the angular frequency is such that the effective product of the magnetic permeability and resistivity of the DUT and the separation distance is located at a point on the excitation circuit impedance plane. Is selected in advance. The method includes the steps of measuring the amplitude (magnitude) of the voltage of the excitation signal, measuring the phase of the excitation signal, generating a signal indicating a point on one excitation circuit impedance plane, one or more desired ones. Generating a signal indicative of the calculated value of the parameter.

[0018]

Embodiments of the present invention will be described below.

As mentioned above, eddy current sensors have been used in a variety of applications, but in general, eddy current sensors are designed to be highly sensitive to one particular parameter, such as distance. I have. The present invention knows a number of parameters, such as thickness and distance, simultaneously and uses the results of one measurement method to compensate for the undesired sensitivity of another measurement. An advantage of the present invention is that it uses one low cost sensor coil and avoids switching the sensor frequency to another frequency. Further, the system has the ability to correct the value of one parameter with the value of another parameter, resulting in excellent accuracy. It is also possible to detect the temperature, so that it can be used as a third correction factor for other parameters.

In general, three major parameters can be sensed by the present system, which are electrical properties, thickness, and distance. The detection by the eddy current sensor is determined by a constant expressed by the product of r ² ωμσ. The parameter “r” indicates the radius of the coil whose configuration can be changed, and is a constant in the present embodiment. The parameter of “ω” is an angular frequency of a current or a voltage used to excite the coil, and can be changed in the present embodiment, but is generally a constant to simplify a connected circuit configuration. is there. “Μ, σ”
Are the magnetic permeability and conductivity of the material. The effective conductivity of the material sensed by the eddy current sensor is determined by the target material or target geometry.
Note that it depends on the thickness of the try). Therefore, the thickness of the material can be determined if the actual values of μ and σ are constants.

The present system measures the thickness of an object to be measured without requiring a standard three-coil configuration. Stated another way, only one coil is used, and there is no need to make the impedance components orthogonal. Sensing distance (or displacement) by using eddy current sensors is another typical application of the system. A system for detecting a distance detects a change in inductance and resistance, or a system that combines both parameters (for example, Q
Value, Q = ωL / R). In general, these known systems rely on properties of the material that are always constant. Material properties that are always constant are desirable because their material properties affect the output signal results.

It has been recognized in the present invention that, under certain distances and certain electrical characteristics, the impedance of the system is at a particular point in the complex impedance plane. In some arrangements, the parameters can be decomposed into mathematically orthogonal equivalents, such that one parameter is a function of another. However, under other circumstances, such analysis is hampered. Regardless, a signal indicative of the impedance of the system will be mapped to a particular point in the impedance plane as a particular set of variables. The output signal corresponds to the real and imaginary impedance portions, phase and magnitude, or other impedance combinations. The set of variables or parameters corresponds to thickness and distance, or material properties and distance.

The scaling parameter described above as r ² ωμσ is commonly used in conventional systems as a means to determine the characteristics of the impedance output and is appropriate for certain materials. However, r, ω,
Even if the impedance characteristics are determined by μ and σ, since the relative magnetic permeability of the material is not unitary, if only the product of these parameters is used as the scaling parameter, very little accuracy can be expected. This means that the factors are complex and difficult to represent by analysis, and are often optimized by numerical analysis.

As a result, the present system can be readily used in steel roller runout or can thickness measurement applications as described above. The system allows for the measurement of the run-out of a steel roller that is insensitive to changes in magnetic permeability within the roller.
In the present invention, the thickness of the can is ascertained simultaneously with the measurement of the centerline position of the punch, thus not only helping in controlling the thickness, but also compensating for the apparent thickness error caused by the repositioning of the punch. Can also be used.

A schematic wiring diagram of a system having a sensor arrangement provided by the present invention is shown in FIG. The system 10 includes an electrical control circuit component 12 that provides an excitation signal to the sensor 16 via line 14. The sensor 16 includes a sensor body 18
And sensor coil 2 arranged at the end of sensor body 18
0. The sensor coil 20 is connected to the object 2
2 is located.

The measured object 22 includes a base 24 and an outer cladding 26. The system can be configured to measure a "lift-off" 28, which corresponds to the gap between the sensor and the workpiece.

The change in impedance of the sensor is a function of several parameters including the excitation signal frequency (ω), the average radius of the sensor coil (r), and the conductivity of the target material (σ). One skilled in the art will recognize that conductivity is simply expressed as 1 / ρ, and “ρ” (low) is resistivity. The magnetic permeability (μ) of the material to be measured and the distance (d) to the object are also factors. If the frequency and diameter are fixed, the impedance will change with σ, μ, or d. Given the diameter of the sensor coil, one can use known numerical methods to find the frequency such that the coil is sensitive to the combined product of σ and μ and d. This frequency depends on the combination of the parameters σ and μ mainly affecting the complex impedance phase, while
The parameter d mainly affects the amplitude (magnitude) of the complex impedance output and can be changed so as to be independent of each other. The relative permeability is uniform, ie, μr =
For one material, the coil frequency is related to the product of σ and μ and d. "Combinations" of σ and μ and d optimized using numerical methods in other situations
Is referred to below as the “effective product”. As mentioned above, the impedance of the real and imaginary parts is mathematically related to the phase and amplitude (magnitude) of the impedance output, and therefore either variable may be used.
Finding a particular frequency is not a requirement, but generally finding a particular frequency is possible because the two effects (phase and magnitude (magnitude) of the impedance output) can be mathematically sorted out. desirable.

The present invention can also perform temperature compensation. If the material parameters (eg, thickness, σ or μ) are constant, the temperature change will cause the sensor coil series resistance to change in proportion thereto. The resistance change appears as a change in the real part of the complex impedance. Correction of temperature change
Therefore, by recognizing that a particular temperature and distance is also located at a particular point on the complex impedance plane,
Can be done. The above technique is used to compensate for temperature changes in distance measurements.

FIG. 2 graphically illustrates the effect of electrical properties and distance on normalized impedance using a known method of numerical analysis. Vertical axis 2 (of the graph)
9 corresponds to the normalized imaginary part coil impedance, and the horizontal axis 30 corresponds to the normalized real part impedance of the sensor coil. Curves 31, 3 shown in FIG.
Reference numerals 2, 34, and 36 indicate cases where γ, σ, μ, ω, and d (displacement) take specific values. The distance is set to infinity at point 38, while the curves 40, 42, 44, 46 correspond to lines of constant displacement. Heading 48 lists the value of ρ (low) in μOhm cm for each material curve.

To generate the proper impedance, the following steps must be performed. First,
A particular set of parameters, or measurement "goals", must be determined as follows.

1) Material (insensitivit of material)
Create a displacement output signal that is not affected by y)).

2) Create an output signal proportional to the resistivity of the material.

3) Create a resistivity output signal and a displacement output signal.

4) Create an output signal proportional to the magnetic permeability.

5) Create an output signal proportional to magnetic permeability and displacement.

6) Create an output signal proportional to the thickness.

7) Create an output signal proportional to thickness and displacement.

8) Create an output signal proportional to temperature and displacement.

9) Create an output signal proportional to temperature and σμ (effective product).

Once one of the above parameter sets has been selected, there are other things that may be supplemented in finding the optimal solution. For example, when compensating for small changes in parameters (for example, when different plating is performed on the same material), a large change in parameters (for example, a change between completely different materials) may be supplemented by this supplement. This is an example. In the example shown in FIG.
This system uses aluminum (ρ = 3.3 μOhm c
m), hafnium (ρ = 30 μOhm cm), stainless steel (ρ = 60 μOhm cm), and inconel (ρ = 30 μOhm cm)
120 μOhm cm). The system configured to form the curves of FIG. 2 has a thickness (of the object to be measured) of 0 to 0.10 cm.
To generate a linear displacement output signal that is not affected by the material of the object to be measured. It should be noted that the teachings of the present invention can be applied to any of the above set of parameters, as well as other conductive materials.

The present system also requires that a particular geometry of the coil be selected. Generally, it is desirable for the coil to have a small diameter, a high Q value, and a low manufacturing cost. The geometry of the coil used to form the curve of FIG. 2 is 0.17 cm inner diameter, 0.38 cm outer diameter, and 0.25 c long.
m, the magnet wire is wound 640 times. In the system, these variables are provided to form an impedance plane. A particular frequency (ω) must be chosen so that it is sensitive to electrical parameters and very sensitive to displacement, and shows a substantially linear output (in the graph). In this system, it is not required that the output be linear when the output signal is generated, which simplifies post-processing of the output signal. Typical frequencies of the signal are between 5 KHz and 10 KHz. The frequency parameters are iterated by the algorithm executed by the system until all parameters of the system have acceptable sensitivity. The algorithm used is one that implements well-known equations using numerical methods. The output from the algorithm used here is graphed to show the relationship between the real part and the constant part for different parameters of displacement and resistivity.

As shown in FIG. 2, for a particular coil geometry where the temperature, frequency, displacement (or lift-off), and the combination of resistivity and permeability are all constant, the constant displacement There is a specific point on the impedance plane that defines the (lift-off) curve. If two of the unknown parameters (eg, resistivity /
If only the combination of permeability and displacement, thickness and displacement, etc. change, then in general the impedance between a particular set of output parameters (eg, displacement and resistivity, etc.) in relation to coil geometry and operating frequency One particular point on the plane is found to correspond.

The preferred embodiment of the present invention shown in the figures
This is illustrated in more detail in FIG. The electronic diagram path 12 of the present system has a transmitter (oscillator) 50, and the oscillator 50 is an impedance network.
52, eddy current sensor 16 and generally parallel resonance (parallel
el resonating) Drive the capacitor 54. Oscillator 50 is driven at a predetermined frequency (W) and amplitude (ZrLO °) and, when measured at 0 degrees, generally excites the impedance net through a series of capacitors. The impedance network, the parallel capacitance and the frequency of the oscillator are chosen to optimize the change in amplitude and phase of the drive signal (ZsLφ °) at the sensor to the oscillator, based on the measurement objectives described above. The sensing signal is provided on line 56 and demodulated by amplitude sensing circuit 58 and phase sensing circuit 60 to produce independent amplitude and phase output signals on lines 62 and 64, respectively. These signals are sent to analog-to-digital converters 66, 68 before being sent to processor 70, so that
The signals used for processing by the processor 70 are the amplitude output signal and the phase output signal (each independently) from the sensor. These signals are processed to provide either digital or analog output signals on line 71 (associated with at least one of the parameters being measured). It will be apparent to one skilled in the art that analog processing may also be used.

The impedance network and the parallel capacitance are chosen such that the (resulting) sensor impedance has a component that translates into the phase and amplitude planes. In the general case, the measured effects need not be orthogonal in the phase and amplitude planes. Rather, if the phase and amplitude coordinates can be translated parallel to resistivity (or other parameters such as thickness) and displacement using a look-up table or a numerical method, then the impedance component may be at a particular plane. It is necessary to be located corresponding to one point. However, by using the numerical analysis (at this time), the phase and amplitude of the output signal have special characteristics (linear displacement, relative stability of temperature, phase effect and amplitude effect are almost orthogonal).
The resonant capacitance and impedance network can be selected to have If the features in phase and features in amplitude are orthogonal, the processing is much easier because the two signals have little effect. As one example, one output signal may be related to distance and the other output signal may be related to material characteristics. However, if one of the parameters is independent and the other parameter is dependent on this independent parameter, the solution is more likely to be obtained. That is, in this case, the solution is much easier to obtain than when the parameters are independent.

To form the curves shown in FIGS. 4 and 5, the impedance network consists of a series of resistors (100Ω) and capacitors (1250 pF). The parallel capacitor is 5000 pF and the sensor has a DC resistance of 45Ω as described above. With this configuration, the displacement appearing mainly in the voltage magnitude of the output signal is measured, and the phase voltage (phase volt) is mainly measured.
age) has the effect of resistivity occurring. In FIG. 4, axis 72 corresponds to the phase voltage, while
The axis 74 shows the magnitude of the voltage of the output signal. The heading 76 indicates different types of materials by their resistivity values. Thus, curves 78-84 show displacement as a function of resistivity. Using the same data and a curve specified by the thickness of each material (see heading 97), FIG.
Can be graphed as a group of displacement curves 86-96 shown in FIG. Again, a particular point on the phase and magnitude plane is shifted to a particular displacement and resistivity.

A group of displacement curves 98-104 formed by the phase voltages measured at several displacements are shown in FIG.
Is shown in FIG. The heading 106 indicates the resistivity of each material. Note that the phase of the output signal relative to the material is relatively independent of displacement, but not completely independent. A simple voltage comparator circuit may be added to the processor circuit of the preferred embodiment to select and identify the material in the experiment.

FIG. 7 illustrates the magnitude of the voltage of the output signal in comparison with the displacement of the sensor. Curve 1
The output signal of 07-112 is characterized by an offset shift for the various materials whose resistivity is indicated in the heading 114. Using the information from the phase voltage to determine the material, the system generates an offset correction signal in a known manner, and the offset correction signal
A displacement output signal that is added to the signal of −112 to be relatively unaffected by the material is created, and at the same time, an output signal that identifies what the material is is created.

The present invention includes another alternative to the system described above. As described above, in the can manufacturing process, punches are used to stretch the aluminum cup body through a series of molds to form a completed can body. The change in punch thickness occurs over a slightly longer period of time as compared to the change in can thickness caused by mold wear and other factors. In addition to the thickness of the can, it is desirable to know the position at which the center line of the punch moves during the above manufacturing process. The structure of the sensor shown in FIG. 8 makes it possible to measure both the thickness of the can and the position at which the center line of the punch moves at the same time, and thus has several advantages over the structure of the sensor described in connection with FIG. It is advantageous in the point.

FIG. 8 shows a pair of opposed sensors 116,
A differential sensor assembly 114 comprising 118 is shown, with two sensors 116, 118 facing a substrate 120 shown in cross-section. Substrate 120
Includes a cladding 122 and a cladding 122
Are received on the outer surface of the punch 124. Line 12
The sensor output signals provided at 6,128 correspond to displacements and are derived from the magnitude of the voltage of each output signal. These signals are differentially combined to create one differential output signal, which is used to calculate the centerline position of the punch. The differential output signal is not significantly affected whether or not the can is there,
Therefore, the present invention is advantageous in this point because the position of the center line of the punch can be measured more accurately. The embodiment of the differential sensor of FIG. 8 also results in a more stable and more orthogonal output signal, which is a phase output signal that is used to measure thickness. It has enough magnitude to be used for lift-off correction.

FIG. 9 shows a first embodiment provided according to the present invention.
FIG. 9 is a simplified schematic diagram of a sensor system as a variation of FIG. System 130 is substantially identical to the system shown in FIG. 1 and includes control circuit components 132 that provide an excitation signal to sensor 136 via line 134.
Inside the sensor 136, a sensor coil 138 is disposed such that one end thereof is adjacent to the measured object 140. The object to be measured 140 includes a base 142 and the outer clatting 14.
4 inclusive.

The system 130 includes a second sensor 146 that receives an excitation signal from the controller via line 148.
Is further included. The sensor 146 is arranged at a distance from the measured object 140 and is not electromagnetically affected by the measured object 140. However, the second sensor 146 does not
It is positioned to be in substantially the same environment as sensor 136, and thus at the same time and at the same temperature as first sensor 136. Accordingly, the signals of the first sensor 136 and the second sensor 146 can be used to eliminate any drift in signal value caused by temperature variations. Second
The signal from the coil of the sensor at a greater distance from the object 140 is received by the controller. A control circuit component 132 having a controller provides compensation (co) achieved by comparing the impedance of the signal from the second coil to the signal from the first coil near the substrate surface.
mpensation term). Hence, any signal drift in the first sensor 136 caused by temperature fluctuations is eliminated. In this configuration, the multiple coils of the present invention are used, but not in the same manner as in prior art devices. Instead of using a set of coils consisting of an excitation coil and a sensor coil as in the prior art, the present invention only uses the second coil for the purpose of temperature compensation.

FIG. 10 shows a second embodiment provided according to the present invention.
FIG. 9 is a simplified schematic diagram of a variation of the system 150, featuring two sensors that are differentially operated to determine the position of the object 151 to be measured. System 150
, Sensors 152 and 154 are connected to lines 158 and 1 respectively.
The controller 156 exchanges information via 60.
The sensors 152 and 156 are operated differentially, and generate a first signal and a second signal indicating the position of the measured object with respect to each sensor. The magnitude of the signal sent and received from sensor 152 is indexed from the magnitude of the signal from sensor 154. The signal indicating the thickness of the object to be measured is
First, it relates to the phase output from each sensor. The signal relating to the thickness is corrected by the controller for an error due to the position due to the differential magnitude signal.
The position output of this second alternative system 150 can be further deviated from the effects of the thickness and temperature of the workpiece because the second sensor is used as described above.

Although the present invention has been shown and described with respect to preferred embodiments thereof, those skilled in the art will appreciate that various other changes, omissions and additions can be made without departing from the spirit and scope of the invention. It will be understood.

[Brief description of the drawings]

FIG. 1 is a simplified schematic diagram of a system provided by the present invention.

FIG. 2 is a graph illustrating the effect of electrical properties and distance on normalized impedance using an algorithm performed by the system of FIG.

FIG. 3 is a more detailed schematic diagram of the electrical circuit components of the system of FIG.

FIG. 4 is a graph showing a system output signal of FIG. 1;

FIG. 5 is a second graph showing the output signal of the figure, shown as a group of displacement curves.

FIG. 6 is a graph showing a group of displacement curves formed by phase voltages measured at a plurality of sensor displacements from the surface of the measurement object.

FIG. 7 is a graph showing the magnitude of the voltage of the output signal provided by the system in comparison with the sensor displacement from the object to be measured.

FIG. 8 is a simplified schematic diagram illustrating a differential sensor assembly that is part of an embodiment of the present invention and is a variation of the system illustrated in FIG.

FIG. 9 is another variation provided by the present invention,
FIG. 2 is a simplified schematic diagram of a system featuring two sensors.

FIG. 10 is another variation provided by the present invention, which is a simplified version of a system featuring two sensors that are differentially operated to determine the position of an object to be measured. It is a schematic diagram.

[Explanation of symbols]

 Reference Signs List 10 Eddy current sensor 12 Signal conditioning electric device 14 Connection cable 20 Coil 22 DUT

────────────────────────────────────────────────── ─── Continuation of front page (73) Patent holder 596111575 1500 Garden of the Gods Road Colorado Springs, COLORADO, USA (56) References JP-A-63-81262 (JP, A) JP-A-6-300593 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01D 21/02 G01B 7/06 G01N 27/90

Claims (4)

(57) [Claims] 1. A method for measuring a physical parameter characteristic of an object to be measured, wherein the physical parameters of the object to be measured include a material, a thickness, a temperature, a magnetic permeability, and a conductivity; Providing a current sensor having an electric coil, positioning the coil at a separation distance from the object to be measured, supplying an excitation signal of a selected angular frequency to the coil, Measuring the parameters of the object to be measured by measuring the excitation circuit impedance determined by the electrical parameters of the system. A step of providing an exciting circuit further comprising: an effective product of the magnetic permeability and the resistivity of the measured part and the separation distance are determined by an exciting circuit Supplying an excitation signal to the coil at one angular frequency selected to be located at a point on the impedance plane; measuring an amplitude (magnitude) of a voltage of the excitation signal; and a phase of the excitation signal. Measuring; a step of generating a signal indicating one point on the excitation circuit impedance plane; and a parameter including the physical parameter and the separation distance.
Generating a signal indicative of the desired two calculated values of the data . 2. The method according to claim 1, wherein the effective product of the magnetic permeability and the electrical conductivity of the object to be measured functions only as an imaginary component of the impedance, and the magnitude of the separation distance functions only as a real component of the impedance. Supplying an excitation signal to the coil at the single angular frequency;
Generating a signal indicative of a calculated value of the product of the magnetic permeability and the conductivity of the device under test. 3. A system for measuring physical parameter characteristics of an object to be measured, wherein the physical parameters of the object to be measured include a material, a thickness, a temperature, a magnetic permeability, and a conductivity. Means for positioning the sensor at a separation distance from the object to be measured, signal generating means for supplying an excitation signal to the sensor at a preselected angular frequency, and measuring the excitation signal to measure the object to be measured. Means for determining a parameter, comprising: an electrical component for determining an electrical parameter of the system; and an exciting circuit further having an exciting circuit impedance determined by the electrical parameter of the system; and A sensor having one electric coil, the diameter of which is pre-selected, and the effective product of the magnetic permeability and resistivity of the object to be measured. Signal generation means for supplying an excitation signal to the coil at one angular frequency selected in advance so that the separation distance is located at one point on an excitation circuit impedance plane; andmeans for measuring the magnitude of the voltage of the excitation signal. Means for measuring the phase of the excitation signal, and parameters including the physical parameters and the separation distance.
Processor means for generating an output signal indicative of a desired two calculated values of the data. 4. The processor means wherein the effective product of the excitability and the conductivity of the measured object functions only as an imaginary component of the impedance, and the magnitude of the separation distance functions only as a real component of the impedance. 4. The system according to claim 3, further comprising means for generating a signal indicative of a calculated value of an effective product of the excitability and the conductivity of the object to be measured.