JPH04155202A - Eddy current type noncontact displacement gage - Google Patents

Abstract

PURPOSE:To eliminate an error in an measured displacement amount owing to temperature change by applying AC current or voltage having two or more frequency components to an L element, separating it per frequency component and extracting and calculating an imaginary number part and a real number part. CONSTITUTION:Oscillators 24, 20 respectively output at frequencies (f), (nf), while they obtain outputs via voltage/current converters 22, 26 from a current synthetic circuit 28, which are to be applied to a detecting head 30. The head 30 has a coil 8 with inductance L1 and a resistance value R1 and separates voltage across the coil 8 respectively into frequency components (f), (nf) via a buffer amplifier 32 and further by synchronous wave detectors 34, 36. For example, pulses based on the output of the oscillator 24 are shifted by 90 deg. by a phase shifter 40 to extract only an imaginary number part, while simultaneously pulses based on the output of the oscillator 20 are shifted by 90 deg. by a phase shifter 38 to extract only an imaginary number part. Then an output of the synchronous wave detecting circuit is inputted to a subtraction circuit 44 as predetermined and applied to a linearizer, whereby voltage in proportion to a distance between an object and the head 30 can be obtained. Since a calculation base does not depend on a L1 value or R1 value of the head, no error occurs due to change in their temperatures.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is an improvement to a non-contact displacement meter that uses eddy current, and in particular, an eddy current non-contact displacement meter that eliminates measurement differences due to temperature changes. It's also about the meter.

[Prior Art] An eddy current type non-contact displacement meter is used to measure the distance (displacement) to an object to be measured, and there is one such as the one shown in FIG. 5, for example. 2 is an LC4 shaker, and this LC
The oscillation output of the oscillator 2 is detected in the wave circuit 4 and then passed through an integrator or the like.

Alive 6 is supplied with the signal to be flattened.

When the coil 8 of the LC oscillator 2 is brought close to the object to be inspected 10, an eddy current is generated in the object to be inspected 10, and the output amplitude of the oscillator decreases. The degree of this reduction depends on the distance between the hand coil 8 and the test object 10.

Therefore, the distance (displacement) between the detection coil 8 and the object to be inspected 10 can be determined based on the linearly aligned output by detecting the oscillation output.

[Problems to be Solved by the Invention] However, conventional eddy current displacement meters have the following problems.

Since the inductance and direct current resistance of the false detection coil 8 change depending on the ambient temperature, the oscillation amplitude and oscillation frequency change accordingly, causing an error in the measured displacement amount.

The purpose of this invention is to solve the above-mentioned problems and provide an eddy current type non-contact displacement meter that does not cause errors in measured displacement due to temperature changes.

= [Means for Solving the Problems] In order to achieve the above object, the present invention provides a composite oscillation circuit that generates an AC current or an AC voltage having at least two or more frequency components, and an object to be measured. The composite oscillation circuit is magnetically coupled and has an inductance value L1 and a resistance value R1.
An inductance element to which AC power is applied from
and a separation/extraction circuit that separates the current flowing through the inductance element or the voltage across the inductance element into each frequency component, and extracts the non-imaginary or real part of each separated frequency component; and a calculation circuit that calculates the displacement of the object to be measured by calculating the voltage or current value independent of the inductance value and the resistance value R2 based on the imaginary part or the real part of the voltage or current. This constitutes an eddy current type non-contact displacement meter.

Here, it is assumed that the AC voltage output by the composite oscillation circuit has a first frequency component and a second frequency component that is n times the frequency of the first frequency component. I can do something.

The arithmetic circuit subtracts the second frequency component from the voltage across the inductance element C or the first frequency component of one current flowing through the inductance element multiplied by n. It can be configured to calculate displacement based on outside imaginary numbers.

In addition, the arithmetic circuit calculates k based on the real number obtained by subtracting the second frequency component from the first frequency component of the voltage across the inductance element or the current flowing through the inductance element. It is also possible to adopt a configuration in which displacement is calculated.

[Function] The eddy current type non-contact displacement meter according to the present invention has the following features:
Alternating current or L having at least two or more frequency components
applies an alternating voltage to the inductance element, separates the current flowing through the inductance element or the voltage across the inductance element for each frequency component, and
Extract the imaginary or real part of each separated frequency component,
Based on this, inductance value L1 and resistance value R
The voltage or current value that does not depend on 3 is calculated and measured, and the displacement of the object is calculated.

That is, since the basis for calculating the displacement of the object to be measured is the inductance value and does not depend on the resistance value R1, the measured displacement is not affected by temperature changes in the inductance value and the resistance value R1.

[Embodiment 1] FIG. 1 shows a block diagram of an eddy current type 1 non-contact displacement meter according to an embodiment of the present invention. In this embodiment, an oscillator 20, a voltage/current converter 22, an oscillator 24, a voltage/current converter 26, and a current combining circuit 28 constitute a composite oscillation circuit. The oscillator 24 outputs an oscillation output with a frequency f, and the oscillator 20 outputs an oscillation output with a frequency n.
It outputs an oscillation output of f. Note that here, n≠1
It is. These oscillation outputs are sent to the voltage/current converter 22.
At 26, after being converted to a current, the current combining circuit 28
given to. Therefore, from the current combining circuit 28,
An alternating current having a frequency f component and a frequency nf component is output. This alternating current is applied to the detection head 30. The detection head 30 includes a coil 8 having an inductance value of 1 and a resistance value of R1.

The voltage across the coil 8 of the detection head 30 is taken out via the buffer amplifier 32. The voltage (ω+nω) across the coil 8 extracted in this way is expressed as follows.

First, the voltage V(ω
) is as shown below.

However, ω=2πf L,: Self-interactance of coil 8 R1: Coil 8
DC resistance L! : Self-inductance of the measurement object 10 R7: DC resistance of the measurement object 10 M: Mutual inductance between the coil 8 and the measurement object IO.

Similarly, the voltage V caused by the component of frequency nf
(nω) is as shown in the following formula.

n"ω"M"n"CLJ'M'V (
nω) = i(R+ ' R”i occupied Rt) + jn
(oi(L+ -iiiim-L已,)...
(2) In other words, the voltage ■(ω) and the voltage V
The combined voltage of (nω) appears. This combined voltage is (1
) As is clear from equation (2), it is a function of LIR2,M. These, , R, , M are the detection head 30
It changes depending on the distance between the object IO and the detection target IO. Therefore, the combined voltage changes depending on the distance between the detection head 30 and the detection target 10.

The calculation process for calculating the distance based on this composite voltage will be shown below.

Multiplying both sides of equation (1) by n and subtracting equation (2), we get “”
'R1)-;(R+昿-1゜21s;
) nV+llJ+ V+nω1=ni(Ru Ni'
i;"UIB,, ncI, 1゜(IJ'M'n'c+
]'M' −jnω1(Hr, stone vB4L+ 1iii';
It becomes +'L-tomi''.

If we rearrange the imaginary part of equation (3), we get ...(4) becomes.

This equation (4) does not include R, or L. Therefore, even if there is a temperature change in R,,L, no measurement error occurs.

In order to realize the above calculation using a circuit and obtain the output of equation 4), first, the output of the buffer amplifier 32 is
■It is necessary to separate into (ω) and V(nω).

The synchronous detection circuits 34 and 36 perform this. The synchronous detection circuit 34 separates and outputs the frequency f component, and the synchronous detection circuit 36 separates and outputs the frequency nf acid component.

FIG. 2 shows an example of a synchronous detection circuit. The output voltage of the buffer amplifier 32 is applied to the terminal 52. switch 54
By turning on and off with a pulse of frequency f, the voltage of the frequency f component is separated from the output terminal 56 of the operational amplifier 50. In this embodiment, a pulse of frequency f is obtained based on the output of the oscillator 24, and after being phase-shifted by the phase shifter 40, it is applied to the switch 54. By shifting the phase by 90' using the phase shifter 40, only the imaginary part is extracted.

Note that the phase shifter used in this example is shown in FIG.

Similarly, a pulse of frequency nf is obtained based on the output of the oscillator 20 and is applied to the synchronous detection circuit 36 to separate the frequency nf acid component voltage. Again, 90
A phase shift of ° is performed to extract only the imaginary part.

Next, the output of the synchronous detection circuit 34 is given to a subtraction circuit 44 via an n-fold amplifier 42. The output of the synchronous detection circuit 36 is directly applied to the other input of the subtraction circuit 44.

Therefore, the voltage value shown in equation (4) is obtained from the output of the subtraction circuit 44.

If this output is applied to the linearizer, a voltage 1 proportional to the distance between the detection object 10 and the detection head 30 can be obtained.

In the above embodiment, the calculation is performed by extracting the imaginary part, but the real part may also be extracted. 'That is, by subtracting equation (2) from equation (1) and drawing the real part, the following equation is obtained.

Re(V tω+ −V tnω,)”” t・ω
'M' (g same yon kaka LJ)...(5) The circuit to obtain the result of equation (5) is shown in Figure 4.
vinegar. The difference from the circuit of FIG. 1 is that phase shifters 38, 40 and n-fold amplifier 42 are not provided. In the circuit shown in FIG. 4 as well, the distance between the detection head 30 and the detection object 10 can be obtained based on the output of the subtraction circuit 44.

Furthermore, in the above embodiment, the detection head 30
Although a current was applied to (coil 8), a voltage may also be applied.

Furthermore, in the above embodiment, the detection head is 30 inches.
Although we have taken the voltage across the coil 8, you can also take the current flowing through it.

Note that it is also possible to prepare three or more oscillators, each with a different frequency, and average the distance calculated using any two frequencies.In other words, by changing frequency B, measurements using two arbitrary frequencies can be performed. The distance may be calculated by averaging the measurement results.

[Effects of the Invention]) The eddy current type non-contact displacement meter according to the present invention applies an alternating current or an alternating voltage having at least two or more frequency components to an inductance element, and applies an alternating current or an alternating voltage having at least two or more frequency components to an inductance element, The voltage at both ends is separated for each frequency component, and the imaginary part or t of each separated frequency component is extracted as a real part, and based on this, the inductance value is calculated, and the voltage or t that does not depend on the resistance value R2 is calculated. The displacement of the object to be measured is calculated by calculating the current value. Therefore, the basis for calculating changes in the object to be measured is the inductance value and the resistance value.
Since it is not dependent on the value R7, the measured displacement is not affected by temperature changes in the inductance value and the resistance value R7. That is, it is possible to create an eddy current non-contact displacement meter that does not cause measurement differences due to temperature changes.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an eddy current type 11 contact displacement meter according to an embodiment of the present invention, Fig. 2 is a diagram showing details of a synchronous detection circuit, and Fig. 3 is a 90°
FIG. 4 is a block diagram of an eddy current type one-contact variable displacement meter according to another embodiment, and FIG. 5 is a block diagram of a conventional eddy current type non-contact displacement meter. 20.24... Oscillator i 30... Detection heads 34, 36.
...Synchronous detection circuit l 44...Subtraction circuit Fig. 2 R Fig. 3

Claims (3)

[Claims] (1) A composite oscillation circuit that generates an alternating current or an alternating voltage having at least two or more frequency components; and a composite oscillation circuit that is magnetically coupled to an object to be measured and has an inductance value L_1 and a resistance value R_1; An inductance element to which AC power of A calculation circuit that calculates the displacement of the object to be measured by calculating a voltage or current value independent of the inductance value L_1 and resistance value R_1 based on the circuit and the imaginary part or real part of the voltage or current separated into each frequency component. An eddy current type non-contact displacement meter characterized by being equipped with. (2) The AC current or AC voltage output by the composite oscillation circuit has a first frequency component and a second frequency component whose frequency is n times the first frequency component, and the arithmetic circuit uses an inductance element. A claim for calculating the displacement based on the imaginary part of the result obtained by subtracting the second frequency component from the first frequency component of the voltage across or the current flowing through the inductance element multiplied by n. The eddy current type non-contact displacement meter according to item 1. (3) The AC current or AC voltage output by the composite oscillation circuit has a first frequency component and a second frequency component whose frequency is n times the first frequency component, and the arithmetic circuit uses an inductance element. From the voltage across or the first frequency component of the current flowing through the inductance element,
2. The eddy current type non-contact displacement meter according to claim 1, wherein the displacement is calculated based on the real number after subtracting the second frequency component.