JPH05231809A - Electromotive force type eddy current displacement gauge - Google Patents

Abstract

PURPOSE:To efficiently detect the lift-off of a metallic object. CONSTITUTION:A detection coil 5 is arranged between an excitation coil 3 and metallic object 4. An electromotive force corresponding to a lift-off between the coil 5 and object 4 is induced across the coil 5 based on an eddy current generated in the object 4 by the magnetic flux of the coil 3. Since the detection coil 5 having a different diameter is provided closely to the single excitation coil 3, the lift-off can be efficiently detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromotive force type eddy current displacement meter which detects a distance from a metallic object by utilizing an electromagnetic induction effect.

[0002]

2. Description of the Related Art A magnetic field is formed by an exciting coil in which a high frequency current is applied, and when a metallic object approaches the magnetic field, the magnetic field causes an eddy current in the metallic object,
An impedance change type eddy current displacement meter is known in which the impedance of the excitation coil is changed based on this eddy current. Such a displacement meter is used not only as a displacement with respect to the detection target object, that is, a distance (lift-off), but also as a proximity switch for detecting the presence or absence of proximity of a certain detection target object.

FIG. 6 shows a schematic structure of such an impedance change type eddy current displacement meter. Reference numeral 21 is a high frequency oscillator, 22 is a power amplifier (including a detector), and 23 is a power amplified high frequency current. It is an exciting coil. Reference numeral 24 denotes a metallic object as an object to be detected, which is arranged so as to face the exciting coil 23.

FIG. 7 illustrates the operating principle of such a displacement meter. The exciting coil 23 forms a magnetic field H by the high frequency current, and the magnetic field H causes a concentric eddy current i ′ to flow through the metallic object 24. The eddy current i produces a magnetic field H'in the direction opposite to the magnetic field H generated by the exciting coil 23. These magnetic fields H and H'are superposed to change the impedance of the exciting coil 23. φ and φ'indicate magnetic fluxes generated by the magnetic fields H and H '.

Therefore, the impedance Z'of the coil 23 in this case becomes smaller than the value Z when the metallic object 24 is not present. This is a high frequency oscillator 2
When the high frequency voltage e generated at 1 is constant, the high frequency current i changes. Further, the magnitude of the eddy current i ′ generated in the metallic object 24 is inversely proportional to the distance L between the exciting coil 23 and the metallic object 24, that is, the lift-off. As a result, the impedance Z of the exciting coil 23
Alternatively, the lift-off can be detected by measuring the current.

Here, a metallic object 24 which is an object to be detected is measured by using such an impedance change type eddy current displacement meter.
In order to detect the close state, the plural kinds of exciting coils are prepared in advance corresponding to the detection distance. For example, a plurality of types such as 5 mm, 10 mm, and 15 mm are prepared. Then, the one that suits the purpose is selected.

[0007]

By the way, in such an impedance change type eddy current displacement meter, a plurality of kinds of exciting coils are prepared in advance according to the detection distance, and the desired one is selected and replaced whenever necessary. Therefore, there is a problem that the detection efficiency is deteriorated and the cost is increased.

The present invention has been made in consideration of the above problems, and is an electromotive force type eddy current displacement meter capable of detecting a wide range of lift-off by using a single exciting coil and exchanging the detecting coil. It is intended to provide.

[0009]

In order to achieve the above-mentioned object, the present invention has a detection coil arranged in the vicinity of an exciting coil in which a high frequency current is passed, and a metallic object is placed in a magnetic field formed by the exciting coil. When an eddy current is generated in the metallic object due to an approach, the electromotive force corresponding to the distance from the metallic object is induced in the detection coil based on the eddy current.

[0010]

According to the structure of the present invention as set forth in claim 1, an eddy current is generated in a metallic object brought close to the magnetic field formed by the exciting coil with the detection coil arranged, and the eddy current is generated based on this eddy current. Then, the detection coil is caused to induce an electromotive force corresponding to lift-off with the metallic object.

According to the configuration of the present invention as set forth in claim 2, the same operation as in claim 1 can be performed in a state where the detection coil is arranged between the exciting coil and the metallic object.

According to the third aspect of the present invention, by setting the diameter of the detection coil in accordance with the measurement range of lift-off with the metallic object, efficient detection can be performed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic constitutional view showing an embodiment of an electromotive force type eddy current displacement meter of the present invention. 1 is a high frequency oscillator, 2 is a power amplifier, 3 is an exciting coil, and 4 is a metallic object. The configuration is the same as the conventional one. Reference numeral 5 is a detection coil and excitation coil 3
It is arranged between the metallic object 4 and the metallic object 4 and induces an electromotive force according to the lift-off L of the metallic object 4 based on the eddy current i ′ flowing in the metallic object 4 as described later. .. 6 is an amplifier for amplifying the induced electromotive force, and 7 is a voltmeter for measuring the induced electromotive force.

In such a structure, the magnetic field generated by the exciting coil 3 and the magnetic field generated by the eddy current flowing in the metallic object 4 are superposed on the detection coil 5 according to the same principle as in FIG. An electromotive force corresponding to the lift-off of is induced. That is, when the magnetic flux φ generated by the exciting coil 3 interlinks with the metallic object 4, an electromotive force is generated in the metallic object 4 by an electromagnetic induction action, and an eddy current i ′ flows. The eddy current i generates a magnetic flux φ ′ in the opposite direction to the magnetic flux φ, and the magnetic flux φ ′ and φ are superposed and interlink with the detection coil 5. Therefore, the eddy current i ′ changes according to the lift-off, so that an electromotive force corresponding to the lift-off with the metallic object 4 is induced in the detection coil 5.

The exciting coil 3 has an average radius of 7 m as an example.
A Brooks-type coil with m and 350 turns was used.
The detection coil 5 is a concentric circular coil having a number of turns N (1 to 5 turns) and a diameter D, and is arranged below the exciting coil 3. Further, the amplifier 6 having a gain of 40 dB was used and connected to the detection coil 5.

The operation of this embodiment will be described below with reference to various characteristics.

FIG. 2 shows the excitation frequency fo (vertical axis) and the diameter D of the detection coil 5 at which the induced electromotive force of the detection coil 5 becomes constant against changes in the lift-off L when an iron plate is used as the metallic object 4. The relationship with (horizontal axis) is shown. As the diameter D on the horizontal axis increases, the excitation frequency fo on the vertical axis
Will fall.

When a certain diameter D is set and an excitation frequency higher than the corresponding excitation frequency fo, that is, an excitation frequency in the region b is selected, the output voltage V of the detection coil 5
The relationship between the (vertical axis) and the lift-off L (horizontal axis) is shown by the characteristic B in FIG. As an example, the detection coil 5 is
Setting D = 82mm, N = 1 turn, f = 47KH
This is shown when z is selected.

On the other hand, when an excitation frequency lower than the excitation frequency fo corresponding to D, that is, the excitation frequency in the region a is selected, the relationship between the output voltage V and the lift-off L is similarly shown as the characteristic A in FIG. Become. As an example, the detection coil 5 is shown in a case where D = 82 mm and N = 1 turn are set and f = 470 Hz is selected as in the above. Here, when the rate of change is the same diameter D, the tendency becomes more prominent as the distance from the excitation frequency fo in FIG. 2 increases.

As is clear from comparison between the characteristics A and B in FIG. 3, when the excitation frequency in the region b higher than the excitation frequency fo corresponding to D in FIG. 2 is selected as in the characteristic B, the output voltage V Changes as the lift-off L increases. Therefore, if the characteristic B is selected, the lift-off can be detected easily. Therefore, an example using the characteristic B will be described below.

FIG. 4 shows the relationship between the output voltage V (vertical axis) and the lift-off L (horizontal axis) when the diameter D of the detection coil 5 is used as a parameter, and the characteristic A is set to D = 60 mm. In this case, the characteristic B shows an example in which D = 150 mm is set. As an example, N = 1 turn, f = 80K
It is shown in the case of selecting Hz and exciting current i = 2 mA.

As is clear from the characteristics A and B of FIG. 4, in the range where the lift-off L is small, the characteristic A having a smaller diameter is more proportional to the change of the lift-off L in the output voltage V, and in the range where the lift-off L is wider. It is understood that the characteristic B having a larger diameter provides the output voltage V in proportion to the change in the lift-off L. Therefore, efficient detection can be performed by setting the diameter D of the detection coil 5 according to the lift-off with the metallic object that is the detection target.

FIG. 5 shows the output voltage V (vertical axis) and the lift-off L (horizontal axis) when iron (○), aluminum (□), and brass (Δ) are used as the metallic object 4. It shows the relationship with. As an example, f = 300KH
It shows a case where z, i = 20 mA, D = 130 mm, N = 5 turns, and amplification degree = 1. Each of the characteristics shows that the lift-off L can be detected with good linearity in the range of 0.5 to 2.5 cm.

As described above, according to this embodiment, the detection coil 5 is arranged between the exciting coil 3 and the metallic object 4, and the metallic object is detected based on the eddy current generated in the metallic object 4. Since the electromotive force corresponding to the lift-offs of 1 and 2 is induced in the detection coil 5, it is possible to detect a wide range of lift-offs by using the detection coils 5 having different diameters D in the single exciting coil 3. In this case, the detection coil 5 having different diameters D is prepared according to the object to be detected, and is selectively used according to the detection range. This detection coil 5
Can be placed by a simple operation, so
No work is annoying. Therefore, unlike the conventional case, it is not necessary to replace the exciting coil 3 depending on the measurement range, and only one exciting coil needs to be prepared, so that lift-off detection efficiency can be improved.

Further, the magnitude of the output voltage V is determined by the detection coil 5
Since it can be taken out in proportion to the number N of turns of N, any number of turns can be selected.

Further, due to the surface roughness of the metallic object 4,
By setting the excitation frequency of the excitation coil 3 in consideration of the skin effect, the diameter D of the detection coil 5 can be freely designed according to the lift-off detection range.

[0028]

As described above, according to the present invention, the exciting coil and the detecting coil are separated, and several detecting coils having different diameters are prepared for a single exciting coil. It is possible to detect lift-off in a wide range from a minute displacement to several cm efficiently and without increasing cost.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an electromotive force type eddy current displacement meter of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the excitation frequency and the diameter of the detection coil, which makes the output voltage irrelevant to lift-off in this embodiment.

FIG. 3 is a characteristic diagram showing the relationship between lift-off and output voltage with the excitation frequency obtained as a parameter in the present embodiment.

FIG. 4 is a characteristic diagram showing the relationship between lift-off and output voltage obtained in this example.

FIG. 5 is a characteristic diagram showing the relationship between lift-off and output voltage obtained in this embodiment.

FIG. 6 is a schematic configuration diagram showing a conventional impedance change type eddy current displacement meter.

FIG. 7 is an explanatory diagram showing the operation principle of the impedance change type eddy current displacement meter.

[Explanation of symbols]

 3 Excitation coil 4 Metal object (Detection target) 5 Detection coil

Claims (3)

[Claims] 1. A detection coil is arranged in the vicinity of an exciting coil in which a high-frequency current is passed, and a metallic object approaches in a magnetic field formed by the exciting coil and an eddy current is generated in the metallic object. An electromotive force type eddy current displacement meter characterized in that an electromotive force is induced in the detection coil based on the eddy current according to the distance from the metallic object. 2. The electromotive force type eddy current displacement meter according to claim 1, wherein the detection coil is arranged at a position between the exciting coil and the metallic object. 3. The electromotive force type eddy current displacement meter according to claim 1, wherein the measuring range of the distance to the metallic object is changed by setting the diameter of the detection coil.