JP2651003B2 - Eddy current displacement sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an eddy current displacement sensor for measuring displacement of a metal conductor.

2. Description of the Related Art An eddy current displacement sensor as shown in FIG. 8 is known as a device for measuring the displacement of a metal conductor. A parallel resonance bridge circuit is formed by the dummy coil B, and when the conductor C close to the coil is displaced, the eddy current flowing on the conductor surface changes and the impedance of the exciting coil changes, and this is measured. Was linearized to obtain an output signal of conductor displacement detection.

[Problem to be Solved by the Invention] In the conventional eddy current type displacement sensor as described above, since the alternating magnetic field of the active coil A is widely dispersed, the conductor target must be larger than the outer diameter of the coil. 5mm × 5
There was a problem that it had to be larger than mm × t1mm.

Accordingly, an object of the present invention is to provide an eddy current displacement sensor capable of accurately measuring the displacement of a small metal conductor.

[Means for Solving the Problems] In order to achieve the above object, an eddy current displacement sensor of the present invention comprises an outer shield plate divided and insulated by an active receiving coil 12, an active high-frequency exciting coil 13, and an insulating slit 15. And an active head 1 having a dummy receiving coil 22, a dummy high-frequency exciting coil 23, and an outer shielding plate 14 having the same configuration as the active head 1. The active head 1 and the dummy head 2 are connected on the same axis. The sensor head 10 is configured such that the magnetic flux concentrates on the insulating slit 15 of the outer shielding plate of the active head 1 to form a non-uniform high-frequency magnetic field for detecting the displacement of the metal conductor. A signal processing circuit having a dynamic amplifying circuit is connected, and the displacement of a metal conductor is measured based on an output signal from the signal processing circuit.

[Function] When a high-frequency exciting current is applied to the exciting coil, an eddy current is induced in the shielding plate bottom plate portion divided and insulated by the insulating slit due to the high-frequency magnetic field. A magnetic field is formed.

In the receiving coil, an induced signal output is generated which changes according to the presence or absence of a metal conductor in the concentrated magnetic flux immediately below the insulating slit and a change in the position of the conductor.

The output of the receiving coil is amplified by a signal processing circuit, sampled and held, linearized to output a signal corresponding to the displacement of the metal conductor, and the displacement of the metal conductor is measured based on the output signal.

The active head and the dummy head are connected to the differential amplifier circuit, so that the measurement error due to the influence of the ambient temperature and the fluctuation of the exciting current is reduced, and the measurement value becomes higher.

Examples Examples of the present invention will be described below with reference to the drawings. FIG. 4 is a view for explaining the structure of a sensor head used for the eddy current type displacement sensor of the present invention. A receiving coil 2 is wound around a ferrite core 1, a high frequency exciting coil 3 is wound around the receiving coil 2, and An outer shielding plate 4 made of copper is provided so as to surround the bottom surface.

The outer shielding plate 4 is constituted by left and right semi-cylindrical portions 4a and 4b, and each of the semi-cylindrical portions has a bottom plate half 4c as shown in a fifth drawing showing the left semi-cylindrical portion 4a. The left and right semi-cylindrical portions 4a and 4b are opposed to each other with a small gap therebetween to form an insulating slit 5 in the diameter direction between the left and right bottom plate halves 4c and 4d as shown in FIG. An outer shielding plate composed of the respective halves divided into right and left by the insulating slit 5 and insulated from each other is formed.

When a high-frequency exciting current is applied to the exciting coil 3, a high-frequency magnetic field is generated, and an eddy current is induced in each of the left and right bottom plate halves 4c and 4d of the outer shielding plate 4 as shown by a dotted line in FIG. Since the eddy current is generated in a direction that hinders the change of the magnetic flux, the composite magnetic flux of the magnetic field generated by the exciting coil 3 and the magnetic field generated by the eddy current of each bottom plate half 4c, 4d has a small magnetic flux density in each bottom plate half 4c, 4d. In the sensor slit, a non-uniform high-frequency magnetic field having a maximum magnetic flux density Bmax is formed at the insulating slit portion SO as shown in FIG.

When the sensor head is placed above a metal wire C such as a copper wire as shown in FIG. 4, when the wire C is located immediately below the insulating slit 5 of the outer shielding plate 4, the magnetic flux density in the space occupied by the wire C is the highest. The shield effect of the outer shield plate 4 is weakest against an AC magnetic field induced by an eddy current of the conductor C. For this reason, when the conductor C is located immediately below the insulating slit 5, the influence of the conductor C on the impedance of the receiving coil 2 of the sensor head is greatest.

The sensor head having the outer shielding plate 4 is
One of them is an active head and the other is a dummy head to constitute the sensor head 10 shown in FIG. In the figure, 1 is an active head, 2 is a dummy head, 3 is a head jig 3 for coupling the two heads 1 and 2 on the same axis, and the active head 1 has an active receiving coil 12 around a ferrite core 11. The active excitation coil 13 is wound around the winding, and the outer periphery and the bottom surface are surrounded by an outer shielding plate 14 made of copper. The outer shielding plate 14 is provided with the above-described FIGS.
Similar to the outer shielding plate shown in FIG. 6, the left and right semi-cylindrical portions 14a and 14b are divided and insulated by the insulating slit 15. Similarly to the active head 1, the dummy head 2 has a configuration in which a dummy coil 21 around the ferrite core 21, a dummy excitation coil 23 on the outer periphery thereof, an outer shielding plate 24, and an insulating slit 25 of the outer shielding plate 24 are provided. To

The surface of each half of the outer shielding plate may be provided with an insulating coating as necessary, and the insulating slit may be formed in a + -shape instead of being formed linearly as described above. Instead, a bobbin made of an insulating material may be used.

A parallel resonance bridge circuit is formed by using the active head 1 and the dummy head 2, and an output signal of the bridge circuit is amplified (about 60 dB) by a signal processing circuit, and the displacement of the metal conductor C is measured.

FIG. 2 shows an example of this signal processing circuit. The active excitation coil 13 and the dummy excitation coil 23 and the active reception coil 12 and the dummy reception coil 22 are connected in series, respectively, as shown in FIG. When the active head 1 is placed above the metal conducting wire C and a high-frequency exciting current flows through the exciting coil, the electromotive force signal induced in the receiving coil is amplified by the differential amplifier circuit and sampled and held at the same frequency as the exciting current. The output is linearized by the LOG amplifier, and an output signal corresponding to the displacement of the metal conductor C located immediately below the insulating slit 5 of the active head 1 is obtained. This is measured to measure the displacement of the metal conductor. It is like that.

The active head 1 and the dummy head 2 form a differential coil by connecting the active receiving coil 12 and the dummy receiving coil 22 and the active exciting coil 13 and the dummy exciting coil 23 in series, and perform differential amplification of a signal processing circuit. The circuit significantly reduces measurement errors due to ambient temperature effects and fluctuations in the excitation current.

The output signal increases as the distance l between the bottom plates 4c and 4d of the outer shielding plate of the active head 1 in FIG. 1 and the metal conductor C decreases, and the rate of change increases as the processing l decreases. FIG. 3 shows the relationship between the distance l and the output signal V when the metal conductor C having a diameter of 0.4 mm is actually measured. The rate of change of the output signal V has an exponential relationship with the distance l. By measuring the output signal V in this way, the displacement of the metal conductor C can be accurately measured, and can be used, for example, for measuring the alignment of twin lead wires. The above-described sensor head can also be used as a proximity sensor.

[Effects of the Invention] As described above, the eddy current displacement sensor of the present invention uses a sensor head that forms a non-uniform high-frequency magnetic field in which magnetic flux is concentrated at the insulating slit of the outer shielding plate of the coil.
Even for a fine metal conductor, its displacement can be accurately measured. In addition, the sensor head consists of an active head and a dummy head, and a differential amplifier circuit is provided, so that measurement errors due to the influence of ambient temperature and fluctuations in the excitation current are greatly reduced, and highly accurate measurement values can be obtained. It is.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a sensor head according to one embodiment of the present invention, FIG. 2 is a signal processing circuit diagram thereof, FIG. 3 is a diagram showing output signal characteristics, FIG. 5 is an explanatory view of the structure of the shielding plate, FIG. 6 is an explanatory view of an induced eddy current of the shielding plate, FIG. 7 is an explanatory view of a state of magnetic flux distribution, and FIG. 8 is a view showing a conventional example. 1: Active head 12: Active receiving coil 13: Active exciting coil 2: Dammy head 22: Dammy receiving coil 23: Dammy exciting coil 4, 14, 24: Outer shielding plate 5, 15, 25: Insulating slit C: Metal conducting wire

Claims (1)

(57) [Claims] An active head and a dummy head coupled to the same axis are provided with a receiving coil, a high-frequency excitation coil, and an outer shielding plate which is divided and insulated by an insulating slit, respectively, so that magnetic flux is concentrated on an insulating slit portion of the active head. An eddy current displacement sensor, comprising: a sensor head having a high-frequency magnetic field formed therein; and a signal processing circuit having a differential amplifier circuit, wherein the displacement of the metal conductor is measured in the non-uniform high-frequency magnetic field.