JPH0850004A - Method for measuring position of magnet - Google Patents

Abstract

PURPOSE:To detect a position of a magnet set to an internal object coated with a non-magnetic body by arranging a plurality of magnetic field detection sensors on a line in a direction orthogonal to a direction connecting N and S poles of the permanent, magnet set to the object, setting a direction in which a magnetic field is to be detected by the sensors to agree with the linear arranging direction of the sensors, and detecting tone magnetic field. CONSTITUTION:A plurality of magnetic field detection sensors 1, e.g. Hall elements are arranged on a line in a direction orthogonal to a direction connecting N and S poles of a permanent magnet, 2. The NS polar direction of the magnet, 2 is set as a Y axis, and the arranging direction of the elements 1 is set as an X axis. The elements 1 are directed in a direction to detect an X-axis component Bx of a magnetic field. A driving current for the elements 1 is supplied to a Z axis at right angles to the X axis. A voltage induced in a Y-axis direction perpendicular to the Z axis is proportional to the X-axis component of the magnetic field. In other words, the magnetic field to be detected by the elements 1 is positioned in the X-axis direction. An output voltage of the elements 1 is amplified, A/D converted and corrected, whereby a value of the magnetic field is obtained. The value is interpolated on the line and a distribution of the Bx on the line is obtained. A moving amount of an object is detected from a relation between an X coordinate value of a point where the Bx becomes zero and an X coordinate value of the magnet 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal object covered with a non-magnetic material, for example, for measuring the amount of movement of the cable core of a power cable having a non-magnetic metal sheath and for measuring changes in the skein of the cable. The present invention relates to a magnet position measuring method for measuring the amount of movement of a magnet by measuring the position of a permanent magnet attached to the object.

[0002]

2. Description of the Related Art Conventionally, as a technique for measuring the movement amount of a cable core of a power cable having a non-magnetic metal sheath such as an aluminum sheath or a lead sheath, for example, Japanese Patent Publication No.
As disclosed in Japanese Patent No. 11, a permanent magnet is attached to a cable core as a signal source, and a moving amount is visually measured from the outside of a non-magnetic metal sheath by using a magnet for detection. Further, conventionally, the amount of movement has been measured by X-ray imaging for such a purpose.

[0003]

However, in the conventional method of this type, since the movement of the detection magnet is judged by the human eye, continuous and automatic measurement during the operation of the cable line is performed. Was unsuitable. In addition, X-ray photography is not suitable for continuous measurement because it is a special work by a qualified person in a dangerous area setting. To know the movement status of the cable core from the photographed photographs, Judgment was needed.

[0004]

The present invention solves the above problems and provides a magnet position measuring method for highly accurately measuring the position of a permanent magnet attached to an internal object covered with a non-magnetic material. Its characteristic is that a plurality of magnetic field detection sensors are arranged on a straight line in a direction orthogonal to the direction of the NS pole of a permanent magnet attached to a movement measurement target, and the magnetic fields of those magnetic field detection sensors are detected. The direction is aligned with the linear direction where the magnetic field detection sensor is arranged, and the magnetic field distribution obtained by interrogating the magnetic field value detected by each magnetic field detection sensor with a straight line or a curve is used to find the point where the magnetic field value becomes zero. A magnet position measuring method for measuring that the position of a magnet is on a plane that includes a point where a magnetic field value on a straight line on which a magnetic field detection sensor is arranged is zero and is orthogonal to a straight line on which a magnetic field detection sensor is arranged.

[0005]

As shown in FIG. 1A, a plurality of magnetic field detection sensors 1, for example, Hall elements are arranged in a straight line in a direction orthogonal to the direction of the NS pole of the permanent magnet 2. That is, the permanent magnet 2
The y-axis is the direction of the NS pole and the x-axis is the arrangement direction of the Hall element 1. As shown in FIG. 1B, the Hall element 1 is arranged so as to detect the Bx of the x-axis component of the magnetic field. That is, the drive current of the Hall element 1 is passed in the direction perpendicular to the x-axis (here, the z-axis direction), and the voltage induced in the direction perpendicular thereto (here, the y-axis direction) is proportional to the x-axis component of the magnetic field. In this way, the direction in which the magnetic field of the Hall element 1 is detected is set in the x-axis direction.

As shown in FIG. 2, the voltage of the Hall element 1 and the applied magnetic field have a linear relationship, but the offset (the voltage that appears when the applied magnetic field is zero) and the sensitivity (the applied magnetic field are changed). The rate at which the voltage changes) has different values for each Hall element 1. These characteristic values are measured in advance.

In the circuit as shown in FIG. 3, the output voltage of each Hall element 1 of FIG. 1 is amplified by the amplifier 4, A / D converted 6 and taken into the microcomputer 7, and the characteristic value (offset of each Hall element 1 And sensitivity) to find the magnetic field value and interpolate with a straight line, B on the straight line where the Hall element 1 is arranged
The distribution of x is obtained. The Bx distribution when the permanent magnet 2 shown in FIG. 1 is moved is shown in FIGS. 4 and 5. Furthermore Bx
FIG. 6 shows the relationship between the x coordinate value of the point where is zero and the x coordinate value of the magnet position. By the above, the x-coordinate value of the permanent magnet 2 can be measured.

As shown in FIG. 7, the permanent magnets 2 are arranged by arranging two or more rows of the Hall elements 1 in parallel.
It is possible to measure the x-coordinate value of the permanent magnet 2 in a wide range even if the position of moves significantly in the y direction or the z direction. It is also possible to measure the x-coordinate value and the y-coordinate value of the permanent magnet 2 by arranging such an array of the Hall elements 1 also in the y-axis direction as shown in FIG.

[0009]

EXAMPLE FIG. 9 is a vertical cross-sectional view of a main portion of a cable connecting portion when the magnet position measuring method of the present invention is applied to a moving amount measurement of a cable core of a power cable. In the drawing, 13
Is a cable core of a power cable, which is configured by providing a cable insulating layer 12 such as oil-impregnated insulating paper or a plastic insulator on a cable conductor 11 in which a large number of copper wires are twisted, and aluminum is provided on the outside thereof. A non-magnetic metal sheath 14 such as stainless steel or lead is provided. The connecting portion 15 of the conductor 11 of such a power cable is provided with a connecting portion reinforcing insulating layer 16, the outside of which is provided with a non-magnetic outer box 17 such as a copper pipe, and both ends thereof are provided with a metal sheath 14 It is connected to the lead by 18 etc.

The connection portion of the power cable as described above can be moved only in the direction perpendicular to the longitudinal direction of the cable by fixing the outer box 17 or the metal sheath 14 to the ground, or by utilizing an offset or the like. On the other hand, when the cable core 13 is energized by the cable conductor 11 and the temperature rises, or when the temperature drops when the energization is stopped, thermal expansion and contraction work of the cable core 13 occurs. It may move relative to each other. In particular, if the power cable is laid on a sloping ground, if it is laid directly under the road and is affected by passing vehicles, or if it is installed on a bridge and subjected to special vibration, the relative movement of the cable core 13 May be accumulated in. When the accumulated movement amount of the cable core 13 increases, the cable core 13
There is a risk that the reinforcing insulating layer 16 of the connection part may be damaged and the power transmission function may be lost.

Therefore, it is important to grasp such a unidirectional movement tendency of the cable core 13 at an early stage and take some measures before the cable core 13 is damaged in the power transmission function. Therefore, as shown in FIG. 9, a permanent magnet 19 that performs the same movement as the cable core 13 is mounted on the connecting portion reinforcing insulating layer 16 of the cable core, and a connecting portion that performs the same movement as the metal sheath 14 of the cable on the other hand. Non-magnetic outer box 17
A sensor housing case 21 in which a plurality of magnetic field detection sensors 20 are arranged in a straight line is attached to the above, and the movement amount of the cable core 13 is measured by using the magnet position measuring method of the present invention described above.

[0012]

As described above, the magnet position measuring method of the present invention has the following effects. (1) The amount of movement of an internal object covered with a non-magnetic material can be measured in a non-contact and non-destructive manner. (2) In the configuration shown in FIG. 1, the x coordinate value of the magnet can be correctly measured even if the position of the permanent magnet is displaced in the y direction and the z direction. This is because the zero point of Bx is not affected by the displacement of the magnet position in the y and z directions. (3) It is possible to reduce the influence of the error in the actual measurement of the offset or sensitivity of the Hall element on the measured value of the permanent magnet position. This is because the rate of change (slope) of Bx is the largest in the magnetic field distribution near the zero point of Bx in FIGS. 4 and 5, so that the error in measuring the characteristics of the Hall element (changing the magnetic field value up and down) changes the Bx zero point ( Figure 4,
This is because the shift to the left and right in FIG. 5) is small. (4) When the method of the present invention is applied to the measurement of the movement amount of the cable core of the power cable, the movement tendency of the cable core can be grasped at an early stage, and the cable core may be damaged in the power transmission function. Prevents it in advance and has an extremely great effect on the maintenance of the power cable.

[Brief description of drawings]

FIG. 1A is an explanatory view of the arrangement of a permanent magnet and a magnetic field detection sensor according to the present invention, and FIG. 1B is an explanatory view of an arrangement direction of a magnetic field detection sensor.

FIG. 2 is a characteristic diagram of a magnetic field detection sensor (Hall element).

FIG. 3 is a configuration diagram of a magnet position measuring circuit of the present invention.

FIG. 4 is an explanatory diagram of magnetic field measurement data (No. 1) according to the present invention.

FIG. 5 is an explanatory diagram of measured magnetic field data (No. 2) according to the present invention.

FIG. 6 is an explanatory diagram of an experimental example relating to measurement accuracy in the present invention.

FIG. 7 is a configuration diagram in which a plurality of magnetic field detection sensor arrays are arranged in parallel.

FIG. 8 is a configuration diagram in which magnetic field detection sensor arrays are arranged in x-axis and y-axis directions.

FIG. 9 is a vertical cross-sectional view of a main part of a cable connecting portion when the magnet position measuring method of the present invention is applied to a moving amount measurement of a cable core of a power cable.

[Explanation of symbols]

 1 magnetic field detection sensor 2 permanent magnet 3 current source 4 amplifier 5 multiplexer 6 A / D converter 7 microcomputer 11 cable conductor 12 cable insulating layer 13 cable core 14 non-magnetic metal sheath 15 conductor connecting portion 16 connecting portion reinforcing insulating layer 17 non Magnetic outer box 18 Lead 19 Permanent magnet 20 Magnetic field detection sensor 21 Sensor storage case

Claims (5)

[Claims] 1. An N of a permanent magnet attached to a moving object to be measured.
A plurality of magnetic field detection sensors are arranged on a straight line in a direction orthogonal to the direction of the S pole, and the magnetic fields of these magnetic field detection sensors are aligned with the linear direction in which the magnetic field detection sensors are arranged. In the magnetic field distribution obtained by interrogating the detected magnetic field value with a straight line or a curve, by finding the point where the magnetic field value becomes zero, the magnetic field value on the straight line where the position of the permanent magnet is located A method for measuring a magnet position, which comprises measuring on a plane including a point which becomes zero and being orthogonal to a straight line where a magnetic field detection sensor is arranged. 2. The magnet position measuring method according to claim 1, wherein the magnetic field detection sensor is a Hall element. 3. The magnet position measuring method according to claim 1, wherein two or more rows of magnetic field detection sensors are arranged in parallel. 4. The magnetic field detection sensors are arranged in a direction orthogonal to a straight line where the magnetic field detection sensors are arranged and also in a direction orthogonal to the direction of the NS pole of the permanent magnet.
2. A magnet position measuring method according to any one of 1. 5. A permanent magnet that performs the same movement as the cable core is disposed on the reinforcing insulator of the cable core of the connection portion of the power cable, which is a non-magnetic metal conductor and has a non-magnetic metal sheath, 5. The magnet position measuring method according to claim 1, wherein a plurality of magnetic field detection sensors are arranged on a straight line in a non-magnetic outer box of a connecting portion that performs the same movement as the metal sheath.