JPS60243559A - Flaw-detecting magnetic sensor - Google Patents

Abstract

PURPOSE:To enable continuous and extensive-range detection, by using a linear detecting element. CONSTITUTION:A flaw-detecting apparatus is composed of a permanent magnet 17 for magnetizing a wire rope 16 up to a point nearly of saturation, a detecting head 18 including a detecting element detecting leakage magnetic fluxes from the wire rope and an output circuit, etc., and a magnetic field is constructed with magnet 17, yoke 19 and rope 16. The head 18 is composed of detecting elements 3a, 4a in a ring shape encircling concentrically the rope 16. If a strand constructing the rope 16 is accompanied with break, scar, etc., these flaws change the magnetic permeability of the location, generating leakage magnetic fluxes and the field is displaced with the rope 16 in the x direction. When the elenent 3a detects the fluxes 20, a positive voltage signal is generated on the output end of the circuit and when the element 4a detects them, a negative voltage signal is generated and thus, a discrepancy is detected on the rope. Further, as the elements 3a, 4a encircle the rope 16, noise produced by the leakage fluxes by the twisted construction of the rope and vibration of the rope is uniformalized in the output circuit without propagating to the outside. Thus, easy detection of flaw becomes available.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic sensor for flaw detection useful for magnetically detecting internal defects in wire ropes, steel plates, and the like.

[Conventional technology]

Flaw detection sensors are generally required to have the ability to detect changes in a two-dimensional magnetic field distributed linearly or planarly. However, conventional magnetic sensors are point-shaped as shown in Figure 11, and only sensors that detect magnetic fields (A) in a narrow range have been put into practical use. Therefore, when performing flaw detection, it is necessary to combine multiple of these point-shaped sensors. I had to use it. but.

If this is done, sufficient accuracy may not be obtained due to uneven performance of each sensor, the structure of the control section becomes complicated, and the flaw detection apparatus becomes expensive.

In addition, to explain the conventional sensor shown in FIG. 11, the code (α) is the core, and (b) is the high frequency power source.

(1) is a diode (d), a capacitor (1), and a resistor q
), etc., is a balanced output circuit. Core (α
) is made to be as small and thin as possible, and to form a closed magnetic path, in order to easily excite the core (, ) to a saturated state and to minimize leakage flux. Therefore, the detection range of the external magnetic field (g) is mostly the core (a
) is limited to a very small space (h) (indicated by a dashed line) around it.

[Problem that the invention seeks to solve]

In view of the above-mentioned drawbacks, the present invention is to provide a magnetic sensor for flaw detection capable of detecting magnetic flux changes in a two-dimensional external magnetic field in the form of a rock or a planar shape. [Means for solving the problems] The magnetic sensor for flaw detection of the present invention that can solve the above problems is as follows:
A plurality of detection elements each having a wire wound around a linear core made of a magnetic material, a high frequency power supply device that supplies a high frequency current to the windings, and each detection element outputs the magnetic flux change detected as a voltage change. It is a combination of electric circuits and can detect changes in the magnetic flux of an external magnetic field at once using a-shaped detection elements, resulting in high detection accuracy and a significant reduction in the number of detection elements. Therefore, it has the advantage that the device can be made smaller and lighter.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
Figures 1 to 10 show the structure, operation explanatory diagram, and wire rope flaw detection device to which the magnetic sensor is applied, which is an embodiment of the present invention. A thin (diameter 01
~0,. 5myI) The diameter of the linear core (1) is 70 μm
Two sensing elements (3) (4) are made by directly winding the winding a (2) in one layer, and - each winding (2) (2) has approximately IM
A high frequency power supply device (5) that supplies a high frequency current of Hz to excite the core to a saturated state, and each detection element (3) (4)
The magnetic flux change detected by the output terminal (
6) It consists of a balanced output circuit (8) which outputs to (7). The output circuit (8) has a resistance R+% as shown in the diagram.
R2, R3, R4 and capacitors C1, C2, C3・
It consists of a diode DI-D2, etc., and has a balance function that is not affected by external conditions (temperature changes, geomagnetic influences, etc.).

Next, to explain the operation of the magnetic sensor, when the core (1) (1) is excited by a high-frequency current from the high-frequency power supply (5) without being separated, a skin with a maximum magnetic permeability of about 7000 and a thickness of about 5 μm due to the magnetic skin effect. Depth (5k
depth ), and only the very surface of the core (1) is excited and becomes saturated. Therefore, even if the core (1) is a long wire of several hundred wires or a round bar with a relatively large diameter, the core (1) reaches a saturation state near the surface.

Next, the inductance (L) of each winding (2) is (1)
It is expressed by the formula.

L-Valve Ichigo・A (1) formula where L is the self-induction coefficient, Φ is the magnetic flux, B is the magnetic flux density,
A is the cross-sectional area of the core (1), and the relationship between the magnetic flux density B of the core (1) and the magnetic field H when there is no external magnetic field is the second
As shown in the figure, it is saturated by the excitation magnetic field (9) from winding a (2), and the change in magnetic flux density due to the magnetic field (9) is indicated by 00 (see the broken line). In this state, when an external magnetic field (field) acts on the core (1), the change in magnetic flux density (c) due to the excitation magnetic field (9) generated by the winding (2) decreases according to equation (1) (see Figure 6). ).As a result, the change in inductance L can be extracted as a voltage change in the output circuit (8).Therefore, as shown in FIG. 4, the external magnetic fields S and N are applied only to the detection element (4) shown in FIG. The output voltage ■ when applied is shown in Figure 5.The output of the 'mα sensor of the present invention using two detection elements (3) and (4) and working differentially (1. Detection element (3)
There is no output change in response to an external magnetic field applied in parallel to (4), but the output that acts differentially is the 6th
As shown in the figure, it is taken out to the outside as a voltage change. Note that 2 in the figure indicates the direction of movement of the external magnetic field a.

FIGS. 7 to 10 show an embodiment of a wire rope flaw detection device to which the present device is applied and explanatory diagrams of its operation. The flaw detection device consists of a permanent magnet (171 and a detection head 08 including a detection element that detects leakage magnetic flux from the wire rope Oej) that magnetizes the wire rope 06 to near the saturation point, and an output circuit (not shown). α force, 0 yokes, and wire rope (4) constitute a magnetic path ・Detection head (G)
consists of a ring-shaped detection element (3α) (shaft) concentrically surrounding the wire rope α0 (see FIG. 9), and the output circuit is the same as that shown in FIG.

When wires constituting the wire rope aO are broken, scratched, fatigued, etc., the magnetic permeability of this part changes, causing leakage magnetic flux -
occurs and moves in the X direction with the rope (arrow k) 0
When the detection element (6α) detects this leakage magnetic flux, a positive voltage signal is generated at the output end of the circuit, and when the detection element (4α) detects this leakage magnetic flux, a negative voltage signal is generated. defects are detected. In addition, the detection element (3
G) (4α) surrounds the wire rope QQ, so leakage magnetic flux due to the twisted structure of the rope and noise due to vibration of the wire rope OQ are averaged within the output circuit (8) and do not appear externally. . Therefore, the presence of defects can be easily detected.

It should be noted that the present invention is not limited only to the above-described embodiments, and it goes without saying that various changes can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, since the magnetic sensor for flaw detection of the present invention uses a linear detection element, it exhibits an excellent first-order effect.

(1) Fluctuations in magnetic fields that spread linearly and planarly can be detected.

(11) Since the detection element can be made flexible, it is possible to configure a detection head that matches the shape of the external magnetic field to be detected.

(iiD) It is possible to continuously detect a wide range without using a combination of multiple dot-shaped detection elements as in the past. Since it is possible to detect the
Detection results can be easily distinguished.

No need to rely on experts.

(V) It is a differential two-dimensional magnetic sensor, and its balance circuit function makes it unaffected by external conditions (temperature changes, geomagnetic influences).

[Brief explanation of the drawing]

1 to 6 are explanatory diagrams of embodiments and operating principles of the present invention, FIG. 1 is a wiring diagram showing the configuration of the device, and FIG. 2 is a B-H curve of the core in the absence of an external magnetic field. Fig. 6 is a B-H curve of the core when an external magnetic field is applied, Fig. 4 is an explanatory diagram of the distribution of the external magnetic field acting on one detection element,
Figure 5 shows the relationship between the excitation magnetic field and the output voltage in the state shown in Figure 4, Figure 6 shows the output voltage when a moving external magnetic field is applied to both sensing elements, and Figure 7 10 to 10 show an embodiment in which this device is applied to wire rope flaw detection, FIG. 7 is a cut side view of the magnetized part, FIG. 8 is a cut side view taken from the ■-■ direction in FIG. 7, FIG. 9 is a perspective view showing the arrangement of detection elements, FIG. 10 is a diagram showing the relationship between the rope moving direction and the output voltage, and FIG. 11 is an explanatory diagram of a conventional magnetic sensor. In the figure, (1) is the core, (2) is the winding, (3H3α) (
4) (4α) is a detection element, (5) is a high frequency power supply device,
(8) is an output circuit. Patent applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Patent applicant: Makome Research Institute Figure 1 Figure 2 Figure 3 Date

Claims (1)

[Claims] A plurality of detection elements each having a wire wound around a linear core made of a magnetic material, a high frequency power supply device that supplies high frequency current to the windings, and a magnetic flux change detected by each detection element outputting as a voltage change. A magnetic sensor for flaw detection characterized by being equipped with an electric circuit.