JPH05172786A - Leakage flux detector - Google Patents

Abstract

PURPOSE:To grasp defect characteristic exactly and quantitatively by extracting feature quantity set in advance from a defect detection signal of a magnet sensor array and detecting defect position. CONSTITUTION:A detected body 30 is magnetized by a direct current electric magnet 10 and magnetic flux leaks from a defect part, which is detected by a magnetic sensor array 21 and the defect detection signal is amplified with an n channel type amplifier 50. A length meter 60 generates a relative position signals of the detected body 30, the electric magnet 10 and the array 21. The defect detection signal and the relative position signal are digitized respectively by an A/D converter 70 and input in a central processing unit 80. The unit 80 detects the defect position from the relative position signal, From the defect detection signal, maximum and minimum values and their signal wave shaped as the feature quantity are extracted and from the maximum and the minimum values, defect depth is presumed from the zero cross point of the signal wave shape, defect size is presumed. In this way, the defect characteristic of the detected body 30 is grasped exactly and quantitatively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flaw detection technique using a magnetic flux leakage method, and more specifically, a flaw detection device for thin steel plates, rod-shaped steel materials, steel pipe materials, etc. The present invention relates to a leakage magnetic flux detection device applied to a pipe inspection device.

[0002]

2. Description of the Related Art As a flaw detection technique, in addition to ultrasonic flaw detection and eddy current flaw detection, detection performance is comparatively excellent even if there is rust or dirt on the surface of the object to be inspected. There is a magnetic flux leakage flaw detection method that is being applied to equipment inspection.

The leakage magnetic flux method is a magnetic flaw detection method for detecting a magnetic flux leaking from a defective portion with a magnetic sensor when a magnetic substance as an object is magnetized to a saturation region to detect a defective portion, and has a structure shown in FIG. Has become.

In FIG. 4, reference numeral 30 denotes a subject, and the electromagnet 10 magnetizing the subject 30 and the magnetic sensor 20 fixed between the poles of the electromagnet 10 constitute a leakage magnetic flux detecting device. In this case, as the magnetic sensor 20, an air core coil, a ferromagnetic core coil, a Hall effect type magnetic sensor,
A magnetoresistive effect type magnetic sensor or the like is used.

[0005]

In the conventional leakage magnetic flux detecting device as shown in FIG. 4, one or a plurality of the magnetic sensors 20 as described above are used. It only measures the magnetic field strength or the vertical component of the leakage flux.

Therefore, in such an apparatus, although the position of the defective portion can be detected with a certain degree of accuracy, it is difficult to quantitatively grasp the defect property, that is, the size, depth and shape of the defect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and an object thereof is to provide a leakage magnetic flux detection device capable of quantitatively measuring a defect property.

[0008]

Means for Solving the Problems The present invention that achieves the above-mentioned object is as follows: (1) A magnet for magnetizing a subject and a magnetization direction in a plane between the magnet and a pole parallel to the plane of the subject. A leakage magnetic flux detector having a magnetic sensor array composed of n individual elements which are arranged so as to form a right angle with the magnetic flux sensor and detects a leakage magnetic flux from the defective portion of the subject, and a defect detection signal of the magnetic sensor array is amplified. A n-channel amplifier, a length measuring device for generating a relative position signal between the subject and the leakage flux detector, and a digitizing defect detection signal of the n-channel amplifier and the relative position signal of the length measuring device A / D
A converter and a central part for extracting a preset characteristic amount from the digitized defect detection signal and detecting a defect position from the digitized relative position signal to quantitatively estimate the defect property. (2) The maximum value, the minimum value of the defect detection signal, and the zero-cross point of the AC component signal are extracted as the characteristic amount.

[0009]

According to the defect detection signal from the magnetic sensor array and the relative position signal from the length measuring device, information about the defect depth is obtained from the feature amount of the defect detection signal, for example, the maximum value and the minimum value, and the feature amount of the AC component signal is obtained. For example, the information on the size of the defect is obtained from the zero-cross point, and the defect position is detected from the relative position signal, so that the defect property can be quantitatively estimated.

[0010]

EXAMPLES Examples of the present invention will now be described with reference to FIGS. FIG. 1 is a schematic configuration diagram.

In FIG. 1, reference numeral 10 is a DC electromagnet for magnetizing the subject 30, and the space between the electromagnet poles is magnetized.

Reference numeral 21 is a magnetic sensor array arranged between the electromagnet poles. The magnetic sensor array 21 is composed of n individual elements arranged in a plane parallel to the plane of the subject 30 (leakage detection plane) and perpendicular to the magnetization direction.
Each element measures the vertical component Hz of the leakage flux. As an example, there is an MR magnetic sensor (magnetoresistive element) having sensitivity directivity only in one axis direction.

In this embodiment, the subject 30 has a thickness of 5 mm.
The steel plate (SS41) of No. 1 having a groove-shaped defect in the central portion on one side thereof, or the circular composite defect artificially formed as shown in FIG. 3 (c) was used.

Reference numeral 40 denotes a magnetic flux leaking from the defective portion due to the magnetization of the subject 30.

Reference numeral 50 is an n-channel type amplifier for amplifying the defect detection signal shown in FIG. 2A by the magnetic sensor array 21 which has detected the leakage magnetic flux.

Reference numeral 60 denotes a length measuring device for generating a relative position signal between the object 30 and the leakage magnetic flux detector composed of the electromagnet 10 and the magnetic sensor array 21, and detects a defect position.

Reference numeral 70 is an A / D converter for digitizing the defect detection signal of the n-channel amplifier 50 and the relative position signal from the length measuring device 60.

Reference numeral 80 denotes a central processing unit for extracting a preset feature amount from the digitized defect detection signal and detecting the defect position from the digitized relative position signal to quantitatively estimate the defect property. Is.

2A and 2B from the defect detection signal detected by the magnetic sensor array 21, amplified by the n-channel amplifier 50 and extracted by the central processing unit 80. ) Is extracted. This feature is a parameter necessary for quantifying the defect property, and the maximum and minimum values shown in FIG. 2A provide information on the depth of the defect. Further, from the signal waveform of the AC component of the defect detection signal (see FIG. 2B), the zero cross point provides information on the size of the defect.

Therefore, a three-dimensional property of the defect can be obtained by processing and analyzing the defect detection signal of the magnetic sensor array 21 composed of n individual elements.

FIG. 3 shows, for example, two circular defects (diameter 15
mm and 10 mm circular and 4 mm deep) composite artificial defects are measured. In FIG. 3, (a) is a defect detection signal from the magnetic sensor array 21,
(B) is a signal waveform of the AC component of this defect detection signal. The central processing unit 80 extracts a predetermined feature amount related to the defect property from the signal waveform and detects the defect position from the relative position signal from the length measuring device 60. As a result, the result of quantification of the defect properties shown in FIG. 3C was obtained and displayed, and it was found that both the size and the depth shape of the measured artificial defect can be sufficiently estimated.

[0022]

As described above, according to the present invention, the defect detection signal from the magnetic sensor array and the relative position signal from the length-measuring device are digitized, and the predetermined feature quantity relating to the defect property is extracted by this digital signal. As well as
By detecting the defect position, the defect property of the object can be grasped accurately and quantitatively.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a waveform diagram of a defect detection signal and an AC component signal.

FIG. 3 is an explanatory diagram showing a defect detection signal (a), an AC signal waveform (b), and an estimated defect property (c) for a specific example.

FIG. 4 is a configuration diagram of a conventional leakage magnetic flux detection device.

[Explanation of symbols]

 10 electromagnet 21 magnetic sensor array 50 n-channel type amplifier 60 length measuring instrument 70 A / D converter 80 central processing unit

Claims (2)

[Claims] 1. A magnetic flux for magnetizing a subject and a magnetic flux leaking from a defective portion of the subject which is disposed between the magnet and a pole between the magnets so as to be perpendicular to the magnetization direction in a plane parallel to the plane of the subject. A leakage magnetic flux detector including a magnetic sensor array composed of n individual elements for detecting a magnetic field; an n-channel amplifier amplifying a defect detection signal of the magnetic sensor array; and the subject and the leakage magnetic flux detector. A length measuring device for generating a relative position signal, an A / D converter for digitizing the relative position signal of the length measuring device of the defect detection signal of the n-channel amplifier, and the digitalized defect detection signal in advance. A central processing unit that extracts a set feature amount and detects a defect position from the digitized relative position signal to quantitatively estimate the defect property. Apparatus. 2. The leakage magnetic flux detection device according to claim 1, wherein a maximum value, a minimum value, and an AC component zero-cross point of the defect detection signal are extracted as feature amounts.