JPS61243356A - Eddy current flaw detection tester - Google Patents

Abstract

PURPOSE:To reduce effect of liftoff due to chattering, vibration or the like of an object to be detected, by connecting exciting coils and detection coils in series. CONSTITUTION:A plurality of detection ends 1-4 are arranged about a rotor 11 and each made up of the even number of detection coils 1A and 1B and one exciting coil 1E, which is connected in series between the detection ends and the detection coils in one of the detection ends are connected in series. An object to be detected 20 moves straight while the detection ends 1-4 are turning thereabout. The sine wave voltage from an oscillator 31 at a control section is supplied to the exciting coil through an amplifier 32. The impedance of the entire exciting coil is kept almost constant as the effect of a gap with the object being detected is canceled and is detected with the detection coil on the top surface of a defect. The voltage change is equalized due to the series connection of the detection coils while the liftoff signal due to the chattering of the object being detected is canceled and thus, is limited to a large extent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an eddy current flaw detection testing device for detecting surface defects in elongated conductors having a circular cross section, such as rods, wires, and tubes.

[Conventional technology]

When performing eddy current testing for the purpose of detecting long defects extending in the axial direction on the outer surface of wires, pipes, etc. (hereinafter referred to as "linear defects"), the probe coil is usually placed around the test object. A so-called rotary flaw detection method is used in which the test object is rotated or the probe coil is fixed and the test object is rotated. FIGS. 2 and 3 are explanatory diagrams of an example of the prior art.

The eddy current flaw detection device is composed of a detection section 110 and a control section 130. In the detection unit 110, the electric motor 112
The rotation of the rotor 111 is transmitted to the rotor 111 by the boot IJ 113 and the belt 114. The rotor 111 has four detection coil pairs A and B (22IA, 221B, 222A,
222B, 223A.

223B, 224A, 224B) are provided.

Briefly explain the operation. The sine wave voltage of the oscillator 131 is power amplified by the power amplifier 132, and the power is amplified by the power amplifier 132.
, are supplied to the detection coil through an electromagnetic coupling 115. Conversely, detection coil pair A.

The signal from B is transmitted to the stator 116 by the electromagnetic coupling 115 and then to the eddy current flaw detector control section 130.
is being transmitted to. In the device shown in this figure, each coil pair includes a bridge circuit 133, an amplifier 134, a phase shifter 135, a phase detection circuit 136, a bandpass filter 137, and a pulse height discrimination circuit 1.
38 etc. are provided. In the case of this figure, since there are four coil pairs, four series of the above circuits are provided. Generally, eddy current flaw detection tests using probe coils have the disadvantage that they are greatly affected by variations in the distance between the test object and the probe coil (hereinafter referred to as "liftoff").

On the other hand, JP-A-58-179354 (5B, 1
As shown in 0.20), a rotary probe-type deep wound device equipped with a distance sensor and a gap adjustment mechanism has been proposed in order to keep the variation in lift-off constant. However, this device requires a distance sensor and has a complicated mechanism. In addition, the third non-destructive inspection
As shown in Vol. 3, No. 2, p. 185 (February 1980), a method has also been proposed in which the influence of lift-off is suppressed by using two frequencies and signal processing. However, with this method, it is necessary to know the phase relationship between the defect signal and the lift-off signal in advance, and if the relationship between the two changes due to changes in the material of the test object, the settings of the eddy current flaw detection device must be reset. The disadvantage is that it does not.

[Problem that the invention seeks to solve]

As mentioned above, eddy current flaw detection equipment that uses conventional probe coils is extremely susceptible to lift-off, and the devices and methods that have been proposed to deal with this are mechanically complex or complex. There is a problem that signal processing is required.

[Means for solving problems]

The present invention has been made in view of the above, and the eddy current flaw detection device according to the present invention has a plurality of mutual induction type probe coils arranged at approximately equal intervals on the surface of a test object, and the excitation coils are connected in series. , and the detection coils are also connected in series.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a diagram showing the basic concept of the present invention. In FIG. 1, 11 is a rotor, around which two or more (four in this figure) detection ends 1, 2, 3, . and 4 are provided. Each of these detection ends is composed of an even number (two in this figure) of detection coils IA, IB and one excitation coil IE. In this case, in order to improve magnetic flux efficiency, the valley detection coil uses magnetic cores IAC and IBC with good high frequency characteristics, such as ferrite cores. The excitation coils are connected in series between each detection terminal, that is, IE-2E-3E-4E (2E to 4E are the excitation coils of detection terminals 2 to 4, although not shown).
Connected. Multiple detection coils within one detection end are
Similarly, LA-2A-3A-4A and IB-
They are connected in series like 2B-3B-4B. The control unit 30 includes an oscillator 31, a power amplifier 32, and one or more (
In this figure, there is one) bridge circuit 33, amplifier 34
, a phase shifter 35, a phase detection circuit 36, a bandpass filter 37, and a pulse height discrimination circuit 38.

[Effect]

Next, the operation will be explained with reference to FIG. Subject 20
travels straight, and the detection ends 1, 2.3 and 4 rotate around it. In this way, the entire surface of the subject is scanned in a spiral manner. The sine wave voltage output from the oscillator 31 of the control section is amplified by the power amplifier 32, and the excitation coil (IE, 2E,
3E and 4E). At this time, the input impedance of the excitation coil viewed from the output end of the power amplifier varies greatly depending on the relative position between the excitation coil and the subject, especially the gap. However, in the method of the present invention, since the excitation coils are connected in series, the impedance of the excitation coil as a whole is canceled out by the influence of the gap between the excitation coil and the subject, and the excitation current is kept almost constant regardless of gap fluctuations. dripping If there is a defect on the surface of the specimen, one of the detection ends 1, 2, 3, and 4 scans the defect, and the excitation current generates an alternating magnetic field, and an induced current ( eddy current) flows. If there is a defect on the surface of the object, the flow of induced current will be disturbed both in direction and quantity. As a result, the magnetic flux due to the induced current changes similarly. The change in magnetic flux is detected as a voltage change by a detection coil on the top surface of the defect. Detection coil I
A, 2A.

3A and 4A (and IB, 2B, 3B and 4B)
Since they are connected in series, they are averaged and the overall voltage change is detected as 1/4 of that change. However, because the four coils are connected in series, lift-off signals due to backlash of the subject are canceled out and become very small. That is, when the subject 1 approaches the detection end 1, the induced voltage in the detection coil IA of the detection end 1 increases, but as the subject 1 moves away from the detection end 3, the induced voltage in the detection coil 3A decreases. Detection coil IA
This is because -2A, -3A, and 4A are connected in series, so the detection coil as a whole is averaged, and the lift-off signal is suppressed. For the above reasons, the defect detection signal will be reduced to approximately 1/4, but since the influence of lift-off will be greatly suppressed, the defect detection ability will be significantly improved compared to the case of each detection end alone. .

(Example) FIG. 4, FIG. 5, FIG. 6, and FIG. 7 are examples of the present invention. 4 and 5 are a side view and a front view of the detection end, and FIG. 6 is a sketch showing the positional relationship of the detection end with respect to the subject.

One detection end includes detection coils IAa, IAb, IAc,
Eight detection coils, IAd and IBa,], Bb, IBc, and LBd, and one excitation coil]E are provided. The four detection ends provided in the circumferential direction are connected as shown in FIG. 7 to form four circuits. By doing this, in addition to the lift-off signal suppressing effect described in (effect), there is an advantage that since the excitation coil is large, the gearing relative to the subject becomes smaller, making it more resistant to lift-off fluctuations. Furthermore, by using multiple small detection coils in this way, it is effective to compensate for the relative decrease in sensitivity due to series connection and to enable high-speed flaw detection. Although the above description has been made regarding a rotary eddy current flaw detection device, it is clear that the present invention can also be applied to a so-called multi-probe method in which a large number of probe-type coils are arranged in the circumferential direction of the test object.

(Effects of the Invention) As explained above, the eddy current flaw detection testing device of the present invention can significantly reduce the influence of lift-off caused by backlash, vibration, etc. of the test object by connecting each excitation coil and detection coil in series. This improves the signal-to-noise ratio of defect detection.
Defect detection ability can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for explaining the invention in detail, and FIG.
Figure 3 is an explanatory diagram of the prior art, Figure 3 is an explanatory diagram of the arrangement of detection coils on the rotor in the prior art, Figure 4 is a side view of the detection end according to the embodiment of the present invention, and Figure 5 is a front view of the same. , FIG. 6 is an explanatory diagram showing the relative positional relationship between the detection end and the subject, and FIG. 7 is an explanatory diagram of the detection coil connection according to the embodiment of the present invention. 1.2, 3.4 Detection end including excitation coil and detection coil IA, IB, 2A, 2B, 3A, 3B, 4A, 4
B Detection coil (used as a pair in A and B) I
Aa, IBa, IAb, IBb, IAc, IBc, IA
d, IBd Detection coil IAC, ABC detection coil magnetic core 1 1E, 22.3E, 4E Excitation coil 10 Detection section 11 Rotor 12 Motor 13
Pulley 14 Held 15 Electromagnetic compression ring
16 Stator 17 Terminal board 20 Test object 30
Control unit 31 Oscillator 32 Power amplifier 33
Bridge circuit 34 Amplifier 35 Phase shifter 36
Detection circuit 37 Bandpass filter 38 Amount of pulse height discrimination circuit Patent attorney for Nippon Steel Corporation Minoru Aoyagi

Claims (1)

[Claims] In an eddy current flaw detection testing device that detects surface defects in elongated conductors with circular cross sections such as rods, wires, and tubes, a plurality of mutual induction type probe coils are placed facing each other at intervals on the surface of the test object. An eddy current flaw detection testing device characterized in that the excitation coils are arranged at approximately equal intervals in the circumferential direction of a test object, and the excitation coils are connected in series, and the detection coils are also connected in series.