JPS62255863A - Eddy current flaw detector - Google Patents

Abstract

PURPOSE:To detect a defect of an object to be inspected with high accuracy, by bringing a signal induced by a search coil through which the object to be inspected passes, to phase detection, and deriving a difference signal between one output signal and an inversion signal obtained by bringing the other output signal to phase inversion. CONSTITUTION:An object to be inspected 18 serving as a metallic pipe is passed through a search coil which is on one side of a bridge circuit 16, and to which an inspecting signal has been applied. A flaw detecting signal Sy induced by a coil 20 is supplied to phase detectors 26A, 26B through a band amplifier 22. A surface defect signal Sya and an internal defect signal Syb which are obtained are supplied to rejection circuits 30A, 30B through BPFs 28A, 28B, respectively, and noises are eliminated. The processed signal Sya, and a signal obtained by passing the processed signal Syb through a phase inverter 32 are supplied to a differential operator 34, and by an output of the operator 34, a defect of the object to be inspected 18 can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Y'f) The present invention is applicable to 9. For example, welding defects on metal pipes obtained by forming and welding sheets of aluminum or other non-ferrous metals or surface scratches on drawn metal pipes. The present invention relates to improvements in eddy current flaw detectors suitable for detecting

(Prior art) In order to detect defects such as pinholes, cracks, and poor welding in metal pipes obtained by forming metal sheets, the frequency of the inspection signal is increased to detect surface defects using the skin effect. , the unevenness of the metal pipe, the surface roughness of the beard 9, the variation in pipe dimensions, etc. are also detected, and there is no difference between the defect signal and the defect signal that should be detected, resulting in a decrease in the S/N ratio. For this reason, the frequency of the inspection signal is lowered to increase the penetration depth to detect defects within a wall thickness of 1 to 2 mm in the metal pipe. However, if this method is used, as shown in Figure 1, if the metal pipe is the outer sheath of the cable, it will penetrate into the internal cable body and detect it, which will increase the noise and similarly reduce the S/N ratio. There was a drawback that it decreased. In FIG. 1, the reference numeral 1 indicates the metal pipe, the reference numeral 2 indicates the cable body, and the reference numerals 1a, lb, and 1c respectively indicate the pinhole, M groove, and welded part of the metal pipe 1.
In order to eliminate these drawbacks, the diameter of the search coil was made as small as possible and the search coil was brought closer to the metal pipe to increase the filling rate and increase the gain of the search coil, but S/
It was not possible to significantly improve the N ratio.

(Purpose of the invention) The object of the present invention is to improve pinholes in metal vibrators.

An object of the present invention is to provide an eddy current flaw detector that can accurately detect defects within wall thickness such as cracks and poor connections.

(Structure of the Invention) The eddy current flaw detector according to the present invention includes a search coil through which an object to be inspected passes, at least two phase detectors for phase detecting the induced signal induced by the search coil, and two phase detectors. It is characterized by comprising a differential arithmetic unit that obtains a difference signal between one of the two output signals and an inverted signal obtained by inverting the phase of the other output signal.

The search coil detects a defect signal, and since this defect No. 48 has a phase difference depending on the depth position of the defect, the defect position can be determined by phase detection. Therefore, the defect within the thickness of the metal vibrator can be detected. can be detected. In addition, if the phase of one phase-detected output is inverted and the other output is applied to a differential multiplier, the difference No. 45 between them is eliminated, but this difference signal is unnecessary. Since noise can be removed, defects with a large S/N ratio can be detected, and defects within the thickness of the metal vibrator can be detected with high accuracy.

(Embodiment) To explain the embodiment of the present invention in detail with reference to the drawings, FIG. 2 shows an eddy current flaw detector 10 according to the present invention, which includes a crystal oscillator 12 and a crystal oscillator. A frequency divider 14 that can obtain inspection signals selected at various frequencies by dividing the frequency of It consists of a search coil 20 through which the object to be inspected (metal vibrator) 18 passes.

In addition, this eddy current flaw detector 10 has two phase detectors in which a flaw detection signal sy induced in a search coil 20 is supplied via a band #g width filter 22, and phase shifters 24A and 24B detect the flaw detection signal in phase using control signals. Detectors 26A, 26B and bandpass filters 28A, 28B, ! that pass only the defective signal portion of the two output signals Sya, Syb from these two phase detectors 26A, 26B. : The outputs of these bandpass filters 28A, 28B are amplitude-discriminated to remove small-amplitude noise parts.
The differential calculation unit 34 calculates a difference signal 5 (ya-yb) between one of the outputs of B and the inverted signal obtained by inverting the phase of the other output via the phase inverter 32. This differential computing unit 3
The output of No. 4 is supplied as it is to a recorder 36, and is also sent to an alarm etc. via a defect discriminator 38 which discriminates defects based on the magnitude of the amplitude.

Next, to describe the operation of the eddy current deep wound device described in Section 2, the object to be inspected 18, which is a metal vibrator, is passed through the search coil 20, which is located on one side of the bridge circuit 16 and to which an inspection signal is applied. If there is a flaw on the object 18, the balance of the bridge circuit 18 is broken and a flaw detection signal S indicating a defect is generated in the search coil 20.
y is induced. Since this flaw detection signal sy is a minute voltage, it is amplified by the band #g amplifier 22.

Phase detection is performed by phase detectors 26A and 26B.

As already mentioned, the search coil 20 induces a flaw detection signal sy with different phases inside and outside the inspected object 18 with respect to the inspection signal, which is a fundamental wave. Therefore, when the flaw detection signal sy is phase detected by the phase detectors 26A and 26B, a surface defect signal Sya indicating one surface defect and an internal defect signal syb indicating an internal defect are obtained. These defect signals Sy
a and Syb are band pass filters 28A and 2, respectively.
The signal passes through 8B and undergoes frequency discrimination, and also passes through rejection circuits 3OA and 30B for frequency discrimination, thereby removing noise corresponding to the frequency and noise corresponding to the amplitude, respectively. Figure 3 (
A) and (B) respectively represent the surface defect signal Sya and the internal defect signal syb processed in this way. The differential arithmetic unit 34 receives the surface defect signal Sya processed in this way as it is, and also receives an inverted signal obtained by inverting the internal defect signal syb by 180', and generates a difference signal S (ya-yb) between them. form. FIG. 3(C) shows the difference signal 5(ya-yb) obtained in this way.As can be seen from FIG. 3, this difference signal 5(ya-yb)
is calculated so that the level of noise not removed by the band pass filters 28A, 28B and the rejection circuits 30A, 30B becomes zero, so only the defect signal portion appears prominently, so the Defects can be easily determined. In addition, in Fig. 3, the St of each signal
indicates an internal defect portion, So indicates a surface defect portion, and Sn indicates a noise portion.

(Effects of the Invention) As described above, according to the present invention, defects within the wall thickness such as pinholes, cracks, and welding defects in metal pipes can be detected with high accuracy, and therefore the reliability of the eddy current flaw detector is improved. There are practical benefits that can improve stability.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of an object to be inspected according to the present invention, Fig. 2 is a schematic system diagram of an eddy current flaw detector according to the present invention, and Fig. 3 (A) and (B) are two-phase A waveform diagram of the output signal of the detector, and (C) a waveform diagram of the difference signal. 10---1 eddy current flaw detector, 16---bridge circuit, 18---1 object to be inspected, 20---search coil, 26A, 26B-1---phase detection vessel, 32
−−−−−Phase inverter. 34---m-Differential arithmetic unit.

Claims (1)

[Claims] A search coil through which an object to be inspected passes, at least two phase detectors that detect the phase of the induced signal induced in the search coil, and one output signal and the other output of the two output signals from the two phase detectors. An eddy current flaw detector characterized by comprising a differential arithmetic unit that obtains a difference signal from an inverted signal obtained by inverting the phase of a signal.