JPH0763730A - Eddy current flaw detector - Google Patents

Abstract

PURPOSE:To obtain eddy current flow-detector which can easily detect flaws or foreign matters generated in a conductor from a near-surface part to a deeper part. CONSTITUTION:An AC bridge circuit 2 is constituted by coaxially and separately arranging a pair of detection coils L1 and L2 along a conductor carrying passage. A sweep voltage generation circuit 16 generates a slowly changing sweep voltage and a VCO(voltage-controlled oscillator) 15 impresses a voltage of a slowly changing frequency upon the AC bridge. Flaws or foreign matters near the surface of a conductor can be detected with high sensitivity from an eddy current generated when the frequency of the impressed voltage is high and those in deeper parts can be detected from another eddy current generated when the frequency is low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector for detecting flaws on a metal material and foreign matter contained therein.

[0002]

2. Description of the Related Art In the process of manufacturing a copper wire or the like, if a foreign material such as an iron piece is mixed in the inside of the copper wire material or if it is scratched, it may cause a break in the wire drawing process. For this reason, it is necessary to inspect for foreign matters and scratches in advance before the wire drawing step.

Conventionally, an eddy current flaw detector as shown in FIG. 2 has been used as an apparatus effective for such inspection.
In the figure, reference numeral 1 is a running conductor, and this conductor 1
The detection coils L1 and L2 are arranged in contact with and coaxial with each other. The detection coils L1 and L2 have resistors R1 and R, respectively.
An AC bridge circuit 2 is configured together with 2. As shown by the arrows in FIG. 2, the detection coils L1 and L2 are differentially connected so that the directions of the magnetic fields are opposite to each other. Then, the AC bridge circuit 2 is in a zero balance state when the conductor 1 passing through the detection coils L1 and L2 is free from scratches and foreign matter, and an output signal is not generated between the terminals A and B. It is set. On the other hand, the detection coils L1 and L2
When a flaw or a foreign object passes through the inside, the eddy current generated in the conductor 1 changes, the inductance of the detection coils L1 and L2 becomes different, and the zero balance is lost, so that an output signal is generated between the terminals A and B. It is possible to detect scratches and foreign substances based on the signal.

Reference numeral 11 denotes an oscillator, which generates a sine wave having a predetermined oscillation frequency, for example, 32 kHz, and the sine wave output is input to the power amplifier 12 and the phase adjusting circuit 20. Then, the sine wave signal input to the power amplifier 12 is amplified by the same amplifier and supplied to one end of the input side coil of the transformer 13. The other end of the input coil is grounded. On the other hand, the output side coil is connected between the terminals C and D of the AC bridge circuit 2 and applies an AC voltage to the AC bridge circuit 2.

The resistors 31 to 34 and the operation amplifier 35 constitute the differential amplifier 30 as a whole, and detect the voltage generated between the terminals A and B of the AC bridge circuit 2. Then, the output of the operation amplifier 35 is supplied to the buffer amplifier 40, and the detection signal S is output from the amplifier 40.

On the other hand, the phase adjustment circuit 20 has a dial for adjusting the phase, and it is possible to finely adjust the phase of the input signal within the range of "0 to 360 °" by operating the dial. That is, the sine wave signal input from the oscillator 11 to the phase adjustment circuit 20 is supplied to the phase distribution circuit 21 after the phase is adjusted to a stable state in this way. Then, the phase distribution circuit 21 outputs the same angular frequency “ω”.
And signals P1 and P2 which are 90 ° out of phase with each other.
Is output.

The signal P1 is supplied to the first input terminal of the phase detection circuit 50, and the detection signal S is supplied to the second input terminal thereof. Similarly, the signal P2 is input to the first input terminal of the phase detection circuit 60, and the detection signal S is input to the second input terminal thereof.
Each is supplied. Both phase detection circuits 50 and 60 have the same function and detect components having the same phase as the signals input from the respective first input terminals from the signals input from the respective second input terminals. Output. Then, the harmonic components of each output signal are removed by the low pass filters 70 and 80, and the output signal is X-axis of the oscilloscope 90.
It is supplied to the axis and Y axis input terminals respectively and observed.

Prior to inspecting the conductor 1, the inspector operates the dial of the phase adjusting circuit 20 in advance so that the Lissajous figure due to the noise signal unrelated to the defect is parallel to the X axis or the Y axis on the screen of the oscilloscope 90. Adjust so that After that, when the conductor 1 is made to travel and defective portions such as scratches and foreign substances pass through the detection coils L1 and L2 in sequence, a detection signal S corresponding to a change in inductance of both coils is obtained. That is, by observing a Lissajous figure having a different inclination with respect to the Lissajous figure due to the noise signal, the defect can be easily inspected.

[0009]

The eddy current generated in the conductor 1 is affected by the skin effect. Therefore, when the frequency of the voltage applied to the AC bridge is high, the eddy current generated by the detection coils L1 and L2 flows near the surface of the conductor 1. On the other hand, when the frequency of the voltage applied to the AC bridge is low, the eddy current generated by the detection coil flows from the surface of the conductor 1 to a deeper portion. Therefore, although it is possible to lower the frequency and set it as a detection target to a deeper portion of the conductor, there is a problem that the detection sensitivity decreases as the frequency decreases. On the contrary, when the frequency is increased, the detection sensitivity is increased, but only the defects near the surface can be detected.

However, in the inspection, it is required to properly use the high and low frequencies to perform the flaw detection on the conductor as deeply as possible and with high sensitivity. Therefore, there has been proposed a device that applies a voltage obtained by mixing a plurality of frequencies to an AC bridge by using a plurality of oscillators having different oscillation frequencies. FIG. 3 shows the configuration of the device. In the figure, components corresponding to those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numerals 11A, 11B ... Are a plurality of oscillators having different oscillation frequencies. The oscillation frequencies of the oscillators 11A and 1B are 1 kHz and 4 kHz, respectively.
z, the oscillator 11C has a frequency of 16 kHz, and the frequency of the next oscillator is four times that of the previous oscillator. Then, the plurality of frequencies are mixed by the mixing circuit 14, and the output is the power amplifier 1
Entered in 2. By mixing the frequencies of the predetermined number in this way, it is possible to easily separate the frequencies later. Then, the output of the power amplifier 12 is similarly supplied to the transformer 13, and the AC voltage having a plurality of frequency components is applied to the AC bridge circuit 2.

The output from the differential amplifier 30 is a filter 41 provided corresponding to each of the above oscillation frequencies.
A, 41B ... Next, the output signals of the respective filters are amplified by the amplifiers 42A, 42B ... And the detection signals S1, S2 ... Are output. The same configuration as that from the phase adjustment circuit 20 to the oscilloscope 90 shown in FIG. 2 is individually provided for each detection signal S1, S2 .... That is, for the oscillation frequency of 1 kHz, the phase adjustment circuit 20A to the oscilloscope 90A, the oscillation frequency of 4
Phase adjustment circuit 20B to oscilloscope 9 for kHz
It has a configuration of 0B, ....

When the conductor 1 is inspected by this structure, since a wide frequency range is covered in a scattered manner to some extent, a defect signal detected in the same frequency range can be detected with sensitivity corresponding to each frequency. Is.
However, since the frequencies are scattered, it is difficult to set the optimum flaw detection range for each part of the conductor 1. In addition, the configuration of providing the detection circuit group for the oscillation frequency is complicated and costly, and in addition, the inspector has to make phase adjustments and pay attention to a plurality of oscilloscope screens. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an eddy current flaw detector capable of continuously changing the oscillation frequency with a simple configuration.

[0014]

In order to solve the above-mentioned problems, in the present invention, a pair of detection coils arranged coaxially and at a distance along a conductor conveying path, and a bridge formed by these detection coils. In the eddy current flaw detector, which has two sides, an AC bridge circuit that outputs an abnormality detection signal by breaking the balance of the bridge when the inductance of each detection coil changes relative to each other, the voltage value changes gradually with time. And a oscillating means for outputting a signal having a frequency corresponding to the voltage value of the sweep voltage to the AC bridge circuit.

[0015]

In this eddy current flaw detector, when the sweep voltage generating means generates a sweep voltage that changes slowly with time,
The oscillating means outputs a signal having a frequency corresponding to the same voltage to the AC bridge circuit. Therefore, eddy currents generated when the frequency of the voltage applied to the AC bridge is high can detect scratches and foreign substances near the surface of the conductor with high sensitivity, while eddy currents generated when the frequency is low cause deeper conductors to be detected. It is possible to detect scratches and foreign matter on the part.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the arrangement of an eddy current flaw detector according to the embodiment of the present invention. In the figure, the sweep voltage generating circuit 16 has a voltage that continuously sweeps slowly over time in a predetermined voltage range, for example, as shown in FIG.
A sine wave voltage having an amplitude of ± 10 V shown in (A) is output.

Reference numeral 15 is a voltage-controlled oscillator (V
CO), and the output voltage of the sweep voltage generating circuit 16 is given as a frequency control voltage. Therefore, in FIG.
As shown in (A), since the output voltage of the sweep voltage generation circuit 16 changes in the range of -10 to + 10V,
The oscillation frequency of the VCO 15 is, for example, 1 kHz to 64 kHz.
It will change continuously in the range of z. In FIG. 4B, the oscillation frequency f of the VCO 15 decreases from high to high as time passes.
It is a model that shows how it changes from low to low.

Further, in this embodiment, the signal switching circuit 43 is provided, and normally the switch (not shown) provided in the circuit is set to the off state. If off,
The signal switching circuit 43 outputs the detection signal S from the buffer amplifier 40 to the phase detection circuits 50 and 60 as it is. On the other hand, when it is on, the detection signal S is output to both phase detection circuits only for a predetermined time after the output voltage of the sweep voltage generation circuit 16 exceeds a predetermined value, for example, 0V. Note that the configuration other than that described above is the same as that in FIG. 2, so elements corresponding to the respective configuration elements in FIG. 2 are assigned the same reference numerals, and descriptions thereof are omitted.

Then, as in the case of the conventional example, the inspector adjusts the Lissajous figure of the noise signal displayed on the oscilloscope 90 by the phase adjusting circuit 20 in advance, and then runs the conductor 1 to detect the defect. Observe the condition. At this time, since the frequency continuously changes as the conductor 1 travels, the oscilloscope 90 continuously displays the Lissajous figure corresponding to the frequency that changes momentarily. For this reason, the inspector can inspect the scratches and foreign substances generated in the deeper portion from the vicinity of the surface of the conductor only by observing the screen of one oscilloscope.

Further, when the switch of the signal switching circuit 43 is turned on by the inspector, the detection signal S is output only for a short time after exceeding 0V, for example.
In the case of (A), a Lissajous figure corresponding to a frequency near 24 kHz is observed. In this way, it is possible to observe the defect state in a state in which the frequency is narrowed down.

The voltage output from the sweep voltage generating circuit 16 is not limited to the sine wave shape, but may be a triangular wave shape, as long as the voltage changes slowly with time.

[0023]

As described above, according to the present invention, an eddy current flaw detector capable of continuously changing the oscillation frequency with a very simple structure can be obtained. Therefore, with respect to detection of various scratches and foreign matter generated from the vicinity of the surface of the conductor to a deeper portion, an appropriate flaw detection range can be obtained for each and an inspection can be easily performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an eddy current flaw detector according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional eddy current flaw detector.

FIG. 3 is a configuration diagram of a conventional eddy current flaw detector.

FIG. 4 is a diagram showing changes in frequency according to an embodiment of the present invention.

[Explanation of symbols]

 15 ... VCO (oscillating means) 16 ... Sweep voltage generating circuit (sweep voltage generating means)

Claims (1)

[Claims] 1. A pair of detection coils coaxially and separately arranged along a conductor conveyance path, and two sides of the bridge are formed by these detection coils, and when the inductance of each detection coil changes relative to each other, In an eddy current flaw detector equipped with an AC bridge circuit that outputs an abnormality detection signal due to an imbalance, a sweep voltage generating means for generating a sweep voltage whose voltage value changes gradually with time, and a voltage value of the sweep voltage An eddy current flaw detection device, comprising: an oscillating unit that outputs a signal of a corresponding frequency to the AC bridge circuit.