KR0163959B1 - Eddy current flaw detection apparatus - Google Patents

Abstract

According to the present invention, a pair of detection coils are disposed on the same axis as the conductors along the conveyance path of the conductors so that the magnetic field generated by the coils is in reverse phase, and the detection coils constitute two sides of the bridge. When the balance of the bridge collapses due to a relative change in inductance, the bridge is disposed on the same axis as the detection coil so that the generated magnetic fields are in phase with each other between the AC bridge circuit for outputting the abnormal detection signal and the detection coil. A eddy current detector having a pair of resonant coils set so that the induced currents cancel each other in a balanced state, and a capacitance circuit connected to the resonant coils for the purpose of resonating the oscillation frequency of the detection coil.

Description

Vortex flaw detector.

1 is a circuit diagram showing a schematic configuration of a vortex flaw detector according to the present invention.

2 is a circuit diagram showing one example of a capacitor circuit in the same apparatus.

3 and 4 show the operation of the apparatus.

5 is a schematic view showing another preferred embodiment of the present invention.

6 is a schematic view showing a conventional vortex flaw detector.

7 and 8 are explanatory diagrams showing problems in the conventional apparatus.

* Explanation of symbols for main parts of the drawings

1: conductor 2: AC power

3: AC bridge circuit 4: Capacitive circuit

24: transformer 30: differential amplifier

35: operational amplifier 50, 60: phase detection circuit

L1, L4: Detection coil L2, L3: Resonant coil

P1, P2: Periodic signal

The present invention relates to a vortex flaw detector for detecting a foreign matter that is damaged or mixed with a metal material.

In a manufacturing process such as copper wire, if foreign matter such as iron pieces or the like is mixed in the copper wire material, or if the material is damaged, the cause of disconnection during the drawing process Becomes

For this reason, it is necessary to inspect the presence of foreign substances or damages before the drawing process.

Conventionally, the vortex flaw detector as shown in FIGS. 6-8 is used for this kind of inspection.

Reference numeral 1 denotes a conductor that travels, and the detection coil La (Lb) is spaced apart from each other on the same axis without contact with the conductor 1.

The detection coil La (Lb) is connected so as to constitute two sides of the AC bridge circuit, and if there is no damage in the conductor 1 passing through the detection coil La (Lb), the terminal (A) (B) The output signal between them is adjusted to zero balance.

According to this apparatus, when damage or foreign matter passes through the center of the detection coil La (Lb), the eddy current in the conductor 1 changes, and the difference in inductance of the detection coil La (Lb) ( I) occurs and the zero balance collapses, so an output signal is generated between terminals A and B, and damage or foreign matter can be detected based on this signal.

The detection coil La (Lb) is a structural view in which copper wires are connected so that the direction of the magnetic field generated as indicated by an arrow in FIG. 7 is in-phase. As indicated by arrows in the figure, a structure in which the magnetic field is differentially connected so that the direction of the magnetic field becomes anti-phase is preferable.

In such a differential connection, for example, the conductor 1 is eccentric in the detection coil La (Lb), or the composition of the conductor 1 is changed so that noise is detected in each detection coil La (Lb). Even if a signal is generated, these noise signals cancel each other, so that the noise component of the output signal can be reduced to increase the SN ratio.

However, in the vortex flaw detector described above, since the detection coil La (Lb) always generates the reverse magnetic field, the mother-of-pearl repels each other and it is difficult for the magnetic field to sufficiently penetrate into the inside of the conductor 1. The partial detection sensitivity is lowered.

For this reason, it is difficult to detect these when small damage or a small amount of foreign matter is located near the center axis of the coil.

This invention is made | formed in order to solve the said subject, and an object of this invention is to provide the vortex flaw detector which can detect small damage and a small amount of foreign substances with high abnormality detection sensitivity.

In order to achieve the above object, the present invention has a pair of detection coils disposed on the same axis as the fire path of the electric conductor along the conveyance path of the conductor so that the magnetic field generated by the coil is reversed. An AC bridge circuit that outputs an abnormal detection signal when the inductance of the detected detection coil changes relative to the bridge and collapses, and a detection coil which is electric so that the generated magnetic fields are in phase with each other between the detected detection coils and It is composed of a pair of resonant coils arranged on the same axis and set in such a way that the induced currents generated in the balanced state of the bridges cancel each other, and a capacitor circuit connected to the resonant coils configured to form a resonant circuit. Provide a vortex flaw detector.

In this vortex flaw detector, in the case where the conductor is free from damage or foreign matter, the induced current generated in each resonant coil due to the induction of electrons from the respective detection coils is reversed in phase and the current value thereof is the same. The currents cancel each other out so resonance does not occur.

On the other hand, if there is damage or foreign matter inside the conductor, there is an imbalance in the magnetic field generated by each of the detection coils. Therefore, a difference occurs in the induced current value generated by each of the resonant coils, and a current corresponding to the difference flows and resonates. The coil resonates.

As a result, the induction of the detection coil is further changed and the balance of the AC bridge circuit is collapsed, so that the detection sensitivity of the abnormal signal can be increased as compared with the conventional apparatus.

EXAMPLE

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

FIG. 1 is a circuit diagram showing one preferred embodiment of the vortex flaw detector according to the present invention. The detection coil L1 and the resonant coil (1) are arranged on the same axis as the conductor along the conductor 1 traveling from all the steps not shown. L2), the resonant coil L3, and the detection coil L4 are arranged at intervals in the axial direction.

The detection coils L1 and L4 are the same as the conventional apparatus, and constitute the AC bridge circuit 3 together with the two resistors R1 and R2, and are differentially connected so that the magnetic fields generated are in phase with each other. have.

When the resistances of R1 and R2 and the inductances of L1 and L4 are not abnormal in the conductor 1, the AC bridge circuit 3 is set to zero balanced so that no signal is generated between the connection points A and B. Is determined.

On the other hand, the resonant coils L2 and L3 are the same, and are copper-connected so that the generated magnetic field is in phase.

These resonant coils L2 and L3 are connected in series to the capacitor circuit 4 to form a resonant circuit.

When there is no abnormality in the conductor 1, the induction current generated in the resonant coil L2 by the electromagnetic induction of the detection coil L1 and the induction generated in the resonant coil L3 by the electromagnetic induction of the detection coil L4. The currents are in reverse phase and their current values are the same, and are set to cancel each other.

The oscillator 21, the phase shift circuit 22, the power amplifier 23, and the transformer 24 are configured to form an AC power supply 2 that supplies power to the AC bridge circuit 3. It is installed.

The oscillator 21 has the same angular frequency ( Generates a two period signal P1 (P2), which has a phase angle of P2 from the phase angle of P1. / 2 sided with.

The phase shift circuit 22 holds, for example, an operation member such as a volume knob.

The oscillator 21 output signal P is supplied to the phase shift circuit 22 to obtain a signal having a phase shifted from the phase of the signal P by a phase shift value corresponding to the operation of the operation member.

Phase shift value is 0 ~ Can be adjusted in the range of.

The output signal of the phase shift circuit 22 is amplified by the power amplifier 23, and the output signal of the power amplifier 23 is supplied to one terminal of the input coil of the transformer 24.

The other terminal of the input coil of the transformer 24 is grounded, and the output coil of the transformer 24 is connected between the connection points C and D of the AC bridge circuit 3.

In addition, resistors 31-34 and operational amplifiers 35 are provided to form a differential amplifier 30 which amplifies the voltage between the connection points A and B of the AC bridge circuit 3.

The output signal of the differential amplifier 30 is supplied to the buffer amplifier 40 to obtain a detection signal.

In addition, two phase detection circuits 50 and 60 having the same function and characteristics are provided so that the periodic signal P1 and the detection signal S are respectively the first and second phase detection circuits 50. The input signal is supplied to the input terminal, and the periodic signal P2 and the detection signal S are supplied to the first and second input terminals of the phase detection circuit 60, respectively.

Each phase detection circuit detects the same phase component which is synchronized with the input signal of the first input terminal from the input signal of the second input terminal.

In addition, two low pass filters 70 and 80 are provided to block high harmonic components from the output signals of the phase detection circuits 50 and 60, and these low pass filters 70 and 80 are provided. The output signal of is supplied to the X-axis and Y-axis input terminals of the oscilloscope (not shown), respectively.

Next, FIG. 2 is a circuit diagram showing a specific example of the capacitor circuit 4. The capacitor circuit 4 mainly includes two operational amplifiers 5, 6, variable resistors 7, 8, and a capacitor 9. And the resonant frequency of the resonant circuit L2 and L3 and the capacitor circuit 4 can be adjusted by adjusting the variable resistor 7, and the variable resistor 8 is adjusted. The resonance Q value of the resonance circuit can be adjusted.

However, in the present invention, not only the circuit of FIG. 2, but also the capacitor circuit may be configured by a simple capacitor, a capacitor variable capacitor, or the like, and other circuits may be changed as necessary.

In the vortex flaw detector having the above-described configuration, when the conductor 1 is free of damage or foreign matter, induction generated in each resonant coil L2 and L3 by electromagnetic induction from each of the detection coils L1 and L4. Since the currents are in phase with each other and the current values are the same, these induced currents cancel each other so that resonance does not occur.

However, if the conductor 1 is damaged or foreign matter passes through the detection coil L1, the inductance of the detection coil L1 changes.

As a result, an imbalance occurs in the magnetic fields of the detection coils L1 and L4. Therefore, a difference also occurs in the induced current generated in each of the resonant coils L2 and L3, and an AC current corresponding to the difference flows to the capacitor circuit 4. ) And the resonant coils L2 and L3 resonate.

When resonating in this manner, the influence further increases the inductance of the detection coil L1.

As a result, since the balance of the AC bridge circuit 3 collapses, a signal is generated between the junction points A and B. FIG.

This signal is amplified by the differential amplifier 30 and the buffer amplifier 40 to obtain a detection signal.

This operation also occurs when damage or foreign matter in the conductor 1 passes through the detection coil L4.

The detection signal includes a detection component S and a noise signal N. The detection component S is generated by the impedance change of the detection coil L1 or the detection coil L4.

3 shows the change in the impedance of the detection coil. When the resonance coils L2 and L3 are not used, the impedance Z of the detection coil is the resistance (R) and the reactance ( L), where the inductance L includes the inductance inherent in the detection coil and the inductance generated by damage or passage of foreign matter.

In the case where the resonant coils L2 and L3 are used, the inductance of the detection coil is, for example, L to L +. Increases to L

Therefore, the impedance of the detection coil changes from Z to Za, and the declination of the impedance == tan ^-1 ( L / R) a〓tan ^-1 { (L + L) / R}.

4 shows one example of the detection component S and the noise signal N included in the detection signal.

The phase of the detection component S is from the phase of the noise signal N. the angle determined by a sided by a '

The detection signal S + N thus obtained is supplied to the phase detection circuits 50 and 60 so that a component synchronized with the periodic signal P1 from the detection signal S + N by the phase detection circuit 50 is detected. do.

Similarly, the component synchronized with the periodic signal P2 is detected from the phase detection circuit 6.

The output signals of the phase detection circuits 50 and 60 are supplied to the X and Y axis input terminals of the oscilloscope through the low pass filters 70 and 80.

As a result, vectors corresponding to the detection component S and the noise signal N are respectively displayed on the oscilloscope in an identifiable manner as shown in FIG. 4, for example.

Before performing damage or foreign matter detection, the operator adjusts the phase shift value of the phase shift circuit 22 so that the vector of the noise signal S is displayed along the X axis or the Y axis.

By this adjustment, the detection component S and the noise signal N can be easily identified.

In the preferred embodiment as described above, since the detection component S of the detection signal can be obtained at a sensitivity higher than that of the conventional apparatus, the detection sensitivity to damage or foreign matter in the conductor 1 can be improved.

In this apparatus, since the separation amount of the detection coils L1 and L4 is increased by providing the resonance coils L2 and L3, the magnetic field of the detection coils L1 and L4 is increased. Since the offsets are reduced, the sensitivity can be improved.

In the device of the present invention, when the material and diameter of the conductor 1 change, the inductance of the resonant coils L2 and L3 changes to change the resonant frequency. However, in the present embodiment, the capacitance circuit 4 By adjusting the variable resistor 7, the resonant frequency of the resonant circuit composed of the capacitor circuit 4 and the resonant coils L2 and L3 can be adjusted, and it is easy to always match the resonant frequency with the AC power supply.

Since the resonance Q value can be adjusted by adjusting the variable resistor 8, the Q value of the resonance circuit composed of the resonance coils L2 and L3 and the capacitor circuit 4 is changed in the resonance state to detect abnormality. You can also set the sensitivity to the optimum value.

In the preferred embodiment of the present invention, the conductors 1 are arranged to penetrate the respective coils L1, L2, L3, and L4. Instead, as shown in FIG. (L1) (L2) (L3) (L4) may be accommodated in the casing 10 on the same axis, and a measuring instrument may be comprised.

In this case, this measurement person also scans the vicinity of the surface of the conductor 1, and detects the abnormality of the conductor 1.

Claims (5)

Holds a pair of detection coils L1 and L4 which are spaced apart on the same axis as the conveying path of the conductors along the conveying path of the conductor 1 so that the magnetic field generated by the coil is reversed, and detects the electric Between the AC bridge circuit 3 which outputs an abnormal detection signal when the inductance of the coil is changed relative to the balance of the bridge and the detection coil which is electric so that the generated magnetic fields are in phase with each other. Arranged on the same axis, the pair of resonant coils L2 and L3 are set so as to cancel the induced currents generated when the bridges are in equilibrium with each other, and the resonant coils electric to form a resonant circuit. Vortex flaw detector, characterized in that consisting of a capacitance circuit (4). The vortex flaw detector according to claim 1, wherein the capacitance circuit (4) is provided with a frequency adjusting device for adjusting the resonance frequency of the electrical resonance circuit. The vortex flaw detector according to claim 1, wherein the capacitance circuit (4) is provided with a Q value adjusting device for adjusting the resonance Q value of the electric resonance circuit. The method according to claim 1, wherein each phase has the same frequency, and one phase is from the other phase. AC power source 2, which is shifted by 1/2 and generates one of the first and second period signals P1 and P2 supplied to the AC bridge circuit 3, one of which is electric, and an electric power to obtain a detection signal. The differential amplifier 30 amplifies a signal generated between two connection points A and B of one AC bridge circuit 3, and is included in the detection signal which is synchronized with the first cycle signal P1. First phase detection circuit 50 for detecting the X-axis component signal and second phase detection for detecting the Y-axis component signal included in the detection signal synchronized with the second periodic signal P2 described above. And a display device which displays a circuit (60) and a vector of the detected detection signals based on the aforementioned X and Y axis component signals. 5. The vortex flaw detector according to claim 4, further comprising a phase adjusting device for adjusting the phase of the periodic signal (P1) supplied to the alternating current bridge circuit (3).