JP2013088345A - Eddy current flaw inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current flaw inspection device for appropriately detecting a position or length of a flaw in a circumferential direction of a conductor.SOLUTION: The eddy current flaw inspection device is provided with: a pair of detection coils (L1A and L2A to L1D and L2D) placed along a carrier path (250) of a conductor (200) to be inspected coaxially and away from it; and a detection part in which two lines of a bridge comprise respective detection coils of the pair of detection coils (L1A and L2A to L1D and L2D) and which includes an AC bridge circuit for outputting a detection signal showing whether or not balance of the bridge is lost. The pair of detection coils (L1A and L2A to L1D and L2D) have electromagnetic shielding bodies (51 to 54) placed at a part in the circumferential direction on a surface facing the carrier path (250) side of the pair of detection coils.

Description

  The present invention relates to an eddy current flaw detector.

  Conventionally, an eddy current flaw detector is used to inspect a defect on a conductor surface. In this eddy current flaw detector, for example, an AC signal is supplied to an AC bridge circuit in which a pair of detection coils are bridge-connected, and an inspection is performed by relatively moving the detection coil and the inspection object. In the eddy current flaw detector, when a defect such as a flaw on the surface of the conductor to be inspected passes through the detection coil, the eddy current generated in the conductor changes and a difference occurs in the inductance of each detection coil of the pair of detection coils. To detect defects. (For example, refer to Patent Document 1).

Japanese Patent No. 28882856

Incidentally, it is desired to detect the position or length of the defect in the circumferential direction of the conductor.
However, in the conventional eddy current flaw detector, although the position or length of the defect in the transport direction in which the detection coil and the conductor to be inspected are relatively moved can be detected, the position of the defect in the circumferential direction of the conductor or The length could not be detected.

  This invention is made | formed in view of such a situation, The objective is to provide the eddy current flaw detection apparatus which can detect appropriately the position or length of the defect in the circumferential direction of a conductor.

  The present invention has been made to solve the above-described problems. The present invention is directed to a pair of detection coils arranged coaxially and apart from each other along the transport path of a conductor to be inspected, and the pair of detection coils. A detection unit including an AC bridge circuit configured to output a detection signal indicating whether or not the bridge is broken by each of the detection coils of the coil, and the pair of detection coils, It is an eddy current flaw detector characterized by having an electromagnetic shielding body arranged in a part of the circumferential direction on the surface of the pair of detection coils facing the conveyance path.

  Moreover, the eddy current flaw detector of the present invention includes a plurality of the AC bridge circuits in the detection unit, and the plurality of AC bridge circuits are arranged at different positions in the conveyance path direction, and each of the plurality of AC bridge circuits. The electromagnetic shielding bodies included in the pair of detection coils are arranged at different positions in the circumferential direction.

  In the eddy current flaw detector according to the present invention, in the detection unit, the electromagnetic shields included in the pair of detection coils of each of the plurality of AC bridge circuits have different circumferential directions over the entire circumference of the surface facing the conveyance path side. It is arranged at a position.

  In the eddy current flaw detector according to the present invention, in the detection unit, based on the detection signal output from the AC bridge circuit and a circumferential position where the electromagnetic shield is disposed, The position of the defect in the circumferential direction is detected.

  In the eddy current flaw detector according to the present invention, in the detection unit, based on the detection signal output from the AC bridge circuit and a circumferential position where the electromagnetic shield is disposed, The length of the defect in the circumferential direction is detected.

  In the eddy current flaw detector according to the present invention, AC currents having different phases are supplied to the detection coils of the pair of detection coils.

  In the eddy current flaw detector according to the present invention, in the detection unit, the AC bridge circuit in which two sides of the bridge are configured by the first detection coil and the second detection coil that are the pair of detection coils. A first power source that supplies an alternating current having a predetermined frequency and a phase of the alternating current supplied to the second detection coil with respect to the alternating current supplied from the power source to the alternating current bridge circuit. The first output signal output as the detection signal of the first detection coil and the change of the inductance of the second detection coil, which are output as the detection signal of the AC bridge circuit A second phase shifter that changes the phase of the first output signal out of the second output signal output in response to the first phase shifter, and the phase change amount of the first phase shifter and the first phase shifter Phase of 2 Wherein the phase change amount of the same change amount.

  According to this invention, the position or length of the defect in the circumferential direction of the conductor to be inspected can be appropriately detected.

It is a schematic block diagram which shows an example of a structure of an eddy current flaw detector. It is a schematic block diagram which shows the structure of the eddy current flaw detector by one Embodiment of this invention. It is a schematic diagram which shows an example of a structure of the electromagnetic shielding body arrange | positioned at a detection coil. It is a figure for demonstrating the phase of the output detected by the alternating current bridge circuit. It is a schematic block diagram which shows an example of a structure of the alternating current bridge circuit of this embodiment. It is a figure which shows an example of the probe 10A of an inner probe type eddy current flaw detector.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing an example of the configuration of an eddy current flaw detector used in the present invention.
First, an outline of a method for detecting a defect due to a flaw, a foreign object, or the like of the conductor 200 to be inspected by the eddy current flaw detector will be described with reference to FIG.

  A pair of detection coils are arranged coaxially and spaced along the transport path 250 of the conductor 200 to be inspected. For example, the pair of detection coils L <b> 1 and L <b> 2 are arranged in a non-contact and coaxial manner with a certain distance from the conductor 200 along the transport path 250 of the conductor 200 to be inspected. Further, the pair of detection coils L 1 and L 2 are arranged coaxially along the conveyance path 250 and separated in the direction along the conveyance path 250. The detection coils L1 and L2 are connected as two sides of the bridge of the AC bridge circuit 3, and the resistances R1 and R2 are connected as the other two sides of the bridge. When an alternating current is supplied from the alternating current power source 31 to the alternating current bridge circuit 3 and an alternating current flows through the detection coils L1 and L2, an eddy current (inductive current) is generated in the conductor 200 by electromagnetic induction.

  If there is no defect in the conductor 200 passing through the detection coils L1, L2, the terminal K1 connected to the connection point between the detection coil L1 and the resistor R1, and the detection coil L2 and the resistor R2 The output signal between the terminals K2 connected to the connection point is adjusted to be zero balance. On the other hand, when the defect of the conductor 200 passes through the detection coils L1 and L2, the eddy current generated in the conductor 200 changes, the inductances of the detection coils L1 and L2 change relative to each other, and a difference occurs. The balance of the bridge is lost and a difference occurs in the output signal between the terminals K1 and K2. Therefore, the eddy current flaw detector detects a defect such as a flaw in the conductor 200 or a foreign object based on an output signal between the terminals K1 and K2, that is, a detection signal indicating whether or not the balance of the bridge is lost.

  The detection coils L1 and L2 are differentially connected such that the direction of the generated magnetic field is in reverse phase as indicated by the arrows in FIG. In general, it is known that a differential connection is preferable to a Japanese-style connection so that the directions of magnetic fields are in phase. For example, in the case of differential connection, even if a noise signal is generated in the detection coils L1 and L2 due to the conductor 200 being eccentric in the detection coils L1 and L2 or the composition of the conductor 200 being changed, etc. Noise signals cancel each other out, and the noise component of the output signal can be reduced to increase the S / N ratio. In the present embodiment, the case of differential connection is taken as an example, but the same can be applied to the case of summing connection. The connection point between the detection coil L1 and the detection coil L2 in FIG. 1 may be connected to GND (ground) and grounded.

  FIG. 2 is a schematic block diagram showing the configuration of the eddy current flaw detector 100 according to one embodiment of the present invention. 2 is a circuit similar to the AC bridge circuit 3 having the pair of detection coils L1 and L2 shown in FIG. 1, and includes four alternating currents indicated by reference signs A, B, C, and D. It is an example provided with bridge circuits 3A-3D. Hereinafter, the four AC bridge circuits 3A to 3D indicated by reference signs A, B, C, and D are respectively referred to as a first detection circuit A, a second detection circuit B, a third detection circuit C, and The fourth detection circuit D is assumed.

The eddy current flaw detector 100 includes a detection unit 10, a control unit 20, and a power supply unit 30.
The detection unit 10 includes a first detection circuit A, a second detection circuit B, a third detection circuit C, and a fourth detection circuit D. The first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D include detection coils L1A and L2A, detection coils L1B and L2B, detection coils L1C and L2C, and detection AC bridge circuits 3A to 3D corresponding to the coils L1D and L2D, respectively, having a pair of detection coils, respectively. The pair of detection coils L1A, L2A to detection coils L1D, L2D are coaxially and spaced apart from each other along the transport path 250 of the conductor 200 to be inspected. The conductor 200 is a cylindrical metal material such as a copper wire, an iron wire, or a steel wire.

  In addition, the detection unit 10 includes a defect detection unit 11, which is output from each of the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D. A detection signal is input. And the defect detection part 11 detects whether the surface of the conductor 200 which is a test object has a defect based on the input detection signal.

  In addition, the defect detection unit 11 detects the position or length of the defect in the circumferential direction of the conductor 200 (for example, the circumferential direction of the cylindrical conductor 200). The position or length of the defect in the circumferential direction is the position of the electromagnetic shielding body that each of the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D has. Based on this, the defect detection unit 11 detects this, and will be described later with reference to FIG.

  The control unit 20 controls each unit included in the eddy current flaw detection apparatus 100. For example, control is performed to display the detection result of the detection unit 10 on a display unit (not shown), or control to output to a display device or printer connected to the outside. For example, the power supply unit 30 converts power supplied from a commercial AC power source into a voltage or current for driving each unit included in the eddy current flaw detector 100 and supplies the converted voltage or current.

Next, processing in which the eddy current flaw detector 100 according to the present embodiment detects the position or length of a defect in the circumferential direction of the conductor 200 will be described with reference to FIG.
FIG. 3 is a schematic diagram illustrating an example of the configuration of the electromagnetic shield disposed in the detection coil. Each of the pair of detection coils of the eddy current flaw detector 100 has an electromagnetic shield disposed in a part of the circumferential direction of the surface facing the conveyance path 250 (that is, the circumferential direction inside the pair of detection coils). Have. Further, these electromagnetic shields have a length corresponding to the width of each detection coil in the direction of the conveyance path 250 (for example, the same length as the width of the detection coils L1A and L2A).

  FIG. 3A is a perspective view with respect to a cross section along the direction of the conveyance path 250, and the configuration of the conductor 200, the electromagnetic shields 51 to 54, the insulators 61 and 62, and the detection coils L1A, L2A to L1D, and L2D. It is a schematic diagram which shows. FIG. 3B is a schematic diagram showing a configuration of the conductor 200, the electromagnetic shields 51 to 54, and the insulators 61 and 62 in a cross section orthogonal to the direction of the conveyance path 250. Here, in FIG.3 (b), illustration of detection coil L1A, L2A-L1D, L2D shown to Fig.3 (a) is abbreviate | omitted.

  For example, as shown in FIGS. 3A and 3B, a pair of first detection circuit A, second detection circuit B, third detection circuit C, and fourth detection circuit D are included. Each of the detection coils has electromagnetic shields 51 to 54 that are sandwiched between the insulator 61 and the insulator 62 and are disposed at different positions in the circumferential direction, respectively, inside the pair of detection coils. ing. The electromagnetic shields 51 to 54 are, for example, copper foil sheets and are made of a material having an action of shielding an electromagnetic field.

  And the electromagnetic shielding bodies 51-54 arrange | positioned at each of a pair of detection coil are arrange | positioned in the mutually different position of the circumferential direction over the perimeter inside a pair of detection coil. For example, the first detection circuit A has a length corresponding to the width of the detection coils L1A and L2A in the direction of the conveyance path 250 over the circumferential section where the central angle is 0 ° to 90 ° (for example, the detection coil). The electromagnetic shield 51 having the same length as the width of L1A and L2A) is disposed. The second detection circuit B has a length corresponding to the width of the detection coils L1B, L2B in the conveyance path 250 direction (for example, the detection coil L1B, over the circumferential section where the central angle is 90 ° to 180 °. An electromagnetic shield 52 having the same length as the width of L2B) is disposed. The third detection circuit C includes a length corresponding to the width of the detection coils L1C and L2C in the conveyance path 250 direction (for example, the detection coils L1C, The electromagnetic shielding body 53 having the same length as the width of L2C) is disposed. The fourth detection circuit D has a length corresponding to the width of the detection coils L1D and L2D in the direction of the conveyance path 250 over a circumferential section where the central angle is 270 ° to 360 ° (0 °) (for example, An electromagnetic shield 54 having the same length as the width of the detection coils L1D and L2D) is disposed.

  FIG. 3C is a diagram in which a cylindrical conductor 200 is developed on a plane, and is a diagram illustrating correspondence between each section in the circumferential direction of the conductor 200 and the positions of the electromagnetic shields 51 to 54. As shown in this figure, in the first detection circuit A, electromagnetic induction does not occur due to the presence of the electromagnetic shield 51 in the circumferential section where the central angle of the conductor 200 is 0 ° to 90 °. Even if the conductor 200 has a defect, the defect is not detected. Similarly, the second detection circuit B is a circumferential section in which the central angle of the conductor 200 is 90 ° to 180 °, and the third detection circuit C is a circle in which the central angle of the conductor 200 is 180 ° to 270 °. In the circumferential section, the fourth detection circuit D does not detect a defect even if the conductor 200 has a defect in a circumferential section where the central angle of the conductor 200 is 270 ° to 360 ° (0 °). . As described above, there is a section in which each detection circuit does not detect a defect even if the conductor 200 has a defect in a different section in the circumferential direction of the conductor 200. Using this, the defect detection unit 11 detects the position or length of the defect in the circumferential direction of the conductor 200.

  For example, the flaw (defect) 211 shown in FIG. 3C is detected by the first detection circuit A, the second detection circuit B, and the fourth detection circuit D, but the third detection circuit C. Is not detected. Therefore, the defect detection unit 11 can detect defects (defects) based on the detection signals output from the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D, respectively. ) 211 can be detected, and it can be detected that the flaw (defect) 211 is located in a circumferential section where the central angle of the conductor 200 is 180 ° to 270 °.

  Further, the scratch (defect) 212 shown in FIG. 3C is detected in all of the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D. . Therefore, the defect detection unit 11 can detect defects (defects) based on the detection signals output from the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D, respectively. ) 212 is detected, and the flaw (defect) 212 is located at all four positions in the circumferential direction of the conductor 200, that is, a flaw (defect) having a length occurring over the entire circumference of the conductor 200. ) Can be detected.

  As described above, the eddy current flaw detection apparatus 100 performs inspection based on the detection signals output from the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D. The position of the defect in the circumferential direction of the conductor 200 is detected based on whether or not there is a defect on the surface of the target conductor 200 and based on the detection signal and the position where the electromagnetic shields 51 to 54 are disposed. Can be detected. The eddy current flaw detector 100 is an inspection object based on detection signals output from the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D. Whether or not the surface of the conductor 200 has a defect is detected, and the length of the defect in the circumferential direction of the conductor 200 (for example, based on the detection signal and the position where the electromagnetic shields 51 to 54 are disposed) It is possible to detect whether or not a defect has occurred all around. Therefore, the eddy current flaw detection apparatus 100 can appropriately detect the position or length of the defect in the circumferential direction (circumferential direction) of the conductor 200 to be inspected.

In addition, since the positions of the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D in the direction of the conveyance path 250 are different from each other, the defect of the conductor 200 is caused by each. The times passing through the detection circuit are different from each other. Therefore, the time when each detection circuit detects the same defect is also different from each other. Therefore, for example, the control unit 20 has a predetermined traveling speed of the conductor 200 so that the difference in time detected by each detection circuit does not affect the position of the defect (so that the same defect is detected as the same defect). If it is slower than this speed, it will not be detected. This predetermined speed is a speed at which the difference in the position of the defect according to the difference in the detected time becomes an allowable error, and the size of the detection coil, the interval between the detection circuits (detection coils), And the speed set according to the size of the defect to be detected.
In addition, the control unit 20 may output the travel start timing, travel speed, and the like of the conductor 200 to the detection unit 10 so that the detection unit 10 can detect the relative position of the conductor 200 in the conveyance path 250 direction. Thereby, the detection unit 10 corrects the difference in the position of the defect caused by the difference in time passing through each detection circuit based on the travel start timing, travel speed, etc. of the conductor 200 input from the control unit 20. Also good.

  Next, in the present embodiment, a configuration when the phases of the AC power supplies supplied to the detection coils of the pair of detection coils are different from each other will be described with reference to FIGS. 4 and 5. Here, the first detection circuit A (AC bridge circuit 3A having detection coils L1A and L2A) will be described as an example. However, the second detection circuit B, the third detection circuit C, and the fourth detection circuit are described. The configuration of the circuit D is the same.

  In the output detected by the first detection circuit A, a current change and a phase change appear because an AC power supply is used. Further, since the output is detected using a coil, a current change value and a phase change value corresponding to a change in the coil inductance appear. Further, when the conductor 200 has a defect, the first detection circuit A detects a current change value and a phase change value corresponding to the defect, but a noise signal corresponding to the influence of the backlash of the electromagnetic shield 51 or the like is detected. The current change value and the phase change value are similarly detected.

  FIG. 4 is a diagram for explaining the phase of the output detected by the first detection circuit A (AC bridge circuit 3A). This figure is a Lissajous waveform showing the noise component N and the defect signal component S detected by the first detection circuit A on the XY axes. As shown in this figure, in the first detection circuit A, the noise component N caused by the influence of the backlash of the electromagnetic shield 51 and the defect signal component S caused by the defect of the conductor 200 are in-phase signals. Further, the noise component N caused by the influence of the backlash of the electromagnetic shield 51 and the defect signal component S caused by the defect of the conductor 200 are signals having the same frequency corresponding to the frequency of the supplied alternating current. Therefore, it is difficult to discriminate between the noise component N detected by the first detection circuit A and the defect signal component S, and the detection accuracy may be lowered. Therefore, the first detection circuit A detects the defect signal component S ′ as a defect signal component S ′ by shifting the phase of the defect signal component S by an angle θ by setting the phases of the alternating currents supplied to the detection coils L1A and L2A to different phases. To do. Thereby, the noise component N and the defect signal component S ′ detected by the first detection circuit A can be separated and discriminated.

  Note that the angle θ, which is a phase change amount for shifting the phase of the defect signal component S, is determined from the phase of the noise component N in order to separate the noise component N and the defect signal component S of the detected signal. This is a change amount set in advance as an amount to shift the phase of the component S. For example, the angle θ is set to −20 °.

  FIG. 5 is a schematic block diagram showing an example of the configuration of the AC bridge circuit of the present embodiment. The configuration of a circuit that detects a defect by shifting the phase in the first detection circuit A will be described with reference to FIG. Here, the detection coils L1A and L2A in FIG. 5 correspond to the detection coils L1 and L2 in FIG. 1, and the resistors R1A and R2A in FIG. 5 correspond to the resistors R1 and R2 in FIG. In FIG. 1, an alternating current is supplied from the alternating current power supply 31 to the alternating current bridge circuit 3, but in FIG. 5, an oscillator 31 </ b> A is used instead of the alternating current power supply 31.

  In the first detection circuit A (AC bridge circuit 3A), a pair of detection coils L1A (first detection coils) and a detection coil L2A (second detection coils) are connected as two sides of the bridge, and resistance R1A , R2A has a balanced circuit (bridge circuit) connected as the other two sides of the bridge. The detection coils L1A and L2A are differentially connected so that the generated magnetic fields are in opposite phases. The oscillator 31 </ b> A generates a sine wave oscillation signal (alternating current) having a constant frequency and supplies it to the amplifier 32 and the phase shifter 33 as an alternating current. The output terminal of the amplifier 32 is connected to one end of the resistor R1A, and the other end of the resistor R1A is connected to one end of the detection coil L1A. The amplifier 32 amplifies the alternating current supplied from the oscillator 31A and supplies it to the detection coil L1A via the resistor R1A.

  The phase shifter 33 (first phase shifter) changes the phase of the alternating current supplied to the detection coil L2A with respect to the alternating current supplied from the oscillator 31A. For example, the phase shifter 33 can change the phase angle of the alternating current supplied from the oscillator 31A and also has an amplifier function. The output terminal of the phase shifter 33 is connected to one end of the resistor R2A, and the other end of the resistor R2A is connected to one end of the detection coil L2A. The phase shifter 33 changes the phase of the supplied alternating current and supplies the amplified alternating current to the detection coil L2A via the resistor R2A.

The connection point between the resistor R1A and the detection coil L1A is connected to one input terminal of the differential amplifier 38 via the phase shifter 34 (second phase shifter). A connection point between the resistor R2A and the detection coil L2A is connected to the other input terminal of the differential amplifier 38.
The connection point between the detection coil L1A and the detection coil L2A is connected to the GND (ground) of the oscillator 31A.

  Similarly to the phase shifter 33, the phase shifter 34 can change the phase angle of the input signal, and the first output signal 35 (detected with the resistor R1A and the detection signal) output according to the change in the inductance of the detection coil L1A. Output signal at the connection point with the coil L1A) and the second output signal 36 (output signal at the connection point between the resistor R2A and the detection coil L2A) output in response to a change in the inductance of the detection coil L2A. 1 of the output signal 35 is changed. Here, the first output signal 35 corresponds to the output signal of the terminal K1 in FIG. 1, and the second output signal 36 corresponds to the output signal of the terminal K2 in FIG.

  The phase change amount of the phase shifter 33 and the phase change amount of the phase shifter 34 are set to be the same change amount. The amount of phase change of the phase shifter 33 and the phase shifter 34 corresponds to the angle θ shown in FIG. 4, and the phase change for enabling the noise component N and the defect signal component S ′ to be separated and discriminated. The amount of change (for example, the amount of change in the phase of “angle θ = −20 °”).

The differential amplifier 38 extracts a difference between the first output signal 35 input via the phase shifter 34 and the second output signal 36 and outputs the detection signal amplified to the terminal 39. That is, the differential amplifier 38 extracts the difference between the output corresponding to the change in the inductance of the detection coil L1A and the output corresponding to the change in the inductance of the detection coil L2A. For example, when there is no defect in the conductor 200 passing through the detection coils L1A and L2A, the output according to the change in the inductance of the detection coil L1A and the output according to the change in the inductance of the detection coil L2A are zero balanced ( The differential amplifier 38 outputs a detection signal indicating that there is a balanced state with no difference. On the other hand, when the defect of the conductor 200 passes through the detection coils L1A and L2A, a difference occurs between the output according to the change in the inductance of the detection coil L1A and the output according to the change in the inductance of the detection coil L2A. The dynamic amplifier 38 extracts the difference and outputs a detection signal indicating that the balance has been lost.
The detection signal output from the differential amplifier 38 to the terminal 39 is supplied to the defect detection unit 11.

  As described above, the first detection circuit A shifts the phase of the alternating current supplied to the detection coil L2A with respect to the alternating current supplied to the detection coil L1A, thereby detecting the detected noise component N and defect signal component. S ′ can be separated and appropriately discriminated. Therefore, the first detection circuit A can detect the defect of the conductor 200 with high accuracy. Further, the second detection circuit B, the third detection circuit C, the fourth detection circuit D, and the first detection circuit A have the same configuration, so that defects in the conductor 200 can be detected with high accuracy. it can. As a result, the defect detection unit 11 causes the first detection circuit A, the second detection circuit B, the third detection circuit C, and the fourth detection circuit D to detect the conductor 200 based on the detection results. While detecting a defect, the position or length of the defect in the circumferential direction (circumferential direction) of the conductor 200 can be detected appropriately.

  As described above, the eddy current flaw detection apparatus 100 according to the present embodiment can detect the defect of the conductor 200 and can appropriately detect the position or length of the defect of the conductor 200. For example, the eddy current flaw detector 100 can detect the position of the defect in the circumferential direction (circumferential direction) of the conductor 200. Further, the eddy current flaw detector 100 can detect the length of a defect in the circumferential direction (circumferential direction) of the conductor 200 (for example, whether or not a defect has occurred over the entire circumference). The eddy current flaw detector 100 can detect the position or length of the defect in the direction of the conveyance path 250 of the defect of the conductor 200 based on the travel start timing, the travel speed, or the like of the conductor 200.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.
For example, in the above embodiment, the configuration of the eddy current flaw detector 100 (penetrating eddy current flaw detector) that detects the defect on the outer peripheral surface of the conductor 200 by passing the conductor 200 to be inspected into the detection coil has been described. The eddy current flaw detector 100 may be of an inner probe type (insertion type) that detects defects on the inner surface of the tubular conductor.
FIG. 6 shows an example of a probe 10A of an inner probe type (insertion type) eddy current flaw detector. In this figure, parts corresponding to those in FIG. 3 are given the same reference numerals. The probe 10A inserted into the tubular conductor 200A is a surface facing the conveyance path 250A side of the detection coils L1A, L2A to L1D, L2D, that is, a surface facing the inside of the tube of the conductor 200A (the outside of the detection coil). By arranging the electromagnetic shields 51 to 54 on the (facing surface), it is possible to appropriately detect the position or length of the defect in the circumferential direction of the inner surface of the conductor 200A as in the above-described embodiment. .

  Further, the inspection target is not limited to a columnar or tubular conductor, and may be a quadrangular columnar conductor, for example. The eddy current flaw detector 100 has a configuration in which an electromagnetic shield is disposed between an inspection object and a detection coil in accordance with the shape of the inspection object, so that the positions or lengths of defects in the circumferential direction of conductors of various shapes. It is possible to detect the thickness appropriately. Further, the winding shape of the detection coil is not limited to a circular shape, and may be another winding shape such as a quadrangle.

  Conventionally, there is an eddy current flaw detection apparatus having a split type detection coil, which is a plurality of (for example, four) detection coils arranged side by side over the entire circumference of an inspection target. In the case of this division type detection coil, the interval between adjacent detection coils becomes wide due to the restriction of the position where the coil is arranged, so that the detection accuracy in the vicinity of the boundary between the divided sections in the circumferential direction is lowered. In contrast, the eddy current flaw detector 100 according to the present embodiment has a configuration in which an electromagnetic shield made of a copper foil sheet or the like is arranged for each section in the circumferential direction. This is unnecessary, and the detection accuracy near the boundary divided in the circumferential direction can be improved.

  In addition, the electromagnetic shielding bodies 51 to 54 of the above-described embodiment may be arranged in each detection coil by a size or shape that overlaps the positions in the circumferential direction. Thereby, the 1st detection circuit A, the 2nd detection circuit B, the 3rd detection circuit C, and the 4th detection circuit D are between the electromagnetic shielding bodies 51-54 each arrange | positioned. It is possible to reduce erroneous detection of a defect that should not be detected at the position. If the overlap amount is excessively increased, a defect to be detected may not be detected by the detection circuit at a position between the electromagnetic shields 51 to 54. Therefore, the electromagnetic shield 51 The overlap amount of .about.54 is desirably set appropriately depending on the type and thickness of the material to be inspected, the strength of the magnetic field generated in the detection coil, and the like. Specifically, the overlapping angle is desirably 2 ° to 15 °.

  Further, the electromagnetic shield disposed in the pair of detection coils is, for example, a length of a circumferential section of less than 50% with respect to the entire circumference of the inspection target (for example, a circle having a central angle of 0 ° to 180 °). It is desirable to be limited to a size that shields the length of the section in the circumferential direction less than the length of the section. This is because, in a pair of detection coils, when a circumferential section of 50% or more is shielded, the detection sensitivity of the detection coil may decrease.

  2 and 3, the eddy current testing apparatus 100 has four detection circuits (four detection circuits each having a pair of detection coils) each having an electromagnetic shield for each section obtained by dividing the entire circumference of the inspection target into four. However, the present invention is not limited to this. For example, the eddy current flaw detector 100 is provided with a number of detection circuits corresponding to the number of divisions each having an electromagnetic shield for each section obtained by dividing the entire circumference of the inspection target by five, six, or more divisions. It is good also as a structure. In this case, the eddy current flaw detector 100 can detect the position of the defect in more detail by increasing the number of divisions. The eddy current flaw detector 100 may have a simple configuration by reducing the number of divisions and the number of detection circuits when it is not necessary to detect the position of the defect in more detail.

  Further, the eddy current flaw detection apparatus 100 is not limited to the configuration in which the electromagnetic shields included in each of the plurality of detection circuits are arranged at different positions in the circumferential direction over the entire circumference of the inspection target. For example, when it is necessary for the eddy current flaw detection apparatus 100 to detect the position of a defect in a partial section of the entire circumference of the inspection target, each of the plurality of detection circuits includes a section obtained by dividing the partial section. It is good also as a structure by which a shield is arrange | positioned. Further, when the eddy current flaw detection apparatus 100 detects whether or not there is a defect in a part of the entire circumference to be inspected, a detection circuit and an electromagnetic shield having an electromagnetic shield in the part of the part. It is good also as a structure provided with the detection circuit which does not have.

  In addition, when the eddy current flaw detector 100 includes one detection circuit having an electromagnetic shield in a part of the entire circumference, the rotational position of the inspection object and the electromagnetic shield is relatively rotated to obtain a predetermined value. The position or length of the defect in the circumferential direction of the inspection target may be detected based on the result detected for each rotation position.

  In addition, in the said embodiment, although the case where the electromagnetic shielding bodies 51-54 were respectively the same length as the length of the width in the conveyance path 250 direction of a pair of detection coil was demonstrated as an example, it is not restricted to this. The length of the width of the electromagnetic shields 51 to 54 in the direction of the conveyance path 250 may be shorter or longer than the width of the pair of detection coils. The width of the electromagnetic shields 51 to 54 in the direction of the conveyance path 250 is the type and thickness of the material to be inspected, the spacing between the pair of detection coils, or the strength of the magnetic field generated in the detection coils. It is desirable to set appropriately.

  Further, the electromagnetic shields 51 to 54 may have a shape in which the width in the direction of the conveyance path 250 is divided into lengths corresponding to the widths of the detection coils of the pair of detection coils. For example, the electromagnetic shield 51 has a shape in which the width in the direction of the conveyance path 250 is divided into two, and each of the divided electromagnetic shields is disposed at a position corresponding to each of the detection coils L1A and L2A. It may be configured.

  Note that, as an AC power supply for supplying an AC current to the bridge circuits in the AC bridge circuits 3A to 3D, the AC power supply 31, or the oscillator 31A, the amplifier 32, or the phase shifter 33 includes the first detection circuit A and the second detection circuit. The circuit B, the third detection circuit C, and the fourth detection circuit D may be provided, respectively, or the first detection circuit A, the second detection circuit B, the third detection circuit C, and the The detection unit 10 may be provided with one or a set of AC power supplies that supply an AC current to each of the four detection circuits D.

  In the above embodiment, the eddy current flaw detector 100 can determine the noise component and the defect signal component separately by setting the phases of the AC power supplies supplied to the detection coils of the pair of detection coils to be different from each other. Although the example which makes it demonstrated was demonstrated, it is not restricted to this. For example, the eddy current flaw detection apparatus 100 may be a rotary phase shift type eddy current flaw detection apparatus, and may detect and distinguish a noise component and a defect signal component by changing the phase of the defect signal component and detecting it. Good. Note that the rotational phase-shifting eddy current flaw detection apparatus has a configuration described in, for example, cited document 1.

  The defect detection unit 11 in FIG. 2 may be realized by dedicated hardware, and is configured by a memory and a CPU (central processing unit) to realize the function of the above-described defect detection unit 11. The function may be realized by loading the program for loading into the memory and executing the program.

  Further, the program for realizing the function of the defect detection unit 11 in FIG. 2 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system and executed, thereby executing the above-described process. You may perform the process of the defect detection part 11. FIG. Here, the “computer system” includes an OS and hardware such as peripheral devices.

Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  3 (3A to 3D) ... AC bridge circuit, 10 ... detection unit, 31 ... AC power supply, 31A ... oscillator, 33 ... phase phase (first phase shifter), 34 ... -Phaser (second phaser), 51-54 ... Electromagnetic shield, 100 ... Eddy current flaw detector, 200 ... Conductor, 250 ... Transport path, L1 (L1A-L1D), L2 (L2A to L2D) ... Detection coil

Claims (7)

A pair of detection coils arranged coaxially and spaced apart along the transport path of the conductor to be inspected;
A detection unit including an AC bridge circuit that outputs a detection signal indicating whether or not the two sides of the bridge are constituted by each detection coil of the pair of detection coils and the balance of the bridge is broken;
With
The pair of detection coils includes an electromagnetic shield disposed on a part of a circumferential direction of a surface of the pair of detection coils facing the conveyance path. The eddy current flaw detector. The detector is
A plurality of said AC bridge circuits,
With
The plurality of AC bridge circuits are arranged at different positions in the conveyance path direction,
The electromagnetic shield included in a pair of detection coils of each of the plurality of AC bridge circuits,
The eddy current flaw detector according to claim 1, wherein the eddy current flaw detectors are arranged at different positions in the circumferential direction. The electromagnetic shield included in a pair of detection coils of each of the plurality of AC bridge circuits,
The eddy current flaw detector according to claim 2, wherein the eddy current flaw detector is disposed at different positions in the circumferential direction over the entire circumference of the surface facing the conveyance path side. The detector is
The position of the defect in the circumferential direction of the inspection target is detected based on the detection signal output from the AC bridge circuit and the circumferential position where the electromagnetic shield is disposed. The eddy current flaw detector according to any one of claims 1 to 3. The detector is
The length of the defect in the circumferential direction of the inspection object is detected based on the detection signal output from the AC bridge circuit and a circumferential position where the electromagnetic shield is disposed. The eddy current flaw detector according to any one of claims 1 to 4. 6. The eddy current flaw detector according to claim 1, wherein alternating currents having different phases are supplied to the detection coils of the pair of detection coils. A power supply unit that supplies an alternating current of a predetermined frequency to the alternating-current bridge circuit in which two sides of the bridge are configured by the first detection coil and the second detection coil that are the pair of detection coils;
A first phase shifter for changing a phase of an alternating current supplied to the second detection coil with respect to an alternating current supplied from the power supply unit to the alternating current bridge circuit;
A first output signal that is output as a change in the inductance of the first detection coil and a change in the inductance of the second detection coil that is output as the detection signal of the AC bridge circuit. A second phase shifter that changes the phase of the first output signal among the second output signals.
With
7. The change amount of the phase of the first phase shifter and the change amount of the phase of the second phase shifter are the same change amount. 7. Eddy current flaw detector.

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