JP2006234750A - Method and device for sensitivity calibration of eddy current tester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device capable of comparably easily and precisely performing sensitivity calibration of an eddy current tester in a short time. <P>SOLUTION: A plurality (N pieces) of the eddy current sensors for detecting the flaw in a running metal band are arranged by winding primary coils on the center legs of E cores, and on both the legs, the secondary coils are differentially connected, and disposed in width direction of a metal band, wherein a tape conductor longer than the whole length of the plurality of eddy current sensors arranged in width direction is disposed under the spaces between the central legs and either of outer legs. At this point, the output V<SB>1k</SB>(k=1 to N, V<SB>1k</SB>>0) are read, and the tape conductor is displaced under the space between the central legs and another outer legs, the output of each eddy current sensor - V<SB>2k</SB>(k=1 to N, V<SB>2k</SB>>0) are read, thereby the sensitivity calibration is performed by making the difference of both the outputs V<SB>1k</SB>-(-V<SB>2k</SB>) a specific value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sensitivity calibration method and apparatus for an eddy current flaw detector that detects a defect present in a surface layer of a metal band that is a conductor.

  As a method for detecting defects present on the surface layer of a metal body that is a conductor, an eddy current flaw detection method is widely used. In the eddy current flaw detection method, an eddy current is generated on the surface layer of a conductor by an excitation (primary) coil, and a defect is detected by detecting an induced voltage generated in the detection (secondary) coil by the eddy current. . When there is a defect on the surface of the metal strip, a change occurs in the flow of eddy current, and the induced voltage changes accordingly, so that the defect can be detected.

  As a sensor used in the eddy current flaw detection method, for example, a sensor having an E shape as disclosed in Patent Document 1 is disclosed. The principle of eddy current flaw detection using an E-type sensor is shown in FIG. In FIG. 2, 1 is a sensor, 1a is a primary coil, 1b and 1c are secondary coils, 4 is a metal strip, and 5 is a defect. Here, an AC power source is connected to both ends 1a1 and 1a2 of the primary coil 1a, whereby an eddy current as shown by an arrow is generated in the metal strip 4. Further, the secondary coils 1b and 1c are differentially connected in series. When AC magnetic fields having the same direction and the same magnitude cross in these detection coils, both ends of the detection coils are canceled by canceling each other. The electromotive force induced between 1b1 and 1c1 is zero.

  When there is no defect in the metal band, the induced voltages generated in the secondary coils 1b and 1c are the same, so the output of the induced voltages of the two differentially connected secondary coils is almost zero. As shown in FIG. 2, when the defect 5 exists only in the vicinity of the secondary coil 1c, a difference occurs in the induced voltage generated in the two secondary coils due to the eddy current change. The voltage difference is not zero, and an output is generated at both ends of the two differentially connected secondary coils. As a result, as shown in the lower diagram of FIG. 2, when the metal strip 4 having the defect 5 moves in the direction of the arrow below the sensor fixed above, the output after phase detection is centered on the sensor 1. A defect can be detected by drawing a waveform having a sine curve shape at the center. Here, 1a is a primary coil, and 1b and 1c are secondary coils. However, since the above difference effect can be obtained even if reversed, 1b and 1c may be primary coils and 1a may be secondary coils.

FIG. 3 is a diagram showing a eddy current flaw detection method for a metal strip. If a plurality of E-type eddy current sensors 1 _k (k = 1 to N) are arranged in the width direction of the traveling metal strip 4 as shown in FIG. 3, it is possible to detect defects in the entire width of the metal strip. It becomes. In order to detect defects with high accuracy and stability over a long period of time, periodic sensitivity calibration is absolutely necessary due to changes in sensitivity and changes over time due to temperature changes in sensors and circuits.

  As a sensitivity calibration device in the eddy current sensor, for example, Patent Document 2 discloses a reciprocation device for sensitivity calibration. FIG. 5 is a diagram showing a schematic configuration of the apparatus disclosed in Patent Document 2. As shown in FIG. In FIG. 5, reference numeral 6 denotes a holding member that holds the sensor 1 of the flaw detection apparatus (not shown), and is attached to the distal end portion of the L-shaped arm 7. In this case, the sensor 2 is held by the holding member 6 so that its detection surface faces downward. Reference numeral 8 denotes a test piece holding member formed in a U-shaped cross section, and holds the test piece 9 so as to be directly below the sensor 1. A standard penetrating portion is formed in the test piece 9. Reference numeral 10 denotes a reciprocating mechanism that moves to the left and right with respect to the coaxial 11 by operating the induction motor 12 and rotating the shaft 11 in a certain direction. In this case, the reciprocating mechanism 10 moves on the shaft 11 while being guided by a guide rod (not shown).

  In FIG. 5, reference numerals 13a and 13b denote reversal stoppers, which are installed by rod members 14a and 14b at positions corresponding to the direction switching levers of the reciprocating mechanism 10 described above. In this case, the reverse stoppers 13a and 13b can be set at arbitrary positions with respect to the rod members 14a and 14b, and the moving range of the reciprocating mechanism 10 can be set arbitrarily.

In this way, when the induction motor 12 is rotated, the standard penetrating portion reciprocates below the sensor, so that sensitivity calibration is possible.
JP-A-7-116732 JP-A-3-264862

  However, the reciprocating device for sensitivity calibration disclosed in Patent Document 2 is not so large in an eddy current flaw detector with a relatively small number of sensors. When a large number of sensors are taken into consideration, calibration of a large number of sensors is required according to the plate width, which causes a problem that a large amount of cost and space are required.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a sensitivity calibration method and apparatus for an eddy current flaw detection apparatus that can perform sensitivity calibration with relatively high accuracy in a short time.

In the invention according to claim 1 of the present invention, there is provided an eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both of the outer legs. A sensitivity calibration method for an eddy current flaw detector using a sensor array in which a plurality (N) of eddy current sensors are arranged in a line in a direction substantially orthogonal to the array direction, wherein the tape is longer than the length of the sensor array in the array direction. Output V _1k (k = 1) of each eddy current sensor obtained when the conductor is disposed only under the gap between the central leg row and the outer leg row of the E-shaped core of the sensor row ˜N, V _1k > 0) and each vortex obtained when the tape-like conductor is disposed only below the gap between the center leg row of the E-shaped core of the sensor row and the other outer leg. From the sensor output −V _2k (k = 1 to N, V _2k > 0) A sensitivity calibrating method for an eddy current flaw detector characterized by calculating a difference V _1k − (− V _2k ) and calibrating the sensitivity of the eddy current flaw detector so that the value of the difference becomes a predetermined value.

In the invention according to claim 2 of the present invention, there is provided an eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both of the outer legs. A sensitivity calibration device for an eddy current flaw detector using a sensor array in which a plurality (N) of eddy current sensors are arranged in a line in a direction substantially perpendicular to the array direction of the sensor array, and longer than the length of the sensor array in the array direction A tape-shaped conductor, N eddy current signal processing amplifiers for amplifying the outputs of the eddy current sensors, N A / D converters for A / D converting the outputs of the eddy current signal processing amplifiers, and the A / D An arithmetic processing unit that performs arithmetic processing based on the output of the converter, and the tape-like conductor is only below the gap between the central leg row and the outer one leg row of the E-shaped core of the sensor row. output _{V 1k} (k = _1~N of each eddy current sensor obtained when placed, _{1k> 0),} the output of the eddy current sensor obtained when said tape-like conductor is arranged only below the gap between the center column of the legs and the outer other leg of E-shaped cores of said sensor arrays - From V _2k (k = 1 to N, V _2k > 0), a difference V _1k − (− V _2k ) between both outputs is calculated, and the eddy current signal is set so that the difference value becomes a predetermined value. A sensitivity calibration device for an eddy current flaw detector, wherein the sensitivity of the eddy current flaw detector is calibrated by a processing amplifier and / or the arithmetic processing unit.

  Furthermore, the invention according to claim 3 of the present invention provides an eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both the outer legs, and the leg of the E-shaped core. A jig for calibrating the sensitivity of an eddy current flaw detector using a sensor array in which a plurality (N) of the eddy current sensors are arranged in a line in a direction substantially orthogonal to the array direction of the sensor array, In this case, a tape-shaped conductor having a width longer than the sensor array length and not exceeding the leg interval of the E-shaped core in a direction orthogonal to the arrangement direction is attached to the surface of the non-metallic plate having a predetermined thickness. Thus, the sensitivity calibration jig of the eddy current flaw detector is characterized in that the non-metal plate is attached below the legs of the sensor row.

According to the present invention, a tape-like conductor that is longer than the N E-shaped eddy current sensors arranged in the width direction is disposed below the gap between the central leg and one outer leg of the eddy current sensor. Then, the output V _1k (k = 1 to N, V _1k > 0) of each eddy current sensor at this time is read, and then the tape-like conductor is placed below the gap between the central leg and the other outer leg. It arranges and reads the output -V _2k (k = 1 to N, V _2k > 0) of the eddy current sensor at this time, and the sensitivity is such that the difference V _1k − (− V _2k ) between the outputs becomes a predetermined value. Since the adjustment is made, calibration can be performed relatively easily and in a short time. Further, in order to remove low-frequency noise, eddy current flaw detection of a traveling metal strip is generally improved in S / N by differentiating, that is, subtracting the sensor output in the steel plate traveling direction. In addition, there is a difference in the sensitivity of the left and right detection coils due to problems in the manufacture of eddy current sensors, and even when the zero point of each eddy current sensor output is shifted in the absence of defects, highly accurate calibration is possible. It is.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a sensitivity calibration method according to the present invention.

  As shown in FIGS. 1 (a) and 1 (b), the detection unit of the eddy current flaw detection apparatus for detecting a defect in the inspection object to which the calibration method of the present invention is applied has an E-shaped core having three legs. The eddy current sensor is configured as a sensor array in which a plurality of eddy current sensors are arranged in a line substantially perpendicular to the direction in which the three legs are arranged. In each eddy current sensor, among the three legs of the E-shaped core, the central leg is wound with a primary coil (excitation coil) and the outer leg is wound with a secondary coil (detection coil). Has been. The two outer secondary coils are differentially connected.

The calibration jig of the present invention has a length W longer than the sensor row length Ws on the surface of a non-metal plate 2 (for example, an acrylic plate or a bake plate) having a predetermined thickness, and the sensor row direction. Calibration with the tape-shaped conductor 3 made of copper, iron, aluminum, etc. attached to the E-shaped core with the width direction orthogonal to the E-shaped core being less than the leg interval (interval between the center leg and the outer leg) The jig is installed below the legs of the sensor row. At this time, the conductor 3 is placed on the surface opposite to the leg portion of the eddy current sensor with the non-metal plate 2 interposed therebetween. The tape-like conductor 3 is attached so as to be positioned parallel to the gap between the central leg and the outer one leg of the E-type eddy current sensor 1 _k (k = 1 to N) in the sensor array (see FIG. 1 (a)). FIG. 1B is a view as seen from the arrow A in FIG. 1A, and shows a state where the tape-like conductor 3 is pasted over the width W of the non-metal plate 2. In the state of FIG. 1A, each eddy current sensor output voltage V _1k (k = 1 to N, V _1k > 0) arranged in the plate width direction is read, or each eddy current sensor output signal is input by a signal processing device. To do.

Subsequently, similarly, the tape-like conductor 3 is now connected to the central leg and the other outer leg of the eddy current sensor 1 _k (k = 1 to N) composed of N E-shaped cores arranged in the width direction. (FIG. 1 (c)). And the output voltage _-V2k (k = 1-N, _V2k > 0) of each eddy current sensor at this time is read, or each eddy current sensor output signal is input with a signal processor. In addition, in the position movement of the tape-shaped conductor 3 from FIG. 1A to FIG. 1C, the tape-shaped conductor is replaced, the tape-shaped conductor is pasted, and the non-metal plate 2 is moved in parallel. Various methods such as rotating the non-metallic plate 2 by 180 degrees with the tape-like conductor attached thereto are conceivable.

Next, the output V _1k − (− V _2k ) (k = 1 to N) is calculated from the eddy current sensor output composed of each E-shaped core, and sensitivity calibration is performed so that this becomes a predetermined value. In the sensitivity calibration, the sensor output may be adjusted in an analog manner, or converted into a digital value and then taken into a personal computer or the like and processed in a software manner. The non-metallic plate 2 may be selected in advance so that the output of the eddy current sensor is investigated in advance for the defect to be detected and an output substantially equivalent to this is obtained. Although the sensor output has been described as a voltage signal, any form may be used as long as it is a value indicating the sensor output, such as a current value or a value subjected to software processing after AD conversion.

FIG. 4 is a block diagram showing an embodiment of the present invention. As described above, the tape-like conductor 3 is positioned in the gap between the central leg and the outer one leg of the N E-type sensors 1 _k (k = 1 to N). The sensitivity volume is adjusted for each eddy current signal processing amplifier 21 _k (k = 1 to N) so that the output after detection becomes a predetermined output value (V ′).

After adjusting the sensitivity volume, the value converted into a digital value by the A / D converter 31 _k (k = 1 to N) is read by the arithmetic processing unit 41 (for example, a personal computer) (the read value at this time is V1 _k = V ′ (k = 1 to N)).

Next, the tape-shaped conductor 3 is positioned in the gap between the central leg and the other outer leg of the N E-type eddy current sensors 1 _k (k = 1 to N) arranged in the width direction. In the same manner as above, the output of the A / D converter 31 _k (k = 1 to N) is read (input) by the arithmetic processing unit 41. At this time, each sensor output is opposite in sign to the first read value V ′, and the absolute value is almost the same. However, due to manufacturing problems, there is variation in individual sensor sensitivity. Are not equal. Therefore, V _1k − (− V _2k ) (k = 1 to N) is calculated for each sensor output, and the correction coefficient is set for each sensor by software so that this becomes a predetermined value (= 2V ′). The correction of the sensor is performed by multiplying the input signal from the sensor at the time of online flaw detection by the correction coefficient by the arithmetic processing unit 41.

  In general, in automatic eddy current flaw detection in a metal band that is transported and traveled on-line, in order to remove DC bias components and slowly changing noise components, the difference in the defect signal can be calculated by making a difference in synchronization with the line speed. The method of taking out is common. Since the above method is sensitivity correction based on the defect signal change, accurate calibration can be realized.

It is a figure explaining the sensitivity calibration method which concerns on this invention. It is the figure which showed the operating principle of the E type eddy current sensor. It is the figure which showed the eddy current flaw detection method of a metal strip. It is the figure which showed the Example of invention. It is a figure explaining the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor 1a Primary coil 1b, 1c Secondary coil 2 Non-metallic plate 3 Tape-shaped conductor 4 Metal strip 5 Defect 6 Holding member 7 L-shaped arm 8 Test piece holding member 9 Test piece 10 Reciprocating mechanism 11 Axis 12 Induction Electric motors 13a and 13b Reversing stoppers 14a and 14b Bar member 21 Eddy current signal processing amplifier 31 A / D converter 41 Arithmetic processing unit

Claims (3)

An eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both of the outer legs, and the eddy current is substantially perpendicular to the row direction of the legs of the E-shaped core. A method for calibrating the sensitivity of an eddy current flaw detector using a plurality of (N) sensors arranged in a row,
Obtained when a tape-like conductor that is longer than the length in the arrangement direction of the sensor row is disposed only below the gap between the center leg row and the outer one leg row of the E-shaped core of the sensor row. The output V _1k (k = 1 to N, V _1k > 0) of each eddy current sensor and the tape-shaped conductor of the gap between the middle leg row of the E-shaped core of the sensor row and the other outer leg From the output −V _2k (k = 1 to N, V _2k > 0) of each eddy current sensor obtained only when arranged below, the difference between the outputs V _1k − (− V _2k ) is calculated. A sensitivity calibration method for an eddy current flaw detector characterized by calibrating the sensitivity of the eddy current flaw detector so that a difference value becomes a predetermined value. An eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both of the outer legs, and the eddy current is substantially perpendicular to the row direction of the legs of the E-shaped core. A sensitivity calibration device for an eddy current flaw detector using a sensor array in which a plurality of sensors are arranged in a row (N),
A tape-shaped conductor longer than the length in the arrangement direction of the sensor row;
N eddy current signal processing amplifiers for amplifying the output of each eddy current sensor;
N A / D converters for A / D converting the output of the eddy current signal processing amplifier;
An arithmetic processing unit that performs arithmetic processing based on the output of the A / D converter,
Output V _1k (k = k =) of each eddy current sensor obtained when the tape-like conductor is disposed only below the gap between the central leg row and the outer leg row of the E-shaped core of the sensor row. 1 to N, V _1k > 0), and each of the tape-shaped conductors obtained when the tape-shaped conductor is disposed only under the gap between the center leg row of the E-shaped core of the sensor row and the other outer leg. From the output of the eddy current sensor −V _2k (k = 1 to N, V _2k > 0), a difference V _1k − (− V _2k ) between the outputs is calculated so that the difference value becomes a predetermined value. A sensitivity calibration device for an eddy current flaw detector, wherein the eddy current flaw detector is calibrated with the eddy current signal processing amplifier and / or the arithmetic processing unit. An eddy current sensor in which a primary coil is wound around the center leg of the E-shaped core and a secondary coil is wound around both of the outer legs, and the eddy current is substantially perpendicular to the row direction of the legs of the E-shaped core. A jig for calibrating the sensitivity of an eddy current flaw detector using a plurality of (N) sensors arranged in a row, the sensor row being longer than the sensor row length in the arrangement direction of the sensor row In a direction orthogonal to the direction, a tape-shaped conductor having a width equal to or smaller than the leg interval of the E-shaped core is attached to the surface of a non-metallic plate having a predetermined thickness, and the non-metallic plate is a leg of the sensor row. A jig for calibrating the sensitivity of an eddy current flaw detector characterized by being attached to the lower part of the device.