JP2000235020A - Eddy-current flaw detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy-current flaw detecting device capable of obtaining difference type signals in spite of having a smaller number of coils making up magnetic field exciting/magnetic field detecting coil pairs. SOLUTION: This eddy-current flaw detecting device is equipped, as its components, with an eddy-current flaw detecting probe made up of a plurality of magnetic field exciting element/magnetic field detecting element pairs, and a control device including means A, B for time-division driving the magnetic field exciting elements and magnetic field detecting elements of the probe, means C for holding output signals of the respective element pairs over several steps of the time-division driving, and a means D for finding a difference between output signals, at least one of which is data held, from two element pairs.

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 used for nondestructive inspection of a thin tube or the like inside a heat exchanger.

[0002]

2. Description of the Related Art An eddy current flaw detection probe having a plurality of magnetic field excitation elements and a magnetic field detection element and used as a mutual induction differential type is disclosed, for example, in JP-A-6-160357. This is shown in FIG.
A set of three pancake coils is arranged on the upper side, and one coil group includes one excitation coil 112 and two detection coils 113 differentially connected.

The feature of this probe is that one coil group detects both a defect existing in the circumferential direction and a defect existing in the axial direction of the heat transfer tube, and prevents a decrease in detectability between the coil groups. To arrange the coil groups alternately in two stages,
A total of eight coil groups are provided inside.

[0004]

However, in the probe described above, the two detection coils of each element pair are always differentially connected, so that the total number of coils is equal to the number of excitation coils and twice the number of detection coils. As a result, three times as many coils as the number of elements are required. If the spatial resolution for the defect is not so required, or if there is no problem even if there is an area where the sensitivity to the defect is low, or if the number of signal lines required for each coil is unlimited, the conventional technique as described above is used. Although there is no inconvenience, the outer diameter of the probe and the outer diameter of the cable containing the signal line group must be at least smaller than the inner diameter of the thin tube in the case of an insertion type probe for flaw detection of a thin tube, and therefore, it is arranged on the outer periphery of the probe. There are restrictions on the number of coils and the number of signal lines.

Further, since two detection coils in one element pair are always connected as a pair, they cannot be used as a detection coil for an excitation coil in another element pair. It is impossible to switch and use a switching circuit by a switching circuit or to change a detection coil to be differentially connected except at the time of designing and manufacturing.

SUMMARY OF THE INVENTION The present invention addresses the above-described situation, and in particular, finds a device for signal difference so as to form a magnetic field excitation / magnetic field detection coil pair with a smaller number of coils as compared with the prior art, while providing a differential. It is an object of the present invention to provide an eddy current flaw detector capable of obtaining a mold signal.

[0007]

That is, a feature of the eddy current flaw detector according to the present invention, which meets the above-mentioned object and solves the above-mentioned problems, is that an eddy current flaw detection probe comprising a plurality of magnetic field excitation element / magnetic field detection element pairs. , The magnetic field excitation element of the probe
Means for time-divisionally driving the pair of magnetic field detecting elements, means for holding the output signal of each element pair over several steps of the time-division driving, and at least one of the outputs from the two element pairs, which is the held data. The present invention has a control device including means for differentiating signals.

A second aspect of the present invention provides a magnetic field excitation element in addition to the above configuration.
At least a part of the means for time-divisionally driving the magnetic field detecting element pair is arranged at or near the probe body.

[0009]

According to the eddy current flaw detector of the present invention, when a signal from the i-th coil is output to the AD conversion circuit, the signal is input to both the data buffer and the arithmetic circuit.
At the same time, the (i-1) -th data whose timing is immediately before is output from the data buffer and input to the arithmetic circuit, and the arithmetic circuit detects the (i-1) -th data which is immediately before the i-th data. The data is subtracted and the result is displayed
Be recorded. Then, (i-1) in the data buffer
The second data is no longer needed, so it is deleted from the buffer and ready for the next data input. By processing the signals of the respective coils in this manner in order, the signals of the adjacent coil pairs are differentiated and operated as a differential probe.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Specific embodiments of the present invention will be described.

FIG. 1 is an external view of a probe used in the eddy current flaw detection apparatus of the present invention. In the figure, reference numeral 101 denotes a cylindrical base body, and a coil group 102 is arranged in an array parallel to the outer circumference of the base body 101 so that a signal A sheath 103 containing the wire is connected.

The coil group 102 is divided into an excitation coil group and a detection coil group, and each coil is connected to a switching circuit (not shown) housed inside the probe body. The probe is connected to the control device by a sheath 103, and an excitation circuit, as shown in FIG.
AD together with main parts such as detection circuit A and AD conversion circuit B
A data buffer circuit C is provided downstream of the conversion circuit B. The outputs from the AD conversion circuit B and the data buffer circuit C are subtracted by the arithmetic circuit D and output and displayed on a display device or a recording device.

FIG. 3 shows a specific operation algorithm for obtaining differential data by the control device. As described in the above operation, the signal from the i-th coil is supplied to the phase discrimination detection circuit A. Output from the AD conversion circuit B, the signal is converted into a data buffer C and an arithmetic circuit D.
, And at the same time the previous timing (i−
The 1) th data is output from the data buffer almost simultaneously and input to the arithmetic circuit D. And data from the i-th coil output from the AD conversion circuit B;
An operation is performed based on the (i-1) -th data output from the buffer C, the latter data is subtracted from the former data, and the result is displayed and recorded. When the calculation is completed, the (i-1) -th data in the data buffer is no longer needed, so that it is deleted from the buffer C and waits for the next data input.

The difference means of the present invention described above differs from two input signals which are simultaneously inputted by the original differential probe, but is substantially completely different because signals which are inputted almost simultaneously are different. It is not a differential probe but a pseudo-differential probe. However, for example, since the traveling speed of the probe is 400 mm / sec and the switching speed of the coil pair is at most 10 μsec to 1 msec, the temperature change during that time can be ignored, and the distance that the adjacent coil pair travels substantially is also small. Since it is 0.4 mm or less, there is no problem compared with the effective flaw detection range of the coil pair of about several mm.

In the above embodiment, the number of coil pairs is eight. However, the present invention is, of course, effective with three or more pairs, and the data holding period is provided by means such as providing one data buffer for one detection coil. Can be extended to change the coil pair to be calculated.

[0016]

As described above, the eddy current flaw detection apparatus of the present invention comprises an eddy current flaw detection probe comprising a plurality of magnetic field excitation elements and magnetic field detection element pairs, and means for time-divisionally driving the magnetic field excitation element / magnetic field detection element pairs of the probe. A differential probe provided with a control device including means for holding output signals of each element pair over several steps of time-division driving, and means for differentiating output signals of adjacent element pairs. While increasing the number of coil pairs to improve the resolution, it is possible to form a differential coil pair with a smaller number of coils than before, and to change the difference by changing the switching timing of the excitation coil / detection coil pair. There is a practical effect that more flexible operation is possible, for example, a dynamic coil pair can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic external view of an eddy current detection probe used in the apparatus of the present invention.

FIG. 2 is an explanatory diagram of a system in a control device in the device of the present invention.

FIG. 3 is a diagram illustrating an operation algorithm for obtaining differential data by a control device according to the present invention.

FIG. 4 is an external view showing an example of a conventional eddy current flaw detection probe.

[Explanation of symbols]

 101 Maternal 102 Coil group 103 Sheath A Detection circuit B A / D conversion circuit C Data buffer D Operation circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 599019948 4495 Wilfrid-Hamel Quebec, Qbec, Canada (72) Inventor Yutaka Harada 1-3-7 Tosabori, Nishi-ku, Osaka-shi Nuclear Engineering Co., Ltd. (72) Invention Person: Junri Shimone 1-3-7 Tosabori, Nishi-ku, Osaka-shi Nuclear Engineering Co., Ltd. (72) Inventor Florian Hardy Canada. St. Augustine, Quebec 121 Rue de Labandiere 121 (72) Inventor Rock Samson St. Nicholas de la Chaudier, Quebec 177 F-term (reference) 2G053 AA11 AB21 BA12 BA23 BA26 BC14 CA03 CB19 CB24 DA01 DA06 DB04 DB27 2G075 AA01 BA17 CA16 CA17 DA16 FA16 FB04 FC04 FC14 GA02 GA25

Claims (2)

[Claims] 1. An eddy current flaw detection probe comprising a plurality of magnetic field excitation element / magnetic field detection element pairs, and means for time-divisionally driving the magnetic field excitation element / magnetic field detection element pairs of the probe, and
The eddy current flaw detection device further comprises a control device including means for holding output signals of each element pair over several steps of time division driving, and means for differentiating output signals of adjacent element pairs. 2. The eddy current flaw detector according to claim 1, wherein at least a part of the means for time-divisionally driving the magnetic field excitation element / magnetic field detection element pair is arranged at or near the probe body.