JPH1090231A - Eddy current flaw detecting probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically improve flaw detecting ability by accurately signaling and sending information on defects eliminating such influences as attenuation and noise and arrange and form in more large numbers of detection coils without limited to such as pipe gauge of the flaw detecting object. SOLUTION: This eddy current flaw detecting probe is provided with a plural number of detection coils 11, 11,... regularly arranged on the outer circumference of the probe correspondingly to exciting coils, a plural number of preamplifiers 21, 21... amplifying signals obtainable from the plurality of detection coils 11, 11... with respective specific amplification factors, a multiplexer 22 time-division multiplexing a plural number of signals sent thereto through the plurality of preamplifiers 21, 21..., and a buffer amplifier 23 outputting time-division multiplexed signals from the multiplexer 22 after amplifying them.

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 detection probe for detecting a defect in a heat exchanger tube of a heat exchanger.

[0002]

2. Description of the Related Art FIG. 4 shows a general configuration of an eddy current flaw detection apparatus for detecting a defect in a heat transfer tube of a heat exchanger. In FIG. 1, an eddy current flaw detection probe 2 in which a plurality of detection coils 1, 1,... Are regularly arranged along a peripheral surface of a substantially cylindrical holder 7 is connected to an eddy current flaw detector 3 of a main body via a cable 4. Is done.

[0003] However, when the eddy current flaw detection probe 2 is inserted into the heat transfer tube 5 of the heat exchanger to be inspected and moved as shown in the figure, one of the detection coils 1, 1, ... When approaching a defect 6 such as a flaw existing in 5, the impedance of the detection coil 1 changes.

[0004] As shown in FIG.
Are obtained by the plurality of signal coils 4a, 4a,.
Are transmitted in parallel to the amplifiers 8, 8,... Of the eddy current flaw detector 3 via.

That is, since the level of each transmitted signal is very small, it is amplified by the amplifiers 8, 8,... At an appropriate predetermined amplification factor. Performs signal detection and other signal processing. In this case, since the amplitude and phase of the signal waveform are determined by the size and shape of the defect 6, the state of the defect 6 can be determined from the signal waveform.

[0006]

FIG. 6 shows the detection coil 1 of the eddy current flaw detection probe 2 and the amplifier 8 of the eddy current flaw detector 3.
And a set of signal lines 4a of a cable 4 for connecting them. As described above, the signal detected by the detection coil 1 is directly transmitted to the signal line 4 a constituting the cable 4.
Is transmitted to the amplifier 8 and then amplified, so that the amplitude of the signal to be transmitted is attenuated by the capacitance and resistance of the signal line 4a, or the noise 9 is superimposed on the signal during transmission. As a result, accurate flaw detection may be alienated.

FIG. 6A shows that the information of the corresponding defect 6 disappears from the signal output from the amplifier 8 because the amplitude of the flaw detection signal obtained by the detection coil 1 is attenuated during the transmission process of the signal line 4a. This indicates a state in which the operation is performed.

FIG. 6 (2) shows that the noise 9 is superimposed on the flaw detection signal obtained by the detection coil 1 during the transmission process of the signal line 4a, so that the S / N ratio of the signal output from the amplifier 8 is reduced. It shows a state that has become very bad.

[0009]

As described above, in the conventional eddy current flaw detector, signals detected by the detection coils 1, 1,... Of the eddy current flaw detection probe 2 are directly transmitted to the signal lines 4a, 4a constituting the cable 4. , Are transmitted to the amplifiers 8, 8,... Of the eddy current flaw detector 3 and then amplified, so that there is a problem that accurate flaw detection cannot be performed.

In order to improve the detection performance of the defect 6, the detection coils 1, 1,.
It is conceivable to increase the number of However, by increasing the number of detection coils 1, 1,..., The number of signal lines 4a, 4a,... Which constitute the cable 4 connecting the eddy current flaw detection probe 2 and the eddy current flaw detector 3 necessarily increases. .. Must have a certain thickness or more in consideration of signal attenuation due to signal resistance as described above, so that the diameter of the entire cable 4 increases and the heat exchanger There is a possibility that the number of the detection coils 1, 1,... Is limited by the inner diameter of the heat exchanger tube 5 to be inspected because the detection coils 1, 2,.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and an object of the present invention is to eliminate the effects of attenuation, noise, and the like, and to accurately transmit defect information while transmitting signals.
An object of the present invention is to provide an eddy current flaw detection probe capable of arranging and forming a larger number of detection coils without being limited by the inner diameter of a tube to be flaw-detected and consequently greatly improving flaw detection performance.

[0012]

According to the first aspect of the present invention,
An excitation coil, a plurality of detection coils regularly arranged on the outer peripheral surface of the probe corresponding to the excitation coil, a plurality of preamplifiers each amplifying a signal obtained from the plurality of detection coils with a predetermined amplification factor, And a buffer amplifier for amplifying the time-division multiplexed signal from the multiplexer and outputting the amplified signal.

With such a configuration, a signal obtained by the detection coil is amplified by a preamplifier close to the detection coil, and further amplified by a buffer amplifier via a multiplexer, and then output. It is not necessary to consider the attenuation of the signal during transmission, and the level of the transmitted signal itself is sufficiently high due to the influence of noise and the like, so that the S / N ratio can be improved to almost negligible level, and the detection is further performed. To time-division multiplex signals from multiple detection coils and transmit them over a cable,
The number of signal lines required for the cable can be reduced to a fraction of the number of detection coils, and a large number of detection coils can be arranged while keeping the cable thin.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an external configuration in which a part is cut out. An eddy current flaw detection probe 12 having a plurality of detection coils 11, 11,... The signal lines 14a, 14a, ...
Is connected to an eddy current flaw detector of a main body (not shown) through a cable 14 composed of

However, as shown, an electronic circuit unit 20 for processing signals detected by the detection coils 11, 11,... Is provided in the holder 17. FIG. 2 mainly shows a detailed configuration in the electronic circuit section 20. Detection signals from the detection coils 11, 11,... Are respectively amplified by predetermined preamplifiers (pre.) 21, 21,. , And is input to the multiplexer 22. Here, the preamplifiers 21, 21, 21
Are low-noise types in consideration of the fact that the detection signals are minute due to the size, performance, etc. of the detection coils 11, 11,.

The multiplexer 22 performs time division multiplexing of the detection signals sent from the detection coils 11, 11,... Via the preamplifier 21 in accordance with the selection signal input via the line receiver 24, and (Bu
f. ) 23.

The buffer amplifier 23 amplifies the time-division multiplexed detection signal sent from the multiplexer 22 with a constant amplification factor, and outputs the amplified signal from the cable 14 to the eddy current flaw detector to detect the signal.

An eddy current flaw detection probe 1 having the above configuration
In (2), since the signal detected by the detection coil 11 is amplified by the preamplifier 21 close to the detection coil 11, the signal is attenuated during transmission on the cable 14 as shown in FIG. Even in the case where the detection has occurred, it is possible to prevent the eddy current flaw detector from disappearing to a level where detection is impossible, and it is possible to reliably perform flaw detection.

Further, as shown in FIG.
Even if the noise 9 is superimposed on the signal during the transmission at 4, the signal component based on the target defect is buried in the noise 9 component since the original signal level is sufficiently large compared to the noise 9. The signal can be transmitted to the eddy current flaw detector without any reduction in the S / N ratio.

Further, since the signal to be transmitted is time-division multiplexed and transmitted to the eddy current flaw detector via the cable 14, the signal lines 14a and 14 constituting the cable 14 are provided.
, can be reduced to a fraction of the number of the detection coils 11, 11,...
Even if a large number of 1, 11,... Are arranged regularly on the outer peripheral surface of the holder 17, the thickness of the cable 14 can be suppressed to a sufficiently small value. , The inspection can be performed with higher accuracy.

From these facts, it becomes possible to detect a finer defect with a higher S / N ratio than was previously impossible. It should be noted that the present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the gist thereof.

[0022]

According to the first aspect of the present invention, a signal obtained by a detection coil is amplified by a preamplifier close to the detection coil, further amplified by a buffer amplifier via a multiplexer, and then output. Therefore, there is no need to consider signal attenuation during cable transmission, and the S / N ratio can be improved to almost negligible level because the level of the transmitted signal itself is sufficiently high due to the influence of noise and the like. Further, in order to transmit the signals from the plurality of detected coils in a time-division multiplexed manner and to transmit the signals via a cable, the number of signal lines required for the cable can be reduced to a fraction of the number of the detected coils. It is possible to adopt a configuration in which a large number of detection coils are arranged while being thin.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration according to an embodiment of the present invention.

FIG. 2 is a block diagram mainly showing a circuit configuration of an electronic circuit unit in FIG. 1;

FIG. 3 is a diagram showing a signal transmission state according to the embodiment;

FIG. 4 is a diagram showing a configuration of a conventional eddy current flaw detector.

FIG. 5 is a diagram showing a signal flow in a conventional eddy current flaw detector.

FIG. 6 is a diagram showing a signal transmission state of a conventional eddy current flaw detector.

[Explanation of symbols]

 1, 11 detection coil 2, 12 eddy current flaw detection probe 3, eddy current flaw detector 4, 14 cable 4a, 14a signal line 6 defect 7, 17 holder 8 amplifier 9 noise 20 electronic circuit Unit 21 Preamplifier 22 Multiplexer 23 Buffer amplifier 24 Line receiver

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Michio Hamana 2-1-1 Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. No. 1-1, Mitsubishi Heavy Industries, Ltd., Kobe Shipyard

Claims (1)

[Claims] An exciting coil, a plurality of detecting coils arranged regularly on an outer peripheral surface of a probe corresponding to the exciting coil, and a plurality of amplifying signals obtained from the plurality of detecting coils with a predetermined amplification factor. A preamplifier, a multiplexer for time-division multiplexing a plurality of signals sent through the plurality of preamplifiers, and a buffer amplifier for amplifying and outputting the time-division multiplexed signal from the multiplexer. And eddy current probe.