JP2961061B2 - Electromagnetic ultrasonic flaw detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic ultrasonic inspection apparatus for performing nondestructive inspection, thickness measurement of a structure, and the like by using an electromagnetic ultrasonic probe having a magnet body, a transmission coil, and a reception coil. It is.

[0002]

2. Description of the Related Art Conventionally, there is an EMAT as one of the electromagnetic ultrasonic probes used for nondestructive inspection of a conductive object. The principle of the electromagnetic ultrasonic probe (EMAT) will be described with reference to FIG. When a magnetic flux B is generated in the magnet body 1 made of a permanent magnet or an electromagnet, when a sinusoidal high-frequency current I flows through the transmission coil 3 provided between the magnet body 1 and the conductive subject 2, the conductive subject An eddy current J is generated on the surface of No. 2 and the interaction between the eddy current J and the magnetic flux B causes Lorentz force F
Is generated, and the ultrasonic wave S is generated using the Lorentz force F as a vibration source.
Occurs. When the ultrasonic wave S is received, the ultrasonic signal is converted into a telegraph signal in a process reverse to the above.

[0003] An electromagnetic ultrasonic probe (E
A conventional example of an electromagnetic ultrasonic flaw detector having MAT) will be described with reference to FIG. 7. Reference numeral 1 denotes a magnet body, 2 denotes a conductive object, 3 denotes a transmission coil, and 4 denotes a reception coil. The subject 2, the transmitting coil 3, and the receiving coil 4 are shown in FIG.
It is arranged as follows. 7 in FIG. 7 is an electromagnetic ultrasonic probe including the magnet body 1, the transmission coil 3, and the reception coil 4, and 7
Is a reception signal amplification amplifier section, 8 is an electromagnetic ultrasonic signal processing section,
12 is a sine wave transmission-like power amplifier unit, 13 is a transmission matching circuit, and 14 is a reception matching circuit.

A sine wave current of several A to several tens A flows from the sine wave transmission-like power amplifier section 12 to the transmission coil 3. In this case, in order to suppress the reflection of the transmission waveform, a transmission matching circuit 13 for matching the load impedance to the output impedance of the amplifier and reducing the oscillation waveform due to the reflection.
Is inserted. Ultrasonic waves are generated and reflected from the target object.
A small signal of V to several hundred μV is induced. This signal is amplified by the reception signal amplification amplifier 7 via the reception matching circuit 14 for matching to the input impedance of the reception signal amplification amplifier 7 in the same manner as in the transmission, and is reflected by the electromagnetic ultrasonic signal processing unit 8. A sound wave signal is detected and displayed. The electromagnetic ultrasonic signal processing unit 8 determines the presence or absence of the target object based on the presence or absence of the reflected ultrasonic signal, and determines the distance to the target object (time × sound speed / 2) based on the time of the reflected ultrasonic signal that is reflected back. : Round trip) is required.

[0005]

In the conventional electromagnetic ultrasonic flaw detector having the conventional electromagnetic ultrasonic probe (EMAT) shown in FIG. 7, the electro-acoustic conversion efficiency is generally low. A large current flows, and a weak signal is detected on the receiving side. Also, when inspecting from one side, the electromagnetic ultrasonic probe (EMAT) has a transmitting coil 3 and a receiving coil 4 arranged close to each other as shown in FIG. Induce. Further, even if a matching circuit is inserted, a slight vibration waveform is generated.
Accordingly, an excessive input is applied to the reception signal amplification amplifier unit 7 for amplifying the minute signal, and the amplifier unit 7 is saturated, so that the measurement impossible time is lengthened as shown in FIG.

For this reason, when measuring a portion close to the probe, such as immediately below the surface of a conductive object, for example, the thickness of a steel material having a thickness of 5 mm, if the sound speed in the steel material is 3.2 mm / sec,
It is necessary to keep the saturation time within about 3 μsec,
At present, there is a problem that the saturation time is too long and measurement becomes impossible. The present invention has been made in view of the above problems, and has as its object the object of the present invention is to measure a portion close to a probe directly below the surface of a conductive test object, and to achieve miniaturization and cost reduction. It is in trying to provide an ultrasonic flaw detector.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an electromagnetic ultrasonic probe having a magnet body, a transmitting coil and a receiving coil for performing nondestructive inspection and the like. In the flaw detector, a reception signal monitoring unit that monitors a reception vibration waveform to the reception coil when a rectangular wave transmission signal driving the transmission coil rises, and a first cycle of the reception vibration waveform based on an output waveform of the reception signal monitor. A rectangular wave time control unit for generating a transmission off signal for detecting a zero cross point of the rectangular wave transmission unit and turning off a transmission coil line to supply a rectangular wave current to the transmission coil by turning a transmission coil line on and off. And the receiving coil is connected to the received signal monitoring unit, the received signal monitoring unit is connected to the rectangular wave transmitting unit, and the rectangular wave transmitting unit is connected to the transmitting coil. It is connected (claim 1).

In the above-mentioned electromagnetic ultrasonic flaw detector, a reception signal amplification amplifier unit for amplifying a weak signal from the reception coil and a reception signal switching unit are provided, and the reception signal amplification amplifier unit is connected to the input side of the rectangular wave transmission unit. And the reception signal switching unit may be provided on the input side of the reception signal amplification amplifier unit, and the output side of the rectangular wave time control unit and the input side of the rectangular wave transmission unit may be connected to the reception signal switching unit. (Claim 2).

[0009]

The electromagnetic ultrasonic flaw detector according to the present invention is configured as described above, and the received vibration waveform caused by the rise of the transmission signal is greatly restricted by adjusting the off timing of the transmission signal and cutting off the transmission coil line. Will be done. In addition, a reception signal switching unit for switching the input signal is provided on the input side of the reception signal amplification amplifier unit, thereby preventing the saturation of the reception amplifier during transmission and greatly preventing the measurement from being performed (amplifier saturation). This enables measurement of a portion near the probe immediately below the surface of the conductive subject.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an electromagnetic ultrasonic flaw detector according to the present invention will be described with reference to an embodiment shown in FIGS. 1 is a magnet body, 2 is a conductive object, 3 is a transmitting coil, 4 is a receiving coil. These magnet body 1, conductive object 2, transmitting coil 3 and receiving coil 4 are arranged as shown in FIG. Are located.

Reference numeral 5 denotes an electromagnetic ultrasonic probe (EMAT). The electromagnetic ultrasonic probe 5 includes a magnet body 1, a transmission coil 3, and a reception coil 4 as in the conventional case. 6 is a reception signal switching unit, 7 is a reception signal amplification amplifier unit, 8 is an electromagnetic ultrasonic signal processing unit, 9 is a rectangular wave transmission unit, 10 is a reception signal monitoring unit, and 11 is a rectangular wave time control unit.

As shown in FIG. 2, the rectangular wave transmitting section 9 can turn on and off the transmitting coil line at high speed by the semiconductor power switch 15 and allow a rectangular wave current of several A to several tens A to flow through the transmitting coil. Thus, the width of the transmission current can be adjusted by the time difference between the transmission start trigger signal from the rectangular wave transmission unit 9 and the transmission off signal from the rectangular wave time control unit 11.

As shown in FIG. 3, the reception signal switching unit 6
The analog switch 16 is switched by the transmission start trigger signal from the rectangular wave transmission unit 9 and the transmission off signal from the rectangular wave time control unit 11, and the reception signal amplification amplifier unit 7
Input is switched. The reception signal monitoring unit 10 is an amplifier for monitoring the frequency of reception to the reception coil 4 when the rectangular wave transmission signal for driving the transmission coil 3 rises.

The rectangular wave time control section 11 detects a zero-cross point in the first cycle of the received vibration waveform from the output waveform of the received signal monitor section 10 as shown in FIG. To generate a transmission off signal. The electromagnetic ultrasonic signal processing unit 8 detects the presence or absence of an object in the conductive subject 2 based on the signal from the reception signal amplification amplifier unit 7 and the transmission start trigger signal from the rectangular wave transmission unit 9, and transmits the signal. The distance is calculated by measuring the time from the start to the detection of the reflected ultrasonic signal.

[0015] In the electromagnetic ultrasonic flaw detector configured as described above, the attenuation and settling of the received vibration waveform can be accelerated. Also, during transmission, the input of the reception signal amplification amplifier unit 7 is connected to the ground, and the input voltage is kept at 0 V, thereby preventing the reception amplifier from being saturated during transmission. Also, by switching to the receiving coil 4 side after the transmission is completed,
The non-measurable time due to the saturation of the receiving amplifier is reduced, and a portion close to the probe such as immediately below the surface of the conductive subject 2 can be measured.

[0016]

The electromagnetic ultrasonic flaw detector according to the present invention is configured as described above, and can reduce the time during which the electromagnetic ultrasonic probe cannot be measured, and can be used for a probe directly below the surface of a conductive subject. Close parts can be measured. In addition, it uses square wave transmission, and the transmission driver can use a high-speed semiconductor switch, eliminating the need to match the impedance of the transmission coil and the reception coil, eliminating the need for a matching circuit, and providing electromagnetic ultrasonic flaw detection. The apparatus can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of an electromagnetic ultrasonic flaw detector according to the present invention.

FIG. 2 is a block diagram of a rectangular wave transmitting unit of the electromagnetic ultrasonic testing device.

FIG. 3 is a block diagram of a reception signal switching unit of the electromagnetic ultrasonic testing device.

FIGS. 4A to 4C are explanatory diagrams showing examples of the arrangement of transmitting and receiving coils of the electromagnetic ultrasonic testing apparatus.

FIGS. 5A to 5C are explanatory diagrams showing transmission / reception waveforms of the electromagnetic ultrasonic flaw detector.

FIG. 6 is an explanatory diagram showing the principle of an electromagnetic ultrasonic probe (EMAT).

FIG. 7 is a system diagram showing a conventional electromagnetic ultrasonic flaw detector.

FIG. 8 is an explanatory diagram showing an example of transmission / reception waveforms of the electromagnetic ultrasonic testing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 magnet body 2 conductive subject 3 transmission coil 4 reception coil 5 electromagnetic ultrasonic probe 6 reception signal switching section 7 reception signal amplification amplifier section 8 electromagnetic ultrasonic signal processing section 9 rectangular wave transmission section 10 reception signal monitoring section 11 Square wave time control section

Claims (2)

(57) [Claims] 1. An electromagnetic ultrasonic flaw detector for performing non-destructive inspection or the like using an electromagnetic ultrasonic probe having a magnet body, a transmission coil, and a reception coil, when a rectangular wave transmission signal driving the transmission coil rises. A receiving signal monitoring unit that monitors a receiving vibration waveform to the receiving coil, and a zero-cross point in a first cycle of the receiving vibration waveform that is detected based on an output waveform of the receiving signal monitor to turn off a rectangular wave transmitting unit to be described later. A rectangular wave time control unit for generating a transmission off signal; and a rectangular wave transmission unit for turning a transmission coil line on and off to flow a rectangular wave current to the transmission coil, and connecting the reception coil to the reception signal monitoring unit. An electromagnetic ultrasonic flaw detector wherein the received signal monitor is connected to the rectangular wave transmitter, and the rectangular wave transmitter is connected to the transmission coil. 2. A reception signal amplification amplifier unit for amplifying a weak signal from the reception coil, and a reception signal switching unit,
The reception signal amplification amplifier section is provided on the input side of the rectangular wave transmission section, and the reception signal switching section is provided on the input side of the reception signal amplification amplifier section, and the output side of the rectangular wave time control section and the rectangular wave 2. The electromagnetic ultrasonic flaw detector according to claim 1, wherein an input side of the transmission unit is connected to the reception signal switching unit.