JPS6011493Y2 - Electromagnetic induction detection device - Google Patents

Description

[Detailed description of the invention] The present invention is based on magnetic materials, non-magnetic materials, shapes of metal bodies (e.g.
It can be used to detect defects on the surface of metal objects (tubes, rods, plates), detect welds, trace the probe in ultrasonic flaw detection, trace the welding rod in grooves, etc. The present invention relates to an electromagnetic induction detection device that can perform

□Generally, eddy current (electromagnetic induction) probe coils include one in which an excitation coil and a detection coil are electromagnetically coupled, or a self-excitation type in which a single coil serves both excitation and detection. This replaces the pedance change with a signal voltage.

In such a device, the impedance of the detection coil must be balanced by an AC bridge, which is affected by changes in the distance between the detection coil and the metal material and changes in the resistance of the detection coil due to heat.

Furthermore, what has been done in consideration of the above circumstances is the patent application No. 49-82383 (Patent Application No.
-124084)).

The present invention is an improvement of the embodiment shown in the above-mentioned publication (the embodiment shown in FIG. 4) in obtaining an electrical signal from the surface of a ferrous or non-ferrous pipe or rod-shaped object.

'That is, in the above embodiment, as shown in FIG.
A detection coil b is provided on the upper side, and an excitation coil a is provided above the detection coil b at a position such that magnetic lines of force can be generated at right angles to the lines of magnetic force to which the detection coil b is sensitive.

However, such a method has the drawback that it is limited to a metal plate, and most of the magnetic lines of force generated from the excitation coil are not necessarily focused and introduced into the specimen.

Conventionally, a method has also been considered in which two detection coils are disposed adjacent to each other and the two detection coils are differentially connected.

□However, since this method uses two detection coils, it is not possible to reduce the distance between the two detection coils. Because of their large size, in the case of misalignment due to vibration of the test material such as a cylinder or round bar, or bending of a plate-like test material, the difference between the two coils will be detected, resulting in unnecessary spurious signal voltage noise) and offset. The voltage has also increased.

For this reason, even though the defects to be detected are becoming smaller year by year, it is impossible to make them smaller with the method using two detection coils.
It is difficult to detect microcracks that are smaller than mm.

The present invention relates to an electromagnetic induction detection device made to solve the above-mentioned conventional problems, and is a U-shaped detection device formed by an excitation side core and magnetic pole side cores attached to both ends of the excitation side core. An excitation coil connected to an oscillation circuit is wound around the excitation side core of the closed magnetic circuit core so that excitation magnetic lines of force flow, and one detection is carried out within the excitation magnetic field focused by the U-shaped closed magnetic circuit core. A signal generation device in which a coil is disposed perpendicular to the excitation coil, a cancellation voltage regulator is connected to the oscillation circuit, and the cancellation voltage regulator and the detection coil are connected in parallel to a differential amplifier. The device is characterized by being equipped with an adjustment circuit.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an example of the present invention, in which a U-shaped closed magnetic circuit core 2 is formed of an excitation side core and magnetic pole side cores provided at both ends of the excitation side core. An excitation coil 1 connected to an oscillation circuit 4 is wound around the excitation side core of , and the excitation coil 1 is excited by the oscillation circuit 4, so that an alternating magnetic flux is caused to flow inside the core 2, and this alternating magnetic flux crosses the air gap. By passing through the metal body 5, which is the material to be inspected, an alternating current frequency is generated in the metal body 5 that makes it easy to extract the electromagnetic response of the metal body 5, and is orthogonal to the alternating magnetic flux passing through the metal body 5. One detection coil 3 is arranged in this way, so that the induced voltage in the one detection coil 3 has an effect of acting as a differential (hereinafter referred to as differential effect).

That is, in the device of the present invention, one detection coil 3 is connected to the metal body 5.
In order to provide a differential effect with one detection coil 3 perpendicular to the magnetic field passing through the coil, a U-shaped closed magnetic circuit core 2 is used.
One detection coil 3 is disposed perpendicular to the magnetic field, so that one detection coil 3 has a differential effect.

The reason why a single detection coil 3 is provided with a differential effect is because it is necessary to make it small in order to detect minute flaws, and if it is made small, the S/N ratio improves.

With the above configuration, the lines of magnetic force generated from the excitation coil 1 can be effectively focused by forming a magnetic circuit using the closed magnetic circuit core 2, and one detection coil 3 can be placed within this focused excitation magnetic field. , perpendicular to exciting coil 1,
That is, since the detection coil 3 is disposed perpendicular to the magnetic field, the single detection coil 3 can induce a disturbance component of the excitation magnetic field lines in response to electromagnetic changes on the surface of the metal body 5.

In the present invention, as mentioned above, one detection coil 3
Because it is necessary to arrange the coil 3 at right angles to the excitation coil 1 in order to have a differential effect, a U-shaped closed magnetic circuit core 2 is used, and one detection coil 3 is connected to the excitation coil. Since it is arranged at right angles to 1, 1
In addition to having a differential effect with the detection coils 3, the single detection coil 3 can be miniaturized and the distance between the magnetic poles can be narrowed, and the S/N ratio can be improved. It is also possible to detect flaws with a width of 10μ or less and a depth of 0.05m or less.

Further, along with this, unnecessary pseudo signals and offset voltages can be reduced.

In this regard, when two detection coils are used as a differential connection, the size is twice as large as when there is only one detection coil, and the range of electromagnetic coupling with the metal body is also widened, resulting in a lower S/N ratio. It is not suitable for detecting minute defects, and the unnecessary offset voltage is large.

In order to prevent a change in the phase of the excitation magnetic field in the excitation coil 1, the closed magnetic circuit core 2 is formed to wrap around the metal body 5 as shown in FIG. It is optional to interpose a ball caster 6 between the leg of the reinforced core 2 and the metal body 5.

Next, the process of adjusting so that no signal is always generated under normal conditions, ie, the signal generation adjustment circuit, will be described with reference to FIG.

The excitation coil 1 is connected to an oscillation circuit 4, and the detection coil 3 disposed orthogonally to the excitation coil 1 is connected to the differential amplifier 7 so that its output is applied to the differential amplifier 7. The voltage is connected to the canceling voltage regulator 8 so that the voltage is input to the regulator 8, which is connected to the differential amplifier 7.

Note that the canceling voltage regulator 8 is unnecessary in principle if the excitation coil 1 and the detection coil 3 are manufactured with a completely right-angled relationship, but in reality the voltage was detected by the detection coil 3. When the signal is electrically expanded and amplified, the induced voltage to the parrot detection mile 3 may not necessarily be zero when the detection coil 3 is made to correspond to a healthy part of the metal material, so the signal is expanded and amplified. This is used as an auxiliary means for operation within the amplification linearity range of the amplifier and for phase discrimination output signal processing.

That is, during initial setting or at all times, a portion of the output from the oscillation circuit 4 is adjusted by the cancellation voltage regulator 8 so that no signal output is generated from the differential amplifier 7 in the normal portion of the metal body 5.

The output of the detection coil 3 is now applied to the differential amplifier 7, and the output of the oscillator circuit 4 is sent to the cancellation voltage regulator 8.

The signal applied to the canceling voltage regulator 8 is
Then, the amplitude and phase are made to be the same as the induced voltage statically induced by the detection coil 3, and this voltage is applied to the differential amplifier 7, and the output voltage of the amplifier 7 becomes zero.

If the adjustment of the cancellation voltage regulator 8 is limited to only the initial setting, the initial setting is used as the origin and is suitable for subsequent absolute value measurement control, for example, shape change tracking.

Further, if additional functions such as constant voltage adjustment are provided and Fourier analysis is performed in signal processing after discrimination, it becomes dynamic signal processing and can have a flaw detection function in non-destructive testing.

At this time, when the metal body 5 is cylindrical or cylindrical, even if the metal body 5 is rotated and slid, or conversely, the device of the present invention can be rotated and slid on the metal body 5.
It may be made to circulate along the inner circumference or outer circumference of.

Therefore, the present invention can overcome the various drawbacks of the device shown in FIG. 5 mentioned above.

That is, the present invention is not limited to only plate-shaped metal materials, and it is possible to focus the lines of magnetic force generated from the excitation coil onto the subject.

It goes without saying that the present invention is not limited to the illustrated and described embodiments, and that various changes may be made without departing from the gist of the present invention.

As described above, the electromagnetic induction detection device of the present invention has a configuration in which one detection coil is arranged orthogonally within the excitation magnetic field focused by the U-shaped closed magnetic circuit core. Therefore, there is no need to balance the coil impedance using an AC bridge, and therefore, it is not affected by changes in resistance due to distance changes to the metal object or temperature, and it is possible to detect flaws on the surface of metal objects, detect welds, and It can be used for tracking in order to reliably follow the probe in sonic flaw detection, the kiln contact rod in the groove, etc., and has a differential effect with one detection coil. 1
Since it is a single detection coil, it can be miniaturized and the distance between the magnetic poles can be narrowed, improving the S/N ratio, and therefore it is suitable for detecting minute flaws.

In addition, there are detection coils that have a simple mechanism and are easy to assemble, and are available in various shapes, but rectangular ones are especially useful for tracing beads, grooves, etc. in the axial direction. It can also prevent visual signal fluctuations, and since it is equipped with a signal generation adjustment circuit, it can be adjusted so that there is no signal output at normal parts of the metal object during initial setting or at all times, improving detection accuracy. Demonstrates excellent effects such as obtaining.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the electromagnetic induction detection device of the present invention, FIGS. 2 and 3 are explanatory diagrams showing other examples of the electromagnetic induction detection device of the present invention, and FIG. Explanatory diagram showing the adjustment process of signal generation in the electromagnetic induction detection device, No. 5
The figure is an explanatory diagram of a conventional example. 1 is an excitation coil, 2 is a closed magnetic circuit core, 3 is a detection coil,
4 is an oscillation circuit, 5 is a metal body, 6 is a ball caster, 7
8 indicates a differential amplifier, and 8 indicates a cancellation voltage regulator.

Claims (1)

[Scope of utility model registration request] An excitation coil connected to an oscillation circuit is wound around the excitation side core of a U-shaped closed magnetic path core formed by an excitation side core and a magnetic pole side core attached to both ends of the excitation side core, so that excitation magnetic force lines flow. In the excitation magnetic field focused by the U-shaped closed magnetic circuit core, one detection coil is disposed perpendicular to the excitation coil, and a cancellation voltage regulator is connected to the oscillation circuit. An electromagnetic induction detection device comprising: a signal generation and adjustment circuit in which the cancellation voltage regulator and the detection coil are connected in parallel to a differential amplifier.