JPH0238882A - Magnetic permeability measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve highly accurate measurement free from effect of a lift off with a simple circuitry by arranging a low frequency magnetization coil, two sets of light frequency magnetization coils with different polarities and a search coil therebetween to allow the outputting of a detection output through an amplifier with a gain thereof adjusted automatically as specified. CONSTITUTION:An object 13 to be measured is magnetized through a low frequency magnetization coil 6 of a U-shaped core 12 of a detection head. An output of the coil 6 is overlapped with a weak output from two sets of high frequency coils 7 and 8 which generate magnetic fields with different polarities and a high frequency component with the magnetization of the object to be measured is detected with a search coil 11 disposed between the coils 7 and 8. Then, a signal corresponding to the maximum magnetic permeability of the object to be measured is outputted through a peak detector 17 and AGC amplifier 20. In this case, a gain of the amplifier 20 is controlled automatically by an output according to a lift off via a phase inverter 18 and a peak detector 19 thereby enabling highly accurate magnetic permeability measurement with a simple circuitry eliminating the preparation a B-4 curve or the like and free from effect of the lift off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic permeability al determination device used for testing the mechanical properties of the material of an object such as a steel plate.

[Prior Art] Conventionally, a method for determining the magnetic properties of such a steel plate is to provide a detection head with an excitation coil and a detection coil wound around a U-shaped core, and place this detection head on the object to be measured. A closed magnetic circuit is formed by contacting an object, the U-shaped core and the object to be measured are magnetized by an excitation coil, and a magnetic flux is exposed by a detection coil, and the relationship between magnetization type tTt (magnetomotive force) and magnetic flux is shown. A method has been implemented in which a B-H curve is created and the maximum magnetic permeability and coercive force are determined based on this curve.

[Problem to be solved by the invention] When determining the maximum magnetic permeability using the method described above, B-
It is necessary to create an H curve and determine the maximum permeability based on it, which poses a problem in that it takes time to read the graph or requires an expensive computer. In addition, in the above method, it is necessary to place the detection head in close contact with the fixed object 91 for measurement, and therefore it is necessary to stop the fixed object 11p1 on the conveyance line of the object to be measured. there were.

The present invention has been made in order to solve the above-mentioned problems, and provides a device that determines the maximum magnetic permeability using an API using a simple circuit configuration. The purpose of this invention is to present a device that can perform 4-j determination.

Means for Solving Problem U] The present invention provides a solution to a low frequency magnetization coil dropped into a core.
In a magnetic permeability measurement device that magnetizes a constant object with a detection head and determines the magnetic properties of the object to be measured,
1 detection head consists of a UT-shaped core into which a low-frequency magnetization coil is dropped, a pair of high-frequency magnetization coils dropped into the tip of this core so that they have opposite polarities, and this pair of high-frequency magnetization coils. A magnetic flux detector is provided between the coils and detects the magnetic properties of a magnetized object under test in a non-contact manner.

Furthermore, in claim (1), there is further provided an amplitude detector for amplitude detecting the detection signal from the magnetic flux detector, a first peak detector for detecting the peak value of the amplitude detector, and a first peak detector for detecting the peak value of the amplitude detector; A phase inverter that performs phase inversion, a second peak detector that detects the peak value of the output of this phase inverter, and automatic gain control (7, first peak detector) according to the output of this second peak detector. It is equipped with an amplifier with an automatic gain control function that amplifies the detector output.

[Function] With the top having the configuration shown in item 1 of rFJ, the object to be measured is periodically magnetized by the low frequency magnetization coil to near saturation magnetization at low frequency. Then, a minute amount of high-frequency magnetization by a high-frequency magnetization coil is superimposed thereon. The magnetic flux detector is installed in the middle of the U-shaped core, so the total magnetic flux (leakage flux) due to the low-frequency magnetization coil is zero.The high-frequency magnetization coil is located at the tip of the U-shaped core with opposite characteristics. Therefore, the magnetic flux (leakage flux) of these high frequency coils interlinks with the magnetic flux detector in one direction.Then, the magnetic flux passing through the magnetic flux detector is
It has a relationship with the magnetic flux passing through the object and the distance between the tip of the detection head and the object to be measured (lift-off).

The high frequency magnetic flux passing through the object to be measured has a relationship with the differential magnetic permeability of the constant object AP1. In other words, when the current in the low-frequency magnetizing coil is small, the differential permeability IJIi of the object to be measured is 5 (because of this, the change in magnetic flux passing through the magnetic flux detector is large, but when the current in the low-frequency coil is large, the object to be measured is As the magnetic saturation approaches and the differential magnetic permeability becomes small, the change in the magnetic flux passing through the magnetic flux detector becomes small.

Therefore, if the current induced by the magnetic flux passing through the magnetic flux detector is rectified and its maximum value is taken, that value corresponds to the maximum value of the differential magnetic permeability, that is, the maximum magnetic permeability.

However, with the configuration shown in item 1 above, although the maximum permeability can be measured with high accuracy when the liftoff is constant, a large error occurs when the liftoff changes.
Uru. On the other hand, in the configuration shown in Section 2 above, the detection signal from the magnetic flux detector is amplitude-detected, passed through a phase inverter, and then peak-detected, so that the constant object is magnetized near magnetic saturation. It is possible to calculate the differential magnetic permeability at the time, calculate the lift-off from this value, and control the output according to the calculated lift-off so that the output does not depend on the lift-off.

[Example] The following is a drawing showing an embodiment of the present invention. I will refer to and explain.

Reference numeral 1 denotes a commercial AC power supply, and a slider 2 for adjusting the voltage and temperature is connected to this power supply 1. A low frequency magnetization coil 6 in a detection radar 5 is connected to the output terminal of the slider 2 through a resistor 3 and a coil/dancer 4 in series.

A pair of high-frequency magnetization coils 7.8 having opposite polarities are also connected in series within the detection head 5, and a high-frequency oscillator 9 to a power amplifier 10 are connected to the series circuit.
A high frequency current is supplied through the

Further, the detection head 5 is provided with a search coil 11 as a magnetic flux detector.

The detection head 5 has a U-shaped core 1 as shown in FIG.
The low frequency magnetizing coil 6 is wound around the center of the core 2, and each tip 12a of the core 12.

1 and 2b are each wound with the high frequency magnetization coil 7.8. The search coil 11 is arranged so as to be located between the high frequency magnetization coils 7.8.

The respective tips 12a and 12b of the core 12 and the search coil 11 are spaced apart from the object to be measured 13 so that magnetic properties can be measured.

The output from the search coil 11 is amplified via a signal amplifier 14 and further supplied to an amplitude detector 15 for amplitude detection, so that, for example, only amplitude changes in a positive waveform are extracted.

The output from the amplitude detector 15 is amplified via a low frequency amplifier 16 and supplied to a first peak detector 17, and is also supplied to a phase inverter 18 for phase inversion and then to a second peak detector 19. supplying.

The first peak detector 17 detects the peak value of the waveform input manually via the amplifier 16, and detects the peak value of the output from the amplitude detector 15. The second peak detector 19 detects the peak value of the waveform input via the phase inverter 18, and detects the peak value obtained by inverting the output from the amplitude detector 15. The minimum value of the output of is detected.

The output of the first peak detector 17 is controlled by automatic gain control (A
GC) is input to the input terminal of the amplifier 20, and the output of the second peak detector]9 is input to the gain control terminal.

The amplifier 20 automatically controls the gain based on the input level from the second peak detector 19, and amplifies the manual power from the first peak detector 17 based on the controlled gain. .

The output from the automatic gain control amplifier 20 is amplified by a DC amplifier 21, and the maximum permeability output is sent out from the amplifier 21 as a magnetic characteristic measurement output.

In this embodiment with such a configuration, the detection head 5 is brought close to the object to be inspected 13, and commercial alternating current is supplied to the low frequency magnetization coil 6, and a pair of high frequency magnetization coils 7 are supplied.
．． When a high frequency current is supplied to the low frequency magnetized coil 6, a magnetic circuit shown by the dotted line in FIG.
As a result, a magnetic circuit shown by a dashed line in FIG. 2 is formed, and a high frequency magnetic flux flows.

The magnetic flux induced by the superimposed currents of these high-frequency currents and low-frequency currents flows through the Δp1 constant 13,
Since the low frequency current is larger, the magnetization of the object to be measured [3] is dominated by the low frequency current. Therefore, the high frequency magnetic flux passing through the object to be measured 13 has a value corresponding to the differential magnetic permeability of the object to be measured 3 magnetized by the low frequency current at a certain point in time. As described above, only high frequency magnetic flux is detected in the search coil 11. In FIG. 3, the voltage induced in the search coil (flj+) is expressed as (a) with respect to the low frequency current shown in (b).

The amplitude of the output voltage is largest when the low frequency magnetizing current is small (0 section), and becomes small and approximately constant when the low frequency current is large and the object to be measured 13 is magnetically saturated (0 section).
.

The output of the search coil 11 is amplified by a signal amplifier 14 and then amplitude detected by an amplitude detector 15 to detect the amplitude of a positive waveform. This amplitude-detected signal is further amplified by a low frequency amplifier 16 and then supplied to a second peak detector 19 via a first peak detector 17 and a phase inverter 18.

The first peak detector 17 detects the peak value of the positive portion of the waveform shown in FIG. 3(a), that is, the level indicated by ■ in the figure. This part is the part corresponding to the maximum magnetic permeability.

Further, the second peak detector 19 detects the peak value when the positive part of the waveform shown in FIG. This will detect the minimum level of the output from the search coil 11. This portion corresponds to the differential magnetic permeability at the point where the object to be measured 13 is magnetized to near magnetic saturation. The differential magnetic permeability at this point is a substantially constant value regardless of the material if the type of the object to be measured 13 is the same. Therefore, this value can be considered to change only due to changes in liftoff. The value of the 0 part changes due to lift-off, but if lift-off is detected, it can be corrected accordingly.

The amplifier 20 with automatic 1+1 gain control function automatically controls the gain based on the peak detection output from the second peak detector 19 and amplifies the peak detection output from the first peak detector 17. Then, the amplified signal is amplified by a DC amplifier 21 and then sent out as a maximum permeability output.

The mechanical properties of the object to be measured 13 can be inspected based on the maximum magnetic permeability output obtained in this way, that is, the magnetic property measurement output.

By using the search coil 11 in this way, the magnetic properties of the M1 constant object 13 can be measured without contact, making it possible to perform online measurements and improve the efficiency of measurement work.

FIG. 4(a) is a graph showing the output voltage change with respect to the lift-off change of the detection head 5 in this example, and it can be seen from this graph that there is almost no variation in the output voltage when measuring various objects to be measured. .

On the other hand, FIG. 4(b) is a graph showing changes in output voltage with respect to lift-off changes when the amplifier 20 with automatic gain control function is not used; in this case, as the lift-off changes increase, the output voltage decreases. It can be seen that there are fluctuations.

Note that the graphs ■, ■, ■ in FIG. 4(a) and the graphs ■, ■, ■ in FIG. 4(b) are for the same test piece, respectively.

[Effects of the Invention] As detailed above, according to the present invention, the magnetic permeability of the object to be measured, such as a steel plate, can be detected by magnetizing the object to be measured, such as a steel plate, without contact, and therefore online measurement is possible. It is possible to provide a magnetic permeability Apj determination device that can improve measurement work efficiency.

Further, even if a lift-off change occurs, it is possible to automatically compensate for the measurement output change due to the change, and therefore it is possible to provide a magnetic permeability all setting that can accurately determine the U+ constant of magnetic permeability even when non-contact measurement is performed.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention; Fig. 1 is a circuit block diagram, Fig. 2 is a diagram showing the configuration of the detection head, and Fig. 3 is a diagram showing the relationship between search coil detection output and low frequency magnetizing current. Waveform diagrams, Figure 4 (a) is a graph showing output voltage changes with respect to detection head lift-off changes in this example, and Figure 4 (b) is a graph showing the detection head slope when an amplifier with automatic gain control function is not used. 5 is a graph showing changes in output voltage with respect to changes in foot-off. 5...Detection head, 6...Low frequency magnetization coil, 7゜8...High frequency magnetization coil, 11...Search coil, 1
7...First peak detector, 18...Phase inverter, 1
9...Second peak detector, 20...Amplifier with automatic gain control function. Figure 2 Figure 3 - 5A Invader 1' + 1 Pene d

Claims (2)

[Claims] (1) In a magnetic permeability measurement device that magnetizes an object to be measured with a detection head having a low-frequency magnetization coil wound around a core and measures the magnetic properties of the object, the detection head includes a low-frequency magnetization coil. A U-shaped core wrapped with A magnetic permeability measurement device characterized by having a magnetic flux detector that non-contact detects magnetic properties of an object to be measured. (2) The magnetic permeability measuring device according to claim (1), further comprising: an amplitude detector that amplitude-detects the detection signal from the magnetic flux detector; and a first peak detector that detects the peak value of the amplitude detector. , a phase inverter that inverts the phase of the signal from the amplitude detector, a second peak detector that detects the peak value of the output of the phase inverter, and a gain that is adjusted according to the output of the second peak detector. A magnetic permeability measurement device comprising an amplifier with an automatic gain control function that automatically controls and amplifies the output of the first peak detector.