JPH03135780A - Method and device for magnetism measurement - Google Patents

Abstract

PURPOSE:To reduce the power consumption and to enable battery driving by applying the coil of a magnetic sensor with a positive and a negative pulse voltage through fixed impedance and detecting the positive and negative peak values of a voltage developed across the coil. CONSTITUTION:A series circuit of a resistance 102 with fixed impedance and the coil 103a wound around the ferromagnetic material core 103b of a magnetic sensor 103 is connected to the output terminal of a pulse voltage generator 10. The core 103b is magnetized into the saturated state with a pulse voltage applied from the generator 101. Then a magnetic field to be measured which puts the sensor 103 close enters a crossing state and the positive and negative voltages corresponding to the polarity and intensity are generated. Consequently, those voltages are detected by positive and negative voltage peak detectors 104 and 105 and added by an adder 106 to find a measured value corresponding to the magnetic field to be measured. Then the use of the pulse voltages reduces the power consumption and a battery is usable as a power source.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic measurement method for measuring leakage magnetic flux generated in, for example, a steel pipe or an iron plate using a magnetic sensor, and a magnetic measurement device using this magnetic measurement method. Regarding.

[Prior Art] For example, ultrasonic flaw detection, eddy current flaw detection, leakage magnetic flux flaw detection, and the like are used as methods for inspecting defects occurring in steel pipes, iron plates, and the like.

Among these methods, the leakage magnetic flux flaw detection method is relatively widely used because it can detect flaws on both sides of a thick steel plate from one side and has high detection sensitivity for defects occurring on the inner and outer surfaces of steel pipes.

Regarding the conventionally known technique for leakage magnetic flux flaw detection, as shown in FIG. 6, DC power is supplied from a DC power source 3 to an electromagnetic coil 2 wound around a magnetizing yoke 1. A test piece 4 is placed on top of the magnetization yoke 1 and is magnetized. If the test piece 4 has a defective part 5, a part of the magnetic flux leaks from the defective part 5 to the outside of the test piece 4 as shown by the dotted line in the figure. Therefore, the defective portion 5 is indirectly detected by detecting leakage magnetic flux using the magnetic sensor 6 and converting it into an electric signal.

For details, please refer to the Nondestructive Testing Handbook (Japanese Nondestructive Testing Association), Volume 2 (P573-599).

By the way, the magnetic flux density leaking from the defective portion 5 is very weak, as shown in FIG. 7 in relation to the distance between the steel surface and the Hall element, which is a magnetic sensor. In addition, FIG. 8 shows the steel material used for the measurement of FIG. 7, W shows the defect width, and d shows the depth of the defect.

From this, the magnetic sensor 6 that detects leakage magnetic flux must: 1) have high detection sensitivity to minute magnetic fields; 2) have small variations in the initial bias voltage of the magnetic sensor;
Good temperature characteristics are required.

However, the detection sensitivity of currently commercially available magnetic sensors to minute magnetic fluxes is extremely low, as shown in FIG. In the figure, graph a uses a magnetic diode as a magnetic sensor, graph b uses a magnetoresistive element, and graph C uses a Hall element.

Furthermore, regarding the variation in the initial bias voltage of the magnetoresistive elements, there was variation as shown in FIG. 10 for the 12 magnetoresistive elements. In other words, there are large variations between each sensor, and if the initial bias is not adjusted for each sensor, it may become saturated during amplification, making flaw detection impossible.

Furthermore, as shown in FIG.
When the temperature change characteristics were measured by connecting the device to the DC power source 9 via the power source 9, the characteristics shown in FIG. 12 were obtained, and there was a problem in that the output change was large due to temperature.

Therefore, the inventor of the present invention has previously developed and filed an application for a magnetic measuring device that has high detection sensitivity to minute magnetic fields, small output changes due to temperature changes, and good temperature change characteristics. (Japanese Patent Application No. 63-50539) The basic principle of this earlier application is as follows.
As shown in FIG. 13, a series circuit of a fixed impedance 12 and a coil 14 wound around a ferromagnetic core 13 is connected to an oscillator 11 which is a constant frequency/constant voltage power source. If AC power with a waveform as shown in (a) is supplied to the coil 14, the coil 1
The voltage generated across the coil 4 is determined according to the resistance value R of the fixed impedance 12 and the impedance Zs of the coil 14. That is, it is expressed as eo −e−Z s/(R+Z s). Note that eo is the voltage across the coil 14, and e is the output voltage of the oscillator 11.

Since the coil 14 is wound around the ferromagnetic core 13, its permeability changes in proportion to the magnetic permeability of the ferromagnetic core 13.

Now, with the magnet 15 for applying an external magnetic field released,
That is, if an alternating current is passed through the coil 14 without applying an external magnetic field, the magnetic permeability characteristic of the ferromagnetic core 13 changes to The result is as shown in FIG. 15(b). Note that n is the number of turns of the coil, and i is the coil current.

Therefore, the output voltage generated across the coil 14 is
The waveform becomes as shown in (b) of the figure. In a state where no external magnetic field is applied, the waveform becomes a positive and negative symmetrical waveform, and the voltage V in the positive direction and the voltage v2 in the negative direction are equal.

However, when the magnet 15 is brought close to the coil 14 as shown by the dotted line in the figure, the magnetic flux crossing the ferromagnetic body 13 becomes a composite magnetic flux of the magnetic field generated by the coil 14 and the external magnetic field. Therefore, the waveform generated at both ends of the coil 14 becomes V>v2 as shown in FIG. 14(C).

Therefore, the external magnetic field can be indirectly measured by comparing the positive side voltage Vl and the negative side voltage v2 of the output voltage generated across the coil 14 and finding the difference. Therefore, if this principle is applied to the leakage magnetic flux flaw detection method, the external magnetic field is generated by the flaw, so that flaws can be detected after all.

Based on this principle, specifically, a circuit shown in FIG. 16 is used. A series circuit of a resistor 22 and a coil 24 wound around a ferromagnetic core 23 is connected to an oscillator 21, and constant frequency, constant voltage AC power is supplied to the series circuit. The output voltage generated at both ends of the coil 24 is supplied to a positive voltage detector 25 and a negative voltage detector 26, respectively. The detection outputs from each of the detectors 25 and 26 are then supplied to an adder 27, which adds them together and outputs an output voltage vO.

In this circuit, first, an alternating current is supplied from an oscillator 21 to a coil 24 via a resistor 22 to magnetize the ferromagnetic material 23 until it is saturated.

Then, the output voltage eo generated at both ends of the coil 24 is detected by detectors 25 and 26, respectively. In the positive voltage detector 25, the output voltage e generated in the coil 24. A DC voltage V, which is proportional to the positive voltage V, is obtained. Further, the negative voltage detector 26 obtains a DC voltage v2 proportional to the negative voltage 2 of the output voltage e0 generated in the coil 24.

The DC voltages V, , V2 are then supplied to an adder 27, where Vl+(-V2) is added and the result is the output voltage (2). The output will be closed.

Therefore, if the external magnetic field does not cross the ferromagnetic core 23, l
Since V+1=lV21, the output voltage is V. becomes OV.

Further, when an external magnetic field crosses the ferromagnetic core 23, the DC voltages V, V2 change depending on the polarity and strength of the external magnetic field, so the output voltage V from the adder 27. -VI+ (
-V2) is a value corresponding to the external magnetic field. Therefore, the minute magnetic flux generated externally can be measured by the output voltage Vo.

When this method is used, as shown in Figure 17, for a minute magnetic flux density of 0 to 10 Gauss, O to approximately 5
Output voltage V of 00mV. was obtained, and the detection sensitivity could be improved.

Therefore, if this magnetic measurement is applied to the leakage magnetic flux flaw detection method for inspecting defects in steel pipes, steel plates, etc., highly accurate defect inspection becomes possible.

[Problem 8 to be solved by the invention] However, since the device of this prior application supplies alternating current power to the coil, there is a problem in that the power consumption is large. In particular, there is a problem that it cannot be applied to battery-operated systems. For example, when inspecting long-distance vibration lines for defects, an inspection head equipped with a magnetic sensor is inserted into the vibrator and the inspection head is driven in a cable-less manner. However, in such a case, the power source for the inspection head is a battery, which is not suitable for such an inspection.

SUMMARY OF THE INVENTION The present invention provides a magnetic measuring method and a magnetic measuring device that can improve detection sensitivity to minute magnetic fields, and also reduce power consumption by driving the coil of a magnetic sensor with a pulse voltage, thereby realizing battery operation. The purpose is to provide

Furthermore, in order to inspect the vibrator, a large number of magnetic sensors are arranged along the inner peripheral surface of the vibrator, but using such a large number of magnetic sensors further increases power consumption.

Therefore, even when a large number of magnetic sensors are used, the present invention can save power by driving the coil of each magnetic sensor with a pulse voltage and sequentially and selectively extracting the voltage generated in each coil. The purpose of the present invention is to provide a magnetic measurement device that can be powered by a battery.

[Means for Solving the Problems] In order to solve the above problems, in the magnetic 11Pj determination method of the present invention, a magnetic sensor formed by winding a coil around a ferromagnetic core is brought close to the lp1 constant magnetic field, and this Supply positive and negative pulse voltages to the coil of the magnetic sensor through a fixed impedance, detect the positive and negative peak values of the voltage generated at both ends of the coil, add the detected positive and negative peak values, and calculate the added value. is the measured value corresponding to the magnetic field to be measured.

Further, the magnetic measurement device of the present invention includes a magnetic sensor formed by winding a coil around a ferromagnetic core, a pulse voltage supply source that supplies positive and negative pulse voltages to the coil of the magnetic sensor via a fixed impedance, and a coil a pair of peak value detection means that respectively detect the positive and negative peak values of the voltage generated at both ends of the voltage, and an adder that adds the positive and negative peak values detected by both of the peak value detection means and sends out a measurement output. It has been established.

A magnetic measurement device according to another invention supplies positive and negative pulse voltages from a pulse voltage supply source to the coils of a plurality of magnetic sensors via a fixed impedance, and selects the voltage generated at both ends of each coil using a selection means. The positive and negative peak values of the voltages sequentially and selectively taken out are respectively detected by a pair of peak value detection means and added by an adder.

A magnetic n1 constant device according to another invention sequentially selectively supplies positive and negative pulse voltages from a pulse voltage supply source to the coils of a plurality of magnetic sensors via a fixed impedance, and generates voltages at both ends of each coil. The voltage is sequentially and selectively extracted by the selection means in synchronization with the supply of pulse voltage from the pulse voltage supply source to each coil, and the positive and negative peak values of the sequentially extracted voltages are respectively detected by a pair of peak value detection means. It is detected and added by an adder.

[Operation] In the magnetic measurement method and magnetic measurement device configured as described above, positive and negative pulse voltages are supplied from the pulse voltage supply source to the coil of the magnetic sensor that is brought close to the magnetic field to be measured,
As a result, the positive and negative peak values of the voltage generated across the coil are detected by a pair of peak value detection means, and each peak value is added by an adder to generate an ill constant magnetic field (external magnetic field) detected by the magnetic sensor. can be measured as a change in voltage level.

In a magnetic measurement device according to another invention, positive and negative pulse voltages are supplied to the coils of a plurality of magnetic sensors,
The voltages generated at both ends of each coil are sequentially and selectively taken out by the selection means, and the positive and negative peak values of the taken out voltages are detected by a pair of peak value detection means and added by an adder. Therefore, the adder sequentially outputs changes in the magnetic field to be measured (external magnetic field) detected by each magnetic sensor as a voltage signal.

In a magnetic measuring device according to still another invention, positive and negative pulse voltages are sequentially and selectively supplied to the coils of a plurality of magnetic sensors, and in synchronization with this, the voltages generated in each coil are sequentially and selectively supplied. I will have to take it out. Therefore, pulse voltage is always supplied to each coil, and the power consumption is the same as when only one magnetic sensor is used.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a magnetic measuring device to which the magnetic measuring method of the embodiment is applied.

In the figure, 101 is a pulse voltage generator constituting a pulse voltage supply means, and positive and negative pulse voltages are generated from this pulse voltage generator 101 at regular intervals. A series circuit of a resistor 102 having a fixed impedance and a coil 103a of a magnetic sensor 103 is connected to the output terminal of the pulse voltage generator 101. The coil 103a is wound around a ferromagnetic core 103b.

The positive and negative peak values of the voltage generated across the coil 103a are detected by a pair of peak value detection means, a positive voltage peak detector 104 and a negative voltage peak detector 105. The peak detection outputs from each of these peak detectors 104 and 105 are supplied to an adder 106 for addition processing, resulting in a measurement output V. I am trying to send out the following.

In this embodiment with such a configuration, the magnetic sensor 1
A pulse voltage is supplied from the pulse voltage generator 101 to the coil 103a of No. 03, and the ferromagnetic material 103b is magnetized to a saturated state by this pulse voltage. and ferromagnetic material 1
When an external magnetic field as a magnetic field to be measured crosses 03b, a positive voltage and a negative voltage are generated in the coil 103a corresponding to the polarity and strength of the external magnetic field.

Therefore, the peak value V1 of the positive voltage is detected by the positive voltage peak detector 1.
04, the peak value V2 of the negative voltage is detected by the negative voltage peak detector 105, and the adder 106 performs addition processing of Vl+(V2) to obtain the measurement output V. will be sent.

Since the pulse voltage is supplied to the coil 103a of the magnetic sensor 103 in this way, the power consumption is lower than that of a device that supplies alternating current power, and power saving can be achieved.

For example, if the ratio of the pulse width τ and the pulse period T of the pulse voltage is set to (10 to 100) τ - T, the average power supplied to the magnetic sensor 103 can be suppressed to about 1/10 to 1/100, and the power source It is fully possible to use the battery as a battery.

In addition, since the peak value of the voltage generated in the coil 103a is detected, even if T/τ is varied over a wide range of 2 to 100, the detection sensitivity of minute magnetic flux is The relative sensitivity of is almost unchanged. On the other hand, in the amplitude detection method as shown in FIG. 16, when T/τ increases by 5 or more, as shown by the graph (■) in FIG. 2, the sensitivity rapidly decreases, making it difficult to save power.

FIG. 3 is a block diagram showing a schematic configuration of a magnetic measuring device according to another embodiment of the present invention. Note that the same parts as those in the embodiment of FIG. 1 are given the same reference numerals, and detailed explanation of the overlapping parts will be omitted.

In this embodiment, the pulse voltage supply source is composed of a rectangular wave oscillator 107, a pulse voltage generator 108, and a pulse power amplifier 109. The square wave oscillator 107
generates a rectangular wave signal shown in FIG. 4(a), and the pulse voltage generator 108 generates positive and negative signals as shown in FIG. 4(c) in synchronization with the rise and fall of this rectangular wave signal. Pulse voltage is generated at regular intervals. This pulse voltage is then amplified by the pulse power amplifier 109 and output.

Also, n magnetic sensors 103. ．． 103□.

...103. and each magnetic sensor 103°~
103. ．． Coils 103+a, 1032a, -1
03 and a are respectively resistors 102. ．． 102□.

...102. It is connected to the output terminal of the pulse power amplifier 109 via.

A multiplexer 11 serving as a selection means selects the voltage across the coils of each of the magnetic sensors 1031 to 1031.
0.

The multiplexer 110 receives input from each coil 103.
．． The voltages generated from a to 103 degrees a are sequentially and selectively extracted and supplied to a positive voltage peak detector 104 and a negative voltage peak detector 105, respectively.

Each of the peak detectors 104, 105 is manually operated by each coil 103+a to 103. The peak values of the output voltage from a are sequentially detected and the detection signals shown in (e) and () in FIG. 4 are output to the adder 106.

Further, a rectangular wave signal from the rectangular wave oscillator 107 is supplied to a frequency divider 111. And with this frequency divider 111, 1/
The frequency is divided by two and the frequency-divided signal shown in FIG. 4(b) is output.

The frequency divided signal from the frequency divider 111 is transmitted to the discharge pulse generator 1.
12 and phase shifter 113, respectively.

As shown in FIG. 4(d), the discharge pulse generator 112 generates a discharge pulse signal synchronized with the rising edge of the input frequency divided signal and supplies it to each of the peak detectors 104 and 105. The output voltage of the detector is cleared to "0".

The phase shifter 113 shifts the phase of the input frequency-divided signal by 90 degrees and supplies it to the multiplexer controller 114.

The multiplexer controller 114 generates a clock signal shown in FIG.
is supplied to.

The multiplexer 110 is controlled by a clock signal to perform selection switching operations.

In this embodiment having such a configuration, positive and negative pulse voltages are generated from the pulse voltage generator 108, and the power of these pulse voltages is amplified by the pulse power amplifier 109 and applied to the resistors 1021 to 102, respectively. via magnetic sensor 1031
~103a coil 103+ a~103,a is supplied.

On the other hand, the multiplexer 110 is connected to the multiplexer controller 1
Each coil 1 is controlled by a clock signal from 14
03. a~103. ．． The voltage generated from a is selectively taken out sequentially and supplied to each peak detector 104 and 105, respectively.

Therefore, from each peak detector 104, 105, each coil 103. The peak values of the voltages generated from the magnetic sensors 1031 to 103aa are sequentially supplied to the adder 106, and are sequentially added by the adder 106 to the respective magnetic sensors 1031 to 103. The measured output will be sent out.

Even if a large number of magnetic sensors are used in this way, the power consumed by all the magnetic sensors is very small because a pulse voltage is supplied to the coil of each magnetic sensor.

Therefore, even if a large number of magnetic sensors are used in this way, battery drive can be realized. In addition, in a device that supplies normal AC power, when a large number of magnetic sensors are used, a large amount of power is supplied to them, so a large capacity amplifier or the like must be used, but in this embodiment, a pulse power amplifier 1 is used.
The capacity of 09 may be small.

Therefore, it is extremely suitable for inspecting long-distance pipelines for defects using a cable-less method.

FIG. 5 is a block diagram showing a magnetic measurement device according to yet another embodiment. Components that are the same as those in the embodiment shown in FIG. 3 described above are given the same reference numerals and redundant explanations are omitted.

In this embodiment, one resistor 102 is used as a fixed impedance, and a pulse voltage from a pulse power amplifier 109 is supplied to a multiplexer 115 different from the multiplexer 110 via this resistor 102. Each output terminal of this multiplexer 115 is connected to the coil 103 of each magnetic sensor 103+-103-. a~103
, , a are connected to each other. Similarly to the multiplexer 110, this multiplexer 115 also has
It is controlled by a clock signal from multiplexer controller 114.

In an embodiment of such a configuration, multiplexer 1
15 by each magnetic sensor 103. ~103° coil 1031 a~103. A pulse voltage is sequentially and selectively supplied to the coils a, and the voltages generated in the coils 103+a to 103,a are sequentially and selectively taken out by the multiplexer 110.

Therefore, even if a large number of magnetic sensors 1031 to 103° are used, the operation is the same as operating one magnetic sensor. That is, when a pulse voltage is supplied to the magnetic sensor 103 by the multiplexer 115,
The magnetic sensor 103. Coil 103. The voltage generated at a will be taken out by multiplexer 110.

Therefore, in this embodiment, the power consumption can be further reduced, and the capacity of the pulse power amplifier 109 can be further reduced.

[Effects of the Invention] As described in detail above, according to the present invention, detection sensitivity to minute magnetic fields can be improved, and power consumption can be reduced by driving the coil of the magnetic sensor with a pulse voltage. Therefore, it is very effective, for example, to realize the magnetism measurement method and magnetism measurement device of the present invention by battery drive.

In addition, even if a large number of magnetic sensors are used, the coil of each magnetic sensor is driven with a pulse voltage, and the voltage generated in each coil is sequentially and selectively extracted, making it possible to save power. It is possible to provide a magnetism measurement method and a magnetism measurement device that are particularly effective in this case.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing a magnetic measurement device to which a magnetic measurement method according to an embodiment of the present invention is applied, and FIG. 2 is a relative sensitivity of minute magnetic flux detection sensitivity when T/τ is changed in the same embodiment. Graphs showing characteristics, FIG. 3 and FIG. 4 show another embodiment of the present invention, FIG. 3 is a circuit block diagram, and FIG. 4 is an output waveform diagram of each part of the same embodiment. Fig. 5 is a circuit block diagram of yet another embodiment, Fig. 6 is a configuration diagram for explaining the conventional leakage magnetic flux flaw detection method, and Fig. 7 shows leakage magnetic flux with respect to the distance between the steel material surface and the Hall element in Fig. 6. Figure 8 is a diagram showing examples of defects in steel materials used to obtain the characteristics shown in Figure 7. Figure 9 is a characteristic diagram showing magnetic flux density-output voltage characteristics of various conventional sensors. Figure 10 is a diagram showing density characteristics. The figure is a graph showing variations in the initial bias voltage of a conventional magnetoresistive element, Figure 11 is an ITFI constant circuit diagram for determining n1 of the temperature-output voltage characteristic of a conventional magnetic diode, and Figure 12 is a graph showing the variation in the initial bias voltage of a conventional magnetic resistance element. Figure 13 is a circuit diagram for explaining the measurement principle using a saturable magnetic sensor, Figure 14 is a diagram showing the power supply waveform to the coil and the output voltage of the coil in Figure 13. A diagram showing waveforms, FIG. 15 is a characteristic diagram showing the hysteresis characteristics and magnetic permeability of the ferromagnetic core in FIG. 13, FIGS. 16 and 17 are examples of the prior application, and FIG. 16 is a circuit block 17 are graphs showing detection sensitivity characteristics. 101.108...Pulse voltage generator, 102°10
21~102o...Resistance (fixed impedance)
103, 1031-103. ...Magnetic sensor 1
03a, 103. a~103 *a...Coil, 1
04...Positive voltage peak detector, 105...Negative voltage peak detector, 106...Adder, 110°115...
・Multiplexer. Figure 1

Claims (4)

[Claims] (1) A magnetic sensor consisting of a coil wound around a ferromagnetic core is brought close to the magnetic field to be measured, and positive and negative pulse voltages are supplied to the coil of the magnetic sensor via a fixed impedance, and generated at both ends of the coil. 1. A magnetic measurement method, comprising: detecting positive and negative peak values of voltage, adding the detected positive and negative peak values, and making the added value a measured value corresponding to the magnetic field to be measured. (2) A magnetic sensor formed by winding a coil around a ferromagnetic core, a pulse voltage supply source that supplies positive and negative pulse voltage to the coil of this magnetic sensor via a fixed impedance, and a voltage generated at both ends of the coil. A pair of peak value detection means for detecting the positive and negative peak values of , respectively, and an adder for adding the positive and negative peak values detected by both of the peak value detection means and sending out a measurement output. Magnetic measuring device. (3) a plurality of magnetic sensors each having a coil wound around a ferromagnetic core; a pulse voltage supply source that supplies positive and negative pulse voltage to the coil of each magnetic sensor via a fixed impedance; A selection means for sequentially and selectively extracting voltages generated at both ends; a pair of peak value detection means for respectively detecting positive and negative peak values of the voltages sequentially extracted by the selection means; and both peak value detection means. 1. A magnetic measurement device comprising: an adder that adds positive and negative peak values of each voltage detected by the sensor and sends out a measurement output corresponding to each of the magnetic sensors. (4) A plurality of magnetic sensors each having a coil wound around a ferromagnetic core, and a pulse voltage supply source that selectively sequentially supplies positive and negative pulse voltages to the coils of each magnetic sensor via a fixed impedance. , a selection means for sequentially and selectively extracting the voltage generated at both ends of each coil in synchronization with the supply of pulse voltage from the pulse voltage supply source to each coil; and A pair of peak value detection means for detecting positive and negative peak values, respectively, and a measurement output corresponding to each magnetic sensor by adding the positive and negative peak values for each voltage detected by both of the peak value detection means. A magnetic measurement device characterized by being provided with an adder for sending out data.