WO1991013366A1

WO1991013366A1 - Method and apparatus for magnetic detection

Info

Publication number: WO1991013366A1
Application number: PCT/JP1991/000250
Authority: WO
Inventors: Corporation Nkk; Seigo Ando
Original assignee: Nippon Kokan Kk
Priority date: 1990-02-28
Filing date: 1991-02-26
Publication date: 1991-09-05

Abstract

A magnetic detector comprises a magnetic sensor (16) having a detecting coil (18) on a ferromagnetic core (17), an exciting signal generating circuit (11) which supplies an ac exciting current having a predetermined effective value to the detecting coil (18) of the magnetic sensor (16) via an impedance element (15) to saturate the core (17), a waveform shaping circuit (19) that normalizes the waveform of detected signal taken out from both terminals of the detecting coil (18) using a predetermined threshold value, and a counter (20) that measures the pulse width of normalized signals output from the waveform shaping circuit (19), in order to detect the intensity of the external magnetic field based on a change in the pulse width caused by the external magnetic field that intersects the magnetic sensor (16).

Description

明 Description

Magnetic detection device and magnetic detection method

[Technical field]

The present invention relates to a magnetic detection device and a magnetic detection method using a saturable magnetic sensor.

[Background technology]

For example, a magnetic leak detection device is used as one of the defect detection devices for detecting defects existing inside or on the surface of a steel sheet. In such a magnetic leakage device, it is necessary to accurately detect the leakage magnetic flux. In recent years, a magnetic detection device using a saturable magnetic sensor has been proposed as a magnetic detection device for detecting magnetism with high accuracy (Japanese Patent Application Laid-Open No. Hei 13-89082).

FIG. 4 is a block diagram showing a schematic configuration of a magnetic detection device using the saturable magnetic sensor. In the figure, reference numeral 1 denotes a rectangular wave generating circuit that outputs a high-frequency rectangular wave signal. The rectangular wave signal output from the rectangular wave generating circuit 1 is supplied to the following differentiating circuit 2 so that the rising and falling times of the rectangular wave are obtained. Is converted into a pulse signal having a trigger waveform shape synchronized with the timing. Then, the pulse signal of the trigger waveform output from the differentiating circuit 2 is applied as a high-frequency excitation signal to the magnetic sensor 4 via the impedance element 3 composed of a resistor. The magnetic sensor 4 is configured by winding a detection coil 6 around a core 5 of a ferromagnetic material formed in, for example, a rod shape. The high-frequency excitation signal e is applied to one end of the detection coil 6 of the magnetic sensor 4 via the impedance element 3, and the other end is grounded. The terminal voltage of the detection coil 6 is the detection signal e of the magnetic sensor 4. And input to the voltage detection circuit 7. Then, the output voltage V corresponding to the intensity of the magnetic field detected by the magnetic detection device from the voltage detection circuit 7. Is obtained.

In such a magnetic detection device, the voltage of the high-frequency square wave signal output from the square wave generation circuit 1 is controlled to increase the current of the high-frequency excitation signal flowing through the detection coil 6 and magnetize the core 5 to the saturable region. I do. Therefore, in this state, the detection signal e indicated by the terminal voltage of the detection coil 5. Figure 5 shows the amplitude of the waveform So that it becomes constant.

When the external magnetic field does not intersect with the saturation magnetic field generated by the detection coil 6, as shown in the detection signal e Q _A on the left side of FIG. 5, the peak value Va on the positive side and the peak value on the negative side of the waveform are obtained. — Vb is equal. When an external magnetic field approaches the core 5 excited to such a saturable region and crosses the saturation magnetic field generated by the detection coil 6, the detection signal e on the right side of FIG. _As shown in _B , the amplitude value does not change, but the positive and negative peak values Va, -Vb change. Therefore, each peak value Va, — Vb is detected by a detector, converted to direct current, and added by an adder to obtain a difference voltage (Va−Vb). And this difference voltage (Va-Vb) is output voltage V. If output from the voltage detection circuit 7 as Corresponds to the external magnetic field applied to the magnetic sensor 4. Therefore, the magnetic field intensity can be detected by this magnetic detection device.

However, the magnetic detection device configured as shown in FIG. 4 still has the following problems.

That is, as described above, it is necessary to supply a high-frequency excitation current to the detection coil 5 wound around the core 5 formed of the ferromagnetic material of the magnetic sensor 4 to magnetize the core 5 to the saturable region. High-frequency excitation applied to the magnetic sensor 4 via the impedance element 3 in order to accurately detect the positive and negative peak values Va and 1 Vb in the detection signal e _Q taken out of the magnetic sensor 4 The signal ei is a trigger waveform pulse signal. Therefore, the current flowing through the detection coil 5 becomes a high-frequency current due to the trigger waveform. Therefore, in order to magnetize the core 5 to a saturable region with the trigger waveform pulse signal, the voltage of the high-frequency excitation signal _ei needs to be significantly increased. For example, even in a small magnetic sensor 4, the voltage is 15-25 V _P - require _P. Therefore, the square wave generating circuit 1 also needs to output a square wave signal having a peak value of 15 to 25 V _P — P. In addition to the 5 V DC power supply used in a normal TTL circuit, Requires a high-voltage DC power supply of 15 to 25V. Also, the detection signal e. Output voltage V corresponding to the external magnetic field applied from the waveform of In the voltage detection circuit 7 for calculating the peak value, a detection circuit for detecting each of the positive and negative peak values Va and one Vb, an addition circuit for adding the obtained peak values Va, — Vb, and the like are incorporated. This complicates the circuit configuration. As described above, since a high-voltage DC power supply, a detection circuit, an addition circuit, and the like are required, not only does the circuit configuration of the entire magnetic detection device become complicated, but also the overall device becomes large.

[Disclosure of the Invention]

The present invention has been made in view of such circumstances, and an object of the present invention is to obtain a detection signal by applying an AC exciting current having a predetermined effective value to a detection coil of the magnetic sensor. The external magnetic field strength can be easily detected from the degree of change in the width of the signal waveform in the detection signal, thereby simplifying the circuit configuration of the entire device, It is an object of the present invention to provide a magnetic detection device and a magnetic detection method capable of reducing the size of the entire device and reducing the manufacturing cost.

In order to solve the above-mentioned problems, a magnetic detection device according to a first aspect of the present invention includes a saturable magnetic sensor having a detection coil wound around a core formed of a magnetic material, and a detection coil of the magnetic sensor. On the other hand, an excitation signal generating circuit for applying an AC excitation current having a predetermined effective value through an impedance element to magnetize the core to a saturation region, and a detection signal waveform extracted from both ends of the detection coil at a predetermined threshold. A comparator for normalizing with a value, and a counter for measuring the pulse width of the normalized signal output from the comparator.

Further, the magnetic detection device of the second invention is provided with a low-pass filter for detecting the pulse width of the normalized signal output from the comparator as an average DC component, instead of the counter.

Further, in the magnetic detection method of the present invention, a magnetic sensor formed by winding a detection coil around a core made of a ferromagnetic material is brought close to a magnetic field to be measured, and the detection coil of the magnetic sensor is connected to the detection coil via an impedance element. A pulse voltage is supplied, positive and negative peak values of a voltage generated at both ends of the coil are detected, and the detected positive and negative peak values are added. The added value is compared with a measured value corresponding to the measured magnetic field. It is characterized by doing. According to the first and second magnetic detection devices of the present invention, an AC excitation current having a predetermined effective value is applied to the detection coil of the magnetic sensor from the excitation signal wave generation circuit. Therefore, the effective current value of the AC exciting current is larger than the pulse signal of the trigger waveform. Therefore, the voltage of the AC exciting current required to magnetize the core of the magnetic sensor to the saturable region can be set low.

According to the first and second magnetic detection devices of the present invention, the core is magnetized in the positive and negative directions by the AC voltage applied to the detection coil, but saturates when the current exceeds a certain current value. The waveform of the detection signal extracted from both ends of the signal has a predetermined width. In a state where a detection signal having a waveform having a predetermined width is output from the detection coil wound around the core magnetized to the saturable region in this way, the detection coil crosses the magnetic field excited by the AC excitation current. When the external magnetic field is applied, the external magnetic field is added to or subtracted from the magnetic field of the AC exciting current, so that a part of the waveform of the detection signal is deformed.

Then, the deformed detection signal waveform is normalized by a predetermined threshold value in a comparator. Then, the degree of deformation of the detection signal waveform is detected by the pulse width of the normalized signal. Therefore, the external magnetic field strength is detected from the change in the pulse width.

According to the first magnetic detection device of the present invention, the pulse width is directly measured at the counter, and according to the second magnetic detection device of the present invention, the pulse width is normally measured by the low-pass filter. The pulse width is measured by detecting the average DC component of the digitized signal.

Further, in the magnetic measurement method of the present invention, a positive or negative pulse voltage is supplied from the pulse voltage supply source to the coil of the magnetic sensor that is close to the magnetic field to be measured, whereby the positive or negative voltage of the voltage generated between both ends of the coil is supplied. A peak value is detected by a pair of peak value detection means, and the change of the magnetic field to be measured (external magnetic field) detected by the magnetic sensor is measured as a change of a voltage level by adding each peak value by an adder. Can be.

According to the magnetic detection device of the present invention, a detection signal is obtained by applying an AC exciting current having a predetermined effective value to the detection coil of the magnetic sensor, and a part of the waveform of the obtained detection signal is an external magnetic field. Is detected. Therefore, the voltage value of the AC excitation signal applied to the magnetic sensor can be significantly reduced, and the external magnetic field strength can be easily detected from the degree of deformation of the signal waveform of the detection signal. As a result, each circuit configuration can be simplified, and the entire detection device can be reduced in size and manufacturing cost can be reduced < Further, according to the magnetic detection method of the present invention, detection sensitivity to a minute magnetic field can be improved, and power can be saved by driving the coil of the magnetic sensor with a pulse voltage. Therefore, for example, it is very effective in realizing the magnetic measurement method of the present invention by battery operation.

[Embodiment]-An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of the magnetic detection device of the embodiment. In the figure, reference numeral 11 denotes an excitation signal generation circuit which outputs, for example, a high-frequency excitation signal having a triangular waveform as an AC excitation signal having a predetermined effective value.The excitation signal wave generation circuit 11 includes a high-frequency oscillator 1 2 and a frequency divider 13 and a triangular wave generation circuit 14. The high-frequency oscillator 12 outputs a clock signal d having a high frequency, for example, 10 MHz. This clock signal d is divided into, for example, 1 by the next frequency divider 13 and then input to the triangular wave generation circuit 14. This triangular wave generation circuit 14 converts a high frequency excitation signal a as an AC excitation signal having a triangular wave shape with a period T 0 as shown in FIG. 3 through an impedance element 15 composed of a resistor, for example, through a magnetic sensor 1. Send to 6.

As shown in the figure, the magnetic sensor 16 is configured by winding a detection coil 18 around a ferromagnetic core 17 formed in, for example, a rod shape. The high frequency excitation signal a via the impedance element 15 is applied to one end of the detection coil 18 of the magnetic sensor 16, and the other end is grounded. Then, the terminal voltage of the detection coil 18 is extracted as a detection signal b of the magnetic sensor 16 and input to the (+) side input terminal of the comparator 19 as a waveform shaping circuit. The (1) side input terminal of this comparator 19 is grounded. Comparator 19 outputs a normalized signal c having a H (high) level when the detection signal b is higher than the ground potential (0 V) and an L (low) level when the detection signal b is lower than the ground potential (0 V). Output. The voltage level of the normalized signal c is a constant level signal of 5 V at H level and 0 V at L level.

The normalized signal c having a constant level output from the comparator 19 is input to the control terminal G of the counter 20 and to the low-pass filter 21. The clock signal d output from the high-frequency oscillator 12 is input to the clock terminal CP of the counter 20. Then, the counter 20 is activated before being applied to the control terminal G. In synchronization with the timing when the normalized signal c rises from the L level to the H level, the counting operation of the number of clocks of the clock signal d is started, and the normalized signal c is changed from the H level to the L level. The count operation ends in synchronization with the falling timing. That is, the counter 20 measures the pulse width T indicated by the H level period of the normalized signal c. The digital pulse width T measured by the counter 20 is sent to an arithmetic circuit 22 composed of, for example, a microcomputer or the like.

On the other hand, the low-pass filter 21 has a relatively large time constant, and cuts off the high-frequency components among the frequency components included in the pulse-like waveform of the normalized signal c, and removes only the low-frequency components. Let it pass. Therefore, this low-pass filter 21 outputs an average DC voltage proportional to the effective average voltage of the normalized signal c. Since the average DC voltage of the normalized signal c corresponds to the pulse width T of the normalized signal c, as a result, the voltage of the analog output signal f of the low-pass filter 21 becomes equal to the pulse of the normalized signal c. Corresponds to the width. Then, the output ftf having a voltage value corresponding to the pulse width T is input to the analog arithmetic circuit 23.

Next, the operation of the magnetic detection device thus configured will be described. Before that, the basic principle of the magnetic sensor 16 will be described with reference to FIGS. 2A and 2B, and FIGS. 6 and 7A and FIG. B, FIG. 7C, FIG. 7D, and FIG. 7E will be described. As shown in FIG. 6, an excitation signal generating circuit 11, an impedance element 15, and a detection coil 18 wound around the outer periphery of a ferromagnetic core 17 are connected in series. The magnet 25 is for applying an external magnetic field to the magnetic sensor 16 including the core 17 and the detection coil 18. The excitation signal generation circuit 11 generates an AC power supply voltage waveform (high-frequency excitation signal) as shown in Fig. 7A. The resistance value of the impedance element 1 5 and R, the impedance of the detection coil 1 8 of the magnetic sensor 1 6 and Z _s, the detection signal taken out from both ends of the detection coil 1 8 is b, the excitation signal generating circuit 1 1 Assuming the high-frequency excitation signal a to be output, the relationship of equation (1) holds.

b = a ♦ Z _s Z (R + Z s) ~ (1)

(1) In the equation, the resistance value R is constant, the detection signal b is changed in accordance with the I impedance Z _s of the detection coil 1 8. Then, the impedance Z _s of the detection coil 1 8 which is卷装core 1 7 of the ferromagnetic material is proportional to the permeability of the core 1 7. Now, in FIG. 6, if an alternating current is applied to the detection coil 18 of the magnetic sensor 16 in a state where the magnet 25 is separated, that is, in a state where no external magnetic field is applied, as shown in FIG. Due to the hysteresis characteristic of the core 17, the magnetic permeability characteristic of the ferromagnetic core 17 becomes as shown in FIG. 2B.

The voltage waveform of FIG. 7A is entirely shifted by the DC component to the positive side as shown in FIG. 7B due to the effect of the external magnetic field. In addition, the voltage waveform in FIG. 7A is shifted to the negative side by the external magnetic field by only the DC component. If the external magnetic field is an alternating magnetic field, the shifts in Figs. 7A and 7B are repeated. Therefore, the output voltage generated across the detection coil 18 has a waveform as shown in FIG. 7D. Then, the waveform of the external magnetic field by the magnet 2 5 with pressurized Erare absence positive, a negative symmetrical waveform, the voltage V ₂ in the positive direction of voltage V and the negative direction are equal.

However, when the magnet 25 is brought close to the detection coil 18 as shown by the dotted line in FIG. 6, the magnetic flux crossing the core 17 becomes a composite magnetic flux of the magnetic field generated by the detection coil 1S and the external magnetic field. For this reason, the voltage waveform generated at both ends of the detection coil 18 is V i> V 2 as shown in FIG. 7E.

Therefore, the external magnetic field can be indirectly measured by comparing the positive voltage V i and the negative voltage v ₂ of the output voltage generated at both ends of the detection coil 18 and obtaining the difference. Therefore, if this principle is applied to the magnetic flux leakage detection method, the external magnetic field is generated by the defect, so that the defect can be detected after all.

On the other hand, as shown in FIG. 2A, in the core 17, even if the exciting current is increased beyond a certain level, the generated magnetic field does not increase beyond a certain level and becomes saturated. In general, it has a hysteresis characteristic as shown. Therefore, the magnetic permeability also changes according to the exciting current value as shown in FIG. 2B. As a result, the impedance Z _s is also the excitation current value of the detection coil 1 8, i.e., which changes depending on the value of the high frequency excitation signal a applied to the detection coil 1 8. Therefore, the impedance Z _s changes rapidly in the process of increasing the high-frequency excitation signal a shown in FIG. 3, and the detection signal b rapidly rises or falls. Therefore, as shown in FIG. 3, the waveform of the detection signal b is a substantially rectangular waveform extending from 0 V to the positive side and the negative side. The pulse width 1 of this substantially rectangular waveform is the period T of the high-frequency excitation signal a. 1 of 2. That is, the input triangular waveform becomes a substantially rectangular waveform. When the detection signal b having such a substantially rectangular wave shape is input to the comparator 19, the threshold value of the comparison circuit 19 is 0 V, so the normalized signal c output from the comparison circuit 19 Has the same pulse width as the pulse width of the detection signal b. The width of the pulse is measured by the counter 20 and sent to the arithmetic circuit 22. The arithmetic circuit 22 has a period T of the known high-frequency excitation signal a. Compared with the detected pulse width and T.

In the case of, it is determined that there is no external magnetic field.

Further, an output signal f having a DC voltage is input from the low-pass filter 21 to the arithmetic circuit 23. Then, the arithmetic circuit 23 determines from the DC voltage V that no external magnetic field is applied.

Then, in such a state, for example, when a DC external magnetic field H ₂ or −H ₃ having an S pole or an N pole crosses the magnetic field generated by the high frequency excitation current of the magnetic sensor 16, the external magnetic fields Η ₂ and H ₃ become or is added to the magnetic field by the high-frequency excitation current, because the magnetic permeability of the subtracted core 17 is changed, Inpidansu Z _s of the detection coil 18 varies greatly. Accordingly, the waveform of the detection signal b of the magnetic sensor 16 changes as you Keru central detection signal b ₂ or the right of the detection signal b ₃ in FIG.

Thus, the pulse width T of the normalized signal c output from the comparator 19 T ₂ or changed to T _3. Thus, it changes from even a pulse width T which is input from the counter 20 to the arithmetic circuit 22 to T ₂ or T _3. Calculation circuit 22 calculates the external magnetic field pulse width state not applied 1 (= Τ. Ζ2) external magnetic field is applied from the pulse width or T ₂ obtained with Eta ₂ or a Eta _3.

The output signal is the external magnetic field Eta input ₂ or pulse width T ₂ or T ₃ corresponding to an Eta ₃ by mouth one pass filter 21 to the arithmetic circuit 23 of the normalized signal c output from the comparator 19 f detected by the DC voltage V ₂ or V _3. Therefore, also in the arithmetic circuit 23 of this § analog, with at comparison with the DC voltage in a state where the external magnetic field is not applied, the applied external magnetic field H ₂ or - _c the amount _of H ₃ is thus calculated, The magnitude and direction of the magnetic field externally applied to the magnetic detection device are calculated digitally or analogly by the arithmetic circuits 22, 23.

According to the magnetic detection device configured as described above, the signal waveform of the high-frequency excitation signal a as the AC excitation current applied to the magnetic sensor 16 has a predetermined effective value as shown in FIG. It has a triangular shape. Since the effective current value of the high-frequency excitation signal a is larger than the trigger signal pulse signal e in the conventional detector shown in FIG. 4, the high-frequency necessary for magnetizing the core 17 of the magnetic sensor 16 to saturable is obtained. The voltage of the excitation signal a can be set low. In the example device, the voltage value of the high-frequency excitation signal a could be reduced to 5 VP-P. Therefore, the DC power supply for driving the high-frequency oscillator 12, the frequency divider 13, and the triangular wave generation circuit 14 of the excitation signal generation circuit 11 is normally at a constant level of 5 V, which is sufficient. That is, a DC power supply of 15 to 25 V is not required unlike the conventional device. As a result, the circuit configuration of the entire device can be simplified.

Further, a circuit for detecting the intensity of the external magnetic field from the detection signal b of the magnetic sensor 16 includes, for example, a waveform shaping circuit composed of a comparator 19 having a simple circuit configuration, a counter 20 and a low-pass filter 21. It can be realized with a low-cost and simple circuit member. Accordingly, the circuit configuration of the excitation signal generation circuit 11 and the signal processing circuits 19, 20 and 21 for the detection signal can be simplified, so that the entire magnetic detection device can be made compact, lightweight and inexpensive. .

In addition, since each of the above-described circuits can be configured by a TTL circuit, IC can be achieved, and the entire device can be further reduced in size.

Further, since the output signal of the counter 20 is a digital signal of a fixed level, it is hardly affected by external noise. In addition, inspection and repair are easy because of the simple configuration. Therefore, sufficient measurement accuracy can be obtained even under adverse environmental conditions such as a factory production line.

Further, when the comparator 19 is used as a waveform shaping circuit as in the embodiment, it can be diverted to, for example, a proximity switch or the like only by changing the threshold value.

Also, conventional magnetic detectors using a simple pickup coil utilizing the electromagnetic induction effect, etc., could measure only a time-varying magnetic field due to the measurement principle, but a saturable magnetic sensor By using 16, it is possible to accurately measure a magnetic field over a wide frequency range from a DC magnetic field to a high-frequency magnetic field.

Also, in the present invention, the degree of deformation (pulse width change) at which a part of the waveform of the detection signal b of the magnetic sensor 16 is deformed due to the external magnetic field is measured, and the external magnetic field strength is determined from the degree of deformation. Has been detected. Therefore, the waveform itself depends on the external environment such as temperature. Since it is hardly affected by the conditions, it is not necessary to take a temperature compensation measure especially for the detection signal b of the magnetic sensor 16.

The present invention is not limited to the embodiments described above. In the embodiment, the case where the DC external magnetic field + H ₂ , —H ₃ is measured has been described, but it is needless to say that the AC external magnetic field can also be measured as described above.

Also, a high-frequency excitation signal a having a triangular wave shape was used as an AC excitation current applied from the excitation signal generation circuit 11 to the detection coil 18 of the magnetic sensor 16 via the impedance element 15, as in the embodiment. external magnetic field + H ₂ DC, if you measure an H ₃ can be used exciting current of a low frequency to obtain a sufficiently high measurement accuracy. That is, the frequency of the AC excitation current applied to the magnetic sensor 16 is desirably about 10 times or more the frequency of the external magnetic field to be measured, but this condition is not necessarily satisfied depending on the magnetic field to be measured. Even without it, it is possible to obtain sufficiently high measurement accuracy.

Further, in the embodiment, the waveform of the AC exciting current applied to the detection coil 18 of the magnetic sensor 16 is a triangular wave shape. There may be.

Next, a magnetic detection method according to the present invention will be described with reference to FIG. FIG. 8 is a block diagram for implementing the magnetic detection method of the present invention. In the figure, reference numeral 101 denotes a pulse voltage generator, from which positive and negative pulse voltages are generated at fixed intervals. The output terminal of the pulse voltage generator 101 is connected to a series circuit of the impedance element 15 and the detection coil 18 of the magnetic sensor 16. The detection coil 18 is wound around a ferromagnetic core 17. The positive and negative peak values of the voltage generated at both ends of the detection coil 18 are detected by a pair of positive voltage peak detectors 104 and negative voltage peak detectors 105. The peak detection output from each of these peak detectors 104 and 105 is supplied to an adder 106 to be added and processed to obtain a measurement output V. Is sent.

In such a configuration, a pulse voltage is supplied from the pulse voltage generator 101 to the detection coil 18 of the magnetic sensor 16, and the pulse voltage magnetizes the ferromagnetic material 103 b to a saturated state. Is done. Then, the ferromagnetic material 103 b as the magnetic field to be measured When the external magnetic fields intersect, a positive voltage and a negative voltage are generated in the coil 18 corresponding to the polarity and strength of the external magnetic field.

Thus the peak value V of the positive voltage is detected by a positive voltage peak detector 1 0 4, the peak value V ₂ of the negative voltage is detected by the negative voltage peak detector 1 0 5, V adder 1 0 6: + (1 V ₂ ) is added and the measurement output V is obtained. ⁷ due to the fact that but sent.

Since the pulse voltage is supplied to the coil 18 of the magnetic sensor 16 as described above, the power consumption is reduced as compared with the one that supplies the AC power, and power can be saved. For example, if the ratio between the pulse width of the pulse voltage and the pulse period T is (10 to 100) and is -T, the average power supplied to the magnetic sensor 16 becomes about 110 to 1Z100. It is possible to use a battery as a power source.

In addition, since the peak value of the voltage generated in the coil 18 is detected, the relative sensitivity of the detection sensitivity of the minute magnetic flux hardly changes even if T / te is changed in a wide range of 2 to 100. . On the other hand, in the case of the amplitude detection method, when T Z increases by 5 or more, the sensitivity sharply decreases and it becomes difficult to save power.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a magnetic detection device according to an embodiment of the present invention, FIG. 2 is a hysteresis characteristic and a magnetic permeability characteristic diagram of a core of a magnetic sensor of the device of the embodiment,

FIG. 3 is a time chart showing the operation of the embodiment device.

FIG. 4 is a block diagram showing a schematic configuration of a conventional magnetic detection device,

Fig. 5 is a time chart showing the operation of the conventional device.

Fig. 6 is a circuit diagram for explaining the measurement principle using a saturable magnetic sensor.

FIG. 7 is a diagram showing a power supply waveform to the coil and an output voltage waveform of the coil in FIG.

FIG. 8 is a block diagram for implementing the magnetic detection method of the present invention.

Claims

[The scope of the claims]

(1) A magnetic sensor in which a detection coil is wound around a core formed of a ferromagnetic material, and an AC exciting current having a predetermined effective value is applied to the detection coil of the magnetic sensor via an impedance element. An excitation signal generating circuit that applies the magnetized coil to a saturation region, a waveform shaping circuit that normalizes a waveform of a detection signal extracted from both ends of the detection coil by a predetermined threshold value, and a waveform shaping circuit. A force counter for measuring a pulse width of the output normalized signal, wherein the external magnetic field strength is detected from a change in the pulse width caused by an external magnetic field crossing the magnetic sensor. Detector.

(2) A magnetic sensor in which a detection coil is wound around a core formed of a ferromagnetic material, and an AC excitation current having a predetermined effective value is applied to the detection coil of the magnetic sensor via an impedance element. An excitation signal generating circuit for applying the magnetization to the core to a saturation region, a waveform shaping circuit for normalizing a waveform of a detection signal taken out from both ends of the detection coil by a predetermined threshold value, and a waveform shaping circuit. A low-pass filter for detecting a pulse width of the output normalized signal as an average DC component, wherein the external magnetic field is determined based on a change in the pulse width caused by an external magnetic field crossing the magnetic sensor. A magnetic detector that detects intensity.

(8) The excitation signal generation circuit according to claim 1 or 2 is a triangular wave shape, a low frequency wave shape, a sine wave shape having a predetermined effective value, a sawtooth wave shape, or a logarithmic wave shape. It outputs any one of the waveform signals.

(4) The waveform shaping circuit according to claim 1 or 2 is a comparator.

(5) A magnetic sensor formed by winding a detection coil around a core made of a ferromagnetic material is brought close to the magnetic field to be measured, and positive and negative pulse voltages are supplied to the detection coil of the magnetic sensor via an impedance element. The positive and negative peak values of the voltage generated at both ends of the coil are respectively detected, and the detected positive and negative peak values are added, and the added value is set as a measured value corresponding to the measured magnetic field. Characteristic magnetic detection method.