JP2005030872A - Magnetic body quantity detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic body quantity detector for accurately detecting a magnetic body quantity included in a magnetic ink on paper sheets. <P>SOLUTION: This magnetic body quantity detector is provided with first and second magnetoresistive elements 4 and 5 disposed so as not to overlap with each other for detecting magneto-resistance of a magnetic body 8 formed on a conveyed medium 7 under detection, and a permanent magnet 6 for giving vertical and horizontal magnetic force to the first and second magnetoresistive elements 4 and 5, respectively. A DC voltage is impressed on the first and second magnetoresistive elements 4 and 5, and a difference between their output signals is used to obtain the body quantity of the magnetic body 8 formed in the medium 7 under detection. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic material amount detection apparatus that detects a signal proportional to a small amount of magnetic material contained in ink used for printing paper sheets or the like.
[0002]
[Prior art]
For example, as a measure to prevent counterfeiting of banknotes and securities, using magnetic ink-printed or paper with a strip-shaped magnetic material inserted in paper, these magnetic ink or It is widely known to perform authenticity determination by detecting a magnetic material.
[0003]
Magnetic heads for detecting the magnetic material of paper sheets used in the authenticity determination device include a differential winding type transformer method, a direct current excitation method, and an impedance method.
[0004]
Among these, the differential winding type transformer system has a 1-shaped winding at the center of the S-shaped core, and a secondary winding is wound around each of the two opening portions set in a minute gap, In this method, a paper sheet is passed close to one of the openings, and a difference between induced voltages caused by two secondary windings is detected (see, for example, Patent Document 1).
[0005]
In the DC excitation method, a minute gap is provided in a part of the annular core provided with the primary winding and the secondary winding, a direct current is applied to the primary winding, and the magnetic material passes through the gap. This is a method of detecting a change in magnetic flux in the annular core during the detection from the induced voltage of the secondary winding.
[0006]
Furthermore, the impedance method provides a small gap in a part of the annular core, and changes in the magnetic flux in the annular core when the magnetic material passes through the gap as an impedance change of the winding wound around the core. This is a detection method using a circuit. Further, there is a method in which a magnetic field bias is applied to the magnetoresistive element by a permanent magnet, and a change in the magnetic field due to the presence or absence of the magnetic material is detected as a change in resistance value.
[0007]
Further, the magnetoresistive element system has a structure in which two magnetoresistive elements are arranged on the same plane in order to reduce the influence of temperature drift, and a magnetic field strength difference between the two elements is output as a signal.
[0008]
[Patent Document 1]
Japanese Examined Patent Publication No. 62-36540 (5th page, FIG. 1)
[0009]
[Problems to be solved by the invention]
In the conventional magnetic body detection method, the differential winding type transformer method using the AC excitation current method is mainly used to detect signals proportional to the amount of magnetic material, but the core and winding are complicated and the magnetic head There was a drawback that the price would be higher.
[0010]
In addition, a method using a magnetoresistive element that detects a magnetic substance by applying a DC voltage has a simple signal detection circuit, but a detection signal generated by a detection target is due to a spatial difference in magnetic field distribution. Therefore, if a paper sheet on which a magnetic material having a uniform concentration is printed is on the magnetic detector, the magnetic signal cannot be output because there is no difference in the magnetic field distribution and the magnetic signal is not output. There are drawbacks.
[0011]
Therefore, the present invention has been made to solve the above-described drawbacks, and it can improve the spatial difference method of the detection method using a magnetoresistive element, and can detect a signal proportional to the amount of magnetic material by simply applying a DC voltage. An object of the present invention is to provide an inexpensive magnetic substance amount detection device.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that the magnetic material of the magnetic material formed on a detected medium that is arranged substantially adjacent to each other on the same plane so as not to overlap each other is conveyed. A first magnetic detection element and a second magnetic detection element for detecting a quantity; a permanent magnet that applies a vertical magnetic force to the first magnetic detection element; and a horizontal magnetic force to the second magnetic detection element; And a signal processing means for applying a DC voltage to the first magnetic detection element and the second magnetic detection element and determining the amount of the magnetic substance from the difference between the output signals.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment of a magnetic substance amount detection device according to the present invention will be described with reference to FIGS.
[0014]
FIG. 1 is a configuration diagram of a first embodiment of a magnetic substance amount detection device according to the present invention. 1A is a plan view, and FIG. 1B is a cross-sectional side view taken along the line AA of FIG. 1A when a paper sheet on which magnetic ink is printed passes. In the figure, the magnetic substance amount detection device includes a detection unit 1 and a printed wiring board 50 for processing a magnetic signal output detected by the detection unit 1.
[0015]
The detection unit 1 includes a case 2 made of a nonmagnetic material, a substrate 3, a magnetoresistive element 4 that is a first magnetic detection element, a magnetoresistive element 5 that is a second magnetic detection element, a permanent magnet 6, and the like. Consists of.
[0016]
The substrate 3 has a concave / convex recess at a predetermined position, and the magnetoresistive elements 4 and 5 are bonded and fixed to the recess, and the substrate 3 is bonded and fixed to the case 2.
[0017]
The permanent magnet 6 is disposed so as to apply a bias magnetic field to the magnetoresistive element 4 with the substrate 3 interposed therebetween, and is disposed so as to apply a magnetic field different from that of the magnetoresistive element 4 to the magnetoresistive element 5. That is, for example, a perpendicular magnetic field is applied to the magnetoresistive element 4 so that the bias magnetic field applied from the permanent magnet 6 to the magnetoresistive element 4 and the magnetoresistive element 5 through the substrate 3 becomes unbalanced, and the magnetoresistive element 5, at least a part of the permanent magnet 6 is disposed below the magnetoresistive element 4 (opposite position) so that a horizontal magnetic field is applied.
[0018]
The printed wiring board 50 of the magnetic substance amount detection device is connected to the board 3 to energize the magnetoresistive elements 4 and 5 and to perform signal processing for detecting the magnetic signal output from the magnetoresistive elements 4 and 5. It has a circuit.
[0019]
Next, the operation of the magnetic substance amount detection device configured as described above will be described. A detected medium 7 shown in FIG. 1B is a sheet of paper on which magnetic ink 8 is printed, and is conveyed in the direction of arrow A with respect to the detection unit 1. In the present invention, as described above, the bias magnetic field is applied unbalanced to the magnetoresistive elements 4 and 5.
[0020]
FIG. 2 shows the state of the bias magnetic field from the permanent magnet 6. The magnetic lines of force generated by the permanent magnet 6 include magnetic lines of force 91 that penetrate perpendicularly to the magnetoresistive element 4 and magnetic lines of force 92 that penetrate horizontally to the magnetoresistive element 5.
[0021]
The magnetoresistive elements 4 and 5 have a high sensitivity for changing the magnetic resistance value in the magnetic force line 91 in the direction perpendicular to the mounting surface of the substrate 3 and have a low sensitivity for changing the magnetic resistance value in the magnetic force line 92 in the horizontal direction. Accordingly, when the paper sheet 7 moves on the detection surface 2a of the detection unit 1 shown in FIG. 1B in the direction of the arrow A and the magnetic ink 8 reaches the magnetoresistive elements 4 and 5, the magnetoresistive element 5 Then, since the magnetic field lines 92 are in the horizontal direction as shown, even if the magnetic field intensity is changed by the magnetic ink 8, the change in the magnetoresistance value is small. In the magnetoresistive element 4, the magnetic field lines 91 are perpendicular to the magnetoresistive element 4. The magnetoresistance value changes greatly with high sensitivity to the change. As a result, only the magnetoresistive element 4 reacts to a change in the magnetic field caused by the magnetic ink 8.
[0022]
Next, the operation of the printed wiring board 50 that processes the magnetic signal output detected by the detection unit 1 will be described.
[0023]
FIG. 3 is a specific example of a detection circuit that detects changes in the magnetoresistance values of the magnetoresistive elements 4 and 5 as electrical signals. The detection circuit includes a bridge circuit 20 that detects a change in the resistance value of the magnetoresistive elements 4 and 5, a DC constant voltage power supply 26 for supplying power to the bridge circuit 20, and a voltage output from the bridge circuit 20. It comprises a differential amplifier 24 and an amplifier 25 for amplifying the change.
[0024]
The bridge circuit 20 includes a first magnetic sensor unit in which a magnetoresistive element 4 as a first magnetic detection element and a fixed resistor 22 are connected in series, and a voltage is output to one of the differential amplifiers 24 from the connection point. A second magnetic sensor unit in which a magnetoresistive element 5 as a second magnetic detection element and a fixed resistor 23 are connected in series, and a voltage is output from the connection point to the other of the differential amplifier 24; A variable resistor 21 for adjusting the balance of the bridge circuit 20 is arranged between the first magnetic sensor unit and the second magnetic sensor unit.
[0025]
The DC constant voltage power supply 26 supplies a DC voltage to the variable connection terminal of the variable resistor 21 constituting the bridge circuit 20 and energizes it. The direct current voltage from the direct current constant voltage power supply 26 has a difference between the value divided by the fixed resistor 22 and the magnetoresistive element 4 and the value divided by the fixed resistor 23 and the magnetoresistive element 5. This is supplied to the dynamic amplifier 24. The magnetic signal corresponding to the change in the resistance value of the magnetoresistive elements 4 and 5 detected by the differential amplifier 24 is further amplified via the amplifier circuit 25 and output as an electric signal.
[0026]
Here, a method for adjusting the bridge circuit 20 will be described. First, the resistance value of the variable resistor 21 is set so that the output of the differential amplifier 24 becomes as small as possible in a state where the magnetic material such as the magnetic ink 8 of the detected medium 7 is not on the detection surface 2a of the detection unit 1. At this time, the voltage at the connection point where the magnetoresistive element 4 and the fixed resistor 22 are connected in series and the voltage at the connection point where the magnetoresistive element 5 and the fixed resistor 23 are connected in series are set to substantially the same value. Is done.
[0027]
Next, when the magnetic ink 8 of the detected medium 7 reaches the detection surface 2a of the detection unit 1, the magnetoresistive value of the magnetoresistive element 4 increases, so that the balance voltage of the bridge circuit 20 changes and the differential amplifier 24 changes. Output voltage is changed, and is output from the amplifier 25 as an electric signal.
[0028]
(Another embodiment of the detection circuit)
FIG. 4 shows another embodiment of a detection circuit that detects a change in the magnetoresistance value of the magnetoresistive elements 4 and 5 as an electric signal. 4 that are the same as those in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted.
[0029]
This detection circuit is different from the embodiment shown in FIG. 3 in the configuration of the bridge circuit. The configuration of the bridge circuit 30 will be described below.
[0030]
The bridge circuit 30 connects the magnetoresistive element 4 that is the first magnetic detection element and the magnetoresistive element 5 that is the second magnetic detection element in series, and outputs a voltage to one of the differential amplifiers 24 from the connection point. A magnetic sensor unit, a fixed resistor 34, a fixed resistor 33, and a variable resistor 32 for adjusting the balance of the bridge circuit 30 are connected in series, and a connection point between the fixed resistors 33 and 34 is connected. A resistor unit that outputs a voltage is connected in parallel to the other side of the differential amplifier 24. A DC voltage for energizing the bridge circuit 30 is applied from this connection point by the DC constant voltage power supply 26.
[0031]
Next, the operation of the detection circuit of FIG. 4 will be described. First, the resistance value of the variable resistor 32 is set so that the output voltage of the differential amplifier 24 becomes as small as possible without a magnetic material such as the magnetic ink 8 of the detected medium 7 on the detection surface 2a of the detection unit 1. . At this time, the voltage at the connection point where the magnetoresistive elements 4 and 5 are connected in series and the voltage at the connection point of the fixed resistors 33 and 34 are set to substantially the same value.
[0032]
Next, when the magnetic ink 8 of the detected medium 7 reaches the detection surface 2a of the detector 1, the magnetoresistive value of the magnetoresistive element 4 increases, so that the balance voltage of the bridge circuit 30 changes and the differential amplifier is changed. The output voltage 24 changes and is output from the amplifier 25 as an electrical signal.
[0033]
Next, temperature drift will be described. Due to the difference in the intensity of the bias magnetic field applied to the magnetoresistive elements 4 and 5, a difference in magnetoresistive values of the magnetoresistive elements 4 and 5 occurs. This difference in the magnetoresistance value is corrected by the variable resistor 32 described above. However, if the ambient temperature changes, the magnetoresistance values of the magnetoresistive elements 4 and 5 also change, resulting in fluctuations in the output of the detection circuit. appear. In this way, output fluctuations that appear with changes in ambient temperature are called temperature drifts.
[0034]
Generally, when the volume of the magnetic material of the medium to be detected is large or the relative permeability is large, the influence of temperature drift is small because the detection signal is large.
[0035]
On the other hand, the detection signal by the magnetic ink 8 printed on the paper sheet such as the detected medium 7 as the detection medium by the magnetic substance amount detection device of the present invention is often small, and it is necessary to increase the gain of the differential amplifier 24. This inevitably increases the ratio of temperature drift to the detection signal. In addition, when detecting a magnetic material of a paper sheet, since the paper sheet is transported at a predetermined speed, the detection signal has a pulse waveform, and a temperature drift with a low frequency is added to the pulse waveform. Become.
[0036]
Next, FIG. 5 shows an embodiment of the detection circuit excluding the influence of this temperature drift. The detection circuit includes a differential amplifier 40 that amplifies a change in the magnetic signal detected by the bridge circuit 20 or 30, a low-frequency cut filter amplifier 41 that cuts a low frequency of the magnetic output signal of the differential amplifier 40, The rectifier circuit 42 rectifies the magnetic output signal of the low-frequency cut filter amplifier 41, and the high-frequency cut filter amplifier 43 smoothes the output signal of the rectifier circuit 42.
[0037]
The low-frequency cut filter amplifier 41 sets the cut-off frequency to a frequency that has a small influence on the detection signal, and removes voltage fluctuation due to temperature drift.
[0038]
The rectifier circuit 42 sets the positive or negative magnetic detection signal output from the low-frequency cut filter amplifier 41 to the same polarity.
[0039]
Further, the high-frequency cut filter amplifier 43 smoothes the output signal of the rectifier circuit 42 into a DC signal having a predetermined voltage.
[0040]
Since the magnetic signal detected by the detection circuit 20 or 30 is proportional to the amount of magnetism, the magnetic signal waveform rectified by removing the low frequency region is also proportional to the amount of magnetism. By adopting such a configuration, it is possible to provide a magnetic substance amount detection device that reduces the influence of temperature drift.
[0041]
(Second Embodiment)
FIG. 6 is a configuration diagram of the second embodiment of the magnetic substance amount detection device according to the present invention. About each part of this 2nd Embodiment, the same part as each part of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted.
[0042]
FIG. 6A is a plan view of the second embodiment of the magnetic substance amount detection device, and FIG. 6B is a side cross-sectional view taken along the line AA of FIG. Note that the detection circuit shown in FIGS. 3 to 5 can be used in this embodiment as well, but the description thereof is omitted because it has already been described.
[0043]
The magnetic substance amount detection device of the second embodiment is configured by further adding a permanent magnet 11 upstream of the permanent magnet 6 in the transport direction of the first embodiment shown in FIG. The permanent magnets 6 and 11 are in an adsorbed state because different polarities are arranged adjacent to each other, and the joint surfaces thereof are arranged to be below the magnetoresistive element 5. In other words, the permanent magnet 6 is arranged via the substrate 3 below the entire width of the magnetoresistive element 4 and a part of the width of the magnetoresistive element 5 (opposite position), and the permanent magnet 11 has the remaining width of the magnetoresistive element 5. It arrange | positions through the board | substrate 3 in the lower part (opposite position).
[0044]
As a result, the bias magnetic field of the magnetoresistive element 5 becomes horizontal in a narrow range of the joint surfaces of the permanent magnets 6 and 11 as shown by the magnetic force lines 122 in FIG. Further, the permanent magnet 6 has a width that sufficiently covers the magnetoresistive element 4 and is arranged so that the bias magnetic field passes through the magnetoresistive element 4 vertically like the magnetic force lines 121. With such a configuration, when the magnetic ink 8 of the detected medium 7 reaches the detection surface 2a of the detection unit 10, the magnetoresistance value of the magnetoresistive element 4 further increases, so that the direction of the bias magnetic field is reliably separated. be able to.
[0045]
With the configuration of the second embodiment, the magnetoresistive element 4 is given a vertical magnetic field, and the magnetoresistive element 5 is given a horizontal magnetic field stably. As a result, the magnetic quantity detection device is more stable than the first embodiment shown in FIG.
[0046]
(Modification of the second embodiment)
In the second embodiment, the permanent magnet 11 is arranged upstream of the permanent magnet 6 in the conveying direction, but the same effect can be obtained even if the permanent magnet 11 is arranged at a symmetrical position downstream of the permanent magnet 6 in the conveying direction. The function and performance of the present invention remains the same.
[0047]
In the present invention, both the first embodiment and the second embodiment have been described using the magnetoresistive element as the magnetic detection element. However, the same effect can be obtained even if the Hall element is used. The configuration will be described below.
[0048]
When a Hall element is used as the magnetic detection element, the configuration of the detection unit is a Hall element instead of the magnetoresistive elements 4 and 5 in FIGS. 1, 2, 6, and 7. For example, when the Hall element 51 is disposed instead of the magnetoresistive element 4 and the Hall element 52 is disposed instead of the magnetoresistive element 5, the Hall element 51 is highly sensitive to changes in the lines of magnetic force because the lines of magnetic force pass vertically, and the Hall element No. 52 has low sensitivity to changes in magnetic field lines because the magnetic field lines pass horizontally. Accordingly, it is possible to detect a change in the magnetic field due to the magnetic material, as in the case of the magnetoresistive element.
[0049]
Next, the configuration and operation of a magnetic substance amount detection circuit using a Hall element will be described with reference to FIG. In FIG. 8, a DC power source 59 is a constant voltage power source or a low current power source, and is connected to one power source terminal 51a, 52a of each of the Hall elements 51, 52. The other power terminals 51b and 52b of the Hall elements 51 and 52 are grounded. In this way, the Hall elements 51 and 52 are energized.
[0050]
The differential amplifier 53 is a differential amplifier for detecting magnetic signals output from the output terminals 51 c and 51 d of the Hall element 51. Similarly, the differential amplifier 54 is a differential amplifier for detecting a magnetic signal output from the output terminals 52 c and 52 d of the Hall element 52.
[0051]
The differential amplifier 55 eliminates the drift due to temperature by taking the difference between the outputs of the differential amplifiers 53 and 54, that is, the signals output from the Hall elements 51 and 52.
[0052]
The differential amplifier 56 amplifies the output signal of the differential amplifier 55. At this time, when a DC voltage is included in the input of the differential amplifier 56, the output signal 57 of the differential amplifier 56 may be swung out beyond the operating range. In order to prevent this, a DC voltage adjusted through the variable resistor 58 is added to one terminal of the differential amplifier 56, and only a subtraction signal is extracted from the DC voltage included in the input of the differential amplifier 56. In this way, the amount of magnetic material can be detected by the Hall elements 51 and 52. Further, the output signal 57 may be input to the circuit of FIG. 5 in order to remove the low frequency component of the signal.
[0053]
【The invention's effect】
According to the present invention, it is possible to provide a magnetic material amount detection device that does not require a differential magnetic head that can detect a signal proportional to the amount of magnetic material by a magnetoresistive element.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of a magnetic substance amount detection device according to the present invention.
FIG. 2 is a diagram illustrating a state of a bias magnetic field of a detection unit according to the first embodiment.
FIG. 3 is a configuration diagram of a detection circuit applied to the magnetic substance amount detection device according to the present invention.
FIG. 4 is a configuration diagram of another detection circuit applied to the magnetic substance amount detection device according to the present invention.
FIG. 5 is a configuration diagram of a detection circuit for removing the influence of temperature drift applied to the magnetic substance amount detection device according to the present invention.
FIG. 6 is a configuration diagram of a second embodiment of a magnetic substance amount detection device according to the present invention.
FIG. 7 is a diagram illustrating a state of a bias magnetic field of a detection unit according to the second embodiment.
FIG. 8 is a configuration diagram of a magnetic substance amount detection circuit using a Hall element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Detection part 2 Case 3 Board | substrate 4, 5 Magnetoresistive element 6, 11 Permanent magnet 7 Detected medium 8 Magnetic ink 9, 91, 121, 122 Magnetic field line 20, 30 Bridge circuit 20, 22, 23, 33, 34 Fixed resistor 21, 32 Variable resistors 24, 40 Differential amplifier 25 Amplifier 26 Constant voltage power supply 41 Low-frequency cut filter amplifier 42 Rectifier circuit 43 High-frequency cut filter amplifier 50 Printed circuit board 51, 52 Hall elements 53, 54, 55, 56 Difference Dynamic amplifier 57 Output signal 58 Variable resistor 59 DC power supply

Claims (9)

A first magnetic detection element and a second magnetic detection element, which are arranged adjacent to each other on substantially the same plane so as not to overlap each other and detect the amount of magnetic substance formed on the conveyed detection medium;
A permanent magnet that applies a vertical magnetic force to the first magnetic detection element and a horizontal magnetic force to the second magnetic detection element;
A magnetic body comprising signal processing means for applying a DC voltage to the first magnetic detection element and the second magnetic detection element, and obtaining a magnetic material amount of the magnetic body from a difference between output signals thereof. Quantity detection device. The magnetic material amount detection device according to claim 1, wherein at least a part of the permanent magnet is disposed at a position facing the first magnetic detection element. A first magnetic detection element and a second magnetic detection element, which are arranged adjacent to each other on substantially the same plane so as not to overlap each other and detect the amount of magnetic substance formed on the conveyed detection medium;
A first permanent magnet that applies a perpendicular magnetic force to the first magnetic sensing element;
Poles different from the poles of the first permanent magnet are opposed to each other, and a second permanent magnet that applies a horizontal magnetic force to the second magnetic sensing element;
A magnetic body comprising signal processing means for applying a DC voltage to the first magnetic detection element and the second magnetic detection element, and obtaining a magnetic material amount of the magnetic body from a difference between output signals thereof. Quantity detection device. The first permanent magnet is disposed at a position where at least a part thereof is opposed to the entire width of the first magnetic detection element and is opposed to a partial width of the second magnetic detection element;
3. The magnetic substance amount detection device according to claim 2, wherein at least a part of the second permanent magnet is disposed at a position facing a width of the remaining part of the second magnetic detection element. . The signal processing means includes
A first magnetic sensor unit configured by connecting the first magnetic detection element and the first resistor in series, and a configuration configured by connecting the second magnetic detection element and the second resistor in series. A bridge circuit configured by disposing a second magnetic sensor unit and a variable resistor between the first magnetic sensor unit and the second magnetic sensor unit;
A direct current power source for applying a voltage from the variable connection terminal of the variable resistor and energizing the bridge circuit;
Amplifying means for amplifying a difference between a voltage at a connection point between the first magnetic detection element and the first resistor and a voltage at a connection point between the second magnetic detection element and the second resistor; The magnetic substance amount detection device according to claim 1, wherein the magnetic material amount detection device is provided. 6. The resistance value of the variable resistor is set so that the output signal of the amplification means is minimized when the magnetic body is not within the detection range of the first and second magnetic detection elements. The magnetic substance amount detection apparatus described. The signal processing means includes
A magnetic sensor unit configured by connecting the first magnetic detection element and the second magnetic detection element in series; and a resistor unit configured by connecting two resistors and a variable resistor in series. A bridge circuit configured by connecting the magnetic sensor unit and the resistor unit in parallel;
A DC power source for energizing the bridge circuit by applying a voltage from a connection point connecting the magnetic sensor unit and the resistor unit in parallel;
And amplifying means for amplifying a difference between a voltage at a connection point of the first magnetic detection element and the second magnetic detection element and a voltage at a connection point of the two resistors. The magnetic substance amount detection device according to claim 1 or 3. 8. The resistance value of the variable resistor is set so that the output signal of the amplification means is minimized when the magnetic body is not within the detection range of the first and second magnetic detection elements. The magnetic substance amount detection apparatus described. A low-frequency cut filter amplifier circuit for reducing temperature drift of the output signal of the amplification means;
A rectifying circuit for rectifying the output signal of the low-frequency cut filter amplifier;
The magnetic substance amount detection device according to claim 5 or 7, further comprising a high-frequency cut filter circuit for smoothing a waveform of the rectifying means.

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