JP2008070148A - Magnetic substance detection system and detection method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic substance detection system and its detection method which surely detect a signal originating from a magnetic substance, by removing the influence due to noise generated between an excitation coil for generating an alternate magnetic field for exciting the magnetic substance, and a detection coil for detecting the signal originating from the magnetic substance, when they are close to each other and noise caused by the system. <P>SOLUTION: The magnetic substance detection system comprises the exciting coil for generating the alternate magnetic field, a receiving coil for receiving the signal originating from the magnetic substance through magnetization reversal due to the alternate magnetic field generated by the exciting coil; an amplification circuit for amplifying the signal received by the receiving coil; a storage means for storing the signal output from the amplifying circuit, under the condition that the receiving signal not be receiving the signal from the magnetic substance; a subtraction means for subtracting the signal stored in the storage means from the output signal of the amplification circuit; and a detection means for detecting the magnetic substance on the basis of the output of the subtraction means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic body detection device and a detection method for detecting a signal generated when a magnetized magnetic body is reversed, and in particular, an excitation winding for generating an alternating magnetic field for exciting a magnetic body, and the magnetic body A magnetic body detection device that removes the influence of noise generated between each winding when the detection winding for detecting the emitted signal and the noise caused by the device are removed, and more reliably detects the signal emitted by the magnetic body, and It relates to the detection method.

  In recent years, various methods and apparatuses for enhancing security, such as prevention of leakage of confidential information and personal information, prevention of counterfeiting of securities and the like, prevention of theft of goods and the like, have been provided.

  For example, in a store that handles merchandise such as goods, a tag is affixed to the merchandise for the purpose of preventing theft of the merchandise, and the merchandise with the tag affixed passes through a tag detection device installed in a gate shape near the entrance of the store In this case, a system is provided that detects the status of a tag by 1-bit ON / OFF to determine whether or not the product has been settled to prevent the product from being stolen.

  As tag types, RFID (= Radio Frequency IDentification) tags, magnetic material tags using magnetic materials, and the like are used, and tag detection devices that can accurately detect these tags near or remotely from the tags. Various types are provided.

  Information stored in the RFID tag is obtained by, for example, transmitting a signal from a reader / writer to activate the RFID tag, and receiving information transmitted from the activated RFID tag by the reader / writer. Can be detected.

  This reader / writer can read information on the RFID tag in a non-contact manner even when the RFID tag is located several centimeters to several tens of centimeters away from the reader / writer. Due to its strength, it is used in various fields such as entrance / exit management, factory production management, and logistics management.

  In addition, a tag made of magnetic material (magnetic material tag) and a magnetic material tag that causes a large Barghausen effect as an application technology of the detection device are attached to the product, and the detection device for the magnetic material tag is installed at the gate. There is also provided an apparatus for detecting a magnetic material tag attached to a product when the detection device passes through the gate and preventing the product from being stolen.

  Magnetic material tags that cause the large Barghausen effect include, for example, magnetic wires of Co-Fe amorphous soft magnetic materials, etc. These magnetic material tags are cheaper than RFID tags, and are applied to a large number of products. Or suitable for use on disposable media.

  Magnetic tags that cause the large Barghausen effect are characterized by steep magnetization reversal when subjected to a magnetic field that exceeds the coercive force inherent to magnetic tags, so the alternating magnetic field generated by the excitation coil of the detector is used as a magnetic material. The magnetic material tag can be detected by applying to the tag and detecting a steep magnetic pulse generated when the magnetic material tag is reversed in magnetization through a detection coil arranged in the vicinity of the magnetic material tag.

  For example, Patent Literature 1 proposes an article monitoring system that prevents goods from being stolen in a store by detecting the movement of an identification mark attached to an article such as a product.

In the proposed article monitoring system, when a tag having a magnetic material attached to a product or the like moves in the detection area of the tag, the magnetic flux density of the magnetic material is changed by a signal generated from the transmitting antenna, and the magnetic flux density is changed. A detection device that detects a signal caused by a change in a reception antenna and detects a product with a tag attached based on the detection signal is proposed, and a transmission antenna housing in which a transmission antenna is incorporated and a reception antenna in which a reception antenna is incorporated A display device is fitted in a useless space of each antenna housing of the detection gate installed opposite to the housing, and product information is displayed on the display device, so that the detection capability of the tag is not reduced. Proposals have been made to make effective use of space.
JP 2002-319077 A

  When the transmitting antenna and the receiving antenna built in each antenna housing are close to each other as shown in Patent Document 1 and the antenna housings are opposed to each other, the influence of crosstalk generated between the coils Therefore, it is required to identify and detect the noise signal due to the noise and the noise signal due to the structure of the device and the signal generated from the other magnetic material.

  Therefore, the present invention relates to noise generated between each winding when an excitation winding for generating an alternating magnetic field for exciting a magnetic body and a detection winding for detecting a signal generated by the magnetic body are close to each other. It is an object of the present invention to provide a magnetic body detection device and a detection method thereof that removes the influence of noise caused by the magnetic field and more reliably detects a signal emitted from the magnetic body.

  In order to achieve the above object, the invention of a magnetic body detection device according to claim 1 receives an excitation winding for generating an alternating magnetic field and a signal generated from the magnetic body due to magnetization reversal by the alternating magnetic field generated from the excitation winding. A receiving winding for amplifying, an amplifying circuit for amplifying a signal received by the receiving winding, and a signal output from the amplifying circuit in a state where the receiving winding does not receive a signal from the magnetic body. Storage means for storing, subtracting means for subtracting the signal stored in the storage means from the output signal of the amplifier circuit, and detecting means for detecting the magnetic body based on the output of the subtracting means.

  According to a second aspect of the present invention, in the first aspect of the invention, the storage unit includes a determination unit that determines whether a predetermined time has elapsed since the signal output from the amplifier circuit was stored, and the determination unit. When it is determined that a certain period of time has passed and a signal in a state where the signal from the magnetic body is not received from the amplifier circuit is updated to update the stored signal with the signal output from the amplifier circuit Means.

  According to a third aspect of the present invention, in the first aspect of the present invention, the storage unit stores one period of a signal output from the amplifier circuit in a state where a signal from the magnetic body is not received.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the storage means generates a signal obtained by averaging a plurality of periods of the signal output from the amplifier in a state where the signal from the magnetic body is not received. Remember.

  According to a fifth aspect of the present invention, there is provided a detection method in which a receiving winding for receiving a signal generated from a magnetic material by magnetization reversal by an alternating magnetic field generated by an exciting winding is not receiving a signal from the magnetic material. The received signal is amplified by the amplification circuit, the amplified signal is stored in the storage means, and the received signal received by the reception winding is subtracted from the signal amplified in the amplification circuit by the amplification circuit. Subtracting means, and detecting the magnetic body based on the output of the subtracting means.

  According to a sixth aspect of the invention, in the fifth aspect of the invention, the storage means determines whether a predetermined time has elapsed since the signal output from the amplifier circuit was stored, and the determination means When it is determined that a certain time has passed and a signal in a state where the signal from the magnetic body is not received from the amplifier circuit is output, the storage signal is updated by the signal output from the amplifier circuit Update.

  According to the magnetic body detection device and the detection method of the present invention, when a signal that does not include a target detection signal to be detected is stored and held every predetermined time and a signal in which the target detection signals to be detected are mixed is received The signal processing that subtracts the signal that contains the detection signal and the signal held in memory and detects the target detection signal to be detected, so noise generated between the transmitting and receiving antennas, noise caused by the device, and aging It is possible to remove the influence of noise caused by the magnetic field and more reliably detect a signal emitted from the magnetic body.

  Hereinafter, an embodiment of a magnetic body detection apparatus and detection method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view of a copying machine 10 to which a magnetic body detection apparatus and a detection method according to the present invention are applied.

  FIG. 1A is a block diagram showing a schematic configuration of the copying machine 10, and FIG. 1B is a schematic perspective view of the copying machine 10.

  As shown in FIGS. 1A and 1B, the copying machine 10 includes a magnetic body detection unit 100, a control unit 11, an image reading unit 12, and an image forming unit 13 of the magnetic body detection apparatus according to the present invention. I have.

  When copying the document 1 placed on the platen glass 14 of the copying machine 10, the magnetic material detection unit 100 detects whether or not the magnetic material 110 indicating that copying cannot be performed is applied to the document 1, and the detection. The operation of outputting the resulting signal to the control unit 11 and its control are performed.

  The image reading unit 12 projects light onto the document 1 placed on the platen glass 14, and a photoelectric conversion element (for example, CCD = Charge Coupled Device or the like) that reflects the reflected light of the document 1 due to the projection. The light is received and converted into an electric signal, and the image information recorded on the document 1 is read and controlled based on the electric signal converted by the photoelectric conversion element.

  The image forming unit 13 prints image information read by the image reading unit 12 on a sheet (not shown) fed from the sheet tray 16, and discharges the sheet information to the sheet discharge tray 17 and controls it.

  The control unit 11 performs overall control of the entire copying machine 10 and performs a copying operation of the copying machine 10 or a prohibition control of the copying operation based on the detection result of the magnetic body 110 applied to the document 1 by the magnetic body detection unit 100.

  Further, a transmission coil 101 is disposed on the back surface of the platen cover 15 of the copying machine 10, and a reception coil 102 is disposed on the back surface of the platen glass 14, so that the document 1 placed on the platen glass 14 is copied. When the platen cover 15 is closed, the transmission coil 101 and the reception coil 102 face each other, and the transmission coil 101 and the reception coil 102 are arranged so as to sandwich the document 1 placed on the platen glass 14.

  Prior to the copying operation based on the user's copy start instruction operation, the copying machine 10 determines whether or not the magnetic body 110 indicating that the original 1 placed on the platen glass 14 cannot be copied is detected. If detected, control for prohibiting the copying operation of the document 1 is performed. If the magnetic body 110 is not detected, the image information of the document 1 is read, and the read image information is fed from the paper tray 16. A copying operation for printing on the paper and discharging it to the paper discharge tray 17 is performed.

  Specifically, the magnetic body 110 applied to the document 1 by the magnetic body detection unit 100 is detected by transmitting an alternating magnetic field from the transmission coil 101 under the control of the magnetic body detection unit 100 and receiving the alternating magnetic field. A steep magnetic pulse generated by the magnetization reversal of one magnetic body 110 is detected via the detection coil 102.

  FIG. 2 is a diagram illustrating the characteristics of the magnetic body 110 applied to the document 1.

  FIG. 2A is a diagram showing an example of the document 1 to which a magnetic material is applied in order to indicate that copying cannot be performed, and FIG. 2B is a diagram showing the magnetic characteristics of the magnetic material 110 applied to the document 1. FIG. 2 (c) is a diagram showing a pulse signal detected corresponding to a steep magnetic pulse generated at the time of magnetization reversal when the magnetic body 110 receives a predetermined alternating magnetic field.

  As shown in FIG. 2A, the original 1 is provided with a magnetic body 110 indicating that copying cannot be performed. This magnetic body 110 undergoes magnetization reversal by receiving a predetermined alternating magnetic field, and at that time, the magnetic body 110 is steep. It has a characteristic of so-called large Barkhausen effect that emits a magnetic pulse.

  The magnetic body 110 is, for example, a magnetic wire made of a Co—Fe amorphous soft magnetic material, and has a magnetic characteristic of a rectangular magnetization curve (BH curve) 200 as shown in FIG. As shown by a curve (BH curve) 200, it has a coercive force H1.

  In general, the intrinsic coercivity of the magnetic material of the amorphous magnetic wire varies depending on the size and shape of the magnetic material, and the intensity and timing of the magnetic pulse generated at the time of magnetization reversal according to the intrinsic coercivity of the magnetic material. Different.

  When an alternating magnetic field having a detection signal waveform 201 detected as shown in FIG. 2C is applied to the magnetic body 110 having such a magnetic characteristic, the magnetic body 110 having the coercive force H1 has a magnetic field of the alternating magnetic field. Magnetization is reversed when an alternating magnetic field with an intensity exceeding H1 or -H1 is received.

At the time of magnetization reversal of the magnetic body 110, a steep magnetic pulse A (when the magnetic field strength in the detection signal waveform 201 is an alternating magnetic field exceeding approximately H1 t1) and the magnetic pulse B (the magnetic field strength in the detection signal waveform 201). T2) is generated when an alternating magnetic field exceeding approximately −H1 is received, and can be detected by receiving these magnetic pulses and performing predetermined signal processing.
However, when an alternating magnetic field is generated in the transmitting coil and a magnetic pulse generated when the magnetic body 110 is reversed by the alternating magnetic field is received and detected by the receiving coil, when the transmitting coil and the receiving coil are arranged close to each other, In addition, noise caused by the crosstalk between coils and noise generated by the operation of metal and various sensors provided in the device (noise caused by the device) may occur. Therefore, it is required to detect the magnetic body 110 with high accuracy.

  Therefore, in the copying machine 10 shown in FIG. 1, a transmission coil that generates an alternating magnetic field for exciting the magnetic body 110 and a reception coil 102 that receives a magnetic pulse generated when the magnetic body 110 is reversed in magnetization are arranged close to each other. Even if it is a case, the magnetic body detection part 100 comprised so that the influence of the noise which generate | occur | produces between each coil and the noise resulting from an apparatus may be removed, and the signal which the magnetic body 110 emits may be detected more reliably. I have.

  FIG. 3 is a block diagram illustrating a configuration of a main part of the magnetic body detection unit 100.

  As shown in FIG. 3, the magnetic body detection unit 100 includes a transmission coil 101, a reception coil 102, a transmission circuit 120, an amplifier 121, a switching circuit 122, a subtraction circuit 123, a band limiting circuit 124, and detection. A circuit 125, a detection circuit 126, and a storage unit 127 are provided.

  The transmission coil 101 is an antenna that transmits an alternating magnetic field for exciting the magnetic body 110 applied to the document 1.

  The receiving coil 102 is an antenna that receives a magnetic pulse generated by reversing the magnetization of the magnetic body 110 that has received the alternating magnetic field transmitted from the transmitting coil 101.

  The transmission circuit 120 performs control for generating an alternating sine wave and transmitting a predetermined alternating magnetic field via the transmission coil 101.

  The amplifier 121 amplifies the reception signal received by the reception coil 102 and outputs the amplified signal.

  The switching circuit 122 performs control to output the amplified signal output from the amplifier 121 to the subtractor circuit 123 and to output the amplified signal output from the amplifier 121 to the storage unit 127 based on a predetermined condition and to store and hold the amplified signal.

  Specifically, of the amplifier signal output from the amplifier 121 in synchronization with the alternating magnetic field transmitted from the transmission coil 101, the amplifier signal when there is no detection signal of the magnetic pulse emitted by the magnetic body 110 is sent to the storage unit 127. Remember me.

  In addition, when a signal without a detection signal of a magnetic pulse generated by the magnetic body 110 at every preset time has been received, an amplified signal stored in the storage unit 127 with the amplified signal (for convenience of explanation, “memory amplification” "Signal").

  The subtracting circuit 123 performs signal processing for subtracting the stored amplified signal stored in the storage unit 127 from the amplified signal output from the amplifier 121, and outputs the signal to the band limiting circuit 124.

  The band limiting circuit 124 filters the amplified signal subtracted by the subtracting circuit 123 with a predetermined bandwidth, and removes in-phase noise components.

  The detection circuit 125 extracts and amplifies a detection signal of a magnetic pulse generated when the magnetic body 110 is reversed in magnetization from the amplified signal output after being filtered by the band limiting circuit 123 with a predetermined band limiting width.

  The detection circuit 126 detects the presence or absence of the magnetic body 110 based on the extracted signal extracted and amplified by the detection circuit 125, and outputs the detection result to the control unit 11 of the copier 10.

  The storage unit 126 stores and holds the amplified signal output from the switching circuit 122.

  Note that the storage unit 126 may be a storage element, or may be configured to store in a storage area developed on a memory (not shown).

  Timing for transmitting an alternating magnetic field from the transmission coil 101 of the magnetic body detection unit 100 and detecting a magnetic pulse emitted from the magnetic body 110 via the reception coil 102 is as follows.

  For example, the transmission circuit 120 controls to generate a current having a predetermined frequency and flow the current to the transmission coil 101, thereby generating an alternating magnetic field from the transmission coil 101.

  The magnetic body 110 applied to the document 1 placed on the platen glass 14 receives an alternating magnetic field generated from the transmission coil 101 and reverses its magnetization to generate a steep magnetic pulse.

  On the other hand, the receiving coil 102 receives signals such as an alternating magnetic field generated from the transmitting coil 101, a magnetic pulse generated by the magnetic body 110, and noise generated between the coils and noise caused by the device. The time when the current value becomes 0 in the rising direction of the current of the predetermined frequency generated by the transmission circuit 120, that is, the time when the current direction reverses from negative to positive is detected, and the alternating magnetic field is detected at the detected time. Detection based on a reference signal output at a timing once per period.

  About the detection method which the magnetic body detection part 100 comprised in this way removes the influence of the noise which generate | occur | produces between each coil, and the noise resulting from an apparatus, and detects the signal which the magnetic body 110 emits more reliably, and its control operation | movement This will be described with reference to FIG.

  FIG. 4 is a flowchart illustrating a method for the magnetic body detection unit 100 to more reliably detect the magnetic body 110 applied to the document 1 by removing the influence of noise generated between the coils and noise caused by the apparatus. .

  As shown in FIG. 4, when a document is placed on the platen glass 14 of the copying machine 10 and the platen cover 15 is closed, power is supplied to the magnetic body detection unit 100 to start up and operate.

  The magnetic body detection unit 100 is configured to start and operate regardless of the presence or absence of a document on the platen glass 14 when the platen cover 15 is closed.

  When the magnetic body detection unit 100 operates, a predetermined alternating magnetic field is transmitted from the transmission coil 101 (step S401).

  Specifically, this operation control is generated by the transmission circuit 120 of the magnetic body detection unit 100 generating an AC sine wave by supplying an operating voltage to a voltage controlled oscillator (VCO = Voltage Controlled Oscillator) (not shown). An AC sine wave is transmitted in a plane on the platen glass 14 via a transmitter and a transmission coil 101 (not shown).

  When a predetermined alternating magnetic field is transmitted from the transmission coil 101, the alternating magnetic field transmitted from the transmission coil 101, the noise generated between the coils and the noise caused by the device, and the magnetic pulse generated at the time of magnetization reversal by the magnetic body 110 A signal including the case where the magnetic material 110 is applied to the document placed on the platen glass 14 is received by the reception coil 102 disposed at a position facing the transmission coil 101 (step S402).

  These signals received by the receiving coil 102 are input to the amplifier 121, amplified to a predetermined level by the amplifier 121, and then output to the switching circuit 122 (step S403).

  The switching circuit 122 determines whether or not the target signal to be detected is mixed in the amplified signal output from the amplifier 121 (step S404).

  Specifically, the operation control is performed by comparing the amplified signal output from the amplifier 121 with the stored amplified signal stored in the storage unit 127, and the amplified signal and the stored amplified signal are equal to or higher than a preset set value. If there is a difference, it is determined that the target signal to be detected is mixed in the amplified signal output from the amplifier 121. If not, it is determined that the target signal is mixed (step S405).

  The storage unit 127 receives a signal including an alternating magnetic field transmitted from the transmission coil 101 without placing a document on the platen glass 14, noise generated between the coils, and noise caused by the device, The amplified signal amplified by the amplifier 121 is stored in advance when the copying machine 10 is shipped.

  The amplified signal stored in the storage unit 127 is an amplified signal corresponding to one cycle of the AC sine wave generated by the transmission circuit 120, and the difference between the amplified signal and the stored amplified signal is output from the amplifier 121. Obtained by the output of the difference between the two input signals of the amplified signal (the amplified signal corresponding to one cycle of the AC sine wave generated by the transmission circuit 120) and the stored amplified signal obtained from the storage unit 127, and set in advance The set values that have been set are stored in the storage unit 127 in advance.

  If the switching circuit 122 determines that the target signal to be detected is not mixed in the amplified signal output from the amplifier 121 (NO in step S405), the current date and time is stored in the storage unit 127. It is determined whether or not a predetermined time has elapsed since the date and time (step S406). If the predetermined time has elapsed (YES in step S406), the stored amplified signal stored in the storage unit 127 is stored. Is rewritten with the amplified signal output from the amplifier 121 and the amplified signal is output to the subtracting circuit 123 (step S407).

  Note that the amplified signal stored in the storage unit 127 is an amplified signal corresponding to one cycle of the AC sine wave generated by the transmission circuit 120 as described above.

  Specifically, this operation control is performed by the switching circuit 122 acquiring the current date / time information from a timer (not shown), the current date / time information acquired from the timer, and the date / time information in which the storage amplification signal is stored in the storage unit 127. If, for example, a preset fixed time is 1 hour and the difference between the current date / time information and the date / time information in which the stored amplification signal is stored is 1 hour or more, the information is stored in the storage unit 127. The operation of rewriting the stored amplified signal with the amplified signal output from the amplifier 121 is repeated at regular intervals.

  In step S405, if the switching circuit 122 determines that the target signal to be detected is mixed in the amplified signal output from the amplifier 121 (YES in step S405), or the stored amplified signal is determined in step S406. If the predetermined time has not elapsed since the time when it was stored in the storage unit 127 (NO in step S406), the amplified signal output from the amplifier 121 is output to the subtraction circuit 123.

  The subtracting circuit 123 performs signal processing for subtracting the stored amplified signal stored in the storage unit 127 from the amplified signal output from the switching circuit 122, and outputs the signal after the signal processing to the band limiting circuit 124 (step S408). ).

  Specifically, the operation control outputs a difference between two input signals, that is, an amplified signal output from the switching circuit 122 and a stored amplified signal acquired from the storage unit 127.

  The band limiting circuit 124 filters the amplified signal subtracted by the subtracting circuit 123 with a predetermined bandwidth, removes the in-phase noise component, and outputs the filtered signal to the detection circuit 125 (step S409).

  The detection circuit 125 extracts and amplifies a pulse signal corresponding to the magnetic pulse generated when the magnetic material 110 applied to the document 1 is reversed from the amplified signal filtered with a predetermined bandwidth by the band limiting circuit 124 (step). S410).

  The detection circuit 126 outputs the detection result of the magnetic body 110 to the control unit 11 of the copier 10 based on the extracted signal extracted and amplified by the detection circuit 125 (steps S411 and S412).

  The control unit 11 of the copying machine 10 reads a document placed on the platen glass 14 if the magnetic material 110 is detected based on the detection result of the magnetic material 110 output from the detection circuit 126 of the magnetic material detection device 100. In the case where the magnetic body 110 is not detected, the copying operation of the document placed on the platen glass 14 is controlled.

  As described above, the magnetic body detection device 100 stores and holds a signal that does not include a target detection signal to be detected at regular intervals, and includes a detection signal when a signal including the target detection signal to be detected is received. A signal generated by a magnetic material that suppresses the effects of noise caused by equipment and noise due to secular change, as it is detected by subtracting the signal that does not contain the target detection signal to be detected that is stored and held at regular intervals from the signal. Can be detected more reliably.

  In the description so far, a signal that does not include the target detection signal to be detected is stored as an amplified signal corresponding to one cycle of the AC sine wave generated by the transmission circuit 120, but n cycles (n is (A preset number of 2, 3, 4,...)) May be stored as an averaged amplified signal (for one cycle of the averaged amplified signal).

  In this case, the switching circuit 122 outputs the amplifier signal when there is no detection signal of the magnetic pulse generated by the magnetic body 110 among the amplifier signals output from the amplifier 121 in synchronization with the alternating magnetic field transmitted from the transmission coil 101. It is set as the structure provided with the means which acquires for a period and calculates the average.

  The present invention can be applied to a device for detecting a magnetic body and a technique for suppressing the effects of crosstalk and noise caused by the device.

1 is a schematic view of a copying machine 10 to which a magnetic body detection apparatus and a detection method according to the present invention are applied. The figure which shows the characteristic of the magnetic body 110 provided to a document The block diagram which shows the structure of the principal part of the magnetic body detection part 100. A flowchart showing a method by which the magnetic body detection unit 100 detects the magnetic body 110 applied to the document 1 more reliably.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Original 10 Copy machine 11 Control part 12 Image reading part 13 Image forming part 14 Platen glass 15 Platen cover 16 Paper tray 17 Paper discharge tray 100 Magnetic body detection part 101 Transmission coil 102 Reception coil 110 Magnetic body 120 Transmission circuit 121 Amplifier 122 Switching Circuit 123 Subtraction circuit 124 Band limiting circuit 125 Detection circuit 126 Detection circuit 127 Storage unit 200 Magnetization curve (BH curve)
201 Detection signal waveform

Claims (6)

An exciting winding that generates an alternating magnetic field;
A receiving winding for receiving a signal generated from a magnetic material by magnetization reversal by an alternating magnetic field generated from the exciting winding;
An amplification circuit for amplifying a signal received by the reception winding;
Storage means for storing a signal output from the amplifier circuit in a state where the reception winding does not receive a signal from the magnetic body;
Subtracting means for subtracting the signal stored in the storage means from the output signal of the amplifier circuit;
The magnetic body detection apparatus provided with the detection means which detects the said magnetic body based on the output of the said subtraction means. The storage means
A discriminating means for discriminating whether a predetermined time has elapsed since storing the signal output from the amplifier circuit;
When it is determined by the determining means that a certain time has elapsed and a signal in a state where a signal from the magnetic body is not received from the amplifier circuit is output, the signal output from the amplifier circuit is a stored signal The magnetic body detection device according to claim 1, further comprising: an updating unit that updates The storage means
The magnetic body detection device according to claim 1, wherein one period of a signal output from the amplifier circuit in a state where a signal from the magnetic body is not received is stored. The storage means
The magnetic body detection device according to claim 1, wherein a signal obtained by averaging a plurality of cycles of a signal output from the amplifier in a state where a signal from the magnetic body is not received is stored. The receiving winding that receives the signal generated from the magnetic material due to the magnetization reversal caused by the alternating magnetic field generated by the exciting winding is amplified by the amplifying circuit in a state where the receiving winding does not receive the signal from the magnetic material. Memorize the signal with the memory means,
Subtracting the signal stored in the storage means from the signal amplified by the amplification circuit received signal received by the reception winding by the subtraction means,
A detection method in which the magnetic body is detected by a detection means based on the output of the subtraction means. The storage means
A determination unit determines whether a predetermined time has elapsed since storing the signal output from the amplifier circuit,
When it is determined by the determining means that a certain time has elapsed and a signal in a state where a signal from the magnetic body is not received from the amplifier circuit is output, the signal output from the amplifier circuit is a stored signal The detection method according to claim 5, wherein the data is updated by the updating means.

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