JP3789618B2 - Metal detection device, detection abnormality investigation method thereof, and subject property change investigation method using a metal detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention is a metal detection device used to inspect and detect the presence or absence of metallic foreign objects that should not be mixed in any non-metallic products such as food, other agricultural and marine products, medicines, clothing and industrial materials., Its detection abnormality investigation method, and subject property change investigation method using a metal detection deviceIt is about.
[0002]
[Prior art]
As a conventional metal detector, for example, there is one as shown in FIG. The metal detector shown in the figure is driven upstream by a motor 25 and driven on a conveyor belt 28 that is driven so as to be fed in the direction of arrow B via a driven vehicle 26 that rotates in the direction of arrow A (lower right in the figure). When the test substance 1 such as frozen food is placed on the side), the test substance 1 is transported in the direction of arrow B by the conveyor belt 28, and in the middle of the transport, a metal foreign substance, such as a screw or a washer, is provided. The presence or absence of contamination is magnetically inspected.
[0003]
A search coil built-in casing 32 having a rectangular tunnel passage 32a is provided above the metal detection device main body 31, and the test substance 1 passes through the tunnel passage 32a of the search coil built-in casing 32. At this time, if a foreign object such as a screw or washer is mixed in the test substance 1 by the search coil in the search coil built-in casing 32, it is magnetically detected.
[0004]
The operation control device 34 for operating the metal detection device by the user operating it or controlling the operation of each part of the metal detection device has a data display unit, operation buttons, etc. on the outside, Various electric circuits such as a CPU (central processing unit, microprocessor) of the microcomputer, wiring furnace, and other electric parts are housed inside.
[0005]
A search coil 100 as shown in FIG. 10 is accommodated in the search coil built-in casing 32. As shown in FIG. 10, the search coil 100 has a combination of a transmission coil 103 and a reception coil 201. Yes. As shown in the figure, the search coil 100 is connected to other circuits via a transmission amplifier 101 and a reception amplifier 202 to constitute a metal detection circuit as a whole.
[0006]
The transmission coil 103 and the reception coil 201 sandwich the conveyor belt 28 on which the test substance 1 shown in FIG. 9 is placed from both the upper and lower directions, and the plane including each coil and the placement surface (the test substance 1 for the test substance 1). The mounting surfaces are arranged so as to face each other in parallel.
[0007]
The transmission coil 103 generates an alternating magnetic field by the high frequency current from the oscillator 102 amplified by the transmission amplifier 101, and the receiving coil 201 is induced by the alternating magnetic field of the transmission coil 103. The receiving coil 201 is composed of two receiving coils in order to improve the disturbance resistance characteristics, and they are configured to be differentially connected to each other.
[0008]
By the way, the metal foreign matter that may be mixed into the test substance 1 is weak but has magnetism and conductivity and has a property of affecting the magnetic field, whereas the test substance 1 itself is Since it does not basically have such properties, the influence of the metal foreign object and the test substance 1 on the magnetic field is generally greatly different.
[0009]
For this reason, the metallic foreign matter mixed in the test substance 1 is transferred to the conveyor belt 28 and moved, thereby changing the interlinkage magnetic flux of the receiving coil 201 due to the magnetic field of the transmitting coil 103, and voltage until then. A voltage is induced between the two differentially connected receive coils where is zero.
[0010]
The induced voltage output from between the two differentially connected receiving coils 201 is amplified by the receiving amplifier 202 and detected by adjusting the reference phase angle by the reference phase angle adjuster 205 in the detection circuit 206. The signal from the detection circuit 206 is passed through the signal filter 204 to remove excess noise, and then a threshold value is set by the sensitivity setting unit 207 in the comparator 203. Output as detection voltage.
[0011]
By the way, as shown in FIG. 11, the metal mixed in the test substance 1 has a phase characteristic peculiar in the detection signal due to a difference in material such as iron Fe, stainless steel SUS, or aluminum AL. On the other hand, in the test substances 1 such as foods A and B, as shown in the figure, the phase characteristics (product effect or Some exhibit material effects.
[0012]
Such a phase characteristic in the test substance 1 such as food is not preferable for the metal detection device, and is one of the causes for reducing the reliability of the detection performance of the metal foreign matter. These test substances 1 such as foods have their own phase characteristics like foods A and B shown in FIG. 11 due to differences in the ingredients used, etc. At that time, every time the test substance is different, the setting of the reference phase angle and sensitivity is changed so that the highest sensitivity is obtained.
[0013]
That is, for example, when food A having a phase angle as shown in FIG. 11 is used as a test substance and a metal contained therein is to be detected, a temporary coordinate axis X orthogonal to the vector having the phase angle of food A ′ Is set, and a value obtained by multiplying the detected vector value by cos θ related to the angle θ with respect to the coordinate axis X ′ is extracted. That is, each detection vector is extracted as a projection vector projected perpendicularly to the coordinate axis X ′. Then, the angle θ between the detection vector of food A and the coordinate axis X ′_AIs 90 °, the value of cos 90 ° is 0, and thus the detection output is 0 (zero).
[0014]
However, in FIG. 11, the angle θ of each detection vector with respect to the temporary coordinate axis X ′ set at the above position, such as iron Fe, aluminum AL, or stainless steel SUS304._Fe, Θ_AL, Or θ_SUS304Is different from 90 °. Therefore, a projection vector projected perpendicularly to the coordinate axis X ′, such as the above-described iron Fe, aluminum AL, or stainless steel SUS304, cannot be zero. As a result, it is possible to detect the discrimination of the set phase angle between the food A having the product effect and other metals. Here, the detection output of the projection vector can be obtained as the absolute value of the scalar quantity component of the projection vector.
[0015]
The inclination angle α of the coordinate axis X ′ from the original X axis on the + (plus) side is the reference phase angle for the food A. In order to obtain the phase angle as shown in FIG. 11, conventionally, by changing the angle of the same test substance little by little, each test substance is sequentially flowed to the line and the phase characteristics are measured. A phase characteristic graph as shown in FIG. 12 can be obtained, and a method of recording the phase characteristic graph has been adopted. For example, the set phase angle A at which the detected voltage has a minimum value in FIG. 12 matches the phase angle of the food A indicated by a vector in FIG.
[0016]
In addition, recent metal detectors store in advance optimal values such as reference phase angles and sensitivities that correspond to the brands of various types of products (substances to be tested). In some cases, optimum values of various values such as phase angle and sensitivity can be set collectively.
[0017]
However, the phase characteristics of test substances such as food are not always stable. For example, when the volume of the food changes or a difference occurs between the components, the phase angle changes and the detection voltage of the metal detection device changes. In addition, there are those in which the phase angle changes depending on the salt concentration or temperature of the test substance, and the detection voltage also changes accordingly. The production line standardizes the quality of the test substance, but some variation cannot be avoided. Such a change in the phase characteristics of the test substance itself may hinder the operation of reliably detecting the mixed metal.
[0018]
Conventionally, in order to deal with the above problems, a monitoring device for monitoring the operation of the metal detection device has been commercialized. This monitoring device, for the metal detection mechanism part, of course, not only the power on / off, but also the history of operations such as setting value change, operation mode change, metal detection and its detected voltage value, abnormal state, etc. At any time, it can be printed or recorded along with the date and time.
[0019]
By examining such prints and records, it is possible to easily know when and what operation was performed, when the metal was detected, and what abnormality occurred. For this reason, it is possible to analyze the operation of the metal detection device properly by periodically examining the monitoring records of such a monitoring device.
[0020]
[Problems to be solved by the invention]
However, the conventional monitoring apparatus can record only a situation at a specific point time (time point, moment). For this reason, in such a conventional monitoring device, the recording of the detection voltage by the metal detection device is limited to only the detection voltage at a specific time such as the set phase angle A in FIG.
[0021]
For this reason, when the phase characteristic changes with the flow of time only at the time of the fixed set phase angle, appropriate detection cannot be performed. For this reason, it is not easy to determine whether the variation factor of the detection voltage is due to the mixed metal or due to a change in the phase characteristic (product effect) of the test substance.
[0022]
Therefore, if you do not know whether the fluctuation factor of the detection voltage is due to the mixed metal or the change of the product effect, the detection voltage of the test substance is compared with the threshold value for determining the metal contamination. There is a possibility that it cannot be determined whether or not it is truly reliable.
[0023]
Furthermore, as described above, in the prior art, by changing the angle of the same test substance little by little, each test substance is sequentially flowed to the detection transport line each time, and its phase characteristics are measured each time. Since the phase characteristic graph as shown in Fig. 12 was obtained and the method for recording it was taken, in a state where a large number of test substances continuously flow and pass through the detection transport line, The phase characteristic graph as shown in FIG. 12 could not be obtained by measuring the phase characteristic of the test substance, and it could not be recorded.
[0024]
Therefore, even if an attempt is made later to investigate the detection status of a product (test substance) in which metal contamination has not been detected even though metal contamination has occurred, the previous metal contamination detection status is completely restored. Could not be accurately grasped and analyzed.
[0025]
  The present invention has the above-mentioned problemsThis is a metal that can be used to visually recognize detailed characteristic information regardless of whether or not the test object is during or after the inspection of a metal foreign object, and whether or not the object contains a metal foreign object. It is an object of the present invention to provide a detection apparatus, a detection abnormality investigation method thereof, and a subject characteristic change investigation method using a metal detection apparatus.
[0026]
[Means for Solving the Problems]
  To solve the above problemsThe present invention relating to a metal detection apparatus detects a disturbance of a magnetic field caused by a metal foreign matter mixed in a subject to be inspected and outputs a detection signal, and the detection signal is expressed in XY coordinates. A trajectory figure drawn by the tip of the detection vector when displayed as a detection vector, and the trajectory figure are projected vertically onto the phase reference axis passing through the origin, and the maximum value is drawn according to the change of the phase reference axis. When the value of the phase characteristic graph at the reference phase angle set corresponding to the substance that constitutes the subject of the subject exceeds the predetermined threshold, the object metal foreign matter is included. A metallic foreign object detection means for determining that it has been detected and outputting a metallic foreign object detection signal, and a memory for continuously storing the data of the locus graphic or phase characteristic graph calculated by the calculation means in time series together with the date and time data at that time hand Equipped with doorIs.
[0027]
  In addition, the trace graphic or phase characteristic graph data at a specific point in the past read from the storage means is displayed on the display means so that the detailed characteristic information of the object detected at that time can be visually recognized. May be.
[0028]
In the present invention relating to the detection abnormality investigation method of the metal detection device, the above A detection abnormality such as a detection leak of a metal foreign matter generated in the metal detection device is investigated based on the past locus graphic or phase characteristic graph of the subject displayed on the display means.
[0029]
  In the present invention relating to the subject characteristic change investigation method using the metal detector, the subject is formed based on the past trajectory graphic or phase characteristic graph of the subject displayed on the display means. It is intended to investigate changes in the properties of substances.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
1 to 7 are diagrams which are referred to for explaining the metal detection device according to the first embodiment of the present invention.
[0031]
The metal detector according to the present embodiment has the same external configuration as that of the conventional metal detector shown in FIG. FIG. 1 is a block circuit diagram of a metal detection circuit of the metal detection device 10 connected to the search coil 100 in the search coil built-in casing 32 of FIG. Components similar to those in the conventional block circuit diagram of FIG. 10 will be described using the same reference numerals.
[0032]
The transmission coil 103 included in the search coil (detection unit) 100 of the metal detection device 10 shown in FIG. 1 converts the amount of electricity from the transmission amplifier 101 into a magnetic field. On the other hand, the receiving coil 201 included in the search coil 100 converts a change in a magnetic field when metal or the like passes into an electric quantity.
[0033]
In other words, the transmission coil 103 generates an alternating magnetic field by the alternating current from the transmission amplifier 101, and the receiving coil 201 is induced by the alternating magnetic field of the transmission coil 103. The receiving coil 201 is composed of two receiving coils in order to improve the disturbance resistance characteristics, and they are configured to be differentially connected to each other.
[0034]
The transmission amplifier 101 connected to the transmission coil 103 of the search coil 100 has a high frequency (1 KHz to 1 MHz, for example) as shown in FIG. About 1) alternating current (carrier current) I to the transmission coil 103.
[0035]
Then, the metal foreign matter mixed in the test substance 1 is transferred to the conveyor belt 28 and moved, thereby changing the interlinkage magnetic flux of the receiving coil 201 due to the magnetic field of the transmitting coil 103, and the voltage until then. A voltage is induced between two differentially connected receive coils 201 that were zero.
[0036]
The induced voltage E output from between the two differentially connected reception coils 201 as described above is modulated by the test substance 1 and modulated as shown in FIG. 3 by the reception amplifier 202 connected to the reception coil 201. The signal is amplified to a wave voltage (detection voltage) F, and a signal of the detection voltage F is input to a synchronous detector (discrimination detection means) 105.
[0037]
Such a detection voltage F has a specific phase angle depending on the material of the test substance 1. As shown in FIG. 4, the detection voltage F is set by the synchronous detector 105 so that the phase angle ψ is inclined with respect to the X axis on the orthogonal coordinates of the X axis and the Y axis. Then, the synchronous detector 105 converts the detected voltage F in such XY orthogonal coordinates to the X-axis component F._XAnd Y axis component F_YIn addition to the extraction, the X-axis component F_X, Y axis component F_YDetect about.
[0038]
In FIG. 4, the detection voltage F is formed by amplitude modulation of the induced voltage E and phase modulation by the phase change range θ of the induced voltage E.
[0039]
Synchronization is established by the X detection clock signal and the Y detection clock signal from the X / Y phase detection arithmetic unit 108 which are input to the synchronous detector 105, and the detected X axis component F is detected from the synchronous detector 105._XAnd Y axis component F_YEach of the signals related to is output separately.
[0040]
Two signal filters 204 are connected to the synchronous detector 105, and each of the signal filters 204 is an X-axis component F output from the synchronous detector 105._XAnd Y axis component F_YIt has a function of outputting a signal corresponding to each component obtained by removing unnecessary noise from the signal.
[0041]
X-axis component F output from the synchronous detector 105_XAnd Y axis component F_YEach of the signals is passed through the signal filter 204, A / D converted (converted from an analog signal to a digital signal), and input to the X / Y phase detection arithmetic unit 108. The X / Y phase detection arithmetic unit 108 is configured to generate an X-axis component F_XAnd Y axis component F_YA phase characteristic graph as shown in FIG. 12 is automatically obtained for the test substance by performing the phase calculation of the test substance based on the signals related to each of the above.
[0042]
That is, first, the X-axis component F_XAnd Y axis component F_YWhen the signals related to are calculated and synthesized by the X / Y phase detection arithmetic unit 108, a so-called Lissajous figure as shown in FIG. 5 is obtained. In the figure, each point P₁, P₂, P_Three... P_nRepresents a vector of the combined detection voltage F.
[0043]
Such a Lissajous figure is formed by moving the starting point P of the detection voltage F in FIG. 4 to the origin (0, 0) of the XY rectangular coordinates and removing the temporal element. The Lissajous figure in FIG. 5 should be restored as a straight line by the synthesis like the detection voltage F in FIG. 4, but the deformed elliptical shape as shown in FIG. This is because the signal waveforms of the X-axis component and the Y-axis component are generally distorted waveforms having a phase difference and an amplitude difference.
[0044]
Hereinafter, a method for obtaining a phase characteristic graph as shown in FIG. 12 from the Lissajous figure obtained as shown in FIG. 5 will be described with reference to FIG. In the figure, P₁, P₂, P_Three... P_nRepresents a vector of the detection voltage F synthesized by the X / Y phase detection arithmetic unit 108.
[0045]
First, go to the XY Cartesian coordinates through the origin and_mAnd the above-mentioned vector P₁, P₂, P_Three... P_nA line perpendicular to the phase reference axis A-A 'is drawn from the tip of each, and the maximum value (absolute value) of the distance between the intersection of the vertical line and the phase reference axis A-A' and the origin of the XY orthogonal coordinates And calculate the maximum value as the angle θ_mThe values at are plotted in FIG.
[0046]
Next, the phase reference axis A-A ′ is set to the angle θ_mThe maximum value (absolute value) is obtained in the same way as described above with a slight shift in the positive direction, and the maximum value is plotted as a value at the slightly shifted angle in FIG. In this way, the phase reference axis A-A ′ is shifted little by little, and the maximum value at each angle is obtained when the phase reference axis A-A ′ is rotated 180 ° (or 360 °) around the origin. Then, a phase characteristic graph as shown in FIG. 12 is obtained.
[0047]
Such a signal processing operation is performed in the X / Y phase detection arithmetic unit 108. A CPU (central processing unit, microprocessor) of a microcomputer is used as the X / Y phase detection arithmetic unit 108 that performs such signal processing operations.
[0048]
In order to make the explanation easy to understand, the elliptical Lissajous figure as shown in FIG. 6 is used for explanation, but the Lissajous figure from which the phase characteristic graph as shown in FIG. 12 is obtained is shown in FIG. It can be said that the Lissajous figure is more appropriate.
[0049]
The phase characteristic graph shown in FIG. 12 discriminates the detection vector of each test substance made of different materials using the reference phase angle, as described with reference to FIG. And the reference phase angle are respectively expressed by comparing them on the X and Y axes of the X and Y orthogonal coordinates. This figure is used as follows.
[0050]
For example, when metal detection is performed on the food A, based on the signals related to the X-axis component and the Y-axis component from the synchronous detector 105, corresponding to those new signal values that are sequentially input, FIG. The phase characteristic graph is updated every moment, and when the detection voltage at the set phase angle A in FIG. 12 is detected to be larger than a predetermined threshold value, metal foreign matter such as stainless steel SUS or iron Fe is mixed. In other words, the X / Y phase detection arithmetic unit 108 outputs a metal detection signal, and can activate the alarm device (not shown) to notify the user.
[0051]
In addition to this, the X / Y phase detection arithmetic unit 108 is also capable of generating an X axis component F_XAnd Y axis component F_YThe data of the signal is continuously sent to the XY data recording device (recording means) 110 without interruption during the operation of the metal detecting device 10.
[0052]
The XY data storage device 110 writes and stores the X-axis component and Y-axis component signal data sent from the X / Y phase detection arithmetic device 108 in a storage medium. As the storage medium, for example, a semiconductor A memory, floppy disk, hard disk, magneto-optical disk, magnetic tape, or the like can be used, but any other form of storage medium may be used.
[0053]
In the XY data storage device 110, in addition to the signal data relating to the X-axis component and the Y-axis component, the following is sent from the XY phase detection arithmetic unit 108 and stored along the time flow. The
(1) “On” and “Off” of the main power switch
(2) “On” and “Off” of the belt conveyor drive power switch
(3) Test mode selector switch “On” “Off”
(4) Presence / absence of transported goods by belt conveyor
(5) Presence or absence of metal detection
(6) Presence / absence of operation of removal device
(7) Metal detection voltage
(8) Applied voltage of control circuit
(9) Sensitivity setting voltage
(10) Set phase angle of test substance
(11) Test substance brand
[0054]
Further, the X / Y phase detection calculation device 108 is based on the X-axis component and the Y-axis component time axis of the detection voltage F in FIG. Graph F_X, F_Y7 calculates the X / Y axis orthogonal coordinate graph of the Lissajous figure of FIG. 7 obtained by synthesizing the X axis component and the Y axis component of the detection voltage F, the phase characteristic graph of FIG. The display unit 112 can display these graphs on the display device 112. The display device 112 can also display the numerical values of the calculation element data of these graphs.
[0055]
As a form of the display device 112, a CRT (CRT), an LCD (Liquid Crystal Screen), a printing device, or the like can be used, but any other form of display device may be used.
[0056]
An operation device 114 that can be operated by an operation panel, a keyboard, or the like is connected to the X / Y phase detection calculation device 108, and this operation device 114 has a sensitivity of a signal processed by the X / Y phase detection calculation device 108 ( Threshold) is set or changed to a predetermined value manually or automatically, or the operation mode of the X / Y phase detection arithmetic unit 108 is set or changed to a desired mode. .
[0057]
According to such a metal detection device 10, the data of the signals related to the X-axis component and the Y-axis component of the detection signal from the reception amplifier 202 are continuously recorded during the operation time of the metal detection device 10 together with the date and time when the data was collected. Since the XY data storage device 110 records data, the operation can be continuously monitored during the operation time, and the operation of the metal detection device 10 can be analyzed in detail over time. . For this reason, even if a metal foreign matter mixed in the test substance is leaked, the cause can be easily and quickly found later, and it is possible to take further measures by taking countermeasures. .
[0058]
In addition, the display device 112 does not stop the operation of the metal detection device 10 and does not affect the detection operation during the operation of the metal detection device 10 even during the operation of the metal detection device 10. The time axis graph calculated by 108 can be displayed immediately. For this reason, it is possible to detect an abnormality immediately by constantly monitoring the display device 112, and even if a metal detection leak is likely to occur, it can be prevented or the detection leak can be minimized. be able to.
[0059]
By the way, as in the second embodiment of the present invention shown in FIG. 8, a data reconfirmation auxiliary device (reproduction means) 116 can be connected to the XY data storage device 110 of the metal detection device 10. . The data reconfirmation auxiliary device 116 includes an XY data reading unit 118 that reads data of signals related to past X-axis components and Y-axis components stored in the XY data storage device 110 of the metal detection device 10, and the signal An XY data processing unit (signal processing means) 120 for calculating the time axis graph of the X-axis component and the Y-axis component based on the data, and a display for displaying the time axis graph calculated by the XY data processing unit 120 Part (display means) 122.
[0060]
If such a data reconfirmation auxiliary device 116 is installed at another location, the past X stored in the XY data storage device 110 of the metal detection device 10 at another location even during actual operation of the metal detection device 10. Data of signals related to the axis component and the Y-axis component can be read out, the data of the signal can be calculated by the XY data processing unit 120, and the time axis graph or the like can be displayed on the display unit 122.
[0061]
For this reason, it becomes possible to analyze the past operation | movement of the metal detection apparatus 10 in detail over time. Therefore, the change transition of the product effect of the test substance (product) is observed and recorded, and by analyzing this, for example, the transition of the dip point (minimum detection value) in the phase characteristic graph of FIG. Since the correlation with the change in the state of the product can be examined, it can be used for quality control of the product.
[0062]
In the unlikely event that a metal detection leak occurs, the cause can be easily found by analyzing the past operation in detail over time. Leakage can be reliably prevented.
[0063]
【The invention's effect】
  Claim 1 as described above~ 3 describedAccording to the invention,Since the storage means stores the data of the trajectory graphic or the phase characteristic graph continuously in time series together with the date and time data at that time, and displays the data on the display means as necessary,The operation can be monitored continuously during the operation time, and the operation of the metal detector can be analyzed in detail over time. For this reason, in the unlikely eventbodyDetection leakage of metallic foreign matter mixed inAbnormal detection of metal detectors such asEven if a problem occurs, the cause can be easily and quickly found, and it is possible to take further measures by taking countermeasures.
[0064]
  According to the invention described in claim 4, since the change in the characteristics of the substance constituting the subject of the subject is investigated based on the past locus graphic or phase characteristic graph of the subject displayed on the display means, the locus Since the correlation between the change in the figure or phase characteristic graph and the change in the state of the substance can be examined, the results of the study can be applied to quality control such as monitoring the change in the state of the productcan do.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram showing a configuration of a metal detection device 10 according to a first embodiment of the present invention.
2 is a waveform diagram of an alternating current I sent from a transmission amplifier 101 to a transmission coil 03. FIG.
FIG. 3 is a waveform diagram of a detection voltage F obtained by modulating an induced voltage E amplified by a reception amplifier 202.
FIG. 4 shows a detected voltage F in X / Y axis orthogonal coordinates, and a time axis graph F of an X axis component and a Y axis component discriminated therefrom._X, F_YFIG.
FIG. 5 is a diagram illustrating a Lissajous figure of a detection voltage based on a vector obtained by synthesizing an X-axis component and a Y-axis component from which noise has been removed by detection.
FIG. 6 is a diagram for explaining a method of creating a phase characteristic graph from a Lissajous figure.
7 is a diagram showing a Lissajous figure of each material corresponding to the phase characteristic graph of FIG.
FIG. 8 is a block circuit diagram showing a configuration of a metal detection device 10 and a data reconfirmation auxiliary device 116 according to a second embodiment of the present invention.
FIG. 9 is a perspective view showing an external configuration of a conventional metal detection device.
10 is a block circuit diagram showing a metal detection control circuit of the metal detection device of FIG. 9;
11 is a diagram showing the magnitude and direction of a vector representing the difference in phase angle depending on the material of the test substance 1. FIG.
12 is a diagram showing a phase characteristic graph of each material corresponding to the Lissajous figure of FIG. 7;
[Explanation of symbols]
1 Test substance
10 Metal detector
25 motor
26 Follower
28 Conveyor belt
31 body
32 Search coil built-in casing
32a Tunnel passage
34 Operation control device
100 search coil
101 Transmitting amplifier
102 oscillator
103 Transmitting coil
105 Synchronous detector
108 X / Y phase detection arithmetic unit
110 XY data storage device
112 Display device
114 controller
116 Auxiliary device for data reconfirmation
118 XY data reading unit
120 XY data processing unit
122 Display section
201 Receiver coil
202 Receiving amplifier
203 Comparator
204 signal filter
205 Reference phase angle adjuster
206 Detection circuit
207 Sensitivity setter

Claims (4)

When detecting a magnetic field disturbance due to a metallic foreign object mixed in a subject to be inspected and outputting a detection signal, and when the detection signal is displayed as a detection vector in XY coordinates The trajectory figure drawn by the tip of the detection vector and the trajectory figure are projected vertically onto the phase reference axis passing through the origin, and the data of the phase characteristic graph in which the maximum value is drawn according to the change of the phase reference axis is calculated. When the value of the phase characteristic graph at a reference phase angle set corresponding to the substance constituting the subject of the subject exceeds the predetermined threshold value, the subject contains a metallic foreign object. A metallic foreign object detection means for discriminating the object and outputting a metallic foreign object detection signal, and data for the locus graphic or the phase characteristic graph calculated by the calculating means are continuously stored in time series together with date / time data at that time. Metal detecting apparatus and means. The trajectory graphic or phase characteristic graph data read from the storage means in the past at a specific time point is displayed on the display means so that detailed characteristic information of the subject detected at that time can be visually recognized. The metal detection device according to claim 1 . 3. The detection abnormality of the metal detection device such as a detection leak of a metal foreign matter generated in the metal detection device is investigated based on a past locus graphic or phase characteristic graph of the subject displayed on the display means. Method of investigating detection abnormality of metal detector . 3. A subject using a metal detection apparatus according to claim 2, wherein a change in characteristics of a substance constituting the subject of the subject is investigated based on a past locus graphic or phase characteristic graph of the subject displayed on the display means. Of investigating changes in the subject's characteristics .

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