JP2019002709A - Metal detector and diagnosis method - Google Patents

Abstract

To provide a metal detector that determines without using a test piece whether or not a transmission circuit and a reception circuit are functioning normally.SOLUTION: The metal detector comprises: a transmission circuit, including a transmission coil, for generating an alternating magnetic field in an inspection area where an inspection object passes through by inputting an alternating current of a set waveform to the transmission coil; a reception circuit including a first reception coil and a second reception coil for outputting a detection signal that corresponds to a flux change in the inspection area; a metal detection unit for detecting metal foreign matter included in the inspection object that passes through the inside of the inspection area, on the basis of a difference signal that represents a difference between the detection signal of the first reception coil and the detection signal of the second reception coil; and a diagnosis unit for changing the set waveform of the alternating current supplied to the transmission coil when the inspection object is not passing through the inside of the inspection area and determining on the basis of the difference signal whether or not the transmission circuit and the reception circuit are functioning normally.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a metal detection device and a diagnostic method.

  Patent Document 1 describes a metal detection device that detects a metal foreign object contained in an object to be inspected by utilizing an interaction between a magnetic field and a metal. The apparatus includes a transmission circuit that generates a magnetic field and a reception circuit that detects a change in magnetic flux. This apparatus diagnoses the foreign object detection function using a test piece containing metal.

JP 2015-1111075 A

  In the method of diagnosing the foreign object detection function using the test piece, it is determined whether or not the metal foreign object is deliberately thrown into the inspection area of the metal detection apparatus and the apparatus can detect it. In order to avoid foreign matter from adhering to or remaining in the inspection region, it is preferable that the number of times of diagnosis using the test piece is as small as possible. Moreover, when diagnosing the foreign object detection function using a test piece, a person who throws in and collects the test piece is required.

  An object of this invention is to provide the metal detection apparatus and diagnostic method which can determine whether the transmission circuit and the reception circuit are functioning normally, without using a test piece.

  A metal detection apparatus according to the present invention includes a transmission coil, a transmission circuit that generates an alternating magnetic field in an inspection region through which an inspection object passes by inputting an alternating current having a set waveform to the transmission coil, and a magnetic flux in the inspection region Based on a reception circuit including a first reception coil and a second reception coil that outputs a detection signal according to a change, and a differential signal that is a difference between the detection signal of the first reception coil and the detection signal of the second reception coil, Change the setting waveform of the alternating current supplied to the transmission coil when the inspection object does not pass through the inspection area and the metal detection part that detects the metallic foreign matter contained in the inspection object that passes through the inspection area A diagnosis unit that determines whether the transmission circuit and the reception circuit are functioning normally based on the difference signal.

  In this apparatus, the setting waveform of the alternating current supplied to the transmission coil when the inspection object does not pass through the inspection region is changed by the diagnosis unit. When the setting waveform of the alternating current changes, the magnetic field in the inspection area changes. For this reason, the detection value of the first receiving coil and the detection signal of the second receiving coil also change. The first receiving coil and the second receiving coil output detection signals that are slightly different even if the magnetic flux change is the same due to a difference in arrangement position or an assembly error. That is, if the transmission circuit and the reception circuit are normal, the difference signal changes (has a value of 0 or more) according to the change in the alternating current setting waveform. This device can determine whether or not the transmission circuit and the reception circuit are functioning normally without using a test piece by verifying the change in the differential signal according to the change in the setting waveform of the alternating current. .

  In one embodiment, the diagnosis unit determines that the transmission circuit and the reception circuit are not functioning properly when the difference signal does not change according to the change in the setting waveform of the alternating current supplied to the transmission coil. May be. When configured in this way, it is possible to detect an abnormality without using a test piece.

  In one embodiment, the diagnosis unit may change the amplitude of the alternating current supplied to the transmission coil and determine whether or not the transmission circuit and the reception circuit are functioning normally based on the amplitude of the difference signal. Good. When configured in this way, it is possible to determine whether or not the transmission circuit and the reception circuit are functioning normally by verifying the amplitude of the differential signal.

  In one embodiment, the diagnosis unit changes the phase or frequency of the alternating current supplied to the transmission coil, and determines whether or not the transmission circuit and the reception circuit function normally based on the phase or frequency of the difference signal. You may judge. When configured in this manner, the phase or frequency of the differential signal can be verified to determine whether the transmission circuit and the reception circuit are functioning normally.

  In one embodiment, the metal detection device further includes a detector that detects an alternating current flowing through the transmission coil, and the diagnosis unit has a normal transmission circuit or reception circuit based on the detection result of the detector and the difference signal. It may be determined whether or not it is functioning. When the alternating current is detected, it can be determined that the transmission circuit is normal, and when the alternating current is not detected, it can be determined that the transmission circuit is not normal. Further, when the transmission circuit is normal and the difference signal does not change according to the change in the alternating current setting waveform (when it remains substantially 0), it is determined that the reception circuit is not normal. Can do. In this way, it is possible to determine which of the transmission circuit and the reception circuit is abnormal.

  In one embodiment, the metal detection device may include a case main body having therein a space through which an inspection object passes due to natural fall, and the inspection region may be set in the space. In an apparatus that drops and inspects an object to be inspected, more people are required for diagnosis using a test piece than an apparatus that inspects an object to be inspected by moving it in a horizontal direction using a belt conveyor or the like. . In an apparatus for dropping and inspecting an object to be inspected, it is possible to reduce the number of personnel required for diagnosis by determining whether or not the transmission circuit and the reception circuit function normally without using a test piece.

  A diagnostic method according to the present invention includes a transmission circuit including a transmission coil, and a reception circuit including a first reception coil and a second reception coil, and changes in magnetic flux caused by a metal foreign object included in an object to be inspected passing through an inspection region. A method for detecting a metal foreign object based on the method for changing a setting waveform of an alternating current supplied to a transmission coil when an object to be inspected does not pass through an inspection region And determining whether or not the transmission circuit and the reception circuit are functioning normally based on a difference signal that is a difference between the detection signal of the first reception coil and the detection signal of the second reception coil.

  According to this diagnostic method, the same effects as those of the metal detection device described above can be obtained.

  According to the present invention, it is possible to determine whether or not the transmission circuit and the reception circuit are functioning normally without using a test piece.

It is a conceptual diagram of the metal detection apparatus which concerns on 1st Embodiment. It is a graph explaining an alternating current, the electric current of a receiving circuit, and a difference output. It is a graph explaining the electric current of a receiving circuit when changing the amplitude of the alternating current of FIG. 2, and a difference output. It is a characteristic curve which shows the relationship between the excitation voltage and phase of a receiving circuit before and behind the phase change of an alternating current. It is a flowchart explaining an example of the diagnostic process of a metal detection apparatus. It is a conceptual diagram of the metal detection apparatus which concerns on 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

[First Embodiment]
[Device configuration]
FIG. 1 is a conceptual diagram of a metal detection device 1 according to an embodiment. A metal detection apparatus 1 shown in FIG. 1 is an apparatus that detects a metal foreign object contained in the inspection object S. The inspection object S is, for example, food. Metal detection is a technique for detecting foreign matter contained in an object to be inspected by utilizing the interaction between a magnetic field and metal.

  The metal detection device 1 includes a case main body 10. The case body 10 has a space in which the inspection object S passes due to natural fall. An inspection region R in which metal detection is performed is set inside the case body 10. The metal detection device 1 includes a transmission circuit 2, a reception circuit 3, and a control unit 4.

  The transmission circuit 2 includes a transmission coil 20. The transmission coil 20 is disposed corresponding to the inspection region R, and converts the amount of electricity into a magnetic field. The transmission circuit 2 determines an alternating current of a setting waveform to be input to the transmission coil 20 based on, for example, a transmission signal having a setting frequency and a setting amplitude transmitted from the control unit 4. The alternating current of the set waveform is a current modulated so as to have a predetermined waveform. In the alternating current of the set waveform, the amplitude and frequency (cycle) are fixed values. The transmission circuit 2 generates an alternating magnetic field in the inspection region R through which the inspection object S passes by supplying an alternating current having a set waveform to the transmission coil 20.

  The receiving circuit 3 includes a first receiving coil 30 a and a second receiving coil 30 b as the search coil 30. The first receiving coil 30a and the second receiving coil 30b are arranged corresponding to the inspection region R. As an example, the first reception coil 30 a and the second reception coil 30 b are disposed to face the transmission coil 20. The inspection region R is interposed between the first receiving coil 30 a and the second receiving coil 30 b and the transmitting coil 20.

  Each of the first receiving coil 30a and the second receiving coil 30b outputs a detection signal corresponding to a change in magnetic flux in the inspection region R. The detection signal is an electrical signal and may be a current or a voltage. The 1st receiving coil 30a and the 2nd receiving coil 30b are comprised by the same winding number and length, and are differentially connected. For this reason, the 1st receiving coil 30a and the 2nd receiving coil 30b become an output of reverse polarity.

  When the metallic foreign object does not pass through the inspection region R, the output signals of the first receiving coil 30a and the second receiving coil 30b have the same amplitude and the same phase and have opposite polarities. For this reason, the output (difference signal) obtained from the two differentially connected receiving coils is substantially zero. On the other hand, when a metal foreign object passes through the inspection region R, a magnetic flux change occurs according to the movement of the metal foreign object. For this reason, the balanced state of the outputs of the first receiving coil 30a and the second receiving coil 30b is broken, and the output obtained from the two differentially connected receiving coils becomes an output having a value (difference signal). A metallic foreign object can be detected by determining the presence or absence of the value of the difference signal.

  The control unit 4 is connected to the transmission circuit 2 and the reception circuit 3. The control unit 4 includes an input / output interface I / O for inputting / outputting signals from / to the outside, a ROM (Read Only Memory) storing a program and information for processing, and a RAM for temporarily storing data. (Random Access Memory), a storage medium such as an HDD (Hard Disk Drive), a CPU (Central Processing Unit), a communication circuit, and the like. The control unit 4 stores input data in the RAM based on a signal output from the CPU, loads a program stored in the ROM into the RAM, and executes the program loaded into the RAM, thereby performing functions described later. Is realized.

  The control unit 4 includes a metal detection unit 40, a diagnosis unit 41, a storage unit 42, and a display unit 43 as functional configurations.

  The metal detection unit 40 generates a transmission signal having a set frequency and a set amplitude. The metal detection unit 40 outputs the generated transmission signal to the transmission circuit 2 via a communication circuit or the like. And the metal detection part 40 acquires a difference signal from the receiving circuit 3 via a communication circuit etc. The metal detection unit 40 detects a metal foreign object included in the inspection object S passing through the inspection region R based on the difference signal. As described above, in the metal detection device 1, the metal detection is performed by the transmission circuit 2, the reception circuit 3, and the metal detection unit 40 operating in cooperation.

  As described above, when the metal foreign object does not exist in the inspection region R, the difference signal is substantially zero. In this case, it is difficult to determine whether the difference signal is substantially zero because no metal foreign matter is mixed in or whether the difference signal is substantially zero because at least one of the transmission circuit 2 and the reception circuit 3 is disconnected. It is. The diagnosis unit 41 has a function of separating such a situation.

  The diagnosis unit 41 diagnoses the metal detection capability of the metal detection device 1. As a more specific example, the diagnosis unit 41 determines whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally. To function normally means to operate without any trouble to detect metal. When functioning normally, an alternating magnetic field is formed by the transmitting circuit 2 and detection according to the alternating magnetic field is performed by the receiving circuit 3. The diagnosis unit 41 performs diagnosis when the inspection object S does not pass through the inspection region R. The diagnosis unit 41 may start diagnosis according to a previously scheduled event or time such as when the metal detector 1 is turned on or at a fixed time, or may start diagnosis manually.

  At the time of diagnosis, the diagnosis unit 41 changes the setting waveform of the alternating current supplied to the transmission coil 20. As an example, the diagnosis unit 41 changes the transmission signal generated by the metal detection unit 40. For example, the diagnosis unit 41 may change the amplitude by multiplying the transmission signal generated by the metal detection unit 40 by a predetermined gain, or apply a modulation filter to the transmission signal generated by the metal detection unit 40. The frequency may be changed.

  The diagnosis unit 41 outputs the generated transmission signal to the transmission circuit 2 via a communication circuit or the like. Thereby, the waveform of the alternating current supplied to the transmission coil 20 changes, and the alternating magnetic field in the inspection region R through which the inspection object S passes changes according to the change. Although the first receiving coil 30a is configured with the same number of turns and length as the second receiving coil 30b, there are attachment positions and assembling errors. The first receiving coil 30a and the second receiving coil 30b including such an error cannot be detected in fully tuned with respect to the change of the alternating magnetic field, and output from the differentially connected receiving coils. Becomes an output (difference signal) having a value.

  The diagnosis unit 41 acquires a differential signal from the reception circuit 3 via a communication circuit or the like. The diagnosis unit 41 determines whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally based on the difference signal. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are not functioning normally when the difference signal does not change according to the change in the setting waveform of the alternating current supplied to the transmission coil 20.

  As an example, the diagnosis unit 41 changes the amplitude of the alternating current supplied to the transmission coil 20. In this case, a difference occurs in the amplitudes of the outputs of the first receiving coil 30a and the second receiving coil 30b, and the difference signal becomes an output having a value. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are functioning normally when the amplitude of the difference signal equal to or greater than a predetermined value can be confirmed. For example, when the circuit is disconnected, the value of the differential signal becomes 0 even if the amplitude of the alternating current is changed. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are not functioning normally when the amplitude of the difference signal equal to or greater than the predetermined value cannot be confirmed.

  As another example, the diagnosis unit 41 may change the phase or frequency of the alternating current supplied to the transmission coil 20. In this case, a difference occurs in the phase of the outputs of the first receiving coil 30a and the second receiving coil 30b, and the difference signal becomes an output having a value. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are functioning normally when the phase change equal to or greater than the predetermined value is confirmed. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are not functioning normally when a phase change of a predetermined value or more cannot be confirmed.

  The storage unit 42 stores the diagnosis result of the diagnosis unit 41 in a storage medium. The display unit 43 displays the diagnosis result of the diagnosis unit 41 on a display device such as a display.

[An example of each signal when detecting metal]
An outline of each signal at the time of metal detection will be given. FIG. 2 is a graph for explaining the alternating current, the current of the receiving circuit, and the differential signal. FIG. 2A is an example of an alternating current. FIG. 2B is an example of detection signals from the first receiving coil 30a and the second receiving coil 30b. (C) of FIG. 2 is an example of a difference signal.

  FIG. 2A shows an alternating current having a predetermined cycle and a predetermined amplitude. By supplying such an alternating current to the transmission coil, an alternating magnetic field is generated. FIG. 2B is an example of detection signals from the first receiving coil 30a and the second receiving coil 30b. A solid line waveform is detected by the first receiving coil 30a, and a broken line waveform is detected by the second receiving coil 30b. The solid line waveform has the same amplitude and phase as the broken line waveform, and the amplitude is reversed. By adding the waveform of the solid line and the waveform of the broken line by differential connection, a differential signal shown in FIG. 2C is obtained. When the metal foreign object does not pass through the inspection region R, the alternating magnetic field is not distorted, so the difference signal is substantially zero. On the other hand, when the metal foreign object passes through the inspection region R, the alternating magnetic field is distorted, so that the difference signal has a value. When the metal detection unit 40 detects a differential signal that is equal to or greater than a predetermined threshold, the metal detection unit 40 determines that a metal foreign object has been mixed.

[Example of each signal during diagnosis]
An outline of each signal at the time of diagnosis will be given. FIG. 3 is a graph for explaining the alternating current, the current of the receiving circuit, and the difference signal when the amplitude of the alternating current of FIG. 2 is changed. FIG. 3A is an example of an alternating current. FIG. 3B is an example of detection signals from the first receiving coil 30a and the second receiving coil 30b. FIG. 3C is an example of the difference signal.

  FIG. 3A shows an alternating current when the amplitude of the alternating current in FIG. 2 is changed. At the time of diagnosis, the diagnosis unit 41 changes the alternating current having the predetermined period and the predetermined amplitude A1 shown in FIG. 2 into the alternating current having the predetermined period and the predetermined amplitude A2 shown in FIG. When such a change is made, a change also occurs in the alternating magnetic field. FIG. 3B is an example of detection signals from the first receiving coil 30a and the second receiving coil 30b. A solid line waveform is detected by the first receiving coil 30a, and a broken line waveform is detected by the second receiving coil 30b. Compared with FIG. 2B, the amplitude of the detection signal of the first receiving coil 30a is larger. For this reason, the differential signal shown in FIG. 3C is obtained. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are functioning normally when a differential signal equal to or greater than a predetermined threshold A is detected. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are not functioning normally when the differential signal equal to or greater than the predetermined threshold A is not detected. The diagnosis unit 41 may determine that the transmission circuit 2 and the reception circuit 3 are functioning normally when the maximum value of the difference signal is in the range of the predetermined threshold A or more and the predetermined threshold B or less.

[Other examples of signals during diagnosis]
Next, an example where the phase of the alternating current is changed will be described. FIG. 4 is a characteristic curve showing the relationship between the output voltage and phase of the receiving circuit before and after the phase change of the alternating current. 4A is excited by the search coil 30 (the first receiving coil 30a and the second receiving coil 30b) when the alternating current shown in FIG. 2A is supplied to the transmitting coil 20. FIG. It is a characteristic curve which shows the relationship between a voltage and a phase. Such a characteristic curve can be obtained by, for example, a known technique described in Japanese Patent No. 3789618.

  4B shows a search coil 30 (first receiving coil 30a and second receiving coil 30b) when the phase of the alternating current shown in FIG. 2A is changed and supplied to the transmitting coil 20. FIG. ) Is a characteristic curve showing the relationship between the voltage excited by the phase and the phase. Thus, the relationship between the excitation voltage and the phase differs before and after the phase change. When the diagnosis unit 41 changes the phase of the alternating current, whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally is determined by determining whether or not there is a change in the relationship between the excitation voltage and the phase. Determine whether or not.

[Diagnosis method]
Next, a diagnostic method for the metal detection device 1 will be described. FIG. 5 is a flowchart for explaining an example of a diagnosis process of the metal detection apparatus. The flowchart shown in FIG. 5 may be started according to a pre-scheduled event or time such as when the metal detector 1 is turned on or at a fixed time, or may be started manually.

  As shown in FIG. 5, the diagnosis unit 41 determines whether or not the inspection object S passes through the inspection region R by a determination process (step S10). For example, the diagnosis unit 41 determines whether the inspection object S passes through the inspection region R based on the detection result of a sensor (not shown) provided in the inspection region R. Alternatively, the diagnosis unit 41 may input the determination result of another component or the worker and determine whether or not the inspection object S passes through the inspection region R.

  When the inspection object S does not pass through the inspection region R (step S10: NO), the diagnosis unit 41 receives an alternating current having a predetermined period and a predetermined amplitude used in metal detection as a magnetic field generation process (step S12). A transmission signal is generated and output to the transmission circuit 2 so as to be generated. As a result, an alternating magnetic field is generated in the inspection region R.

  Subsequently, the diagnosis unit 41 changes the transmission signal to be output to the transmission circuit 2 as a transmission waveform change process (step S14: step of changing the set waveform). The diagnosis unit 41 changes the amplitude to be larger, for example, by adding a predetermined gain to the amplitude.

  Subsequently, the diagnosis unit 41 determines whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally based on the difference signal acquired from the reception circuit 3 as a diagnosis process (step S16: determination step). To do. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are functioning normally when the amplitude of the difference signal equal to or greater than a predetermined value can be confirmed. The diagnosis unit 41 determines that the transmission circuit 2 and the reception circuit 3 are not functioning normally when the amplitude of the difference signal equal to or greater than the predetermined value cannot be confirmed. If necessary, the diagnosis unit 41 stores the determination result in the storage unit 42 and causes the display unit 43 to display the determination result.

  When the inspection object S passes through the inspection region R (step S10: YES) or when the diagnosis process (step S16) is completed, the flowchart shown in FIG. 5 is ended.

  As described above, according to the metal detection device 1 and the diagnosis method according to the first embodiment, the diagnosis unit 41 detects the alternating current supplied to the transmission coil 20 when the inspection object S does not pass through the inspection region R. The setting waveform changes. When the setting waveform of the alternating current changes, the magnetic field in the inspection region R changes. For this reason, the detection value of the 1st receiving coil 30a and the detection signal of the 2nd receiving coil 30b also change. The first receiving coil 30a and the second receiving coil 30b output detection signals that are slightly different even with the same magnetic flux change due to a difference in arrangement position or an assembly error. That is, if the transmission circuit 2 and the reception circuit 3 are normal, the difference signal changes (has a value of 0 or more) according to the change in the alternating current setting waveform. The metal detection device 1 determines whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally without using a test piece by verifying the change in the differential signal according to the change in the setting waveform of the alternating current. can do.

  Moreover, the metal detection apparatus 1 can reduce the number of personnel required for diagnosis by determining whether the transmission circuit and the reception circuit function normally without using a test piece.

[Second Embodiment]
Compared to the metal detection device 1 according to the first embodiment, the metal detection device 1A according to the second embodiment is provided with a detector that detects an alternating current flowing through the transmission coil 20, and the diagnosis unit is The difference is that it is determined whether or not the transmission circuit or the reception circuit is functioning normally using the detection result of the detector, and the others are the same.

  FIG. 6 is a conceptual diagram of a metal detection device according to the second embodiment. The metal detection device 1 </ b> A includes a detector 21 that detects an alternating current flowing through the transmission coil 20. The detector 21 may be an ammeter. The detector 21 outputs the detection result to the control unit 4.

  The diagnosis unit 41A determines whether the transmission circuit or the reception circuit is functioning normally based on the detection result of the detector 21 and the difference signal. As in the first embodiment, the diagnosis unit 41A determines whether or not the transmission circuit 2 and the reception circuit 3 are functioning normally using the difference signal. Here, when the difference signal is equal to or smaller than the threshold value, the diagnosis unit 41A determines whether or not an alternating current is detected by the detector 21.

  The diagnosis unit 41A determines that the receiving circuit 3 is not functioning normally when the difference signal is equal to or smaller than the threshold value and the alternating current is detected by the detector 21. The diagnosis unit 41A determines that at least the transmission circuit 2 is not functioning normally when the differential signal is equal to or less than the threshold value and no alternating current is detected by the detector 21. Other functions are the same as those of the first embodiment.

  According to the metal detection apparatus 1A according to the present embodiment, it is possible to determine which of the transmission circuit 2 and the reception circuit 3 is abnormal.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment.

  For example, although the example of the apparatus (so-called circular type inspection apparatus) for inspecting the inspection object S that falls naturally is shown, the present invention is not limited to this. The metal detection apparatus includes a conveyor that conveys the inspection object S in the horizontal direction, and a case main body that allows the inspection object S that is conveyed by the conveyor to pass therethrough, and an inspection region is set inside the case main body 10. May be.

  DESCRIPTION OF SYMBOLS 1 ... Metal detection apparatus, 2 ... Transmission circuit, 3 ... Reception circuit, 4 ... Control part, 10 ... Case main-body part, 20 ... Transmission coil, 21 ... Detector, 30 ... Search coil, 30a ... 1st reception coil, 30b ... 2nd receiving coil, 40 ... Metal detection part, 41, 41A ... Diagnosis part.

Claims (7)

A transmission circuit including a transmission coil and generating an alternating magnetic field in an inspection region through which an object to be inspected passes by supplying an alternating current of a set waveform to the transmission coil;
A receiving circuit including a first receiving coil and a second receiving coil that outputs a detection signal corresponding to a magnetic flux change in the inspection region;
A metal detection unit that detects a metal foreign object contained in the inspection object that passes through the inspection region based on a difference signal that is a difference between the detection signal of the first reception coil and the detection signal of the second reception coil. When,
When the inspection object does not pass through the inspection area, the setting waveform of the alternating current supplied to the transmission coil is changed, and the transmission circuit and the reception circuit function normally based on the difference signal. A diagnostic unit for determining whether or not
A metal detection device comprising:   The diagnosis unit determines that the transmission circuit and the reception circuit are not functioning normally when the difference signal does not change in accordance with a change in the setting waveform of the alternating current supplied to the transmission coil. The metal detection device according to claim 1.   The diagnosis unit changes an amplitude of an alternating current supplied to the transmission coil, and determines whether or not the transmission circuit and the reception circuit are functioning normally based on an amplitude of the differential signal. 3. The metal detection device according to 1 or 2.   The diagnostic unit changes the phase or frequency of the alternating current supplied to the transmission coil, and determines whether the transmission circuit and the reception circuit function normally based on the phase or frequency of the differential signal The metal detection device according to any one of claims 1 to 3. A detector for detecting an alternating current flowing through the transmission coil;
The diagnosis unit determines whether the transmission circuit or the reception circuit is functioning normally based on a detection result of the detector and the difference signal. Metal detection apparatus as described in.   The metal detection device according to any one of claims 1 to 5, further comprising a case main body having therein a space through which the inspection object passes due to natural fall, and the inspection region is set in the space. A transmission circuit including a transmission coil and a reception circuit including a first reception coil and a second reception coil are provided, and the metal foreign object is detected based on a magnetic flux change caused by the metal foreign object included in the inspection object passing through the inspection region. A diagnostic method for a metal detector that performs
Changing the setting waveform of the alternating current supplied to the transmission coil when the inspection object does not pass through the inspection area;
Determining whether or not the transmission circuit and the reception circuit are functioning normally based on a differential signal that is a difference between a detection signal of the first reception coil and a detection signal of the second reception coil;
A diagnostic method comprising:

Images