JP2000314776A - Metal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erroneous determination from being generated by fluctuation of a degree affected to a magnetic field by an inspected object itself, and fluctuation of a noise level. SOLUTION: Determination-objective values as to an inspected object W are stored in order by an affected value storing means 45 as affected values for indicating affected degrees affected to a magnetic field by the inspected object W itself, detection signals when the object W does not exist within the magnetic field are stored in order as noise level values by a noise level storing means 46, and the affected values stored in the affected value storing means 45 and the noise level values stored in the noise level storing means 46 are graphically displayed on an image plane of a display 48 by a display control means 47 to allow discrimination for change with the lapse of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting a metal mixed in a test object using a magnetic field so that the metal can always be detected under the best conditions.

[0002]

2. Description of the Related Art In a production line for foods and the like, in order to inspect on a line whether or not metal is mixed in a product, FIG.
The metal detector 1 shown in FIG.

The metal detector 1 excites the transmission coil 3 with a sine wave signal from the signal generator 2 to generate an alternating magnetic field on the transport path C of the device under test.

[0006] The two receiving coils 4 and 5 arranged along the transport path C receive a magnetic field almost equally.

The two receiving coils 4 and 5 are differentially connected. When there is no test object in an alternating magnetic field, the signals induced in the two receiving coils 4 and 5 are opposite in phase shift and have the same level. The voltage at the connection point is almost zero, and when the device under test passes through the alternating magnetic field, the signals induced in the two coils change individually as the device under test passes. Occurs.

The voltage at the connection point between the two receiving coils 4 and 5 is amplified by an amplifier 6 and input to a detection circuit 7.

The detection circuit 7 receives the sine wave signal output from the signal generator 2 via the phase shifter 8, and multiplies the output of the amplifier 6 by the sine wave signal shifted by the phase shifter 8 for detection. I do.

The phase shifter 8 has a small detection output when an object to be inspected with no metal mixed therein passes through an alternating magnetic field.
In addition, the phase shift amount is set in advance so that the detection output when the test object containing the metal passes through the alternating magnetic field increases.

The detection output of the detection circuit 7 is input to the judgment value detection means 8. The determination target value detection means 8 detects a determination target value for determining the presence or absence of metal from the detection output when the test object passes through the magnetic field, for example, a maximum value of the detection signal, Output.

[0010] The judging means 10 compares the judgment object value detected by the judgment object value detecting means 9 with a preset reference value. This reference value is set based on the detection output when a sample to be inspected in which metal is not mixed is passed through a magnetic field as a sample, and when the sample is passed through an alternating magnetic field during actual operation. The judgment target value detected at
If it is equal to or more than this reference value, it can be understood that metal is mixed in the inspection object.

The result of the judgment by the judging means 10 is displayed on a judgment result display 11 and output to a sorter (not shown) to remove the object to be inspected judged to be mixed with metal from the line.

In the metal detector configured as described above, before starting operation for a new type, adjustment of the phase shift amount of the phase shifter 8 and adjustment of the phase shift amount of the phase shifter 8 are performed so as to obtain the best inspection conditions for the new type. The setting of the judgment reference value was performed.

[0013]

However, the influence of the test object itself, in which metal is not mixed, on the magnetic field is as follows.
Even for the same type of product, it varies depending on the production lot, etc., and the effect on the magnetic field fluctuates in the case of a test object containing a large amount of moisture, responding sensitively to changes in ambient temperature and humidity. However, there is a problem that the detection of the mixed metal cannot be performed smoothly due to such a variation.

That is, when the influence on the magnetic field of the test object itself is small, the operation is started after setting the phase shift amount, the reference value, and the like, and then the characteristics of the test object itself with respect to the magnetic field, environmental changes, and the like are changed. When the degree of influence on the magnetic field of the test object itself increases, the detection output tends to increase, and erroneous determination of the presence of metal occurs frequently in the determination unit 10.

In the case where the erroneous determination of the presence of metal frequently occurs, the probability that the object to be inspected is removed from the line increases, so that many objects to be inspected removed from the line must be re-inspected. No.

When the operation is started after setting the reference value or the like when the object to be inspected has a large influence on the magnetic field, the object to be inspected may be changed due to a change in characteristics of the object to the magnetic field, a change in environment, or the like. Even if the influence on the magnetic field of the body itself is small, the judgment is made with a large reference value,
Metals cannot be detected with high sensitivity, and fine metals may be missed.

In such a device that uses a magnetic field to determine the presence or absence of metal by comparing the level of the detection output with a reference value, the influence of noise entering from the power supply line and the magnetic field leaking from other magnetic field generating devices is considered. If the degree of influence fluctuates, the noise level of the detection output will fluctuate, and as in the case of the fluctuation of the degree of influence of the test object itself, problems such as erroneous determination and reduction in detection sensitivity will occur.

An object of the present invention is to provide a metal detector which solves this problem and can promptly respond to the degree of influence on the magnetic field of the test object itself, fluctuations in noise, and the like.

[0019]

According to a first aspect of the present invention, there is provided a metal detector which generates a magnetic field in a passage of an object to be inspected and which passes through the magnetic field. The change of the magnetic field due to is detected, a determination target value for determining the presence or absence of metal from the detection signal is detected, and the detected determination target value is compared with a reference value to determine the presence or absence of metal in the test object. An influence value storing means for sequentially storing a value to be determined for an object to be inspected as an influence value indicating a degree of influence of the object to be inspected on a magnetic field; a display device; Display control means for graphically displaying the influence value stored in the means on the screen of the display device so that a change with time can be identified.

Further, the metal detector according to claim 2 of the present invention comprises:
2. The metal detector according to claim 1, further comprising: noise level storage means for sequentially storing a level of the detection signal when the object to be inspected is not present in the magnetic field as a noise level value, wherein the display control means comprises: In addition to the above, the noise level value stored in the noise level storage means is graphically displayed on a screen of the display device so that a change with time can be identified.

Further, the metal detector according to claim 3 of the present invention comprises:
A magnetic field is generated from a magnetic field generator on a passage of the test object, and a change in the magnetic field due to the test object passing through the magnetic field is detected.
A metal detector that detects a determination target value for determining the presence or absence of a metal from the detection signal and compares the detected determination target value with a reference value to determine the presence or absence of a metal in the test object. Influence value storage means for sequentially storing the determination target value of the test object as an influence value indicating the degree of influence of the test object on the magnetic field; and an influence value based on the influence value stored in the influence value storage means. Control means for variably controlling a detection condition for detecting a change in a magnetic field due to the test object or a reference value for determination is provided.

Further, the metal detector according to claim 4 of the present invention comprises:
4. The metal detector according to claim 3, further comprising: a noise level storage unit that sequentially stores a level of the detection signal when the test object is not present in the magnetic field as a noise level value, wherein the control unit is configured to control the influence value. Variably controlling a detection condition or a reference value for determination for detecting a change in a magnetic field due to the test object based on the influence value stored in the storage means and the noise level value stored in the noise level storage means. Features.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a metal detector 20 according to the embodiment.

The magnetic field generator 21 of the metal detector 20
The transmission coil 23 is excited by a sine wave signal output from the signal generator 22 to generate an alternating magnetic field in the transport path C of the device under test W.

The magnetic field may be not only an AC magnetic field but also a DC magnetic field, or a magnetic field having both an AC magnetic field and a DC magnetic field. Or a DC current may be passed from the signal generator 22 to the transmission coil 22.
In this case, a phase shifter 29, a phase shift amount setting means 30, and a detection circuit 31, which will be described later, become unnecessary, and the output of the amplifier 28 may be directly input to the determination target value detection means 40.

The two receiving coils 24 and 25 arranged along the transport path C receive the magnetic flux of the magnetic field generated by the magnetic field generating unit 21 at substantially equal amounts, and detect a change in the magnetic field due to the test object.

The arrangement of the transmitting coil 23 and the receiving coils 24 and 25 includes a facing type and a coaxial type. In the case of the opposed type, as shown in FIG. 2A, the transmitting coil 23 is arranged on one side with the transport path C interposed therebetween, and the two receiving coils 24 and 25 are opposed to the transmitting coil 23 on the other side. To place. In the case of the coaxial type, as shown in FIG.
The transmitting coil 23 is arranged so as to surround the transport path C, and the receiving coils 24 and 25 are arranged coaxially before and after the transmitting coil 23.

An entry sensor 26 for detecting the inspection object W entering the magnetic field is provided on the entrance side of the transport path C. The entry sensor 26 may be any of an optical type (light shielding type, reflection type) and a mechanical type.

The receiving coils 24 and 25 are differentially connected via a variable resistor 27. The variable resistor 27 is used to correct a slight level difference between AC signals induced in the two receiving coils 24 and 25 when the test object W is not in the alternating magnetic field when the alternating magnetic field is used. And is adjusted in advance so that the output voltage becomes zero. The output voltage of the variable resistor 27 is amplified by the amplifier 28 and output to the detection circuit 31.

On the other hand, the sine wave signal output from the signal generator 22 is input to the detection circuit 30 via the phase shifter 29. The phase shift amount of the phase shifter 29 is set by the phase shift amount setting means 30.

The detection circuit 31 includes receiving coils 24, 25,
Along with the amplifier 28, this is for detecting a change in the magnetic field due to the test object passing through the magnetic field. The output of the amplifier 28 is multiplied and detected by a sine wave signal from the phase shifter 29.

As the detection circuit 31, a two-phase detection circuit that detects and outputs two signal components whose phases differ from each other by 90 ° from the output of the amplifier 28, or a single-phase detection circuit can be used.

In the case of a two-phase detection circuit, the output of the amplifier 28 and the output of the phase shifter 29 are connected to the mixer 3 as shown in FIG.
Multiply by 2 and output LPF (low-pass filter)
33, the magnetic field frequency component is removed, and the signal x is converted to A
The output of the amplifier 28 and the output of the 90 ° phase shifter 36 are multiplied by a mixer 37, and the output of the amplifier 28 and the output of a 90 ° phase shifter 36 are multiplied by a mixer 37. , And the signal y is sampled by the A / D converter 39, converted into a digital value Y, and sequentially output. In addition,
Here, the 90 ° phase shifter 34 delays the output of the phase shifter 29 by 90 ° and outputs it.

The two-phase detection circuit 31 can use one detection output X to determine the presence or absence of a ferrous metal, and use the other detection output Y to determine the presence or absence of a non-ferrous metal. This is based on the fact that the optimum detection phases of the ferrous metal and the non-ferrous metal are shifted by about 90 °.

In the case of a single-phase detection circuit, FIG.
90 ° phase shifter 36, mixer 37, LPF 38
And the A / D converter 39 may be omitted.

The amount of phase shift by the phase shifter 29 is small for an object to be inspected in which metal to be described later is not mixed, and is smaller for an object to be detected in which metal to be detected is mixed. On the other hand, a larger value is set in advance.

As described above, the phase shifter 29, the phase shift amount setting means 30, and the detection circuit 31 are necessary components when an alternating magnetic field is used, and are omitted when a DC magnetic field is used. , The output of the amplifier 28 is directly input to the determination target value detection means 40.

The determination target value detection means 40 is provided by the entry sensor 2
6, the signal output from the detection circuit 31 is monitored for a certain period of time (until the test object passes through the magnetic field) after the detection of the entry of the test object into the magnetic field. Is detected as a determination target value for determining the presence or absence of metal.

If the detection circuit 31 is of the two-phase type, the maximum values Xm and Ym of the two detection outputs X and Y and the phase (X / Y) obtained from the detection outputs X and Y, respectively.
The maximum value φm of the arc tangent value of Y) is detected as the determination target value.

When the detection circuit 31 is of the single-phase type, the maximum value Xm of the detection output X is detected as a judgment target value.

When a DC magnetic field is used, the peak value Zm of the output signal Z of the amplifier 28 is detected as a judgment target value.

The judging means 41 includes a judging value detecting means 40
Is compared with a reference value set in advance by the reference value setting means 42 to determine the presence / absence of metal and output a determination result signal.

As described above, when the detection circuit 31 is of the two-phase type, the maximum value Xm and the reference value Xr, the maximum value Ym and the reference value Yr, and the maximum value φm and the reference value φr are compared. If one of them is larger than the reference value, a judgment signal indicating that there is metal is output, and if any one is equal to or less than the reference value, a judgment signal indicating that there is no metal is output.

When the detection circuit 31 is of a single-phase type, the maximum value Xm is compared with a reference value Xr, and when the maximum value Xm is larger than the reference value Xr, a judgment signal indicating the presence of metal is output. If the value is equal to or smaller than the value Xr, a determination signal indicating that there is no metal is output. When a DC magnetic field is used, the peak value Zm of the output signal of the amplifier 28 is compared with the reference value Zr.

The judgment result display 43 is for displaying the judgment result in the form of a lamp, characters, or the like.
When a determination result signal indicating that there is no metal is received from 1, a green lamp is lit, or a character "OK" is displayed. When a determination result signal indicating that there is metal is received, a red lamp is lit.
The character "NG" is displayed.

On the other hand, the influence value storage means 45 is
The determination target value when it is determined that there is no metal by 1 is
It is sequentially stored in an internal memory (not shown) as a value indicating the degree of influence of the test object itself on the magnetic field (hereinafter referred to as an influence value). In addition, you may store including the determination target value when it is determined that there is metal.

The noise level storage means 46 receives a signal from the ingress sensor 26 and outputs a signal output from the detection circuit 31 when the device under test does not exist in the magnetic field (when the detection circuit 31 is a two-phase type). In the case of a single-phase type, the signal X and Y, and in the case of a single-phase type, the peak level of the signal output from the amplifier 28 when the test object is not present in the magnetic field. Is stored in a memory (not shown) at predetermined timings as a noise level value.

The display control means 47 includes an influence value storage means 45
And the noise level value stored in the noise level storage means 46 are graphed and displayed on the display device 48 so that the temporal variation of the magnitude can be visually recognized.

The display control means 47 is a first display mode for displaying the storage values of the influence value storage means 45 and the noise level storage means 46 in a single bar graph so that the fluctuation tendency in a relatively short time can be recognized. An average value or a maximum value of a plurality of stored values is obtained so that a change tendency over a relatively long time can be recognized, and the average value or the maximum value is stored in the influence value storage means 45 and a second display mode in which the average value or the maximum value is displayed as one bar graph. A third display mode for automatically shifting from the first display mode to the second display mode in accordance with the number of affected values and the number of noise level values stored in the noise level storage means 46. The display is performed in the mode designated by the display switching means 49.

If a display device having a wide display area is used as the display device 48, it is possible to simultaneously display the graph of the influence value and the noise level value. And the noise level value can be displayed in a graph, and the one designated by the display switching means 49 is selectively displayed.

The display switching means 49 has operation keys (not shown), and the display control means 47 is operated by the key operation.
Switch the display mode and the content to be displayed.

Next, the operation of the metal detector will be described. Prior to the operation, a phase shift amount of the phase shifter 29 and a reference value of the determination means 41 are set using a good sample in which metal is not mixed and a defective sample in which metal of a known size is mixed. I do.

When the operation is started and the test object W on the transport path C passes through the magnetic field, the two receiving coils 24,
The voltage induced at 25 becomes unbalanced, the unbalanced component is detected by the detection circuit 31, and the determination target value is detected by the determination target value detection means 40 from the detection output,
In the judgment means 41, it is compared with a reference value.

As described above, when the DC magnetic field is used, the judgment target value is detected by the judgment target value detection means 40 from the unbalanced component, and is compared with the reference value by the judgment means 41.

Here, if the detected value to be determined is equal to or less than the reference value, it is determined that no metal is mixed in the inspection object W, and the determination result display 43 displays a message indicating that there is no metal. .

If the detected value to be determined is larger than the reference value, it is determined that metal is mixed in the inspection object W, and the determination result display 43 displays that metal is present. .

Similarly, every time the test object W passes through the magnetic field, the detection target value of the test object W is detected and determined. In this case, the determination target value is sequentially stored in the influence value storage unit 45 as an influence value on the magnetic field of the test object itself. The noise level value when the test object W is not present in the magnetic field is sequentially stored in the noise level storage means 46.

Here, for example, the detection circuit 31 is of a two-phase type, and the first display mode is designated to the display control means 47 and an instruction for displaying an influence value on one detection output X is given. Is performed, the display control means 47
For example, as shown in FIG.
Are displayed as bar graphs so that the change over time in the magnitude can be visually recognized.

When the display switching means 49 gives an instruction to display the influence value for the other detection output Y, the display control means 47 stores the influence value, for example, as shown in FIG. Influence value Ym stored in means 45
(1), Ym (2),... Are displayed as bar graphs so that the change with time of the size can be visually recognized.

When the display switching means 49 gives an instruction to display the influence value on the phase, the display control means 47 stores the influence value in the influence value storage means 45, for example, as shown in FIG. Influence values φm (1), φm
(2),... Are displayed in a line graph so that the change over time in size can be visually recognized.

When the display switching means 49 gives an instruction to display the noise level value of the detection output X,
The display control means 47 converts the noise level values Nx (1), Nx (2),... Stored in the noise level value storage means 46 over time, as shown in FIG. A bar graph is displayed so that various changes can be visually recognized, and the detection output Y
When the user gives an instruction to display the noise level value of FIG.
(E), the noise level values Ny (1), Ny (2),...
A bar graph is displayed so that the change with time of the size can be visually recognized.

From these displays, it is possible to grasp the influence on the magnetic field of the test object itself in which metal is not mixed and the fluctuation state of noise in a short time.

When, for example, one of the detection output X and the second display mode is designated by the display switching means 49, the display control means 47 controls the influence value Xm (1) stored in the influence value storage means 45. , Xm (2),... Are divided into k groups G (1), G (2),... In the order stored, and the maximum (or average) M of the influence values in each group is M
.., x (1), Mx (2),... are displayed as bar graphs, for example, as shown in FIG.

When the other detection output Y is designated in the second display mode, the display control means 47 sets the influence values Ym (1), Ym stored in the influence value storage means 45.
(2), ..., k groups G (1), G (2),
, And the maximum (or average) of the influence values My (1), My (2),... In each group are changed over time, for example, as shown in FIG. A bar graph is displayed so that the change can be visually recognized.

When the phase is designated in the second display mode, the display control means 47 sets the influence value storage means 45.
The influence values φm (1), φm (2),...
Are divided into groups G (1), G (2),..., The maximum (or average) Mφ (1) of the influence values in each group,
Mφ (2),..., For example, as shown in FIG.
A line graph is displayed so that a change with time of the size can be visually recognized.

When the noise level of the detection output X is designated in the second display mode, the display control means 47
The influence value Nx (1), N stored in the influence value storage means 45
x (2),... are stored in k groups G in the order in which they are stored.
(1), G (2),..., And the maximum (or average) influence value Mnx (1), Mnx (2),
Are displayed as a bar graph so that the change with time of the size can be visually recognized, for example, as shown in FIG.

When the noise level of the detection output Y is designated in the second display mode, the effect values Ny (1), Ny (2),... Stored in the effect value storage means 45 are stored. K groups G (1), G (2),...
, And the maximum value (or the average value) Mny (1), Mny (2),... Of the influence values in each group are changed over time as shown in, for example, FIG. Is displayed in a bar graph so that can be visually recognized.

From these displays, it is possible to grasp the influence on the magnetic field of the test object itself in which metal is not mixed and the fluctuation state of noise over a long period of time.

When the third display mode has been designated for the display control means 47, the influence value of the object to be inspected determined to be free of metal is a predetermined number j for one type.
Until the number reaches 500 (for example, 500), the influence value and the noise level value are graphically displayed in the first display mode, and after reaching the predetermined number j, the influence value and the noise level value are displayed in the second display mode. Is displayed as a graph.

The length of the graph that can be displayed on the screen of the display device 48 is limited by the number of dots in the width direction of the display device 48. For this reason, after the influence value and the noise level value corresponding to this limit are stored, the display control means 47 displays the graph with priority given to the newer stored value.

As described above, in the metal detector of the embodiment,
The fluctuation of the degree of influence of the test object on the magnetic field and the fluctuation of noise can be constantly monitored on the screen of the display device 48.

For this reason, the fact that the effect of the test object itself on the magnetic field or the noise level has increased is as follows.
It is possible to know before the erroneous determination of the presence of metal occurs frequently, and it is possible to prevent the erroneous determination beforehand by resetting the phase shift amount of the phase shifter 29 or the reference value of the determination means 41. In addition, it is possible to know that the influence of the test object itself on the magnetic field is decreasing, and accordingly, the phase shift amount of the phase shifter 29 and the reference value of the determination means 41 are increased so that the sensitivity to metal increases. The value can be reset, and the oversight of the minute metal can be prevented.

By comparing the change in the influence value with the change in the noise level, it is possible to determine whether the change in the influence value is caused by the change in the noise or the change in the degree of influence of the test object on the magnetic field. Can be grasped, and an erroneous adjustment operation need not be performed.

The metal detector 20 is graphically displayed on the display device 48 so that the influence of the test object itself on the magnetic field and the fluctuation of the noise level can be confirmed. However, the metal detector 20 'shown in FIG. As described above, based on the influence value stored in the influence value storage means 45 and the noise level value stored in the noise level storage means 46, detection conditions for detecting a change in the magnetic field due to the test object (in this case, The control unit 50 variably controls the phase shift amount of the phase shifter 29) and the reference value of the determination unit 41, so that the adjustment operation during operation can be performed in response to the influence of the test object on the magnetic field and the fluctuation of the noise level. Metal detection under the best conditions is always possible without performing.

That is, the control means 50 controls the phase shift amount setting means 3
0 and the initial phase shift amount φ 0 input from the reference value setting means 42 and the initial reference value R 0
Set each to 1.

The initial phase shift amount φ0 is such that, for example, the determination target value Za (influence value) when a sample in which metal is not mixed passes through the magnetic field is small, and the sample in which metal to be detected is mixed has a magnetic field. Determination target value Zb when passing
Is set to be large, and the initial reference value R0 is a determination target value Za for a sample in which no metal is mixed.
It is assumed that the threshold value is set to a value approximately in the middle of the determination reference value Zb for the sample mixed with the metal.

After the operation is started, the control means 50 detects the influence value sequentially stored in the influence value storage means 45 and the tendency of the fluctuation of the noise level value sequentially stored in the noise level storage means 46.

The detection of the fluctuation tendency is performed, for example, by determining the average value of a plurality of (M) consecutively stored influence values (which may be an average value of different stored values or a moving average value). It is sequentially calculated, and when the calculated average value continuously increases a plurality of times (N times), it is determined to be an increasing tendency, and when the average value continuously decreases a plurality of times (N times), it is determined to be a decreasing tendency. .

Similarly, the average value of a plurality of (M ′) consecutively stored noise levels is sequentially calculated. When the average value continuously increases a plurality of times (N ′ times), the average value increases. When the tendency and average value continuously decrease a plurality of times (N 'times), it is determined that the tendency is decreasing, and the average fluctuation amount is obtained.

The calculation of the average value of the influence value and the noise level value is performed so that the fluctuation tendency in substantially the same time zone is obtained. The calculation of the average value does not include the influence value of the test object determined to have metal.

Here, the control means 50 compares the variation tendency of the influence value with the variation tendency of the noise level, and determines whether there is a variation in the degree of influence on the magnetic field by the test object itself and whether the noise level varies. It is determined whether or not there is a change in the degree of influence of the test object itself on the magnetic field, and the amount of phase shift of the phase shifter 29 and the reference value of the determination means 41 are variably controlled to reduce the noise level. On the other hand, the reference value of the determination means 41 is variably controlled.

That is, when the influence value and the noise level are both increasing, and the fluctuation amounts of the two substantially correspond to each other, or
If both of them tend to decrease and the fluctuations of both correspond roughly, the degree of influence of the test object on the magnetic field has not changed, and the influence value has increased due to the increase or decrease of the noise level. It is determined that the value has increased or decreased, and the reference value is changed to a value that is substantially intermediate between the final average value of the influence values at this time and the determination target value Zb for the sample mixed with the metal.

If the fluctuation of the influence value is increasing and no fluctuation of the noise level is recognized, it is determined that the influence on the magnetic field of the test object itself is large, and the change of the magnetic field by the test object is determined. The phase shift amount of the phase shifter 29, which is a detection condition for detecting the phase shift, is variably controlled in a direction to suppress the tendency of the influence value to increase. If the increasing tendency of the influence value cannot be sufficiently suppressed by the variable control of the amount of phase shift, control is performed to increase the reference value in the same manner as described above.

Also, when the fluctuation of the noise level tends to decrease in the state where the fluctuation of the influence value is not recognized, it is determined that the influence of the test object itself on the magnetic field is large.
The phase shift amount of the phase shifter 29 is variably controlled so that the influence value decreases in accordance with the noise level decreasing tendency. When the influence value is reduced by this control, control is performed so as to lower the reference value accordingly.

When the influence value is decreasing and the noise level does not change, it is assumed that the degree of influence of the test object on the magnetic field is decreasing, and the influence value is adjusted in accordance with the decreasing tendency of the influence value. Control to lower the reference value.

Note that the reference value is varied with respect to the determination target value Z for the sample in which the metal is mixed.
Since the value lower than b becomes the upper limit value and the phase shift amount also has the upper limit value and the lower limit value, when the reference value and the phase shift amount reach these upper limit value and lower limit value, the control unit 50 issues an alarm. Output to notify that the control limit has been reached.

As described above, the detection condition for detecting the change in the magnetic field due to the object to be inspected and the reference value for determination are variably controlled in accordance with the change in the influence value and the change in the noise level, so that the best condition is always obtained. Can be used to detect metal, and erroneous determination due to a change in the degree of influence on the magnetic field or a change in the noise level due to the test object itself can be prevented.

When the detection condition and the reference value are automatically variably controlled as described above, the display function of the influence value and the noise level value can be omitted. Is performed in the same manner as in the above-described embodiment, the effect of suppressing the fluctuation of the influence value by the control unit 50 or the like is confirmed.
It is possible to check the noise generation factor and the like, and it can also be used as a guide when adjusting the control parameters of the control means 50.

[0089]

As described above, according to the first aspect of the present invention,
The metal detector sequentially stores the value to be determined as an influence value indicating the degree of influence of the test object itself on the magnetic field, and displays the value on a screen of a display device in a graph so that its variation with time can be identified. are doing.

For this reason, it is possible to easily grasp the tendency of the variation of the degree of influence of the test object itself on the magnetic field, to take appropriate measures before erroneous determination or the like due to the variation, and to always detect the metal under the best conditions. it can.

Further, in the metal detector according to the present invention, since the fluctuation of the noise level can be grasped together with the influence value, the metal detector can be based on the fluctuation of the degree of influence on the magnetic field of the test object itself and the fluctuation of the noise level. Appropriate measures can be taken before erroneous determinations or the like due to such fluctuations occur, and metal can always be detected under the best conditions.

Further, the metal detector according to claim 3 sequentially stores the value to be determined as an influence value indicating the degree of influence of the test object itself on the magnetic field, and based on the influence value, the magnetic field generated by the test object. Variably controls the detection condition for detecting the change in the threshold value or the reference value for determination.

For this reason, it is possible to prevent erroneous determination due to a change in the degree of influence on the magnetic field by the test object itself without performing an adjustment operation or the like during driving, and it is possible to always detect metal under the best conditions.

Further, in the metal detector according to the present invention, the noise level is sequentially stored together with the influence value, and the detection condition and the judgment condition for detecting the change of the magnetic field due to the test object based on the influence value and the noise level are determined. Since the reference value can be variably controlled, the influence on the magnetic field of the test object itself and the influence of noise can be distinguished, and more accurate control can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of an arrangement of a transmission coil and a reception coil according to the embodiment;

FIG. 3 is a block diagram illustrating a configuration example of a detection circuit.

FIG. 4 is an exemplary view showing a display example for explaining the operation of the embodiment;

FIG. 5 is a view showing a display example for explaining the operation of the embodiment;

FIG. 6 is a block diagram showing the configuration of another embodiment of the present invention.

FIG. 7 is a block diagram showing the configuration of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20, 20 'Metal detector 21 Magnetic field generating means 22 Signal generator 23 Transmitting coil 24, 25 Receiving coil 26 Ingress sensor 29 Phase shifter 30 Phase shift amount setting means 31 Detection circuit 40 Judgment value detecting means 41 Judging means 42 Reference Value setting means 43 Judgment result display 45 Influence value storage means 46 Noise level storage means 47 Display control means 48 Display device 49 Display switching means 50 Control means

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryuji Nozaki 5-10-27 Minamiazabu, Minato-ku, Tokyo Anritsu Corporation F-term (reference) 2G005 CA02

Claims (4)

[Claims] A magnetic field is generated in a passage of a test object, a change in a magnetic field caused by the test object passing through the magnetic field is detected, and a determination target value for determining the presence or absence of metal from the detection signal is determined. A metal detector for detecting and comparing the detected determination target value with a reference value to determine the presence or absence of metal in the test object, wherein the test target value of the test object is determined by the magnetic field of the test object itself. Value storage means for sequentially storing as an influence value indicating the degree of influence on a display device; and a screen of the display device so that the influence value stored in the influence value storage means can be identified by a change with time. And a display control means for displaying a graph. 2. The apparatus according to claim 1, further comprising noise level storage means for sequentially storing, as a noise level value, the level of the detection signal when the object to be inspected is not present in the magnetic field; 2. The metal detector according to claim 1, wherein the noise level value stored in the level storage means is graphically displayed on a screen of the display device so that a change with time can be identified. 3. A method for generating a magnetic field from a magnetic field generator in a path of a test object, detecting a change in a magnetic field caused by the test object passing through the magnetic field, and judging the presence or absence of metal from the detection signal. A metal detector for detecting a value to be determined and comparing the detected value to be determined with a reference value to determine the presence or absence of a metal in the object to be inspected. Influence value storage means for sequentially storing as an influence value indicating the degree of influence of the body itself on the magnetic field; and detection for detecting a change in the magnetic field due to the test object based on the influence value stored in the influence value storage means. A metal detector provided with control means for variably controlling a condition or a reference value for determination. 4. A noise level storage means for sequentially storing, as a noise level value, the level of the detection signal when the test object is not present in the magnetic field, wherein the control means is stored in the influence value storage means. And variably controlling a detection condition for detecting a change in a magnetic field due to the test object or a reference value for determination based on the influence value and the noise level value stored in the noise level storage means. 3. The metal detector according to 3.