JP2011145213A - System, device and method for detecting metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal detection system, a metal detection device and a metal detection method, for improving measurement accuracy for metal detection by increasing a magnetic changing rate caused by existence of a metal. <P>SOLUTION: The metal detection system 10 for detecting a metal includes a detection coil 11 arranged in a detection area, a capacitor 12 connected in series to the detection coil 11, and an ammeter 15 or a lock-in amplifier 16 for detecting a metal based on a magnitude change or a phase angle change in an impedance or a current of the detection coil 11 and the capacitor 12 with respect to a state where a current is made to flow into the detection coil 11 and the capacitor 12 with a frequency for resonating in series the detection coil 11 and the capacitor 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a system, apparatus, and method for detecting various metals.

  Conventionally, metal detection has been performed for various purposes. For example, there is buried object detection (or nondestructive inspection) for examining the presence of metal pipes, electric wires, reinforcing bars or the like embedded in a concrete body constituting a wall or floor of a building structure. In addition, there are metal detections for checking the presence of metal carried by visitors and visitors for security purposes in airports and buildings, or to prevent metal from being brought into the MRI room. Alternatively, in a food factory or the like, there is metal detection for confirming that a foreign object such as a metal piece is not mixed in food. An electromagnetic induction method is known as one principle for performing such metal detection.

  For example, in Patent Document 1, a measuring element 11 that measures a magnetic field at a measurement point P, a detection coil that generates a first magnetic field with respect to the measurement point P, and the detection coil are configured separately. Then, by generating a second magnetic field in the direction opposite to the first magnetic field with respect to the measurement point P, the combined magnetic field of the first magnetic field and the second magnetic field at the measurement point P is substantially zero. And a metal detector for detecting metal by measuring a magnetic field at the measurement point P with a pickup coil 11b. According to this metal detector, since it is possible to determine the presence or absence of metal in the measurement object, the position of the metal in the measurement object, the size of the metal, and whether the metal is a conductor or a magnetic body, Useful for metal detection. In particular, since the combined magnetic field at the measurement point is set to substantially zero, even if the output change is very small, it can be easily determined, a small magnetic field change can be captured, and a high S / N ratio can be detected.

JP 2009-186337 A

  However, in the metal detection device described in Patent Document 1, in order to make the combined magnetic field of the first magnetic field and the second magnetic field at the measurement point P substantially zero, the detection coil and the outer coil 13 are wound as designed. It is necessary to make a mechanical adjustment, such as configuring by a number, or installing the pickup coil 11b at the center position of the detection coil or the outer coil 13 without inclination. However, in practice, it is not easy to mechanically adjust the metal detection device to a desired state, and it is not easy to sufficiently perform initial adjustment of the composite magnetic field at the measurement point P. In the detection of fine metals such as, it has not always been easy to ensure desired measurement accuracy.

  The present invention has been made to solve the above-described problems, and by increasing the magnetic change rate due to the presence or absence of metal, the metal detection can improve the measurement accuracy of metal detection. It is an object to provide a system, a metal detection device, and a metal detection method.

  In order to solve the above-described problems and achieve the object, the metal detection system according to claim 1 is a system for detecting metal, and a detection coil disposed in a detection region, and the detection coil And a change in magnitude or phase angle of impedance or current of the detection coil and the capacitor with respect to a state in which current is passed through the detection coil and the capacitor at a frequency at which the detection coil and the capacitor are in series resonance. And a measuring means for detecting the metal based on the change of.

  A metal detection system according to a second aspect of the present invention is the metal detection system according to the first aspect, wherein the measurement means includes an impedance meter for measuring the impedance.

  A metal detection system according to a third aspect is the metal detection system according to the first or second aspect, wherein the detection coil is formed of a litz wire.

  The metal detection system according to claim 4 is the metal detection system according to any one of claims 1 to 3, wherein the measurement unit has a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. The iron as the metal is detected based on a change in magnitude or phase angle in the impedance or current with respect to a state in which current flows through the detection coil and capacitor.

  The metal detection system according to claim 5 is the metal detection system according to any one of claims 1 to 3, wherein the measurement means has a frequency exceeding about 100 kHz that causes the detection coil and the capacitor to resonate in series. The iron or copper as the metal is detected based on a change in magnitude or phase angle in the impedance or current with respect to a state in which current flows through the detection coil and capacitor.

  The metal detection system according to claim 6 is the metal detection system according to any one of claims 1 to 3, wherein the measurement unit has a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. Based on a change in magnitude or phase angle in the impedance or current with respect to a state in which current flows through the detection coil and capacitor, iron as the metal is detected, and the detection coil and the capacitor are caused to resonate in series. Based on a change in magnitude or phase angle in the impedance or current and a detection result of iron with a frequency of about 100 kHz or less with respect to a state in which current flows through these detection coils and capacitors at a frequency exceeding about 100 kHz. The copper as the metal is detected.

  A metal detection system according to a seventh aspect is the metal detection system according to the first aspect, wherein the measuring means includes an ammeter for measuring a current flowing through the detection coil and the capacitor.

  The metal detection device according to claim 8 is a device for detecting metal, a detection coil arranged in a detection region, a capacitor connected in series to the detection coil, the detection coil, and the Measuring means for detecting the metal based on a change in magnitude or phase angle in impedance or current of the detection coil and the capacitor with respect to a state in which current flows through the detection coil and the capacitor at a frequency at which the capacitor is series-resonated. With.

  The metal detection method according to claim 9, which is a method for detecting metal, a detection coil arrangement step of arranging a detection coil in a detection region, and a capacitor connection step of connecting a capacitor in series to the detection coil. And, based on a change in magnitude or phase angle in impedance or current of the detection coil and the capacitor with respect to a state in which current flows through the detection coil and the capacitor at a frequency at which the detection coil and the capacitor are series-resonated, And a measuring step for detecting the metal.

  The metal detection method according to claim 10 is the metal detection method according to claim 9, wherein in the measurement step, current is supplied to the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. The iron as the metal is detected on the basis of a change in magnitude or phase angle in the impedance or current with respect to a state in which a current flows.

  The metal detection method according to claim 11 is the metal detection method according to claim 9, wherein, in the measurement step, a current is passed through the detection coil and the capacitor at a frequency exceeding about 100 kHz that causes the detection coil and the capacitor to resonate in series. The iron or copper as the metal is detected on the basis of a change in magnitude or phase angle in the impedance or current with respect to a state in which a current flows.

  The metal detection method according to claim 12 is the metal detection method according to claim 9, wherein in the measurement step, a current is supplied to the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. A first measuring step for detecting iron as the metal based on a change in magnitude or phase angle in the impedance or current with respect to a state of flowing current, and after the first measuring step, A change in magnitude or phase angle in the impedance or current and a measurement result in the first measurement step with respect to a state in which current flows through the detection coil and the capacitor at a frequency exceeding about 100 kHz that causes the capacitor to resonate in series; And a second measurement step of detecting copper as the metal.

  According to the metal detection system according to claim 1, the metal detection device according to claim 8, or the metal detection method according to claim 9, the detection coil and the capacitor are made to resonate in series, thereby detecting the detection coil and the capacitor. Can be reduced to a value substantially equal to the resistance, and it becomes easy to capture a change in impedance and a change in current with respect to this value. In addition, by causing the detection coil and the capacitor to resonate in series, it is possible to change the rate of change in impedance by approximately the square of the change in inductance of the detection coil. From these things, it becomes possible to measure the change of the impedance and the change of the current due to the presence of the metal with a high SN ratio, and it is possible to improve the metal detection accuracy. Further, by measuring changes in impedance phase angle and current phase angle, it is possible to distinguish a plurality of types of metals such as iron and copper from each other. Furthermore, in order to adjust the zero point in this metal detection, it is only necessary to make an electrical adjustment in which the detection coil and the capacitor are in series resonance, and there is no need to perform a mechanical adjustment due to the configuration or arrangement of the detection coil. Therefore, the initial adjustment can be performed more easily and with high accuracy.

  According to the metal detection system of claim 2, the metal detection system can measure the impedance with an impedance meter, compared with a case where the current is measured using an oscillator, an amplifier, an ammeter, and a lock-in amplifier. Can be configured more simply and at a lower cost.

  According to the metal detection system of claim 3, by forming the detection coil with a litz wire, the inductance can be increased without increasing the resistance of the detection coil, specifically, the skin effect and proximity Since the resistance can be reduced and the Q value can be increased by suppressing the effect, the detection accuracy can be further increased.

  According to the metal detection system according to claim 4 or the metal detection method according to claim 10, the phase angle of the current flowing through the series resonance circuit is obtained by causing the detection coil and the capacitor to resonate in series at a frequency of about 100 kHz or less. Whether or not the metal is iron can be specified by determining whether or not the metal to be delayed (metal that advances the phase angle of impedance) is detected.

  According to the metal detection system according to claim 5 or the metal detection method according to claim 11, the phase angle of the current flowing through the series resonance circuit is obtained by causing the detection coil and the capacitor to resonate in series at a high frequency within a predetermined range. By determining whether or not the metal to be advanced (metal that delays the phase angle of impedance) is detected, it is possible to specify whether or not the metal is iron or copper. In particular, by causing the detection coil and the capacitor to resonate in series at a frequency exceeding about 100 kHz, it is possible to increase the rate of change in impedance and current when the metal is copper, and it is easy to identify the metal as copper. .

  According to the metal detection system according to claim 6 or the metal detection method according to claim 12, first, the detection coil and the capacitor are series-resonated at a frequency of about 100 kHz or less, so that the current flowing through the series resonance circuit is reduced. By determining whether or not a metal that delays the phase angle (metal that increases the phase angle of impedance) is detected, it is possible to specify whether or not the metal is iron. Next, it is determined whether or not a metal that advances the phase angle of the current flowing through the series resonant circuit (metal that delays the phase angle of the impedance) is detected by causing the detection coil and the capacitor to resonate in series at a frequency exceeding about 100 kHz. Thus, it can be specified whether the metal is iron or copper. In particular, by causing the detection coil and the capacitor to resonate in series at a frequency exceeding about 100 kHz, it is possible to increase the rate of change in impedance when the metal is copper, and it is easy to identify the metal as copper. Furthermore, by excluding the metal specified as iron in the first measurement from the metal specified as iron or copper in the second measurement, the metal detected in the second measurement can be specified as copper. it can. That is, by combining series resonance at a low frequency and series resonance at a high frequency, it becomes possible to detect iron and copper while distinguishing them from each other.

  According to the metal detection system of the seventh aspect, by measuring the current flowing through the detection coil and the capacitor with an ammeter, it is possible to measure the impedance change in the current and detect the metal.

It is a figure which shows the voltage change of a LCR series resonance circuit when using Q value as a parameter. It is a figure which shows the relationship between the absolute value of the impedance when using resonance, and the absolute value of the impedance when not using resonance. It is a figure which shows the relationship between the change rate of the impedance when using a resonance, and the change rate of the impedance when not using a resonance. It is a figure which shows an analysis model in order to analyze the relationship between the variation | change_quantity of an inductance, and a frequency. It is a figure which shows the analysis result by the analysis model of FIG. It is a schematic diagram which shows the metal detection system which concerns on Embodiment 1 of this invention with a measuring object. It is sectional drawing of the detection coil of FIG. It is a schematic diagram which shows the metal detection system which concerns on Embodiment 2 with a measuring object. It is a figure which shows the test body used for experiment, (a) is a top view, (b) is a side view. It is a figure which shows the measurement result of an impedance. It is a figure which shows the measurement result of the phase angle of an impedance. It is a figure which shows the measurement result of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 5.01 kHz. It is a figure which shows the measurement result of the phase difference of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 5.01kHz. It is a figure which shows the measurement result of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 43.34kHz. It is a figure which shows the measurement result of the phase difference of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 43.34kHz. It is a figure which shows the measurement result of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 816.9kHz. It is a figure which shows the measurement result of the phase difference of an impedance, and is a figure which shows the measurement result using the detection coil of resonance frequency = 816.9kHz. It is a figure which shows collectively the measurement result of FIGS. 12-17.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, [I] the basic concept common to each embodiment was explained, then [II] the specific contents of each embodiment were explained, and [III] finally, a modification to each embodiment was explained. To do. However, the present invention is not limited to each embodiment.

[I] Basic concept common to the embodiments First, the basic concept common to the embodiments will be described. The metal detection system, the metal detection device, and the metal detection method according to each embodiment are for detecting metal.

(metal)
The type and structure of the metal to be detected are arbitrary, and when receiving a magnetic field from a detection coil described later, the impedance of a series resonance circuit constituted by the detection coil and a capacitor described later or the current flowing through the series resonance circuit Including metals of all materials and shapes that can change the size and phase angle of, for example, metals containing iron or copper, configured as metal pipes, wires, rebars, dangerous goods, or metal pieces Including things. The existence form of this metal is also arbitrary, for example, when the metal is arranged exposed in the detection target space, when it is carried by a human body, or when it is buried inside another object Including. Examples of the object in which the metal is embedded include a concrete body constituting a wall, a floor, a pillar, or a ceiling of a building structure or a civil engineering structure.

(Summary of features)
One of the features of the metal detection system, the metal detection device, and the metal detection method according to each embodiment is that a detection coil and a capacitor are roughly connected in series to form a series resonance circuit. The point is that metal is detected based on a change in magnitude or phase angle in impedance or current of the detection coil and capacitor with respect to a state in which current flows through the detection coil and capacitor at a frequency at which series resonance occurs. In this way, by detecting the series resonance state as the initial state, the impedance of the detection coil and the capacitor can be reduced to a value substantially equal to the resistance, and the change in impedance and the change in current with respect to this value can be captured. Becomes easy. In addition, a change in magnitude or phase angle in impedance or current due to metal can be increased, and metal can be detected with high accuracy.

(Detection principle)
Hereinafter, the detection principle of the metal according to each embodiment found by the present inventor will be described. In general, an impedance Z of an LCR series resonant circuit configured by connecting an inductance L, a capacitance C, and a resistor R in series with each other is expressed by the following equation (1). Note that ω is an angular frequency.

Here, when the inductance L changes by a change amount δ, that is, when the changed inductance L ′ = L (1 + δ), the impedance Z ′ after the change is expressed by the following equation (2). Here, Q is a value generally used as a value indicating the sharpness of the resonance peak of the series resonance circuit, and Q = ωL / R.

Since the impedance Z ₀ at the time of resonance of the LCR series resonance circuit is equal to the resistance R, the ratio between the impedance Z ′ after the change and the impedance Z ₀ at the time of resonance is expressed by the following equation (3), and the absolute value thereof is expressed by the following equation ( 4). The phase angle of the current flowing through the LCR series resonance circuit is expressed by the following equation (5).

  From the equation (4), it can be seen that the change δ of the inductance L is amplified Q times in the absolute value of the impedance. Similarly, from the equation (5), it can be seen that the change δ of the inductance L is amplified Q times also in the phase angle of the current flowing through the LCR series resonance circuit.

In order to examine the influence of this Q value, the voltage change of the LCR series resonance circuit when this Q value is used as a parameter is shown in FIG. In FIG. 1, the horizontal axis represents the change δ of the inductance L, and the vertical axis represents the voltage amount Z / Z ₀ (absolute) in the case of impedance Z with respect to voltage Z ₀ (absolute value) in the case of impedance Z ₀ at resonance. Data), and data in three cases of Q value = 10, 50, 86 are plotted. As is apparent from FIG. 1, the voltage change amount Z / Z ₀ (absolute value) with respect to the change amount δ of the inductance L increases as the Q value increases. Therefore, it can be seen that by configuring the metal detection system so as to increase the Q value, the change δ of the inductance L can be amplified and detected.

(Detection principle-Reduction of absolute value of impedance by using resonance)
Next, the effect of using resonance is examined by comparing the case where resonance is used with the case where resonance is not used (when only inductance L and resistor R are connected in series). First, it is examined how the absolute value of the impedance is affected when resonance is used and when resonance is not used.

When resonance is not used, the impedance Z is expressed by the following equation (6).

Here, when the inductance L changes by a change amount δ, that is, when the changed inductance L ′ = L (1 + δ), the changed impedance Z ′ is expressed by the following equation (7).

Further, the ratio between the impedance Z ′ after the change and the resistance R is expressed by the following equation (8), and the absolute value thereof is expressed by the following equation (9). Further, the phase angle of the current is expressed by the following equation (10).

  Here, FIG. 2 shows the relationship between the absolute value of the impedance when the resonance shown by the equation (4) is used and the absolute value of the impedance when the resonance shown by the equation (9) is not used. In FIG. 2, the horizontal axis represents the change δ of the inductance L, and the vertical axis represents the absolute value of the impedance. Here, Q value = 86. As apparent from FIG. 2, the impedance component ωL becomes dominant with respect to the absolute value of the impedance when the resonance is not used, and the value of the resistance R can be almost ignored. Therefore, the Q value (= ωL / R = Here approximately 86). On the other hand, the absolute value of the impedance when using resonance is the resistance R. Therefore, it can be seen that the absolute value of the impedance when using the resonance is about 1 / Q of the absolute value of the impedance when not using the resonance.

(Principle of detection-Increasing the rate of change of impedance by using resonance)
Furthermore, it will be examined how the rate of change of impedance is affected when resonance is used and when resonance is not used. First, from the equation (4), the change rate ΔZ ′ of the impedance Z ′ becomes the following equation (11).

On the other hand, when resonance is not used, the absolute value of the ratio between the impedance Z ′ and the resistance R after the change is expressed by the following equation (12), and the rate of change ΔZ ′ of the impedance Z ′ is expressed by the following equation (13).

Comparing equation (11) and equation (13), the change rate ΔZ ′ of impedance Z ′ when using resonance is equal to the change rate ΔZ ′ of impedance Z ′ when not using resonance. 1/2) δ ² Q ² It can be seen that the rate of change ΔZ ′ can be increased by utilizing resonance, and that the rate of change ΔZ ′ can be increased as the Q value is increased.

  In order to further examine this point, FIG. 3 shows the relationship between the impedance change rate ΔZ ′ when the resonance is used and the impedance change rate ΔZ ′ when the resonance is not used. In FIG. 3, the horizontal axis represents the change δ of the inductance L, and the vertical axis represents the impedance change rate ΔZ ′ (%). Here, Q value = 86. As is apparent from FIG. 3, the impedance change rate ΔZ ′ when the resonance is not used is substantially linear. However, when the resonance is used, the impedance change rate ΔZ ′ is approximately δ. It can be seen that the square increases to a quadratic curve.

(Sensing Principle-Conclusion on Impedance Change)
Here, as described above with reference to FIG. 2, it can be said that by utilizing resonance, the absolute value of the impedance can be reduced to approximately 1 / Q, and the change δ of the inductance L can be easily captured. . Also, from the above description regarding FIG. 3, it can be seen that the rate of change in impedance can be changed by the square of δ by using resonance. In particular, it is clear that these effects increase as the Q value increases. Therefore, in the metal detection system and the metal detection method according to each embodiment, based on this detection principle, it is possible to use resonance and adopt a configuration and procedure that can increase the Q value as much as possible. The detection accuracy is improved.

(Detection principle-change in phase angle)
Further, as a result of various experiments described later, the inventor of the present application has found a relationship between the phase angle of the current flowing through the series resonant circuit, the impedance change rate, the resonant frequency, and the metal type. That is, when the resonance frequency is a low frequency within a predetermined range (hereinafter referred to as the first resonance frequency; for example, the predetermined range = a frequency of about 100 kHz or less), and the metal is iron, the current flowing through the series resonance circuit It has been found that the phase angle of is delayed (however, the phase angle of impedance is advanced). This is considered to be due to an increase in inductance L due to the influence of the magnetization of the reinforcing bar. Further, it has been found that when the metal is copper, the phase angle of the current flowing through the series resonant circuit is advanced (however, the phase angle of the impedance is delayed). This is presumably because the conductivity of copper is higher than that of iron and the influence of magnetization is close to 0, so that a large amount of eddy current flows and a reaction magnetic field is generated. On the other hand, when the resonance frequency is a high frequency within a predetermined range (hereinafter, the second resonance frequency; for example, the predetermined range = a frequency exceeding about 100 kHz), the metal is iron and the metal is copper. In both cases, it was found that the phase angle of the current flowing through the series resonant circuit advances (however, the phase angle of impedance is delayed). Furthermore, it has been found that the rate of change in impedance when the resonance frequency is the second resonance frequency is greater when the metal is copper than when the resonance frequency is the first resonance frequency.

The result of analyzing the relationship between the change δ of the inductance L and the frequency is shown. FIG. 4 is a diagram showing an analysis model. This analysis model is a 1/4 region analysis model considering symmetry with respect to a test body 30 of FIG. 9 described later. However, the cylindrical CD tube 32 having a diameter of 36 mm of the test body 30 is replaced with a rectangular tube CD tube 32 having a side of 36 mm, and a circular detection coil 21 to be described later is a square detection having a side of 116 mm. The coil 21 was replaced. With this detection coil, magnetic fields having three frequencies of 5 kHz, 40 kHz, and 800 kHz are applied, and in the case of only the concrete body 31, copper (4 mm square with a 14 mm ² copper wire replaced inside the CD tube 32 is used. Inductance L is compared between the case where three copper wires are inserted and the case where iron (a 13 mm square bar with a diameter of 13 mm is replaced. The amount of change δ was determined. The electrical conductivity of concrete, copper wire, and rebar was 10 ⁻⁵ , 5 × 10 ⁷ , and 2 × 10 ⁶ S / m, respectively, and the relative permeability of the rebar was 1,000. FIG. 5 is a diagram showing the analysis results, in which the horizontal axis represents the magnetic field frequency and the vertical axis represents the change δ of the inductance L. As shown in FIG. 5, when the metal is iron and the magnetic field frequency is 100 kHz or less, the phase angle of the current flowing through the series resonant circuit is delayed (however, the impedance phase angle is advanced). The change δ becomes positive. When the magnetic field frequency is 100 kHz or more, the phase angle of the current flowing through the series resonance circuit advances (however, the impedance phase angle is delayed), and the change δ of the inductance L becomes negative. .

  From these things, when there is a possibility that both types of metals of iron and copper exist in the detection region, it is possible to detect iron and copper while distinguishing them by performing the following measurement. I understand that. That is, first, detection is performed with the resonance frequency as the first resonance frequency, and when a metal that delays the phase angle of the current flowing through the series resonance circuit (metal that advances the phase angle of the impedance) is detected, the metal Can be identified as iron. Next, detection is performed using the resonance frequency as the second resonance frequency, and metal is detected, and the detected metal is in a position different from the metal detected using the resonance frequency as the first resonance frequency. In some cases, the metal can be identified as copper.

[II] Specific Contents of Each Embodiment Next, specific contents of each embodiment of the metal detection system and the metal detection method for detecting metal based on the detection principle described above will be described.

[Embodiment 1]
First, the first embodiment will be described. In the first embodiment, the change in impedance is measured using an ammeter. First, after describing the configuration of the metal detection system according to the first embodiment, a metal detection method will be described.

(Constitution)
FIG. 6 is a schematic diagram showing the metal detection system 10 according to the first embodiment together with the measurement target. An embedded object 2 (here, a cable wire inserted into the inside of a CD tube) is embedded in the concrete body 1 to be measured, and a metal detection system 10 is disposed in the vicinity of the concrete body 1. The metal detection system 10 is configured by connecting a detection coil 11, a capacitor 12, an oscillator 13, an amplifier 14, an ammeter 15, and a lock-in amplifier 16 through lines 17 to 19 as illustrated.

  The detection coil 11 is a solenoid coil formed by winding an electric wire in a cylindrical shape with a constant diameter. By passing the current output from the amplifier 14 through the detection coil 11, A magnetic field is formed along the axial direction of the detection coil 11. Here, the detection coil 11 is arranged such that the axial direction of the detection coil 11 is along the direction from the surface of the concrete body 1 to the position where the embedded object 2 can exist (the Z direction shown in FIG. 6; hereinafter, the detection direction). Place.

  Here, as explained in the detection principle, it is preferable to increase the Q value as much as possible. That is, since the Q value (= ωL / R) as described above, it is possible to increase the inductance L by increasing the number of turns of the detection coil 11, but when the number of turns of the detection coil 11 is increased. Does not contribute to increasing the Q value because the resistance R also increases. Therefore, the inventor of the present application paid attention to the material of the electric wire constituting the detection coil 11. That is, by configuring the detection coil 11 using an electric wire having a small resistance R (for example, a litz wire (enamel stranded wire)), the skin effect and the proximity effect are suppressed, the resistance R is lowered, and the Q value is increased. It was decided to. Further, the detection coil 11 is configured by a multi-layer winding to suppress mutual induction and increase the inductance L.

  FIG. 7 shows a cross-sectional view of the detection coil 11 configured as described above. FIG. 7 is a cross-sectional view of the state in which the detection coil 11 is cut along a cut surface along the axis thereof. For example, a two-layer winding is made up of a litz wire 11a constituting an inner layer and a litz wire 11b constituting an outer layer. It is configured as a coil. A spacer 11c is sandwiched between the litz wire 11a and the litz wire 11b, and the litz wire 11a and the litz wire 11b are arranged at a predetermined interval (about 3 mm in FIG. 8). In each layer, the litz wires 11a adjacent to each other and the litz wires 11b adjacent to each other are arranged at a predetermined interval (about 3 mm in FIG. 8).

  The capacitor 12 is a compensation capacitor that forms a series resonance circuit together with the detection coil 11 by being connected in series to the detection coil 11.

  The oscillator 13 is a reference current source that outputs a current having a predetermined resonance frequency (the above-described first resonance frequency and second resonance frequency) for resonating the series resonance circuit. The amplifier 14 amplifies the current output from the oscillator 13 and outputs the amplified current to the series resonance circuit. The ammeter 15 is connected to a line 17 extending from the series resonance circuit to the amplifier 14, and measures and outputs a current value flowing through the line 17. A current output from the ammeter 15 is input to the lock-in amplifier 16 as a measurement signal, and a current output from the oscillator 13 is input as a reference signal. Of the currents output from the ammeter 15, the oscillator A voltage value having a frequency component equal to the current output from 13 is output. As the line 17 that connects the detection coil 11 and the amplifier 14 to each other, it is preferable to use a twisted conductor in order to reduce the influence of the magnetic field generated by the line 17 itself as much as possible. The oscillator 13, the amplifier 14, the ammeter 15 and the lock-in amplifier 16 constitute a measuring means in the claims.

  Here, the relationship between the inductance Lc of the detection coil 11 or the capacitance Cp of the capacitor 12 and the resonance frequency will be described. As the resonance frequency, it is preferable to use a resonance frequency corresponding to the type of metal that may exist in the detection region. For example, when the metal that can exist in the detection region is a metal having a relatively high relative permeability such as “iron”, the impedance change due to the influence of magnetization also at the first resonance frequency (low frequency) described above. It is easy to detect the metal based on the rate. On the other hand, when the metal that can exist in the detection region is a metal having a relatively small electrical resistance such as “copper”, the eddy current is not sufficiently generated at a low frequency. It is necessary to generate and detect a sufficient eddy current at (frequency).

Here, the resonance frequency f is expressed by the following equation (14), where Lc is the inductance of the detection coil 11 and Cp is the capacitance of the capacitor 12.

  For this reason, in order to utilize the resonance by the desired first resonance frequency or the second resonance frequency, the inductance Lc of the detection coil 11 or the detection coil 11 so as to match the first resonance frequency or the second resonance frequency. It is necessary to set the capacitance Cp of the capacitor 12. Therefore, in the first embodiment, a plurality of detection coils 11 having different inductances Lc and a plurality of capacitors 12 having different capacitances Cp are prepared in advance, and the detection coils meeting a desired resonance frequency and other conditions are prepared. 11 and capacitor 12 are selectively used.

(Metal detection method)
Next, a metal detection method performed using the metal detection system 10 configured as described above will be described. In this method, initial adjustment is performed first. Specifically, the metal detection system 10 is configured by using the detection coil 11 having the inductance Lc matching the first frequency and the capacitor 12 having the capacitance Cp, and the oscillator without the metal around the detection coil 11 13 is activated to pass a current at the first resonance frequency, and it is confirmed that the output (voltage value) of the lock-in amplifier 16 is an initial value (theoretically, a value corresponding to the resistance component). Here, it is not necessary to perform mechanical adjustment of the pickup coil or the like as in the prior art, and the initial adjustment can be performed simply by electrically setting the frequency of the oscillator 13, so that the initial adjustment is easy.

  Next, the detection coil 11 is moved to the detection area. For example, the detection coil 11 is disposed so as to be close to the surface of the concrete body 1 disposed in the detection region or in contact with the surface of the concrete body 1, and the detection coil 11 is arranged along the surface of the concrete body 1. Move sequentially to multiple measurement positions. When a metal exists in the magnetic field formed by the detection coil 11 at each measurement position, an eddy current is generated in the metal (here, a cable wire inserted into the CD tube) by electromagnetic induction, and the magnetic field is generated by the eddy current. As a result, the impedance of the series resonant circuit changes. Since this change in impedance can be measured as a voltage change in the lock-in amplifier 16, it is possible to detect metal in the detection region based on this measurement result. In particular, since the Q value is increased, the rate of change in impedance can be increased, and detection with a high S / N ratio can be performed.

  Further, when a metal exists in the magnetic field formed by the detection coil 11, the phase angle of the current of the series resonance circuit changes depending on the type of the metal. This change in phase angle can be measured by the lock-in amplifier 16 as a change based on the phase angle of the reference signal. Here, when it is found that metal is present in the detection region based on the voltage change and the phase angle is delayed, it can be specified that the metal is iron (first measurement step). If the phase angle is advanced at this point, the metal can be identified as copper. However, in the experiments so far, the change in the impedance of copper due to the first resonance frequency is very small. Therefore, it is not always easy to detect.

  Therefore, the metal detection system 10 is reconfigured by using the detection coil 11 having the inductance Lc that matches the second frequency and the capacitor 12 having the capacitance Cp, and the oscillator 13 is operated in a state where there is no metal around the detection coil 11. It is activated and a current is passed at the second resonance frequency, and it is confirmed that the output (voltage value) of the lock-in amplifier 16 is an initial value (theoretically, a value corresponding to a resistance component).

  Then, similarly to the case of the first measurement step, the detection coil 11 is moved to the detection region, and the metal in the detection region is detected based on the impedance change of the series resonance circuit. Also at this time, since the Q value is increased, the rate of change in impedance can be increased, and detection with a high S / N ratio can be performed. In particular, since the change in the impedance of copper is greater at the second resonance frequency than at the first resonance frequency, copper can be detected relatively easily. Moreover, it can specify that the metal except the iron already detected at the 1st measurement process among the metals detected here is copper (2nd measurement process).

  The determination of whether the metal is iron or copper as described above can be made, for example, while the user can visually determine the output of the lock-in amplifier 16, but can also be made automatically. For example, as a part of the measurement means, a determination unit (not shown) (comprising a CPU and software) is provided, the output of the lock-in amplifier 16 is input to the determination unit, and the position where metal is detected in the first measurement step is determined. Automatically determined as the iron detection position, the position where the metal was excluded in the first measurement process from the position where the metal was detected in the second measurement process is automatically determined as the copper detection position, and this determination result is displayed You may make it make it equal. At this time, each time the user moves the detection coil, the position information may be input via an arbitrary input means by absolute coordinates or relative coordinates based on an arbitrary position, or the detection coil. The position information may be automatically acquired from the means (high-precision GPS or distance measuring means using a wheel as described in a modified example described later).

(Effect of Embodiment 1)
As described above, according to the first embodiment, by causing the detection coil 11 and the capacitor 12 to resonate in series, the impedance of the detection coil 11 and the capacitor 12 can be reduced to a value substantially equal to the resistance, and the impedance changes with respect to this value. It becomes easy to capture the minute. In addition, by causing the detection coil 11 and the capacitor 12 to resonate in series, the impedance change rate can be changed by approximately the square of the change in the inductance of the detection coil 11. From these things, it becomes possible to measure a change in impedance with a high S / N ratio, and it is possible to improve metal detection accuracy. Further, by measuring the change in the phase angle of the current, it is possible to distinguish a plurality of types of metals such as iron and copper from each other. Furthermore, in order to adjust the zero point in the metal detection, it is only necessary to perform electrical adjustment in which the detection coil 11 and the capacitor 12 are in series resonance, and it is necessary to perform mechanical adjustment by arrangement of the detection coil 11 or the like. Therefore, the initial adjustment can be performed more easily and with high accuracy.

  Further, by forming the detection coil 11 with a litz wire, the inductance can be increased without increasing the resistance of the detection coil 11, the skin effect and the proximity effect are suppressed, the resistance R is lowered, and the Q value is reduced. Therefore, the detection accuracy can be further increased. Furthermore, by increasing the inductance L by winding the coil in multiple layers, the Q value can be increased, and the detection accuracy can be further increased.

  Further, by making the detection coil 11 and the capacitor 12 in series resonance at a frequency of about 100 kHz or less, it is determined whether or not a metal that delays the phase angle of the current flowing through the series resonance circuit is detected, so that the metal is made of iron. Whether or not there is can be specified.

  Further, by making the detection coil 11 and the capacitor 12 in series resonance at a frequency exceeding about 100 kHz, it is determined whether or not the metal that advances the phase angle of the current flowing through the series resonance circuit has been detected. Or it can be specified whether it is copper. In particular, by causing the detection coil 11 and the capacitor 12 to resonate in series at a high frequency within a predetermined range, it is possible to increase the rate of change in impedance when the metal is copper, and it is easy to identify the metal as copper. .

  Further, by measuring the current flowing through the detection coil 11 and the capacitor 12 with the ammeter 15, it is possible to measure the impedance change in this current and detect the metal.

  First, by detecting whether a metal that delays the phase angle of the current flowing through the series resonance circuit is detected by series resonance of the detection coil 11 and the capacitor 12 at a frequency of about 100 kHz or less, the metal is detected. Whether or not is iron can be specified. Next, the detection coil 11 and the capacitor 12 are series-resonated at a frequency exceeding about 100 kHz, thereby determining whether or not a metal that advances the phase angle of the current flowing through the series resonance circuit is detected. Or it can be specified whether it is copper. In particular, by causing the detection coil 11 and the capacitor 12 to resonate in series at a frequency exceeding about 100 kHz, it is possible to increase the rate of change in impedance when the metal is copper, and it is easy to identify the metal as copper. . Furthermore, the metal detected in the second measurement is specified as copper by excluding the metal specified as iron in the first measurement from the metal specified as iron or copper in the second measurement. Can do. That is, by combining series resonance at a low frequency and series resonance at a high frequency, it becomes possible to detect iron and copper while distinguishing them from each other.

[Embodiment 2]
First, the second embodiment will be described. In the second embodiment, a change in impedance is directly measured. However, configurations and procedures that are not particularly described in the second embodiment are the same as those in the first embodiment, and the same configurations and procedures as those in the first embodiment are the same as those used in the first embodiment as necessary. The description is abbreviate | omitted by attaching | subjecting the same code | symbol. First, after describing the configuration of the metal detection system according to the second embodiment, a metal detection method will be described.

(Constitution)
FIG. 8 is a schematic diagram showing the metal detection system 20 according to the second embodiment together with a measurement target. The metal detection system 20 is configured by connecting a detection coil 21, a capacitor 22, and an impedance meter 23 via lines 24 to 28 as shown in the figure. The detection coil 21 and the capacitor 22 can be configured in the same manner as the detection coil 11 and the capacitor 12 in FIG.

  The impedance meter (LCR meter) 23 outputs a current having a predetermined resonance frequency (the above-described first resonance frequency and second resonance frequency) for resonating the series resonance circuit to the series resonance circuit. Further, the impedance meter 23 receives the current output from the series resonance circuit, and measures the impedance and phase angle of this current. Thus, by directly measuring the change in impedance with the impedance meter 23, the oscillator 13, the amplifier 14, the ammeter 15, and the lock-in amplifier 16 in the first embodiment are replaced with a single impedance meter 23. Compared to the metal detection system 10 in the first embodiment, the metal detection system 20 can be configured more simply and at a lower cost. This impedance meter 23 constitutes the measuring means in the claims. The coaxial cable 26 is used to connect the impedance meter 23 and the series resonant circuit. However, in order to increase the Q value, a normal cable line may be used instead of the coaxial cable 26.

(Metal detection method)
Next, a metal detection method performed using the metal detection system 20 configured as described above will be described. In this method, initial adjustment is performed first. Specifically, the metal detection system 20 is configured by using the detection coil 21 having the inductance Lc that matches the first frequency and the capacitor 22 having the capacitance Cp, and the oscillator without the metal around the detection coil 21 13 is activated to pass a current at the first resonance frequency, and the impedance measured by the impedance meter 23 at this time (theoretically, a value corresponding to the resistance component) is set as an initial value.

  Next, the detection coil 21 is moved to the detection area. At this time, when a metal is present in the magnetic field formed by the detection coil 21, the impedance of the series resonance circuit changes from the initial value, and this impedance change can be measured by the impedance meter 23. Based on this, it becomes possible to detect the metal in the detection region. In particular, since the Q value is increased, the rate of change in impedance can be increased, and detection with a high S / N ratio can be performed. Moreover, when the phase angle measured by impedance is advanced, it can identify that the said metal is iron (1st measurement process).

  Next, the metal detection system 20 is reconfigured by using the detection coil 21 having the inductance Lc that matches the second frequency and the capacitor 22 having the capacitance Cp, and the oscillator 13 is operated in a state where there is no metal around the detection coil 21. The current is passed at the second resonance frequency after starting, and the impedance (theoretically, a value corresponding to the resistance component) measured by the impedance meter 23 at this time is set as an initial value.

  Next, similarly to the case of the first measurement step, the detection coil 21 is moved to the detection region, and the metal in the detection region is detected based on the impedance change of the series resonance circuit. Also at this time, since the Q value is increased, the rate of change in impedance can be increased, and detection with a high S / N ratio can be performed. In particular, since the change in the impedance of copper is greater at the second resonance frequency than at the first resonance frequency, copper can be detected relatively easily. Moreover, it can specify that the metal except the iron already detected at the 1st measurement process among the metals detected here is copper (2nd measurement process).

(Experimental result)
Next, the result of the experiment by the present inventor conducted using the metal detection system 20 according to the second embodiment will be described. FIG. 9 is a view showing a test body 30 used in the experiment, where (a) is a plan view and (b) is a side view. As shown in FIG. 9, with respect to a concrete body 31 having a width of 300 mm, a length of 800 mm, and a thickness of 85 mm, a cylindrical shape having a diameter of 36 mm along the width direction at a substantially central position in the length direction and the thickness direction. A CD tube 32 was placed. Inside the CD tube 32, a cable wire 33 (three copper wires having a diameter of 8 mm ² ) or a reinforcing bar 34 (one reinforcing rod having a diameter of 12 mm) was selectively inserted.

First, a three-dimensional magnetic field analysis was performed using the test body 30 of FIG. 9 as a model, and the SN ratio of the inductance was obtained. Here, assuming that the magnetic flux is applied at 795 kHz by the detection coil 21, the electrical conductivity of the concrete body 31, the cable wire 33, and the reinforcing bar 34 is set to 1 × 10 ⁻⁵ , 5 × 10 ⁷ , and 2 × 10 ⁶ S, respectively. / M, and the relative permeability of iron was 1,000. As a result, the S / N ratio of the inductance is 0.047%, the cable wire 33 is present, and the cable wire 33 is not present when the rebar 34 is present and when there is no rebar 34 (only with a CD tube) ( In the case of only a CD tube), the SN ratio of the inductance was 0.261%, and since the SN ratio was low in all cases, it was confirmed that measurement was difficult by magnetic field measurement using a conventional pickup coil.

  Next, the measurement result when metal detection using the metal detection system 20 of FIG. 8 was performed on the test body 30 of FIG. 9 was predicted by numerical calculation. Here, the detection coil 21 is configured as a 10-turn coil having a diameter of 115 mm using a litz wire, and the capacitor 22 is set to 1700 pF. In this case, since ω = 2πf = 2 × 3.1415 × 795 kHz, L = 30 μH, and R = 2Ω, the Q value = ωL / R = about 75.

The Q value = about 86 and the equation (4), the S / N ratio of the inductance when the reinforcing bar 34 is present and when the reinforcing bar 34 is not present = 0.047% = 0.00047, the case where the cable line 33 is present, and the cable line When Z / Z ₀ (absolute value) is calculated from the S / N ratio of inductance in the absence of 33 = 0.261% = 0.00261, the rebar 34 is 1.0006 and the cable 33 is 1.018, respectively. It was predicted that the S / N ratio could be increased to 0.06% and 1.8%. That is, it has been theoretically verified that the rate of change in impedance can be greatly increased by increasing the Q value.

  In particular, in this case, the initial value of the impedance can be lowered from 200Ω to 2Ω by configuring the series resonance circuit using the capacitor 22, and it is easy to detect a minute change in impedance. The theoretical resonance frequency is about 884 kHz based on the equation (14) and the capacitance Cp = 1700 pF of the capacitor 22 and the reactance Lc = 30 μH of the detection coil 21. It can be confirmed that it substantially coincides with 795 kHz applied to the coil 21.

  Thereafter, metal detection using the metal detection system 20 of FIG. 8 was performed on the test body 30 of FIG. 9. Specifically, the detection coil 21 is moved from the measurement position P1 (position 200 mm on the left side in the figure from the center position in the length direction) to the measurement position P2 (from the center position in the length direction to the right side in the figure) indicated by an imaginary line in FIG. The impedance and phase angle were measured at each measurement position while sequentially moving the measurement positions at regular intervals (20 mm pitch) until the position reached 200 mm.

  FIG. 10 is a diagram illustrating impedance measurement results, in which the horizontal axis represents the measurement position X and the vertical axis represents the impedance Z. As shown in FIG. 10, the ratio of the impedance of the reinforcing bar 34 and the ratio of the impedance of the cable wire 33 with respect to the area where there is no metal is 9.1% and 2.8%, respectively. Ratio. In particular, the ratio of the cable line 33 = 2.8% is almost the same as the above-described SN ratio of 1.8% predicted from the equation (1) using the Q value = 75, and the result as designed is obtained. It was.

  FIG. 11 is a diagram illustrating the measurement result of the phase angle of the impedance, where the horizontal axis indicates the measurement position and the vertical axis indicates the phase angle. As shown in FIG. 11, the ratio of the phase angle of the reinforcing bar and the phase angle of the cable wire with respect to the area where there is no metal is 5.7% and 3.6%, respectively, and the rate of change of the phase angle is high. It was possible to measure by the S / N ratio.

Furthermore, the influence of the difference in the resonance frequency was tested by measuring the test body 30 in FIG. 9 using a plurality of detection coils 21 having different resonance frequencies. Here, a total of three types of detection coils 21 of resonance frequency = 5.01 kHz (low frequency), 43.34 kHz (medium frequency), and 816.9 kHz (high frequency) were switched and used. The measurement objects include iron (the above-mentioned reinforcing bar 34 inserted into the CD tube), copper (three 8 mm ² copper wires inserted into the CD tube), and copper (14 mm diameter inserted into the CD tube). ² copper wires x 3).

  12, 14, and 16 are diagrams illustrating impedance measurement results, and FIGS. 13, 15, and 17 are diagrams illustrating measurement results of changes in the phase angle of the impedance (phase difference) with respect to the phase angle of the resonance frequency, FIGS. 12 and 13 show the measurement results using the detection coil 21 having a resonance frequency of 5.01 kHz, FIGS. 14 and 15 show the measurement results using the detection coil 21 of 43.34 kHz, and FIGS. 16 and 17 show the detection coils of 816.9 kHz. It is a figure which shows the measurement result using 21. FIG. 18 collectively shows the results of these experiments.

  As shown in FIGS. 12 to 18, when the measurement object is iron, the SN ratio decreases when the resonance frequency increases, and when the measurement object is copper, the SN ratio decreases when the resonance frequency increases. It was confirmed that the ratio was improved. Also, when the object to be measured is iron, when the resonance frequency is low, the impedance phase difference is positive (although the impedance phase is advanced), the resonance frequency is high. In this case, it was confirmed that the phase difference of the impedance was negative (the phase of the impedance was delayed). Further, when the object to be measured was copper, it was confirmed that the impedance phase difference was negative (impedance phase was delayed) at any resonance frequency.

(Effect of Embodiment 2)
As described above, according to the second embodiment, in addition to the same effects as those of the first embodiment, the impedance or the phase angle is measured by the impedance meter 23, so that the oscillator 13, the amplifier 14, the ammeter 15, and the lock-in Compared to the case where the current is measured using the amplifier 16, the metal detection system 20 can be configured more simply and at a lower cost.

[III] Modifications to Each Embodiment While each embodiment according to the present invention has been described above, the specific configuration and means of the present invention are the same as the technical idea of each invention described in the claims. Modifications and improvements can be arbitrarily made within the range. Hereinafter, such a modification will be described.

(About problems to be solved and effects of the invention)
First, the problems to be solved by the invention and the effects of the invention are not limited to the above contents, and may vary depending on the implementation environment of the invention and the details of the configuration, and only a part of the problems described above. May be solved, or only some of the effects described above may be achieved. Furthermore, according to the present invention, problems not described above may be solved or effects not described above may be achieved.

(Resonance frequency)
As the resonance frequency, in addition to the two types of frequencies such as the first resonance frequency and the second resonance frequency described above, a further resonance frequency may be set.

(About measurement order)
In each of the above embodiments, iron is first detected at a low frequency and then copper is detected at a high frequency, but this measurement order may be reversed. That is, the position of iron or copper is first identified by performing detection at a high frequency, and then the position of iron is identified by performing detection at a low frequency, and this iron position and the first identified iron Alternatively, the copper position may be specified from the copper position.

(About metal detection system configuration)
As described above, when using a plurality of resonance frequencies such as the first resonance frequency and the second resonance frequency, the plurality of detection coils 11 and 21 having different inductances and the plurality of capacitors 12 and 22 having different capacitances are provided. Prepare and combine them with each other. In this case, a plurality of detection coils 11 and 21 and a plurality of capacitors 12 and 22 are incorporated in the metal detection systems 10 and 20 in advance, and the detection coils 11 and 21 matched with a desired resonance frequency using a switching means such as a switch. The capacitors 12 and 22 may be selected.

  Further, further improvements can be applied to the actual configuration of the metal detection systems 10 and 20. For example, when the measurement is performed at a plurality of measurement positions as in the above-described experiment, the detection coils 11 and 21 are easily moved to each of the plurality of measurement positions. The detection coils 11 and 21 may be moved to the respective measurement positions by loading the metal detection systems 10 and 20 including the power supply 21 and the power source and moving the carriage. At this time, for example, a distance measuring means for measuring the moving distance of the carriage based on the rotation speed of the wheel of the carriage is provided, and the positions of the detection coils 11 and 21 are determined based on the moving distance measured by the distance measuring means. You may decide. Also, the carriage is provided with a display unit for displaying the measurement result of the measuring means such as the impedance meter 23, and the position of the metal is monitored by moving the carriage while observing the measurement result displayed on the display unit. Also good. Further, the carriage is provided with storage means for storing the measurement results of the measurement means such as the impedance meter 23, and the storage means stores the measurement results in an arbitrary storage medium such as a magnetic card, and the storage medium is taken out and externally stored. You may make it usable for the input of the measurement result to an apparatus.

  In addition, as long as measurement is performed based on changes in impedance and phase angle with respect to the initial value set at the resonance frequency, various methods can be used as a determination method and output form of the measurement result. For example, a threshold value is set for the change in impedance or phase angle with respect to the initial value, and when an impedance or phase angle change exceeding the threshold value is measured, an alarm sound or an indicator lamp is used to output a metal. The user may be notified of the fact that is detected.

(About the configuration of the metal detector)
Moreover, you may comprise the metal detection system 10 demonstrated so far as a metal detection apparatus. For example, an oscillator 13, an amplifier 14, an ammeter 15, a lock-in amplifier 16, and circuits that perform the functions of the lines 18 and 19 are integrally housed inside the housing, and the detection coil 11 is placed outside the housing. Alternatively, the capacitor 12 may be replaced and connected to the oscillator 13 or the like via the line 17. With such an integrated configuration, it is possible to more easily perform detection work at a construction site or the like. Moreover, although the metal detection system 20 demonstrated so far is demonstrated as a metal detection system, since it comprises only the impedance meter 23 as a measurement means and is comprised simply, it thinks that it comprises a metal detection apparatus. Also good.

DESCRIPTION OF SYMBOLS 1 Concrete body 2 Embedded object 10, 20 Metal detection system 11, 21 Detection coil 11a, 11b Litz wire 11c Spacer 12, 22 Capacitor 13 Oscillator 14 Amplifier 15 Ammeter 16 Lock-in amplifier 17-19, 24-28 Line 23 Impedance meter 30 Test body 31 Concrete body 32 CD pipe 33 Cable line 34 Reinforcing bar

Claims (12)

A system for detecting metal,
A detection coil arranged in the detection region;
A capacitor connected in series to the sensing coil;
Based on a change in magnitude or phase angle in impedance or current of the detection coil and the capacitor with respect to a state in which current flows through the detection coil and the capacitor at a frequency at which the detection coil and the capacitor are in series resonance, the metal Measuring means for detecting,
A metal detection system comprising: The measuring means includes an impedance meter for measuring the impedance.
The metal detection system according to claim 1. The detection coil was formed of litz wire.
The metal detection system according to claim 1 or 2. The measuring means is based on a change in magnitude or phase angle in the impedance or current with respect to a state in which a current is passed through the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. Detecting iron as the metal,
The metal detection system as described in any one of Claim 1 to 3. The measuring means is based on a change in magnitude or phase angle in the impedance or current with respect to a state in which a current is passed through the detection coil and the capacitor at a frequency exceeding about 100 kHz that causes the detection coil and the capacitor to resonate in series. Detecting iron or copper as the metal,
The metal detection system as described in any one of Claim 1 to 3. The measuring means is based on a change in magnitude or phase angle in the impedance or current with respect to a state in which a current is passed through the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. The change in magnitude in the impedance or current with respect to a state in which current is passed through the detection coil and the capacitor at a frequency exceeding about 100 kHz that detects iron as the metal and causes the detection coil and the capacitor to resonate in series. Detecting copper as the metal based on the change in phase angle and the detection result of iron at a frequency of about 100 kHz or less,
The metal detection system as described in any one of Claim 1 to 3. The measurement means includes an ammeter for measuring a current flowing through the detection coil and the capacitor.
The metal detection system according to claim 1. A device for detecting metal,
A detection coil arranged in the detection region;
A capacitor connected in series to the sensing coil;
Based on a change in magnitude or phase angle in impedance or current of the detection coil and the capacitor with respect to a state in which current flows through the detection coil and the capacitor at a frequency at which the detection coil and the capacitor are in series resonance, the metal Measuring means for detecting,
A metal detection device comprising: A method for detecting metal,
A detection coil arrangement step of arranging a detection coil in the detection region;
A capacitor connection step of connecting a capacitor in series to the detection coil;
Based on a change in magnitude or phase angle in impedance or current of the detection coil and the capacitor with respect to a state in which current flows through the detection coil and the capacitor at a frequency at which the detection coil and the capacitor are in series resonance, the metal Measuring process to detect,
Metal detection method including. In the measurement step, based on a change in magnitude or phase angle in the impedance or current with respect to a state in which current flows through the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. Detecting iron as the metal,
The metal detection method according to claim 9. In the measurement step, based on a change in magnitude or phase angle in the impedance or current with respect to a state in which current flows through the detection coil and the capacitor at a frequency exceeding about 100 kHz that causes the detection coil and the capacitor to resonate in series. Detecting iron or copper as the metal,
The metal detection method according to claim 9. In the measurement step,
As the metal based on a change in magnitude or phase angle in the impedance or current with respect to a state in which a current is passed through the detection coil and the capacitor at a frequency of about 100 kHz or less that causes the detection coil and the capacitor to resonate in series. A first measurement step of detecting iron of
After the first measurement step, a change in magnitude or phase angle of the impedance or current with respect to a state in which current flows through the detection coil and the capacitor at a frequency exceeding about 100 kHz that causes the detection coil and the capacitor to resonate in series. Based on the change and the measurement result of the first measurement step, a second measurement step of detecting copper as the metal is performed.
The metal detection method according to claim 9.

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