JPH0894306A - Method for detection of metal - Google Patents

Abstract

PURPOSE: To dispense with zero adjustment, to suppress a noise, to reduce a distance to a detection conductor and to realize highly accurate detection by a method wherein an auxiliary coil of which size or position is different from that of a main excitation coil is provided and a condition for canceling a magnetic field of a detection conductor is obtained based on a relative operation of the main excitation and auxiliary coils. CONSTITUTION: A main excitation coil 1 and an auxiliary coil 2 are incorporated on an identical center axis having a distance αand each of the coils 1, 2 is driven by using respective driving circuits 5, 6 each current is controlled by a driving current control circuit 7. The respective driving currents each is in a pulse wave generate magnetic fields of which magnetic poles are different from each other and simultaneously applied thereto. The magnetic field is detected by a magnetic field detection device 3 to be amplified by an amplifier 4. The amplifier 4 comprises a mask circuit and cuts the magnetic field due to the residual currents of the coils 1, 2. The control circuit 7 controls such that the output of the amplifier 4 becomes zero (a field of a detection conductor becomes zero), then a ratio of the currents of the driving circuits 5, 6 is obtained by a current ratio detector 8 so that the value is converted to a distant to the detection conductor by a linearizer 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a highly sensitive metal detector, which can detect a conductor in an invisible portion and can measure not only the presence or absence of a detector conductor but also the distance and size. Since it does not require zero adjustment and has high sensitivity, it can be used as an industrial proximity switch, a non-contact distance sensor, a vehicle detector, a film thickness meter, and a three-dimensional non-contact position detector.

[0002]

2. Description of the Related Art As a method for detecting metal, a change in magnetic field,
Some of them utilize electromagnetic waves, ultrasonic waves, X-rays, etc., and each has its own characteristics. The one using the electromagnetic wave is the one using the radar system and the one using the change of the equivalent impedance of the detection coil due to the change of the induced current and the magnetic permeability. The radar system has a drawback in that the cost of the device is high and that when detecting a buried object, it is affected by geology and water content.

The method of detecting a detecting conductor by utilizing the fact that the induced current and the magnetic permeability change depending on the detecting conductor has a characteristic that it is relatively unaffected by the geology when the signal frequency for detection is lowered, and it is buried in the ground. It is advantageous for detecting objects. The method of utilizing the change in the equivalent impedance of the detection coil is generally to connect two coils differentially or to increase the sensitivity by a bridge circuit, and the sensitivity and directivity are not sufficient, and even the detection conductor It was impossible to find the distance.

As a method for measuring the distance of a conductor, as disclosed in Japanese Patent Application Publication No. Sho 49-9388, a conductor is connected to a detecting conductor, and an electric current is directly applied to the conductor. There are methods such as measuring the distance of the conductor, but there is no specific method to flow the current to the detection conductor in a non-contact manner without affecting the measurement.Even if the current is directly passed, the value depends on the shape of the detection conductor. When the distance was changed or the detection distance was increased, it was difficult to detect the difference in the magnetic field with respect to the distance, and the error was increased.

Further, in the conventional method, the output basically changes due to the change of the constant of the detection coil and the like, so that when the sensitivity is forcibly increased, zero adjustment is always required or a special temperature correction circuit is required. However, there were many problems even for industrial use. Furthermore, increasing the sensitivity of the detector makes it more susceptible to external noise, and when detecting reinforcing bars in road buried objects or concrete in houses, commercial frequencies leaking from electric wires such as underground wires and indoor wiring. In addition, there is a defect that a magnetic field or an electric field due to this harmonic is also received at the same time to cause a malfunction, or when the coil is moved, the magnetic field may be felt to cause a malfunction.

[0006]

As described above, in the conventional detection method, the zero point drift due to the fluctuation of the constants of the exciting coil and the detecting coil has been a major obstacle in increasing the detection sensitivity. In addition, there is a drawback that it will be affected by the magnetic field due to alternating current such as power cables, and if it moves the detection coil, it will malfunction due to the influence of the earth's magnetism. Solving this problem is a sensitive metal detector with high sensitivity. It was a challenge to obtain.

In order to solve these drawbacks, an exciting coil is used to apply an induced current to the detection conductor, and by utilizing the difference between the time constant of the excitation coil and the time constant of the detection conductor, only the signal returned from the detection conductor is detected. The present applicant has already proposed a method of selectively detecting, and in principle, a constant change of the exciting coil or the detecting coil does not affect the drift. However, the magnitude of the detection signal by this method changes with two parameters of the size and distance of the detecting conductor even when the materials of the conductors are the same, and it is impossible to independently obtain the distance and the magnitude.

The present invention is intended to measure the distance to the detection conductor and to estimate the size of the detection conductor from the relationship between the distance and the intensity of the signal returned from the detection conductor. further,
Not only does the detector output the presence / absence of a conductor, but also the method of outputting the distance eliminates the need for zero adjustment, and suppresses signals returned from areas other than the desired detection range to reduce measurement errors when there are multiple conductors. It is what

[0009]

[Means for Solving the Problem] In order to solve such a problem, an auxiliary coil having a different size or position is provided outside the main exciting coil, and a specific distance is obtained by the interaction with the magnetic field of the auxiliary coil. The condition for canceling the magnetic field applied to the detecting conductor in (1) or the condition for equalizing the magnetic fields by both coils is obtained, and the distance of the detecting conductor is known from this condition. If this canceling condition is performed by feedback, the problem of the zero point shift of the detector can be solved, external common-mode noise can be suppressed, and many problems can be solved at the same time. Moreover, it is possible to cancel the return signal from an unnecessary range by the same principle.

[0010]

When the exciting current is passed through the exciting coil to generate the pulse magnetic field, the current also flows through the detecting conductor in the magnetic field by induction. During a period in which a current flows in the exciting coil, a current called an induced current that is substantially proportional to the current flowing in the exciting coil also flows in the detection conductor. When the current flowing in the exciting coil is rapidly cut off, the current flowing in the detecting conductor becomes Te = Le / Re, where the equivalent inductance of the current loop flowing in the detecting conductor is Le and the equivalent resistance is Re. Decays at.

Therefore, when the current cutoff time of the exciting coil is cut off in a time sufficiently shorter than that of Te, and the energy remaining in the exciting coil is sufficiently attenuated and then received by the detecting coil, it flows into the detecting conductor. It becomes possible to selectively detect only the magnetic field generated by the current to detect the presence of the detecting conductor.

Therefore, when the mask circuit that cuts off the operation of the receiver by the switch circuit is set so as not to receive the signal during the excitation and the period when the energy remains in the exciting coil, the signal entering the receiver is transmitted from the detection conductor. Only weak signals can be received without saturation even with a highly sensitive receiver. By this method, by increasing the exciting current and increasing the sensitivity of the receiver, it is possible to significantly increase the sensitivity as compared with the conventional balanced type.

Here, a coil B is provided in a shape different from that of the exciting coil A or at a different position, and a current is passed through the coil B in synchronism with the exciting coil A, and its direction and amount are adjusted to make a target detecting conductor. It is possible to make the mutual magnetic field at the position of zero. Since the condition for making this magnetic field zero is determined by the ampere-turn of the exciting coil A and the ampere-turn and the position of the exciting coil B, the position of the detection conductor can be determined from this condition.

As a simplest example, as shown in FIG. 1, a current I1 is passed through a coil 1 having a radius a1 and a number of turns N1, and the center axis of this coil is set as an origin to a distance d, and the center axis is made equal to a radius a2. When the coil 2 having the number of turns N2 is placed and the current I2 in the opposite direction is passed, the magnetic field H on the central axis at the distance x from the origin is given by the equation (1) of the equation 1. In this equation, the first item on the right side is the magnetic field H1 by the coil 1 and the second item is the magnetic field H2 by the coil 2. Figure 1 shows each magnetic field
Becomes Distance X from the origin where the magnetic field H becomes zero on the central axis
As for 0, the value of X0 at which the magnetic flux becomes zero is obtained by the equation (3) of the equation 1 when the value of k is the equation (2) of the equation 1.

[0015]

[Equation 1]

Therefore, if the exciting current flowing through each coil is adjusted to arbitrarily set the value of k and the condition for the return magnetic field from the detection conductor to become zero is obtained, the value of k is expressed by the equation (3) of Equation 1. To obtain the distance X0, and by fixing the coil radii a1 and a2 and the winding ratio under this condition, the current ratios flowing in the respective windings can also be obtained.

FIG. 1 shows a radius a1 of 5 cm and a radius a2 of 10.
It shows the relationship between the distance from the origin on the central axis, the magnetic field, and the difference (absolute value) between the respective magnetic fields when the central axes of cm are arranged on the same plane. A coil with radius a1 is 100 ampere turns and a coil with radius a2 is 35 amps.
It is the result of the simulation when excited by 5.6 ampere turns. A coil having a large diameter has a characteristic that the magnetic field is less attenuated with respect to the distance than a coil having a small diameter, and as a result, the two magnetic fields become equal and a point where the magnetic field strength values intersect is generated. In FIG. 1, the point is 30 cm from the origin. The present invention utilizes the fact that when the ampere-turn of each exciting coil is controlled so that the magnetic field of the detecting conductor becomes zero, the return signal from the detecting conductor also becomes zero. It tries to find the distance.

This operation can be performed manually, but if the value of k is automatically changed by the output of the detected magnetic field strength so that the input of the detector is always zero, the feedback conductor automatically detects it. The value of k is set under the condition that the average magnetic field of is zero. The distance to the detection conductor can be obtained from the value of k at this time. The detection distance X0 can be obtained from the equation (3) of Equation 1, but it is also possible to obtain the relationship between k and the detection distance X0 by an experimental value and obtain X0 from k by regression, or from table data using memory. .

In this method, the main coil A and the auxiliary coil B are
Since electric currents that flow in opposite directions to each other are applied to the detection conductor, the magnetic field applied to the detection conductor, such as the combined magnetic field shown in FIG. 1, is extremely small in the vicinity of the detection distance, and the detection sensitivity is lowered. . As a method to eliminate this drawback,
An exciting current is passed through the main coil A at the excitation time T1, a mask period T2 is taken, and a return signal from the detection conductor due to the excitation of the main coil A is received during the reception period T3.
Then, the auxiliary coil B is excited so that the polarity of the received signal is opposite to that of the auxiliary coil B. The mask period T5 is taken again and the signal from the detection conductor due to the excitation of the auxiliary coil B is received at T6. Here, when the signal of T3 and the signal of T6 are differentially amplified and fed back so as to change the value of k so that the output amplified by the synchronous amplifier becomes zero, the equation (3) of Formula 1 is automatically obtained. K is set as the condition.

Under this condition, the absolute value of the magnetic field produced by the exciting coil A and the absolute value of the magnetic field produced by the exciting coil B are equal in the vicinity of the detection conductor, and the mutual polarities differ depending on the characteristics of the synchronous amplifier, and usually have opposite polarities. Moreover, since the respective magnetic fields do not cancel each other due to the time lag,
Not only can the sensitivity be significantly increased compared to the case where both coils are excited at the same time as described above, but common-mode noise such as commercial frequency detected by the magnetic field detector and random noise are also affected by the characteristics of the synchronous amplifier. Significantly suppressed.

When the two coils are arranged in the same plane, the detection distance has a characteristic that the detection distance greatly changes even with a very small change of the ampere-turn ratio when the detection distance becomes large. If the coils are not placed in the same plane but are spaced apart from each other by d on the central axis, the linearity of the change of the distance with respect to the ratio of ampere turns can be increased and the detection accuracy can be increased.

However, the characteristics of the ampere-turn ratio and the distance largely change depending on the method of arranging the coils with each other, so that it is necessary to take an optimum arrangement. In this case, the present invention can be implemented with the coil arrangements shown in FIGS. 2, 3, and 4, but the detection distance is narrow and the ampere-turn ratio (N
1I2 / N2I2) has a complicated detection distance characteristic and sometimes has two types of detection distance for one ampere-turn ratio, which is an inconvenient characteristic for automatic control.

As shown in FIG. 5, when a coil having a large size is arranged on the opposite side with respect to the detection direction, a coil arranging method which does not cause such a problem is such that the distance between the coils is increased so as to increase the distance between the coils. The linearity of turn ratio and detection distance increases. FIG. 6 shows the combined magnetic field due to the mutual coils with respect to the distance in this case, which shows that the detection distance can be freely adjusted by the coil interval d even with the same ampere-turn ratio. Therefore, it is possible to measure the distance to the detection conductor by changing the coil distance d instead of changing the current flowing through the coil, and relatively good results can be obtained even when the coil diameters are the same.

The main coil A is used for the purpose of eliminating the influence of interfering conductors other than the detection target, which are located off the central axis of the main coil.
And an auxiliary coil B for making the central axes equal, and the magnetic field detector DT1 is attached so that the central axis direction has the maximum sensitivity. Further, a canceling coil C is provided so as to be orthogonal to the central axes of the main coil A and the auxiliary coil B, and a canceling current is passed through the canceling coil C in synchronism with the exciting currents of these coils. A magnetic field detector DT2 having the maximum sensitivity is placed in the direction of the central axis of the signal and this signal is amplified by an amplifier having a similar mask period. When the main coil and the auxiliary coil are made to have the same timing and an exciting current is passed through the coil C under the condition that the signal received by the magnetic field detector DT2 is minimized, interference occurs in directions other than the central axis of the main coil A. The influence of the signal returned from the detection conductor can be eliminated, and the measurement error can be prevented by preventing the returned signal from the disturbing conductor around the detection conductor from reaching the detector DT1.

In this method, it is impossible to cancel the influence of the interfering conductor on the same plane as the canceling coil due to the directivity of the coil, but the canceling coil and the magnetic field detector DT.
2 is rotated about the axis of the main coil to obtain the best condition, or the centers are made equal to each other, and the canceling coil D and the magnetic field detector DT3 are added to the surface orthogonal to the surface of the canceling coil C. It is also possible to obtain a cancellation effect in all directions. The magnetic field generated from each cancellation coil is always zero on the central axis of the main coil A and does not affect the error in distance measurement. These two canceling coils can be switched depending on the direction, or the ratio of the currents flowing through the respective coils can be changed to obtain a canceling effect with the combined magnetic field. If the number of canceling coils and magnetic field detectors is increased, a plurality of disturbing conductors can be obtained. The effect of can be removed.

Further, in order to remove the influence of the disturbing conductor on the back surface of the main coil on the central axis of the main coil, a canceling coil is provided in a position parallel to the surface of the main coil and close to the detecting conductor, and the current of this coil is increased. It is possible to remove the influence of the disturbing conductor behind the main coil by adjusting the, but the magnetic field generated by the canceling coil on this surface contains a component that makes the center axis equal to the main coil and affects the detection distance. , This correction is necessary, and it is effective when removing the influence of the disturbing conductor in a fixed position.

[0027]

EXAMPLES Examples will be described with reference to the drawings.
In FIG. 7, one excitation coil A and two excitation coils B are placed at a distance d with their central axes equal, and a drive current control circuit 7 controls the current value of the drive circuit A 5.
Driving circuit B 6 drives each exciting coil. The drive current is driven in a pulsed waveform, and when the invention is carried out, the currents which generate magnetic fields having mutually different polarities are simultaneously driven, and when the invention is carried out, the outputs of the amplifiers have opposite polarities. The exciting coils are alternately driven with a polarity that generates a magnetic field.

The amplifier 4 is an amplifier having a function of blocking a signal by a mask circuit during the excitation of the exciting coil and when a current remains in the exciting coil. The amplifier 4 amplifies the output of the magnetic field detector 3 and The magnetic field due to the induced current flowing in the detection conductor due to the coupling with is detected. This amplifier amplifies the input signal only in the unmasked period in the case of claim 1, and in the case of claim 2, assuming that the signal induced by the exciting coil A is positive, the signal induced by the exciting coil B is negative and the difference is obtained. Dynamic amplification. At this time, a high-pass filter may be inserted before differential amplification to remove components below the repetition frequency and prevent low-frequency noise. Of course, for these functions, the output of the magnetic field detector may be converted into digital data by the AD converter, and the difference between the respective signals may be obtained by digital processing.

The magnetic field detector 3 has a simple coil detector and can be shared with one of the exciting coils. However, a magnetic detecting element such as a Hall element, a magnetoresistive element, a quadrature fluxgate sensor or an SQUID is used. Can achieve similar results. The sensitivity of this detecting element is arranged so as to have the maximum sensitivity to the magnetic field in the central axis direction of the exciting coil. The magnetic field detector 3 outputs an absolute value with respect to the polarity of the magnetic field, and when the direction cannot be detected, it is necessary to detect the polarity by applying a DC or AC magnetic bias to the detection element. Is.

Drive current control circuit 4 and drive current control circuit 5
Controls manually or automatically so that the output of the amplifier 4 becomes zero. In the case of automatic control, this operation is
Controlling to perform the back operation makes it possible to realize a stable and easy-to-handle metal detector. In this case, one of the driving current values can be fixed and the other exciting current can be made variable, and the ratio of the ampere-turn of each coil is controlled so that the average magnetic field of the detection conductor becomes zero or the same. To control the ampere turn of each coil. The drive current value of the exciting coil only needs to be able to control the current immediately before it is cut off, and the same purpose can be achieved by controlling the voltage applied to the exciting coil and the pulse width. At this time, the distance from the exciting coil to the detecting conductor can be obtained by the equation (3) of Equation 1 or an experimental value.

The value of k shown in the equation (2) of the equation 1 is determined by the current ratio I1 / I2 flowing in each coil when the diameter of the coil and the number of turns are fixed. The current ratio detector 7 is a circuit that detects the ratio I1 / I2 of the current values flowing in the respective drive coils. As a specific example, the current flowing in each drive coil is detected by a current detector such as a resistor and converted into a voltage, and this peak value is sampled and held,
In addition to the multiplier / divider, the output of each ratio is obtained. The multiplier / divider feeds back from the output of the operational amplifier to the input by the multiplier and adds a signal to the other input of the multiplier,
Further, there is a method of adding the other input signal to the operational amplifier through a series resistor. Of course, the values obtained by detecting the respective currents may be added to the AD converter, converted into digital values, and calculated by the microprocessor.
Further, when controlling the current of the drive coil by the voltage applied to the coil, it is possible to obtain the distance by this voltage ratio instead of detecting the current value.
If the denominator of equation (2) is fixed, it can be replaced with a simple amplifier, and the current ratio detector can be simplified. The arrangement of the coils shown in FIG. 5 makes it possible to detect a wide distance by merely fixing the current value of the coil having a large outer diameter and changing the exciting current of the inner coil corresponding to the numerator.

The linearizer 9 uses the equation (3) of the equation 1 or
It is a circuit that converts the current ratio of each drive coil into a distance from the experimental value. When a microprocessor is used for signal processing, the microprocessor calculates the equation (3) and displays the result on the display 9, or refers to the relation between the current ratio and the detection distance as table data. ,
The distance may be displayed from this result. Further, when the meter using the pointer is used as the display device, the linearizer can be omitted by making the scale of the meter a non-linear characteristic.

The crystal oscillator 11, the frequency divider 12, and the timing generator 13 frequency-divide the accurate clock signal to determine the accurate timing of the excitation signal and the mask signal of the amplifier.
This synchronous signal is also obtained at the synchronous amplifier.

When used not as a metal detector but as a position detector for conductors such as metals, the target object is placed at a position where the output of the receiver becomes zero due to the mutual magnetic fields of the exciting coils, and the output of the receiver is set. The position deviation and direction of the target object can be output from the voltage and its polarity. In this case, the combination of the exciting coil and the magnetic field detector is arranged orthogonally to each other, and the outputs of them can be combined to output the displacement and the direction of the three-dimensional position of the target object, thus providing a non-contact three-dimensional position detector. It becomes possible to use.

Further, in order to remove the influence of the disturbing conductors around the detector, a canceling coil C is provided so as to be orthogonal to the central axis of the exciting coil 1, and the canceling coil C is synchronized with the exciting currents of these coils. Then, a current for canceling is passed, and the coil C and the magnetic field detector DT2 having the maximum sensitivity are placed in the central axis direction. When the excitation current is passed through the coil C with the timings of the main coil and the auxiliary coil being equalized, and the current is passed through the canceling coil under the condition that the signal received by the magnetic field detector DT2 becomes the minimum, the other than the central axis of the main coil A It is possible to eliminate the influence of the return signal from the interference detection conductor in the direction of, and to prevent the measurement error due to the interference conductor around the detection conductor.

In this method, it is impossible to cancel the influence of the disturbing conductor on the same plane as the canceling coil due to the directivity of the coil, but the canceling coil and the magnetic field detector DT.
2 is rotated about the axis of the main coil to obtain the best condition, or the centers are made equal to each other, and the canceling coil D and the magnetic field detector DT3 are added to the surface orthogonal to the surface of the canceling coil C. It is also possible to obtain a canceling effect in all directions, and the magnetic field generated from this canceling coil is always zero on the central axis of the main coil A and does not affect the error in distance measurement. These two canceling coils can be switched depending on the direction, or the ratio of the currents flowing through the respective coils can be changed to obtain a canceling effect with the combined magnetic field. If the number of canceling coils and magnetic field detectors is increased, a plurality of disturbing conductors can be obtained. The effect of can be removed.

Further, in order to remove the influence of the disturbing conductor on the back surface of the main coil on the central axis of the main coil, a canceling coil is provided at a position parallel to the surface of the main coil and close to the detecting conductor, and the current of this coil is changed. Although it is possible to remove the influence of the disturbing conductor behind the main coil by the adjustment method,
The magnetic field generated by the canceling coil on this surface contains a component that makes the center axis equal to that of the main coil, and this correction is necessary because it affects the detection distance.This is effective when removing the effect of the disturbing conductor at a fixed position. Become.

The simplest way to eliminate the influence of disturbing conductors in the vicinity of the magnetic flux passing through the coil by the canceling coil is to simplify the circuit by sharing the canceling coil with the magnetic field detector. Prepare an operational amplifier with a frequency characteristic that responds sufficiently to the excitation pulse, insert a cancellation coil between this input and output, and insert a series resistor that detects the coil current between the input and the common terminal. In this method, the operational amplifier operates so that the current flowing through the coil is always zero, so that the magnetic flux passing through the coil is always zero. If the response of the operational amplifier is poor, it can be synchronized with the excitation pulse, and a more reliable effect can be obtained by canceling with a switch and releasing or short-circuiting the coil.

The embodiment of FIG. 1 is an example in which an analog amplifier is used as the amplifier 4, but for the purpose of digitally processing this portion, the received signal is converted into digital data by an AD converter, and the received signal of T3 is received. The same purpose can be achieved by digitally subtracting the received signals at T6 and T6 and averaging the results, and outputting the results. The feedback in this case can also be digitally processed, and the basic principle is common even if the DSP or the microprocessor is used to perform the digital processing, and the rights of the present invention are covered.

In the embodiment, the exciting coils are circular coils and the center lines thereof are arranged at the same position, but rectangular or polygonal,
It is also possible to use an exciting coil having a shape other than a circular shape, such as a saddle-shaped coil, to arrange the coils differently or to increase the number of exciting coils to obtain a desired magnetic flux distribution. In this case, for the magnetic field with respect to the distance, the formula (1) of Formula 1 cannot be applied, but each magnetic field distribution can be obtained by using the experimental value, the finite element method, or the Legendre function, and the same purpose can be obtained. It is possible to obtain the magnetic field distribution obtained by these methods, not only the central axis of the coil, but also the magnetic field distribution at all points. It is also possible to provide a plurality of detectors, connect similar receivers to each, detect the reception level and phase, and calculate the three-dimensional position of the detection conductor from this condition.

When a coil is used as the magnetic detector, the exciting coil can also be used as the receiving coil. When a receiving coil is separately provided, an iron core or a ferrite core with less loss can be used to obtain a detector with sharp directivity and high sensitivity. In this case, it is necessary to consider the disturbance of the magnetic flux distribution due to the core.

In a special example of the coil arrangement, a magnetic field is generated in a direction orthogonal to a line connecting the two exciting coils having the same shape with the magnetic detector as the center, or a direction symmetrical to the line connecting the two exciting coils. When the pulse currents are applied to the exciting coils simultaneously or alternately with polarities in which the receiver outputs have opposite polarities to each other,
When the output of the receiver is at its lowest, it indicates that there is a sensing conductor at a point equidistant from each coil. in this case,
Although the distance cannot be specified, in the exploration of the buried objects, it is shown that the detecting conductors are arranged symmetrically with respect to each coil immediately below the magnetic detector, and the plane position and the laying direction of an elongated pipe such as a water pipe are shown. This is useful when you want to know exactly.

Further, the plane position where the coils are attached is inclined with respect to the ground, and the angle and position where the receiver output becomes the minimum are searched for at a plurality of different points, and from the center point of the line connecting the respective coils. The position of the detection conductor can also be known from the intersection of the orthogonal lines. In this case as well, similar to the other cases, the same effect can be obtained by omitting the magnetic detector and sharing each exciting coil as a receiving coil.

Two-dimensional detection is performed by a plurality of exciting coils that apply exciting signals synchronized with each other and a large number of receiving coils arranged in an array, and this output is displayed as it is or the difference between the outputs of adjacent detectors is displayed. It is also possible to display the image of the detection conductor more realistically. It is also possible to use a minute detection coil instead of switching the coil, and physically scan this coil to display the distribution of the detection conductors in two-dimensional or three-dimensional manner, which is a non-destructive inspection device. Can also be used as.

A minute spiral excitation coil is formed by etching or the like, and is excited by an auxiliary coil surrounding it, and one of the coils is also used as a magnetic field detection coil to detect metal at a minute distance. It is also possible to measure the film thickness of the paint or the like in micrometer units. In this case, if the base metal of the film is a conductor regardless of whether it is a magnetic substance or a non-magnetic substance, a great feature that the measurement can be performed under the same conditions is obtained. This eliminates the drawback of the conventional film thickness meter, which measures the magnetic substance and the non-magnetic substance separately.

By partially changing this detecting device, stopping the excitation of the auxiliary coil, and using this coil as a negative feedback coil for stabilization, it is possible to change to the stable metal detector already applied for. In this case, the strength of the return magnetic field differs depending on the size of the detection conductor if the distance is the same. Therefore, the size of the detection conductor can be experimentally estimated from the relationship between the intensity of the return magnetic field and the detection distance obtained by such a method.

[0047]

The greatest feature of the effect of the present invention is that not only the presence or absence of the detection conductor but also the distance to the detection conductor can be measured. Moreover, the conventional detector has zero drift, and the sensitivity varies depending on this adjustment method, and there are drawbacks such as individual differences in detection, and the sensitivity decreases if feedback is increased to correct zero drift. There was also a problem such as. In the present invention, if feedback is performed so that the currents flowing through the coils are automatically adjusted so that the magnetic fields of the plurality of coils may be offset or at the same point, in principle, the feedback does not lower the sensitivity and also reduces drift and noise. it can.

When this detector is used, the distance to the detection conductor can be output, so that the adjustment of the zero point shift, which is required in the conventional detector, is not necessary and the handling is convenient. Therefore, it is possible to realize a metal detector which is extremely high in sensitivity, is not affected by external noise, is easy to handle, and is capable of measuring distance, which has never been obtained.

In the detection of an underground buried object, an iron pipe for protecting a power cable being energized can be accurately detected at a distance of 30 cm by a small exciting coil having a diameter of several centimeters. Since the sensitivity of this detector is proportional to the square of the exciting coil diameter and the exciting current, it is possible to detect a distance of 3 m or more and measure the distance by using a large exciting coil. Further, the influence of the disturbing conductor, which is a problem, can be reduced by increasing the detecting distance, and the detecting conductor on the center axis of the exciting coil can be selectively detected, which enables many applications.

As an application other than the metal detector, a minute spiral coil and an exciting coil surrounding the outer periphery of the coil may be formed by etching or the like, and a distance in micrometer units may be measured through an insulator to be used as a film thickness meter. It will be possible.
Unlike the conventional film thickness meter, this film thickness meter has a great feature that it is not affected by the underlying metal material. Further, when used as a proximity switch, it is possible to perform an accurate operation that is hardly affected by the material and shape of the symmetrical object, and it is also possible to know the direction of deviation from the target of the symmetrical object. For example, maximum diameter 5
It is easy to obtain a reproducibility of 1 mm or less at a distance of 20 cm in the detection of an iron plate that is sufficiently larger than this coil diameter by using an excitation coil of cm. The value can also be detected.

Further, a combination of opposing exciting coil pairs of the same shape and a magnetic detector are arranged on each surface of the cube so as to be orthogonal to each other, and a conductor is attached to the center of the cube, and x, y of the conductor are attached. Alternatively, it can be used as a two-dimensional or three-dimensional non-contact position detector by measuring the position in the x, y, and z directions, and can also be used as a pointing device for a small computer that replaces a joystick or a mouse without contacts. It is possible. In this case, it is convenient for the magnetic detector to share one of the exciting coil pairs as the magnetic detector and simplify the detector.

[Brief description of drawings]

FIG. 1 shows a magnetic field and a composite value thereof with respect to a distance between two coils arranged on the same plane.

[Fig.2] Coil layout and detection distance vs. ampere frequency ratio

[Fig. 3] Coil layout and detection distance to ampere frequency ratio

[Fig. 4] Coil layout and detection distance to ampere frequency ratio

FIG. 5: Coil layout and detection distance vs. ampere frequency ratio

FIG. 6 is a layout diagram of coils and a composite magnetic field with respect to distance when the coil spacing is changed.

FIG. 7 is a block diagram illustrating the present invention.

[Explanation of symbols]

 Figure 7 1. Excitation coil A 2. Excitation coil B 3. Magnetic field detector 4. First stage amplifier (receiver with mask) 5. Drive circuit A 6. Drive circuit B 7. Drive current control circuit 8. Current ratio detector 9. Linearizer 10. Display 11. Crystal oscillator 12. Frequency divider 13. Timing generator circuit

Claims (8)

[Claims] 1. A pulsed magnetic field is generated by passing a pulsed current through a plurality of exciting coils having different amperes / times and their directions, shapes, and positions, and the pulsed magnetic field is used to detect mutual inductance through a mutual inductance with a detecting conductor. In a metal detection device in which an induction current is passed through a detection conductor and a magnetic field due to this induction current is received by a receiving coil or a magnetic sensitive element,
A pulse current for excitation is applied to the excitation coil, and the decay time of this pulse current is cut off at a fall time faster than the equivalent time constant of the detection conductor.The excitation circuit cuts off the energy remaining in the excitation coil. The masking period is set to stop the reception until the signal is received by the receiving circuit that has the switch function to detect the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the exciting current. In a metal detection device that selectively receives only signals, find the condition that the magnetic field applied to the detection conductor becomes zero due to the interaction of the magnetic fields generated in each exciting coil, and the received signal becomes the minimum. A metal detection method for detecting and detecting the position of a conductor. 2. A pulsed magnetic field is generated by passing a pulsed current through a plurality of exciting coils having different amperes / times and directions, shapes, and positions, and a mutual inductance with a detection conductor to be detected by the pulsed magnetic field is used. In a metal detection device in which an induction current is passed through a detection conductor and a magnetic field due to this induction current is received by a receiving coil or a magnetic sensitive element,
A pulse current for excitation is applied to the excitation coil, and the decay time of this pulse current is cut off at a fall time faster than the equivalent time constant of the detection conductor.The excitation circuit cuts off the energy remaining in the excitation coil. A masking period is set to stop the reception until the signal is received by the receiving circuit that has a switch function that detects the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the excitation current, and by the synchronous amplifier synchronized with the excitation pulse. In the metal detection method for detecting the detection conductor, at this timing, one excitation coil A is excited by the excitation A of T1 and the mask of T2, T3
Has a reception period of T4, the other excitation coil B is excited by the excitation B of T4, and it is operated by the sequence having six kinds of timings, that is, the mask of T5 and the reception of T6, and the reception signal of T3 and the reception signal of T6 are Analog or digital differential amplification is performed to produce an output, and the strength and direction of the magnetic field due to excitation A and excitation B are adjusted so that this output becomes zero. Mutual strength is determined from the respective magnetic field strength and the position and shape of the excitation coil. The metal detection method that finds the condition that the magnetic field strength due to the excitation of the excitation coil is the same or cancels, and detects the detection conductor and measures the position from this condition. 3. A pulsed magnetic field is generated by passing a pulsed current through an exciting coil, and an induced current is caused to flow through the sensing conductor through mutual inductance with the sensing conductor to be sensed by the pulsed magnetic field. In the metal detection device that receives by the receiving coil or the magnetic sensitive element,
A pulse current is applied to the exciting coil, and the decay time of this pulse current is cut off at a fall time faster than the equivalent time constant of the detecting conductor.An exciting circuit is received until the energy remaining in the exciting coil is sufficiently attenuated. There is a mask period to stop the signal, and only the signal due to the induced current that flows in the sensing conductor is received by the receiving circuit that has the switch function to detect the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the exciting current. In a metal detector that selectively receives signals, a backside antireflection coil is provided on the back side of the exciting coil, and a magnetic field detector placed near the backside conductor detects the magnetic field, and this magnetic field becomes zero. As described above, the current generated by the antireflection coil is excited by a controlled value, and the conductor on the back side of the excitation coil is made undetectable, so that the excitation coil Metal detection device to detect only square of the detection conductor. 4. A pulsed magnetic field is generated by passing a pulsed current through an exciting coil, and an induced current is caused to flow through the detecting conductor through mutual inductance with the detecting conductor to be detected by the pulsed magnetic field, and a magnetic field generated by the induced current is generated. In the metal detection device that receives by the receiving coil or the magnetic sensitive element,
A pulse current is applied to the excitation coil, and the decay time of this pulse current is cut off at a fall time that is faster than the equivalent time constant of the sensing conductor, and until the energy remaining in the excitation coil is sufficiently attenuated. Only a signal due to the induced current that flows in the sensing conductor is received by the receiving circuit that has a masking period to stop the reception and has a switch function that detects the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the exciting current. In the metal detection device adapted to selectively receive, a canceling coil that generates a magnetic field orthogonal to the magnetic field generated from the exciting coil is provided,
A metal detection device in which the magnetic fields of the canceling coils cancel the exciting magnetic fields applied to the conductors other than the front of the central axis of the exciting coil, and the conductors other than the target cannot be detected. 5. The metal detecting method according to claim 1 or 2, wherein two exciting coils of different sizes are arranged with their center axes being equal to each other, and a surface of the large exciting coil is arranged with respect to a surface of the small exciting coil. A metal detector that is placed on the opposite side of the detection direction to increase the detection distance and increase the linearity of the detection distance characteristics with respect to the ampere-turn ratio of each coil. 6. A magnetic field is generated in a direction parallel to or orthogonal to a line orthogonal to a midpoint of a line connecting the two exciting coils having the same shape centering on the magnetic detector and connecting the coils. The pulsed magnetic field is generated by simultaneously or alternately applying pulse currents with the same current value to each exciting coil and with the outputs of the receiver having opposite polarities. There is sufficient energy remaining in the exciting circuit and the exciting circuit that cuts off the exciting current at the fall time faster than the equivalent time constant of the detecting conductor by passing the induced current through the mutual inductance through the detecting conductor. A switch that detects the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the exciting current, by providing the mask period to stop the reception until it attenuates. The signal is received by a receiving circuit having a function, a search is made for a point at which the return signal due to the excitation of each coil of this received signal is the same or equal, and the detection conductor is placed on the extension of the position orthogonal to the center of the line connecting the two exciting coils A metal detection device that knows that there is something, and the same condition is obtained at different positions and angles, a line orthogonal to the center of the line connecting the coils at each position and angle is obtained, and the position of the detection conductor is measured from the intersection of the lines. Metal detector. Also, in the same device, the magnetic detector is omitted, and each exciting coil is also used as a magnetic detector. 7. A plurality of exciting coils having different amperages and their directions, shapes, and positions are arranged, and a pulsed magnetic field is generated by simultaneously or alternately applying a pulse current to each exciting coil, and the pulsed magnetic field is generated. An exciting circuit that cuts off the exciting current at a fall time faster than the equivalent time constant of the sensing conductor by passing an induced current through the target conductor through mutual inductance with the sensing conductor A masking period is provided to stop the reception until the energy remaining in the coil is sufficiently attenuated, and the voltage is detected by the receiving circuit that has a switch function that detects the magnetic field by the voltage of the detection coil or the magnetic sensitive element only during the period when there is no influence of the exciting current. A position detection device that outputs the position of the target conductor and the moving direction according to the polarity and strength of the received signal. Also, an exciting coil for generating magnetic fields in the x, y or x, y, z directions orthogonal to each other and a return magnetic field detector are arranged, and the two-dimensional or three-dimensional position of the target conductor is output from the output and polarity of this detector. Position detection device. 8. The method according to claim 1, wherein the distance between the detection conductors is measured, a part of the circuit is switched, and the magnetic field strengths returned from the detection conductors are set so that the received signals are not canceled by the mutual magnetic fields. A metal detection method in which the size of a detection conductor is measured and measured from the relationship between the detection distance and the return magnetic field.