RU2817670C2 - Method for detecting reflected signal from target in induction resonance metal detector in presence of influence of destabilizing factors in process of searching and detecting of same, device implementing the same - Google Patents

Abstract

FIELD: metal detection.

SUBSTANCE: invention is related to the field of detecting conductive and ferrimagnetic objects using induction coils that create an alternating magnetic field. The invention is a method that consists of converting the voltage from the sensor coil into antiphase, comparing it with the voltage on the capacitor, the resulting voltage is converted into a constant resulting voltage, and the deviation of the resulting direct voltage in the process of searching for a target is more than the value of the voltage the minimum possible threshold for detecting a signal reflected from the target will indicate detection of the target. The device implementing the method contains an alternating voltage generator, a serial oscillating LC circuit consisting of a sensor coil, a capacitor, two galvanically isolated power supplies, a passive adder containing three resistors, a buffer amplifier, optical isolation, an indication module and a correction module, except In addition, a transformer, a synchronous detector, a rectifier filter.

EFFECT: improve of reliability of detecting a reflected signal from a target in an induction resonant metal detector in presence of the influence of destabilizing factors.

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Description

The invention relates to the field of detecting conductive and ferromagnetic objects using induction coils that create an alternating magnetic field.

Devices for searching in various environments for metallic and ferromagnetic objects, hereinafter referred to as “targets”, are mainly carried out using the following principles: frequency beating, pulse induction, transmission-reception, induction type.

Due to the relative simplicity of the design, its mechanical stability, and, as a result, overall stability, the ability to discriminate a target based on its magnetic permeability and conductivity, induction-type metal detectors are the most promising in detecting metal and ferromagnetic targets in a variety of environments.

There is a known method for constructing an induction metal detector [1] Art. 70-75., in which the reflected target signal is isolated by subtracting from the electrical signal present in the coil of the metal detector sensor, which is part of a parallel oscillatory LC circuit, a signal of the same shape, frequency, phase and amplitude as the signal in the metal detector sensor coil, in the absence of a target in the search area. This method is implemented in that an alternating current of stable amplitude and frequency is supplied to a parallel oscillating LC circuit, the coil of which is the metal detector sensor, at which the voltage amplitude and its phase on the sensor coil are equal to the amplitude and phase of the voltage of the AC voltage master oscillator, in the absence targets near the metal detector sensor coil. When a target appears near the metal detector sensor coil, a reflected signal is induced in it, changing the parameters of the metal detector sensor coil, while the amplitude and phase of the voltage on the sensor coil, which is part of the parallel LC oscillatory circuit, changes. The amplitude and phase of the alternating voltage that sets the alternating voltage generator are compared with the amplitude and phase of the alternating voltage on the metal detector sensor coil, which is part of the parallel oscillating LC circuit, their imbalance is recorded, and based on its result, a conclusion is made about target detection. The disadvantages of this method include: instability of the sensor parameters due to destabilizing factors, temperature drift of the ohmic resistance of the coil, high requirements for the stability of the capacitor of the parallel oscillating LC circuit, the difficulty of isolating a small useful signal, against the background of a large electrical excitation signal, of the metal detector sensor coil. The amplitude ratio of these signals can reach , which is the minimum possible threshold for detecting a signal reflected from the target.

Another solution is the patent [2], which implements a method for detecting changes in the impedance of the magnetic field receiver of a metal detector, i.e. identifying the reflected signal from the target. This method for detecting changes in the impedance of a magnetic field receiver of a metal detector, including: the presence of a first network of passive components, including the impedance of the magnetic field receiver; the presence of a second network of passive components, excluding the impedance of the magnetic field receiver; processing the first measurement signal from the first node of the first network; processing a second measurement signal from a second node of the second network; comparing them to detect changes in magnetic field receiver impedance. In this case, the first network, the second network, the first node, the second node are configured in such a way that in the absence of an external influence that affects the impedance of the magnetic field receiver, the first measuring signal is essentially the same as the second measuring signal and in the presence of an external influence, the first measuring signal is different from the second measuring signal.

The above method and the device that implements it have certain disadvantages: the impedance of the receiver, or jointly the receiver and transmitter, as part of the first network of passive components, which is a series oscillating LC circuit, namely: inductance, capacitance, ohmic resistance of the coil having a temperature drift, necessitate the need to take them into account, and the possible presence of intra-circuit parasitic connections requires the presence of two antiphase generators, with the ability to adjust the phase and amplitude of one of them. The presence of ohmic resistances in the first and second networks of passive components, for the successful implementation of the method, requires them to have high temperature and time stability.

A progressive solution is a patent [3], option 3 adopted as a prototype. This is a method and a device that implements it, through which a sinusoidal alternating voltage is supplied to a serial oscillatory LC circuit, the coil of which is the sensor of a metal detector, with a frequency equal to its natural frequency, and the voltage amplitudes on the sensor coil and the capacitor are compared.

For this purpose, the voltage from the sensor coil and the capacitor, relative to the common point of the series oscillating LC circuit, is converted into constant voltages equal to their amplitude, and the voltage from the sensor coil is converted into a positive constant voltage, and from the capacitor into a negative one. A comparison is made of the constant voltage corresponding to the voltage amplitude on the sensor coil with the constant voltage corresponding to the voltage amplitude on the capacitor by adding them. As a result of the comparison, the resulting direct voltage is revealed, the maximum value of which should not exceed the breakdown value of the electronic components of the metal detector. In this case, the series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and the capacitor must be equal, during the search process, under various destabilizing factors, in the absence of a reflected signal from the target.

In the process of searching for a target, a deviation of the resulting direct voltage by more than the voltage value of the minimum possible threshold for detecting a signal reflected from the target will indicate the detection of a target, and the polarity of the resulting direct voltage determines the nature of the target material: ferromagnetic or diamagnetic, and the voltage value determines the volume of the target and burial depth.

This method and the device that implements it are easy to implement and allow you to detect and identify targets at great depths, comparable to metal detectors implemented on the principle of pulse induction. At the same time, it has a certain disadvantage, namely: comparison of the voltage amplitudes on the sensor coil and the capacitor is carried out as a result of converting them into constant voltages, which introduces some limits on the reliability of detecting the reflected signal from the target.

The purpose of the present invention is: to improve the reliability of detecting a reflected signal from a target in an induction, resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, namely: temperature instability of the sensor, electronic components of the metal detector, the level of soil mineralization and protection of the electronic components of the metal detector from electrical breakdown.

In FIG. Figure 1 shows a block diagram of the proposed device that implements a method for detecting a reflected signal from a target in an induction resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, containing: 1 - voltage generator; 2 - shielded sensor coil; 3 - capacitor; 4 - transformer; 5 - passive adder, consisting of: 6 - first, 7 - second and 8 - third resistors; 9 - buffer amplifier; 10 - synchronous detector; 11 - smoothing filter; 12 - correction module; 13 - optical isolation; 14 - display module; 15 - first power source; 16 - second power source.

In FIG. Figure 2 presents graphs illustrating the operation of a device that implements a method for detecting a reflected signal from a target in an induction resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it.

This goal is achieved by the fact that in a series oscillatory LC circuit, the coil of which is a metal detector sensor, into which a sinusoidal alternating voltage is applied, with a frequency equal to its natural frequency, the voltage amplitudes on the sensor coil and the capacitor are compared. In this case, the series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and the capacitor must be equal, during the search process, under various destabilizing factors, in the absence of a reflected signal from the target.

The proposed method differs in that in a series oscillating LC circuit, the alternating voltage on the sensor coil is inverted, and the inverted alternating voltage of the coil is compared with the alternating voltage on the capacitor, relative to a common point. The resulting alternating voltage identified as a result of comparison is converted with a given periodicity into a full-wave rectified resulting voltage, the polarity of which is determined by the difference between the inverted alternating voltage and the alternating voltage on the capacitor. If the inverted AC voltage is greater than the AC voltage across the capacitor, the polarity of the full-wave rectified resulting voltage is positive. If the inverted AC voltage is less than the AC voltage across the capacitor, the polarity of the full-wave rectified resulting voltage is negative. The full-wave rectified resulting voltage is converted into a resulting direct voltage, which characterizes the presence or absence of a target during the search process.

In the process of searching for a target, a deviation of the resulting direct voltage by more than the voltage value of the minimum possible threshold for detecting a signal reflected from the target will indicate the detection of a target, and the polarity of the resulting voltage determines the nature of the target material: ferromagnetic or diamagnetic, and the voltage value determines the volume of the target and depth.

To ensure high accuracy of conversion of the resulting alternating voltage into a full-wave rectified resulting voltage, it is carried out in at least two periods of sinusoidal alternating voltage supplied to a serial oscillating LC circuit, with a conversion frequency of T = 0.2-0.05 Sec

Monitoring the equality of voltage amplitudes on the sensor coil and the capacitor, during the search process, under various destabilizing factors, in the absence of a reflected signal from the target, is carried out with a delay, after converting the resulting alternating voltage into a full-wave rectified resulting voltage, for 1-2 msec.

A device that implements a method for detecting a reflected signal from a target in an induction resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, containing: an alternating voltage generator, a series oscillating LC circuit consisting of a shielded coil, which is a metal detector sensor and a capacitor, two galvanic isolated power supply, a passive adder containing three resistors, a buffer amplifier, optical isolation, a correction module and an indication module, equipped with a transformer, a synchronous detector, and a smoothing filter. Moreover, the first terminal of the generator output is connected to the first terminal of the coil and the beginning of the primary winding of the transformer, the beginning of the secondary winding of the transformer is connected to the first terminal of the first resistor of the passive adder, the second terminal of the generator output is connected to the first terminal of the capacitor and to the first terminal of the second resistor, passive adder, the second terminals of the first and second resistors are connected to the first terminal of the third resistor of the passive adder and the input of the buffer amplifier, whose output is connected to the input of the synchronous detector, its output connected to the input of the smoothing filter, which is connected by its output to the inputs of the indication module and the correction module, the first output of which is connected to the control input of the synchronous detector, the second through optical isolation - to the control input of the generator. The screen of the sensor coil, the ends of the primary and secondary windings of the transformer, the second terminals of the sensor coil, capacitor and third resistor, passive adder, are connected to the neutral wire of the buffer amplifier. The first power source is connected to the power circuits of the generator, the second - to the power circuits of the buffer amplifier, indication module, and correction module.

The proposed device (Fig. 1), which implements a method for detecting a reflected signal from a target in an induction resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, works as follows.

Sinusoidal AC voltage , frequency from the output of alternating voltage generator 1 is supplied to a serial oscillating LC circuit formed by sensor coil 2 and capacitor 3, as a result of which alternating voltages are generated on them respectively, relative to the common point of the serial oscillatory LC circuit, the second terminal of the third resistor 8, the second ends of the primary and secondary windings of the transformer 4 and the neutral wire of the buffer amplifier 9. Alternating voltage from the sensor coil 2 is supplied to the primary winding of transformer 4, in which it is inverted, while an inverted alternating voltage is formed on its secondary winding , the amplitude of which is equal to the amplitude of the alternating voltage on coil 2.

In resonance mode, the maximum voltage amplitudes on the sensor coil and the capacitor and the secondary winding of the transformer reach the following values:

Where: - amplitude of alternating voltage at the output of alternating voltage generator 1;

- amplitude of alternating voltage on sensor coil 2;

- amplitude of alternating voltage on capacitor 3;

- amplitude of the inverted alternating voltage on the secondary winding of transformer 4;

Q is the quality factor of the series oscillatory LC circuit.

- instantaneous value of alternating voltage at the first terminal of coil 2, relative to the neutral wire;

- instantaneous value of alternating voltage at the first terminal of capacitor 3, relative to the neutral wire;

- instantaneous value of the inverted alternating voltage at the beginning of the secondary winding of transformer 4, relative to the neutral wire.

Variable voltage , from the beginning of the secondary winding of the transformer 4, an alternating voltage is supplied to the first terminal of the first resistor 6, passive adder 5 from capacitor 3 is supplied to the first input of the second resistor 7, passive adder 5. In the passive adder node 5, formed by connecting the second terminals of the first 6, second 7 resistors and the first terminal of the third 8 resistor, an alternating voltage is released, which is supplied to the input of the buffer amplifier 9. At The output of buffer amplifier 9 generates the resulting alternating voltage:

The instantaneous value of which will be determined by the expression:

if ; if ; Where: - specified scaling factor of the passive adder 5; - specified gain of buffer amplifier 9.

In this case, the following condition must be met: R1=R2 (9). The specified gain of the buffer amplifier 9 is taken equal to the value of the specified scaling factor of the passive adder 5, i.e.

Hence:

if ; if .

From the output of buffer amplifier 9, the resulting alternating voltage is supplied to the signal input of the synchronous detector 10. From the first output of the correction module 12, the control voltage is supplied to the control input of the synchronous detector 10 in the form of a bipolar meander, in phase with the alternating voltage at the output of generator 1, at least two periods with a periodicity of T = 0.2 - 0.05 Sec. At the output of synchronous detector 10, a full-wave rectified resulting voltage is formed .

- instantaneous value of the full-wave rectified resulting voltage at the output of the synchronous detector 10, relative to the neutral wire.

Full-wave rectified resulting voltage is supplied to the input of smoothing filter 11, at the output of which the resulting DC voltage is formed equal to the amplitude of the full-wave rectified resulting voltage , which is supplied to the inputs of correction module 12 and display module 14.

If: resulting DC voltage , If resulting DC voltage .

If there is no target in the search area, and therefore no reflected signal from the target, equality (1) must be observed. Failure to comply with it means that the influence of destabilizing factors has not been eliminated, as a result of which automatic frequency correction is performed alternating voltage generator 1.

In correction module 12 at the second output, with a delay after comparing the values And , correction impulses are formed duration 1-2 mSec, the corresponding polarity of the resulting direct voltage is sign , at the time of correction, which change the frequency alternating voltage generator 1, by the amount equal to the step of frequency change corresponding to the voltage, the minimum possible threshold for detecting the signal reflected from the target.

If (Fig. 2, section I, II), the frequency of alternating voltage generator 1 increases by one frequency change step after comparing the values , thereby increasing the voltage and reducing tension by the voltage value corresponding to the minimum possible threshold for detecting the signal reflected from the target.

If (Fig. 2, section III), the frequency of alternating voltage generator 1 is reduced by one frequency change step after comparing the values , thereby reducing tension and increasing tension by the voltage value corresponding to the minimum possible threshold for detecting the signal reflected from the target.

State of periodic change of sign of the resulting direct voltage , in the absence of a reflected signal from the target, (Fig. 2, section III, IV) indicates the elimination of the influence of destabilizing factors, i.e. and correspondingly Deviation, during the search process, of the resulting DC voltage from zero, by an amount exceeding the voltage of the minimum possible threshold for detecting the signal reflected from the target, recorded by the display module 11, will indicate the detection of the target. Moreover, the polarity of the resulting direct voltage determines the nature of the target material: ferromagnet (Fig. 2, section V) or diamagnetic (Fig. 2, section VI), and the value is the volume of the target or its depth.

Information sources

1. Book. A. Shchedrin, I. Osipov “Metal detector for searching treasures and relics.” Moscow, Radio and communications: Hotline-Telecom., 2000.

2. US 9557390, 01/31/2017 Noise reduction circuitry for a metal detector.

3. RU 2 768 205, 01/27/2020 A method for detecting a reflected signal from a target in an induction resonant metal detector, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, a device that implements it (options).

Claims (7)

1. A method for detecting a reflected signal from a target in an induction resonant metal detector in the presence of the influence of destabilizing factors in the process of searching and detecting it, carried out by applying a sinusoidal alternating voltage to a series oscillating LC circuit, the coil of which is the sensor of the metal detector, with a frequency equal to its natural frequency, in which the voltage amplitudes on the sensor coil and the capacitor are compared relative to the common point of the serial oscillatory LC circuit, while it is maintained in a balanced state in which the voltage amplitudes on the sensor coil and the capacitor are equal during the search process in the presence of destabilizing factors, in the absence of reflected signal from the target, characterized in that the alternating voltage on the sensor coil is inverted and compared with the alternating voltage on the capacitor relative to the common point of the serial oscillatory LC circuit, the identified resulting alternating voltage with a given periodicity is converted into a full-wave rectified resulting voltage, the polarity of which is determined by the difference of the inverted alternating voltage and alternating voltage on the capacitor, if the inverted alternating voltage is greater than the voltage on the capacitor, the polarity of the full-wave rectified resulting voltage is positive, if the inverted alternating voltage is less than the alternating voltage on the capacitor, the polarity is negative, the full-wave rectified resulting voltage is converted into the resulting direct voltage, which its sign and magnitude characterizes the presence or absence of a target during the search process, while the polarity of the resulting direct voltage determines the nature of the target material: ferromagnetic or diamagnetic, and the magnitude determines the volume of the target or its depth. 2. The method according to claim 1, characterized in that the conversion of the resulting alternating voltage into a full-wave rectified resulting voltage is carried out in at least two periods of sinusoidal alternating voltage supplied to a series oscillating LC circuit, with a conversion frequency T = 0.2-0 .05 s. 3. The method according to claim 1, characterized in that control of the equality of voltage amplitudes on the sensor coil and the capacitor, during the search process, under various destabilizing factors, in the absence of a reflected signal from the target, is carried out with a delay, after converting the resulting alternating voltage into a full-wave rectified the resulting voltage within 1-2 ms. 4. A device that implements a method for detecting a reflected signal from a target in an induction resonant metal detector in the presence of the influence of destabilizing factors in the process of searching and detecting it according to claim 1, containing: an alternating voltage generator, a series oscillating LC circuit consisting of a shielded coil, which is a sensor metal detector and capacitor, two galvanically isolated power supplies, a passive adder containing three resistors, a buffer amplifier, optical isolation, an indication module and a correction module, characterized in that it is equipped with a transformer, a synchronous detector, a smoothing filter, and the first terminal of the generator output is connected to the first terminal of the coil and the beginning of the primary winding of the transformer, the beginning of the secondary winding of the transformer is connected to the first terminal of the first resistor of the passive adder, the second terminal of the generator output is connected to the first terminal of the capacitor and to the first terminal of the second resistor, passive adder, the second terminals of the first and second resistors are connected to the first the output of the third resistor and the input of the buffer amplifier, which is connected with its output to the input of the synchronous detector, respectively, with its output connected to the input of the smoothing filter, which is connected with the output to the inputs of the indication module and the correction module, the first output is connected to the control input of the synchronous detector, the second, through the optical decoupling - to the generator control input, the sensor coil screen, the ends of the primary and secondary windings of the transformer, the second terminals of the sensor coil, capacitor, third resistor are connected to the neutral wire of the buffer amplifier, the first power source is connected to the generator power supply circuits, the second - to the buffer power supply circuits amplifier, display module, correction module. 5. The device according to claim 4, characterized in that the impedance of the transformer is greater than the impedance of the sensor coil of the serial oscillating LC circuit at the resonance frequency by at least 1000 times. 6. The device according to claim 4, characterized in that in the passive adder the first and second resistors have the same resistance value. 7. The device according to claim 4, characterized in that the specified scaling factor of the passive adder is equal to the specified gain of the buffer amplifier.

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