RU2768205C9 - Method for detecting reflected signal from target in induction, resonant metal detector, in presence of the effect of destabilizing factors, in process of searching and detecting it, device which implements it (versions) - Google Patents

Abstract

FIELD: electrical communication equipment.

SUBSTANCE: invention relates to the field of detecting current-conducting and ferromagnetic objects using induction coils which generate an alternating magnetic field. Group of inventions comprises methods consisting in converting voltages from a sensor coil and a capacitor, comparing them by adding or subtracting from a constant voltage, note here that deviation of the resultant constant voltage in the process of target search by more than the voltage value of the minimum possible detection threshold of the signal reflected from the target indicates its detection. Group of inventions also includes devices for implementing the methods, comprising: an alternating voltage generator, serial oscillatory LC-circuit consisting of a coil of a metal detector, characterized by that it is equipped with indication and correction modules, optical isolation, two power supplies.

EFFECT: improved reliability of detection of reflected signal from target in induction, resonant metal detector in presence of destabilizing factors.

23 cl, 13 dwg

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 a variety of environments, metal and ferromagnetic objects, hereinafter referred to as "target", 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 - the overall stability, the ability to discriminate the target by its magnetic permeability and conductivity, induction-type metal detectors are the most promising in detecting metal and ferromagnetic targets in a variety of environments.

Known metal detector [1], containing an AC voltage source, an AC bridge formed by two series circuits of reactive elements, in two adjacent arms of which inductors of equal size are included, and in two opposite ones - capacitors with equal capacities, a capacitor connected in parallel to the bridge, forming parallel oscillatory circuit, the frequency of which is equal to the frequency of series oscillatory circuits. With the obvious simplicity of the device, its performance is limited by the stability of individual elements of the bridge.

Another solution is the method of building an induction metal detector [2] Art. 70 -75, in which the reflected target signal is isolated by subtracting from the electrical signal present in the metal detector sensor coil, which is part of the parallel oscillatory LC circuit, a signal of the same shape, frequency, phase and amplitude as the signal in the metal detector sensor coil, when there is no target in the search area. This method is implemented by the fact that an alternating current of stable amplitude and frequency is supplied to a parallel oscillating LC circuit, the coil of which is a 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 master alternating voltage generator, in the absence targets near the metal detector's 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 oscillatory LC oscillatory circuit, changes. The amplitude and phase of the alternating voltage of the master 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 oscillatory LC circuit, their unbalance is fixed and, based on its result, a conclusion is made about the detection of the target. 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 oscillatory 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 10 ^-5 ÷10 ^-6 , which is the minimum possible threshold for detecting a signal reflected from the target.

A progressive solution is the patent [3], adopted as a prototype, which implements a method for detecting a change in the impedance of the magnetic field receiver of a metal detector, i.e. detection of the reflected signal from the target. This method for detecting a change in the impedance of a magnetic field receiver of a metal detector, including: having 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 the second measurement signal from the second node of the second network; comparing them to detect a change in the impedance of the magnetic field receiver. 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 measurement signal is essentially the same as the second measurement signal, and in the presence of an external influence, the first measurement signal differs. from the second measuring signal.

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

The above allows us to assert the complexity of the implementation of this method and devices in practice, which is indirectly illustrated by the use of this patent in metal detectors of the initial and intermediate level: Minelab Go-Find 20, Minelab Go-Find 22, Minelab Go-Find 40, Minelab Go-Find 44 , Minelab Go-Find 60, Minelab Go-Find 66 [4].

The purpose of the invention is: improving 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, which is carried out by comparing the voltage amplitudes, in a series oscillating LC circuit, on a capacitor and a coil, which is a metal detector sensor.

On FIG. 1 shows a series oscillatory circuit R, L, C with an alternating voltage source U _G.

On FIG. 2 shows a vector diagram of voltage resonance in a series oscillatory circuit R, L, C with an alternating voltage source U _G.

On FIG. 3 shows a real series oscillating LC circuit with an AC voltage source U _G.

On FIG. 4 shows a diagram of the equality of voltages U _LR and U _C in a real, series oscillatory LC circuit, with an alternating voltage source U _G.

On Fit. 5 shows a vector diagram in a real, serial oscillating LC circuit, with |U _LR |<|U _C |.

On FIG. 6 shows a vector diagram in a real, serial oscillating LC circuit, with |U _LR |>|U _C |.

On FIG. 7 shows the graphs of the dependence of I, R, X _G , X _L , U _r , U _L , U _C in a series oscillatory circuit on the frequency of the AC voltage source U _G.

On FIG. 8 shows a block diagram of the proposed device, option 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, containing: 1 - alternating voltage generator; 2 - shielded sensor coil; 3 - capacitor; 4 - the first power supply; 5 - second power supply; 6 - first peak detector with reset; 7 - second peak detector with reset; 8 - correction module; 9 - optical isolation; 10 - adder; 11 - display module; 12 - the first voltage divider, consisting of: 13 - the first and 14 - the second resistors; 15 - the second voltage divider, consisting of: 16 - the third and 17 - the fourth resistors.

On FIG. Figure 9 shows graphs, option 1, 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.

On FIG. 10 shows a block diagram of the proposed device, option 2, 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, containing: 1 - alternating voltage generator; 2 - shielded sensor coil; 3 - capacitor; 4 - the first power supply; 5 - second power supply; 6 - first peak detector with reset; 7 - second peak detector with reset; 8 - correction module; 9 - optical isolation; 10 - adder; 11 - display module; 13 - the first resistor; 14 - second resistor; 18 - the first voltage limiter; 19 - second voltage limiter;

On FIG. 11 shows graphs, option 2, 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.

On FIG. 12 shows a block diagram of the proposed device, option 3, 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, containing: 1 - alternating voltage generator; 2 - shielded sensor coil; 3 - capacitor; 4 - the first power supply; 5 - second power supply; 6 - first peak detector with reset; 7 - second peak detector with reset; 8 - correction module; 9 - optical isolation; 11 - display module; 20 - passive adder, consisting of: 13 - first, 14 - second and 16 - third resistors; 21 - buffer amplifier.

On FIG. 13 shows graphs, option 3, 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.

The proposed method for detecting a reflected signal from a target in an induction, resonant metal detector, in the presence of destabilizing factors in the process of searching and detecting it, is based on using the phenomenon of voltage resonance in a series oscillatory LC circuit, the coil of which is a metal detector sensor.

Based on the theoretical foundations of electrical engineering [5], the rationale for the implementation of the proposed invention is given below.

On FIG. 1 shows a series oscillatory LC circuit with an alternating voltage source U _G. Its vector diagram (Fig. 2) illustrates the state of the vectors U _Г , U _R , U _L , U _C at voltage resonance. In this case, the coil L has an inductive resistance component, which is possible only in an ideal series oscillatory circuit. On FIG. 3 shows a real series oscillating LC circuit with an alternating voltage source U _G , the coil of which has a complex resistance Z _LR . Its vector diagram (Fig. 4) illustrates the state of the vectors U _Г , U _LR , U _C at voltage resonance.

In the case of using a real series oscillatory LC circuit with a coil as a metal detector sensor, when the coil field is applied to the target - diamagnet, the ratio of voltages on it and the capacitor (Fig. 5) are characterized by the expression:

When the field of the coil acts on the target - a ferromagnet, the ratio of the voltages on it and the capacitor (Fig. 6) are characterized by the expression:

Where: |U _LR | - coil voltage module;

|U _C | - capacitor voltage module.

In the proposed invention, the detection of 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, is carried out by comparing the voltage amplitudes on the sensor coil and capacitor.

Comparison of the voltage amplitudes, with their pre-established equality, on the coil, which is the metal detector sensor, and the capacitor allows you to fix the voltage difference, which is the reflected signal from the target.

In reality, the voltage resonance state occurs when the amplitudes on the coil and capacitor are somewhat different from their maximum values (Fig. 7).

The voltage across the capacitance reaches its maximum at the frequency ω _Сmax , somewhat less than the resonant one, the expression:

Where: ω ₀ - resonant frequency;

Q - quality factor of the oscillatory circuit.

The magnitude of the voltage across the inductance reaches a maximum at a frequency ω _Lmax , somewhat higher than the resonant one, the expression:

The influence of the deviation of the voltage peaks on the capacitor and the coil, which is the metal detector sensor, can be neglected, because the normal value of the quality factor of the circuit is usually determined by the value: Q≥200, mainly determined by the quality factor of the sensor coil, while ω _Lmax ≥1.00000625, and ω _Сmax ≤0.99999375, which is comparable to the sensitivity threshold of the proposed method. The temperature instability of the ohmic resistance of the sensor coil does not violate the pre-established equality of the voltage amplitudes on the coil, which is the metal detector sensor, and the capacitor, because its deviation by ±20%, in the natural temperature range, slightly affects the quality factor of the sensor coil. Those. the unbalance of the pre-established equality of the voltage amplitudes on the coil, which is the metal detector sensor, and the capacitor, caused by a change in the quality factor, is less than the minimum possible threshold for detecting a signal reflected from the target. Which can be confirmed by calculations using formulas (3) and (4).

OPTION 1.

This goal is achieved by the fact that in a series oscillatory LC circuit, the coil of which is a metal detector sensor, to which a sinusoidal alternating voltage is supplied, with a frequency approximately equal to its natural frequency, the voltage amplitudes on the sensor coil and capacitor are compared. For this, the voltage amplitudes from the sensor coil and capacitor, relative to the common point of the series oscillatory LC circuit, are converted by dividing by a stable scaling factor into scaled voltages.

The maximum amplitudes of the scaled voltages must not exceed the breakdown of the electronic components of the metal detector, because the voltage amplitudes on the sensor coil and capacitor, due to resonance, can reach values of several hundred volts.

The scaled voltages are converted into constant voltages of the same polarity, equal to their amplitude and, accordingly, proportional to the amplitude of the voltages from the sensor coil and capacitor. Allocate the difference of constant voltages, for which from the constant voltage corresponding to the amplitude of the voltage on the coil of the sensor, subtract the constant voltage corresponding to the amplitude of the voltage on the capacitor. The DC voltage difference is converted to the resulting DC voltage by multiplying the detected DC voltage difference by a stable scaling factor. During the search for a target, the deviation of the resulting DC voltage by more than the value of the voltage of the minimum possible threshold for detecting a signal reflected from the target will indicate the detection of the target, and the polarity of the resulting voltage determines the nature of the target material: ferromagnet or diamagnet, and the voltage value determines the volume of the target and depth of occurrence.

A series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and capacitor must be equal, during the search, with various destabilizing factors, in the absence of a reflected signal from the target. Accordingly, the resulting DC voltage should not exceed the voltage of the minimum possible threshold for detecting a signal reflected from the target. Failure to fulfill the condition of equality of voltage amplitudes on the sensor coil and capacitor will mean that the effect of destabilizing factors has not been eliminated, which necessitates correction of the frequency of the sinusoidal alternating voltage, which is carried out as follows. With a given frequency, the resulting constant voltage is monitored in the absence of a reflected signal from the target. If the polarity of the resulting DC voltage is negative, then the frequency of the sinusoidal AC voltage is increased step by step, by an amount equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to positive. If the polarity of the resulting DC voltage is positive, the frequency of the sinusoidal AC voltage is reduced step by step, by an amount equal to the frequency step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to negative. The state of periodic sign change of the resulting constant voltage indicates that it is less than the voltage of the minimum possible threshold for detecting a signal reflected from the target, i.e. is practically equal to zero, respectively, the voltage amplitudes on the sensor coil and capacitor are equal, therefore, the series oscillatory LC circuit is brought into a balanced state.

The specified frequency of control of the resulting direct voltage is selected with a frequency of 5-20 Hz, a duration of 1-2 milliseconds.

Correcting the frequency of a sinusoidal alternating voltage does not introduce significant errors in the results, because the given frequency of correction and the step of changing the frequency of the sinusoidal alternating voltage does not allow the resulting direct voltage to be reduced to zero in the presence of a reflected signal, since destabilizing factors make changes much slower and less than the impact of the reflected signal from the target.

The disturbing effect on the resulting DC voltage caused by the reflected signal from the target is temporary, and the equality of the voltages on the coil of the sensor and the capacitor is violated, which is restored after the termination of the disturbing effect from the reflected signal.

A device that implements the first version of the 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 oscillatory LC circuit consisting of a shielded coil, which is a metal detector sensor, and capacitor, equipped with the first voltage divider containing the first and second resistors, the second voltage divider containing the third and fourth resistors, two peak detectors with reset, an adder, display and correction modules, optical isolation, two power supplies. Moreover, the first output of the generator output is connected to the first outputs of the coil and the first resistor, connected by the second output to the first output of the second resistor and the input of the first peak detector with reset, the output is connected to the direct input of the adder, the second output of the generator output is connected to the first outputs of the capacitor and the third resistor, connected by the second output to the first output of the fourth resistor and the input of the second peak detector with reset, the output connected to the inverse input of the adder, which is connected with its output to the inputs of the indication module and the correction module, the first output of which, through an optical isolation, is connected to the generator control input, and the second - to the reset inputs of the first and second peak detectors with reset. The screen of the sensor coil, the second terminals of the sensor coil, capacitor, second and fourth resistors are connected to the zero wire of the adder. The first power supply is connected to the power supply circuits of the generator, the second - to the power supply circuits of the adder, display module, correction module, while the first and second power supplies are galvanically isolated.

The proposed device (Fig. 8), which implements the first version of the method, works as follows. A sinusoidal alternating voltage, from the output terminals of the alternating voltage generator 1, U _G , with a frequency F _G , is fed to a series oscillatory LC circuit formed by a sensor coil 2 and a capacitor 3. As a result, voltages U _L and U _C are formed on them, respectively, relative to the common point of the series oscillatory LC circuit, the second terminals of the second 14, fourth 17 resistors and the zero wire of the adder 10. In this case, in the resonance mode, the value of the maximum voltage amplitudes on the sensor coil 2 and capacitor 3 reaches the value:

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

U _Lm - voltage amplitude on the sensor coil 2;

U _Cm - voltage amplitude on the capacitor 3;

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

The first voltage divider 12, formed by the first 13 and second 14 resistors, as well as the second voltage divider 15, formed by the third 16 and fourth 17 resistors, reduce by a stable scaling factor K, the voltage from the sensor coil 2 and capacitor 3, supplied to the inputs of the first 6 and second 7 peak detectors with reset. A stable scaling factor is selected from the conditions:

Based on the conditions (6), the amplitude of the scaled voltages at the inputs of the first 6 and second 7 peak detectors with a reset, hereinafter referred to as PDSS, will be respectively equal to:

The voltage U _{Lmm is} converted by the first PDSS 6 into a constant voltage U _{Lmm_} equal to its amplitude. The voltage U _{Cmm_ is} converted by the second PDSS 7 into a constant voltage U _{Cmm_} equal to its amplitude. The voltage U _{Lmm_} from the output of the first PDSS 6 is fed to the direct input of the adder 10, and the voltage U _{Cmm_} from the output of the second PDSS 7 is fed to the inverse input of the adder 10, in which they are compared. The selected difference of constant voltages is converted at the output of the adder 10 into the resulting constant voltage:

The resulting constant voltage Upez from the output of the adder 10 is fed to the inputs of the correction modules 8 and display 11.

In the absence of a target in the search area, respectively, the absence of a reflected signal from the target, equality (5) must be observed, i.e. _{Ures ≈0} . Failure to comply with these conditions means that the influence of destabilizing factors has not been eliminated, as a result of which the frequency F _G of the alternating voltage generator 1 is automatically corrected. Correction module 8, at the first output, generates correction pulses U _ynp with a frequency of 5 Hz<F _K <20 Hz, duration 1 -2 ms, sign corresponding to the polarity of the resulting direct voltage U _res , at the time of correction, which change the frequency F _G of the alternating voltage generator 1, by the value ΔF _G «F _G , equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target , at the second output it generates unipolar reset pulses U _cb , with the same frequency-time parameters, which reset the previously recorded constant voltage U _{Lmm_ by} the first PDSS 6 and the constant voltage U _{Сmm_ by the} second PDSS 7 with the trailing edge. After that, they fix new values of constant voltage U _{Lmm_} and U _{Сmm_} .

In the event that U _res <0, (Fig. 9, section I, II), the frequency of the alternating voltage generator 1 increases by one frequency step ΔF _G , immediately after comparing the constant voltages U _{Lmm_} and U _{Cmm_} , thereby increasing the voltage UL and reducing the voltage U _C by the value of the voltage corresponding to the minimum possible threshold for detecting the signal reflected from the target. If U _res >0, (Fig. 9, section III), the frequency of the alternating voltage generator 1 is reduced by one step of changing the frequency ΔF _G , immediately after comparing the constant voltages U _{Lmm_} and UC _{mm_} , thereby reducing the voltage U _L and increasing the voltage U _C by the voltage value corresponding to the minimum possible threshold for detecting the signal reflected from the target.

The state of periodic sign change of the resulting DC voltage _Ures , in the absence of a reflected signal from the target, (Fig. 9, section III, IV) indicates the elimination of the influence of destabilizing factors, i.e. U _{Lmm_} ≈U _{Cmm_} and, accordingly, U res _≈0 .

Deviation in the search process, the resulting constant voltage _Ures from zero, by a value exceeding the voltage of the minimum possible threshold for detecting a signal reflected from the target, fixed by the display module 11, will indicate the detection of the target. Moreover, the polarity of the resulting constant voltage _Ures determines the nature of the target material: ferromagnet (Fig. 9, section V) or diamagnet (Fig. 9, section VI), and the value determines the volume of the target and the depth of occurrence.

OPTION 2.

This goal is achieved by the fact that in a series oscillatory LC circuit, the coil of which is a metal detector sensor, to which a sinusoidal alternating voltage is supplied, with a frequency approximately equal to its natural frequency, the voltage amplitudes on the sensor coil and capacitor are compared. To do this, the voltage amplitudes from the metal detector sensor coil and the capacitor, relative to the common point of the series oscillatory LC circuit, are converted into isolated voltages, for which a stable threshold voltage is subtracted from their amplitudes.

The maximum value of the amplitudes of the isolated voltages should not exceed the breakdown value of the electronic components of the metal detector, because the voltage amplitudes on the sensor coil and capacitor, due to resonance, can reach values of several hundred volts.

The isolated voltages from the metal detector sensor coil and from the capacitor are converted into constant voltages of the same polarity, equal to their amplitude, respectively. The resulting DC voltage is isolated, for which a DC voltage corresponding to the voltage amplitude on the capacitor is subtracted from the DC voltage corresponding to the voltage amplitude on the sensor coil.

During the search for a target, the deviation of the resulting DC voltage by more than the value of the voltage of the minimum possible threshold for detecting a signal reflected from the target will indicate the detection of the target, and the polarity of the difference in DC voltages determines the nature of the target material: ferromagnetic or diamagnetic, and the voltage value determines the volume of the target and depth of occurrence.

A series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and capacitor must be equal, during the search, with various destabilizing factors, in the absence of a reflected signal from the target. Accordingly, the resulting DC voltage should not exceed the voltage of the minimum possible threshold for detecting a signal reflected from the target. Failure to fulfill the condition of equality of voltage amplitudes on the sensor coil and capacitor will mean that the effect of destabilizing factors has not been eliminated, which necessitates correction of the frequency of the sinusoidal alternating voltage, which is carried out as follows. With a given frequency, the resulting constant voltage is monitored in the absence of a reflected signal from the target. If the polarity of the resulting DC voltage is negative, then the frequency of the sinusoidal AC voltage is increased step by step, by an amount equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to positive. If the polarity of the resulting DC voltage is positive, the frequency of the sinusoidal AC voltage is reduced step by step, by an amount equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to negative. The state of periodic sign change of the resulting constant voltage indicates that it is less than the voltage of the minimum possible threshold for detecting a signal reflected from the target, i.e. is practically equal to zero, respectively, the voltage amplitudes on the sensor coil and capacitor are equal, therefore, the series oscillatory LC circuit is brought into a balanced state.

The specified frequency of control of the resulting direct voltage is selected with a frequency of 5-20 Hz, a duration of 1-2 milliseconds.

Correcting the frequency of a sinusoidal alternating voltage does not introduce significant errors in the results, because the given frequency of correction and the step of changing the frequency of the sinusoidal alternating voltage does not allow the resulting direct voltage to be reduced to zero in the presence of a reflected signal, since destabilizing factors make changes much slower and less than the impact of the reflected signal from the target.

The disturbing effect on the resulting DC voltage caused by the reflected signal from the target is temporary, and the equality of the voltages on the coil of the sensor and the capacitor is violated, which is restored after the termination of the disturbing effect from the reflected signal.

A device that implements the second version of the 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 oscillatory LC circuit, consisting of a shielded coil, which is a metal detector sensor, and capacitor is equipped with two voltage limiters, two resistors, two peak detectors with reset, an adder, display and correction modules, optical isolation, two power supplies. Moreover, the first output of the generator output is connected to the first outputs of the coil and the first voltage limiter, which is connected by the second output to the first output of the first resistor and the input of the first peak detector with reset, the output is connected to the direct input of the adder, the second output of the generator output is connected to the first outputs of the capacitor and the second voltage limiter, which is connected by its second output to the first output of the second resistor and the input of the second peak detector with reset, the output is connected to the inverse input of the adder, which is connected with its output to the inputs of the display module and the correction module, the first output of which, through an optical isolation, is connected to the input generator control and the second output - to the reset inputs of the first and second peak detectors with reset. The screen of the sensor coil, the second terminals of the sensor coil, capacitor, first and second resistors are connected to the zero wire of the adder. The first power supply is connected to the power supply circuits of the generator, the second - to the power supply circuits of the adder, display module, correction module, while the first and second power supplies are galvanically isolated.

The proposed device (Fig. 10), which implements the second version of the method, works as follows. A sinusoidal alternating voltage U _G , frequency F _G from the output terminals of the alternating voltage generator 1, is fed to a series oscillatory LC circuit formed by the sensor coil 2 and capacitor 3. As a result, voltages U _L and U _C are formed on them, respectively, relative to the total points of a series oscillatory LC circuit, the second terminals of the first 13, second 14 resistors and the zero wire of the adder 10. In this case, in the resonance mode, the value of the maximum voltage amplitudes on the sensor coil 2 and capacitor 3 reaches the value:

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

U _Lm - voltage amplitude on the sensor coil 2;

U _Cm - voltage amplitude on the capacitor 3;

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

Voltage limiters 18 and 19 have a stable threshold voltage, determined by the condition:

Where: | U _w | - the module of the specified voltage, the value of which is taken to be less than 2v than the voltage of the second 5 power source multiplied by the quality factor of the series oscillatory LC circuit;

|U _Гm | - amplitude module of the alternating voltage of the alternating voltage generator 1 supplied to the series oscillatory LC circuit.

The voltage module from the sensor coil 2, through the first voltage limiter 18, is allocated to the first resistor 13:

The voltage module from the capacitor 3, through the second voltage limiter 19, is allocated to the second resistor 14:

Where: |ΔU _Lm | - the module of the selected voltage from the voltage amplitude to the coils 1 of the sensor 2;

|ΔU _Сm | - the module of the selected voltage from the amplitude of the voltage on the capacitor 3.

The selected voltages ΔU _Lm and ΔU _Cm are fed to the inputs of the first PDSS 6 and the second PDSS 7, respectively, where they are converted into DC voltages of the same polarity ΔU _{Lm_} and ΔU _Cm equal to their amplitude. The voltage ΔU _{Lm_} from the output of the first PDSS 6 is supplied to the direct input of the adder 10, the voltage ΔU _{Cm_} from the output of the second PDSS 7 is fed to the inverse input of the adder 10, in which the resulting constant voltage is allocated:

The resulting constant voltage L _res , from the output of the adder 10 is fed to the inputs of the correction modules 8 and indication 11. If there is no target in the search area, respectively, the absence of a reflected signal from the target, equality (10) must be observed. Failure to comply with it means that the impact of destabilizing factors has not been eliminated, as a result of which the frequency F _G of the alternating voltage generator 1 is automatically corrected. Correction module 8 at the first output generates correction pulses U _ynp with a frequency of 5 Hz<F _K <20 Hz, duration 1-2 ms, sign corresponding to the polarity of the resulting direct voltage U _res , at the time of correction, which change the frequency F _G of the alternating voltage generator 1, by the value ΔF _G «F _G , equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target. At the second output, it generates unipolar reset pulses U _c6 , with the same frequency-time parameters, which, with a trailing edge, reset the previously recorded constant voltage ΔU _{Lm_ by} the first PDSS 6 and the constant voltage ΔU _{Cm_ by the} second PDSS 7. After that, they fix new values of constant voltages ΔU _{Lm_} and ΔU _{Cm_} .

In the event that U _res <0 (Fig. 11, section I, II), the frequency of the alternating voltage generator 1 increases by one frequency step ΔF _G immediately after comparing the constant voltages ΔU _{Lm_} and ΔU _{Сm_} , thereby increasing the voltage U _L and reducing the voltage U _C by the value of the voltage corresponding to the minimum possible threshold for detecting the signal reflected from the target. If U _res >0 (Fig. 11, section III), the frequency of the alternating voltage generator 1 decreases by one step of changing the frequency ΔF _G immediately after comparing the constant voltages ΔU _{Lm_} and ΔU _{Cm_} , thereby reducing the voltage U _L and increasing the voltage U _C by the voltage value corresponding to the minimum possible threshold for detecting the signal reflected from the target.

The state of the periodic sign change of the resulting DC voltage _Ures , in the absence of a reflected signal from the target (Fig. 11, section III, IV) indicates that the influence of destabilizing factors has been eliminated, i.e. ΔU _{Lm_} ≈ΔU _{Cm_} and, accordingly, U res _≈0 . Deviation, during the search, of the resulting constant voltage _Ures from zero, by an amount exceeding the voltage of the minimum possible threshold for detecting a signal reflected from the target, fixed by the display module 11, will indicate the detection of the target. Moreover, the polarity of the resulting constant voltage _Ures determines the nature of the target material: ferromagnet (Fig. 11, section V) or diamagnet (Fig. 9, section VI), and the magnitude of the voltage determines the volume of the target and the depth of occurrence.

OPTION 3.

This goal is achieved by the fact that in a series oscillatory LC circuit, the coil of which is a metal detector sensor, to which a sinusoidal alternating voltage is supplied, with a frequency approximately equal to its natural frequency, the voltage amplitudes on the sensor coil and capacitor are compared. For this, the voltage from the sensor coil and the capacitor, relative to the common point of the series oscillatory LC circuit, is converted into DC voltages equal to their amplitude, and the voltage from the sensor coil is converted into a positive DC voltage, and from the capacitor into a negative one. A comparison is made of a constant voltage corresponding to the voltage amplitude on the sensor coil with a constant voltage corresponding to the voltage amplitude on the capacitor, by adding them. As a result of the comparison, the resulting constant voltage is revealed, the maximum value of which should not exceed the breakdown value of the electronic components of the metal detector.

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

A series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and capacitor must be equal, during the search, with various destabilizing factors, in the absence of a reflected signal from the target. Accordingly, the resulting DC voltage should not exceed the voltage of the minimum possible threshold for detecting a signal reflected from the target. Failure to fulfill the condition of equality of voltage amplitudes on the sensor coil and capacitor will mean that the effect of destabilizing factors has not been eliminated, which necessitates correction of the frequency of the sinusoidal alternating voltage, which is carried out as follows. With a given frequency, the resulting constant voltage is monitored in the absence of a reflected signal from the target. If the polarity of the resulting DC voltage is negative, then the frequency of the sinusoidal AC voltage is increased step by step, by an amount equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to positive. If the polarity of the resulting DC voltage is positive, the frequency of the sinusoidal AC voltage is reduced step by step, by an amount equal to the frequency change step corresponding to the voltage of the minimum possible threshold for detecting a signal reflected from the target, until the sign of the resulting DC voltage changes to negative. The state of periodic sign change of the resulting constant voltage indicates that it is less than the voltage of the minimum possible threshold for detecting a signal reflected from the target, i.e. is practically equal to zero, respectively, the voltage amplitudes on the sensor coil and capacitor are equal, therefore, the series oscillatory LC circuit is brought into a balanced state.

The specified frequency of control of the resulting voltage is selected with a frequency of 5-20 Hz, a duration of 1-2 milliseconds.

Correcting the frequency of a sinusoidal alternating voltage does not introduce significant errors in the results, because the given frequency of correction and the step of changing the frequency of the sinusoidal alternating voltage does not allow the resulting direct voltage to be reduced to zero in the presence of a reflected signal, since destabilizing factors make changes much slower and less than the impact of the reflected signal from the target.

The disturbing effect on the resulting DC voltage caused by the reflected signal from the target is temporary, and the equality of the voltages on the coil of the sensor and the capacitor is violated, which is restored after the termination of the disturbing effect from the reflected signal.

A device that implements the third version of the 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 oscillatory LC circuit consisting of a shielded coil, which is a metal detector sensor, and capacitor is equipped with two peak detectors with reset, a passive adder containing three resistors, a buffer amplifier, display and correction modules, optical isolation, two power supplies. Moreover, the first output of the generator output is connected to the first output of the coil and the input of the first peak detector with reset, the output is connected to the first output of the first resistor, passive adder, the second output of the generator is connected to the first output of the capacitor and the input of the second peak detector with reset, the output is connected to to the first output of the second resistor, a passive adder, the second outputs of the first and second resistors are connected to the first output of the third resistor and the input of the buffer amplifier, which is connected with its output to the inputs of the display module and the correction module, the first output of which, through an optical isolation, is connected to the control input generator, the second - to the reset inputs of the first and second peak detectors with reset. The screen of the sensor coil, the second terminals of the sensor coil, capacitor, third resistor are connected to the neutral wire of the buffer amplifier. The first power supply is connected to the power supply circuits of the generator, the second - to the power supply circuits of the buffer amplifier, display module, correction module, while the first and second power supplies are galvanically isolated.

The proposed device (Fig. 12), which implements the third version of the method, works as follows. A sinusoidal alternating voltage U _G , frequency F _G from the output of the alternating voltage generator 1, is fed to a series oscillatory LC circuit formed by a sensor coil 2 and a capacitor 3, as a result of which voltages U _L and U _C are formed on them, respectively, relative to the common point of the series oscillatory LC circuit, the second output of the third resistor 16, and the neutral wire of the buffer amplifier 21. In this case, in the resonance mode, the value of the maximum voltage amplitudes on the sensor coil and capacitor reaches the value:

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

U _Lm - voltage amplitude on the sensor coil 2;

U _Cm - voltage amplitude on the capacitor 3;

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

The voltage from the first output of the coil 2 is fed to the input of the first PDSS 6, which is converted in it into a positive DC voltage U _{Lm_} , equal to the voltage amplitude U _Lm on the sensor coil 2. The voltage from the first output of the capacitor 3 is fed to the input of the second PDSS 7, which is converted in it into a negative constant voltage U _{Cm_} , equal to the amplitude of the voltage U _Cm on the capacitor 3. The voltage U _{Lm_} is supplied to the first output of the first resistor 13, the passive adder 20, U _{Cm_} is supplied to the first output of the second resistor 14, the passive adder 20. In the node passive adder 20, formed by connecting the second outputs of the first 13, second 14 resistors and the first output of the third 16 resistor, the difference in constant voltages is allocated:

Where: K _ZKM - the specified scaling factor.

In this case, the condition must be met:

The difference of constant voltages ΔU_ is fed to the input of the buffer amplifier 21, in which it is converted into the resulting constant voltage:

From the output of the buffer amplifier 21, the resulting constant voltage _Ures is supplied to the inputs of the display module 11 and the correction module 8. If there is no target in the search area, respectively, the absence of a reflected signal from the target, equality (15) must be observed. Failure to comply with it means that the impact of destabilizing factors has not been eliminated, as a result of which the frequency F _G of the alternating voltage generator 1 is automatically corrected. Correction module 8 at the first output generates correction pulses U _ypr with a frequency of 5 Hz<F _K <20 Hz, duration 1-2 ms, sign corresponding to the polarity of the resulting direct voltage U _res at the time of correction, which change the frequency F _G of the alternating voltage generator 1, by the value ΔF _G <<F _G equal to the frequency change step corresponding to the voltage, the minimum possible threshold for detecting a signal reflected from the target, at the second output it generates unipolar pulses U _cb with the same frequency-time parameters, which reset the previously recorded voltage U _{Lm_ by} the first PDSS 6 and the voltage U _{Cm_ by the} second PDSS 7 with the trailing edge. After that, they fix new voltage values U _{Lm_} and U _Cm _ .

In the event that U _res <0 (Fig. 13, section I, II), the frequency of the alternating voltage generator 1 increases by one frequency step ΔF _G immediately after comparing the values of U _{Lm_} and U _{Cm_} , thereby increasing the voltage U _L and reducing the voltage U _C by the value of the voltage corresponding to the minimum possible threshold for detecting the signal reflected from the target.

If U _res >0 (Fig. 9, section III), the frequency of the alternating voltage generator 1 is reduced by one step of changing the frequency ΔF _G immediately after comparing the values of U _{Lm_} and U _{Cm_} , thereby reducing the voltage U _L and increasing the voltage L _C by the value of the voltage corresponding to the minimum possible threshold for detecting the signal reflected from the target.

The state of periodic sign reversal of the resulting DC voltage _Ures , in the absence of a reflected signal from the target, (Fig. 13, section III, IV) indicates the elimination of the influence of destabilizing factors, i.e. U _{Lm_} ≈U _{Cm_} and, accordingly, U res _≈0 . Deviation, during the search, of the resulting constant voltage _Ures from zero, by an amount exceeding the voltage of the minimum possible threshold for detecting a signal reflected from the target, fixed by the display module 11, will indicate the detection of the target. Moreover, the polarity of the resulting constant voltage _Ures determines the nature of the target material: ferromagnet (Fig. 13, section V) or diamagnet (Fig. 13, section VI), and the value determines the volume of the target and the depth of occurrence.

Sources of information:

1. AC USSR G01V 3/00, 05/28/75 No. 741216 Metal detector.

2. Book. A. Shchedrin, I. Osipov "Metal detectors for searching for treasures and relics", Moscow, Radio and Communications: Hotline - Telecom, 2000

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

4. http://www.minelab.com/russia/patents.

5. studopedia.ru Series oscillatory circuit. Lecture 15

Claims (23)

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 oscillatory LC circuit, the coil of which is a metal detector sensor, with a frequency approximately equal to its natural frequency, characterized in that in order to improve the reliability of detecting the reflected signal from the target, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, the amplitudes of the voltage on the sensor coil and capacitor are compared, while the voltage from the sensor coil and capacitor, relative to common point of a series oscillatory LC circuit, convert by dividing by a stable scaling factor into scaled voltages, which are converted into constant voltages of the same polarity equal to the amplitude of the scaled voltages, compare them subtract by dividing from a constant voltage corresponding to the amplitude of the voltage on the sensor coil, a constant voltage corresponding to the amplitude of the voltage on the capacitor, the obtained difference of constant voltages is multiplied by a scaling factor, as a result, the resulting constant voltage is revealed. 2. The method according to claim 1, characterized in that the scaling factor is selected from the conditions under which the maximum values of the amplitudes of the scaled voltages from the sensor coil and capacitor should not exceed the electrical breakdown of the electronic components of the circuit. 3. 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 a metal detector sensor, with a frequency approximately equal to its natural frequency, characterized in that in order to improve the reliability of detecting the reflected signal from the target, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, the amplitudes of the voltage on the sensor coil and capacitor are compared, while the voltage from the sensor coil and capacitor, relative to common point of a series oscillatory LC circuit, are converted into isolated voltages, for which voltages are isolated from the voltage amplitudes on the sensor coil and capacitor, exceeding, in modulus, a stable threshold voltage, the selected voltages are converted into constant e voltages of the same polarity, they are compared by subtracting from the constant voltage corresponding to the voltage amplitude on the sensor coil, the constant voltage corresponding to the voltage amplitude on the capacitor, as a result, the resulting constant voltage is revealed. 4. The method according to claim 3, characterized in that a stable threshold voltage is selected from the conditions under which the maximum amplitudes of the emitted voltages from the sensor coil and capacitor should not exceed the electrical breakdown of the electronic components of the circuit. 5. 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 a metal detector sensor, with a frequency approximately equal to its natural frequency, characterized in that in order to improve the reliability of detecting the reflected signal from the target, in the presence of the influence of destabilizing factors, in the process of searching and detecting it, the amplitudes of the voltage on the sensor coil and capacitor are compared, while the voltage from the sensor coil and capacitor, relative to the common point of a series oscillatory 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, they are compared by adding the constant voltage corresponding to the amplitude of the voltage on the coil of the sensor with a constant voltage corresponding to the amplitude of the voltage on the capacitor, as a result, the resulting constant voltage is detected. 6. The method according to claim 5, characterized in that the maximum value of the resulting constant voltage should not exceed the breakdown value of the electronic components of the metal detector. 7. The method according to any one of paragraphs. 1, 3, 5, characterized in that the deviation of the resulting constant voltage in the process of searching for a target by more than the value of the voltage of the minimum possible threshold for detecting a signal reflected from the target will indicate the detection of the target. 8. The method according to any one of paragraphs. 1, 3, 5, characterized in that the polarity of the resulting constant voltage determines the nature of the target material: ferromagnet or diamagnet, and the value determines the volume of the target and the depth of occurrence. 9. The method according to any one of paragraphs. 1, 3, 5, characterized in that the series oscillatory LC circuit is maintained in a balanced state, in which the voltage amplitudes on the sensor coil and capacitor must be equal during the search, with various destabilizing factors, in the absence of a reflected signal from the target. 10. The method according to claim 9, characterized in that in order to establish equality of the voltage amplitudes on the sensor coil and the capacitor, the resulting constant voltage is monitored at a given frequency: when the voltage exceeds the minimum possible threshold for detecting a signal reflected from the target, in the absence of a reflected signal from the target, and negative polarity of the resulting DC voltage, the frequency of the sinusoidal AC voltage is reduced step by step by an amount equal to the step of frequency change corresponding to the voltage of the minimum possible threshold for detecting the signal reflected from the target, until the sign of the resulting DC voltage changes to positive, if the polarity of the resulting DC voltage is positive, the frequency of the sinusoidal AC voltage is increased step by step, by an amount equal to the frequency change step, until the sign of the resulting voltage changes to negative. 11. The method according to claim 10, characterized in that the specified frequency of control of the resulting voltage is selected with a frequency of 5-20 Hz, a duration of 1-2 milliseconds. 12. A device that implements the method according to claim 1, containing: an alternating voltage generator, a series oscillatory LC circuit, consisting of a metal detector sensor coil, the first output connected to the first output output of the generator, a capacitor, the first output connected to the second output output of the generator, which differs in that it is equipped with display and correction modules, optical isolation, two power supplies, two voltage dividers consisting of four resistors, two peak detectors with reset, an adder, and the first output of the first resistor, the first voltage divider, is connected to the first outputs of the sensor coil and the output of the generator, and the second output is connected to the first output of the second resistor, the first voltage divider, and the input of the first peak detector with reset, the output is connected to the direct input of the adder, the first output of the third resistor, the second voltage divider, is connected to the first output of the capacitor and the second output output generator ora, the second output is connected to the first output of the fourth resistor, the second voltage divider, and the input of the second peak detector with reset, the output is connected to the inverse input of the adder, which is connected with its output to the inputs of the display module and the correction module, the first output of which, through an optical isolation, connected to the generator control input, and the second output - to the reset inputs of the first and second peak detectors with reset, the second outputs of the sensor coil, capacitor, second and fourth resistors are connected to the zero wire of the adder, while the first power supply is connected to the power supply circuits of the generator, the second - to the power circuits of the adder, display module, correction module. 13. The device according to claim 12, characterized in that the parameters of the first and second voltage dividers are the same. 14. The device according to claim 12, characterized in that the stable scaling factor of the first and second voltage dividers is greater than the quality factor of the series oscillatory LC circuit. 15. The device according to claim 12, characterized in that the input resistances of the first and second dividers are at least 1000 times greater than the complex resistances of the sensor coil and capacitor, a series oscillatory LC circuit. 16. A device that implements the method according to claim 3, containing: an alternating voltage generator, a series oscillatory LC circuit, consisting of a metal detector sensor coil, the first output connected to the first output output of the generator, a capacitor, the first output connected to the second output output of the generator, which differs in that it is equipped with display and correction modules, optical isolation, two power supplies, two voltage limiters, two resistors, two peak detectors with reset, an adder, the first output of the first voltage limiter is connected to the first outputs of the sensor coil and the generator output, the second output connected to the first terminal of the second resistor and the input of the first peak detector with reset, the output connected to the direct input of the adder, the first terminal of the second voltage limiter, connected to the first terminal of the capacitor and the second terminal of the generator output, the second terminal is connected to the first terminal of the second resistor and the input of the watt high peak detector with reset, the output connected to the inverse input of the adder, which is connected with its output to the inputs of the display module and the correction module, the first output of which, through optical isolation, is connected to the generator control input, the second output is connected to the reset inputs of the first and second peak detectors with reset, the second terminals of the sensor coil, capacitor, first and second resistors are connected to the zero wire of the adder, while the first power source is connected to the power supply circuits of the generator, the second - to the power supply circuits of the adder, display module, correction module. 17. The device according to claim 16, characterized in that the first and second voltage limiters are bipolar, microcurrent zener diodes. 18. The device according to claim 17, characterized in that the stabilization voltage of bipolar, microcurrent zener diodes is the same and equal to a value less than 2 V than the voltage of the second power source multiplied by the quality factor of the series oscillatory LC circuit. 19. A device that implements the method according to claim 5, containing: an alternating voltage generator, a series oscillatory LC circuit consisting of a metal detector sensor coil, the first output connected to the first output output of the generator, a capacitor, the first output connected to the second output output of the generator, which differs in that it is equipped with display and correction modules, optical isolation, two power supplies, two reset peak detectors, a passive adder containing three resistors, a buffer amplifier, the first reset peak detector being connected to the first output terminal of the generator and the first output of the coil , and the output is connected to the first output of the first resistor, passive adder, the second peak detector with reset input is connected to the second output output of the generator and the first output of the capacitor, and the output is connected to the first output of the second resistor, passive adder, the second outputs of the first and second resistors are connected to first conclusion ohm of the third resistor and the input of the buffer amplifier, which is connected with its output to the display module and the correction module, the output of which, through optical isolation, is connected to the generator control input, and the second output is connected to the reset inputs of the first and second peak detectors with reset, the second outputs of the coil sensor, capacitor, third resistor are connected to the neutral wire of the buffer amplifier, the first power supply is connected to the power supply circuits of the generator, the second power supply is connected to the power supply circuits of the buffer amplifier, display module, correction module. 20. The device according to claim 19, characterized in that the input impedance of the first and second peak detectors with reset, together with a passive adder, is greater than the complex resistances of the sensor coil and capacitor, a series oscillatory LC circuit, at a resonance frequency, at least 1000 times . 21. The device according to claim 19, characterized in that in the passive adder the first and second resistors have the same resistance value. 22. The device according to claim 19, characterized in that the given scaling factor of the passive adder is equal to the gain of the buffer amplifier. 23. The device according to any one of paragraphs. 12, 16, 19, characterized in that the first and second power supplies are galvanically isolated.

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