SELECTIVE IMPULSE EDDY CURRENT METAL DETECTOR Russian patent published in 2023 - IPC G01V3/10 

FIELD: electrical engineering.

SUBSTANCE: the invention relates to electrical engineering, and is designed for the search and detection of any hidden metal objects in non-conductive and weakly conductive media. The metal detector contains: an inductance coil, current-limiting resistors, a voltage limiter, a comparator as an inverting signal amplifier, a configurable signal filter based on a comparator, a key based on a field-effect transistor controlled by another low-power bipolar transistor, a computational microcontroller, a keyboard, a graphic display, a sound indication, a light indication, a voltage stabilizer for powering the device. The principle of operation of this metal detector is that short pulses of electric current are fed to the winding of the copper wire that is part of the coil, when interrupted, an EMF of self-induction occurs in the winding. The self-induction EMF of the winding forms an electromagnetic field around itself, if metal objects fall into this field, then eddy currents are also formed in them, which in turn, forming their own electromagnetic field, help to maintain the electromagnetic field of the winding for some time. From this, the voltage drop after the termination of the pulse on the winding is stretched over time. With a short attenuation of the pulse, there is no metal, with a long attenuation of the pulse, there is metal in the sensitivity zone of the sensor. The task of the device is to measure the pulse length in the first and second cases and issue a metal detection signal. This invention distinguishes from all other pulse metal detectors the possibility of selectivity of metal detection, as well as the possibility of more accurate calculation of the signal from a metal target using a microcontroller. Selectivity is achieved by measuring the residual pulse on the winding from two alternately supplied types of signals. These signals, which are the same in frequency, have different boreholes: a depleted signal with a borehole of 1-15% and a saturated signal with a borehole of 20-40%. When measuring the difference between the changes in the durations of the residual pulses of signals with different frequencies (ΔT1 is a depleted signal, ΔT2 is a saturated signal) we will get a value that will characterize the inductance and conductivity of a metal object as the difference in the possibility of maintaining EMF at saturated and depleted signals from the coil (S1=ΔT2-ΔT1). And we can calculate the average change in the duration of the residual pulses as S2=(ΔT2+ΔT1)/2. The constant value D, which characterizes the inductance and conductivity of an individual metal, can be calculated as the ratio of S2 and S1, D =(S2/S1) ⋅ 100%. As an example, we imagine the numbers for some metals obtained according to the electrical diagram below: for iron 70 units, for zinc 87 units, for brass 96 units. The advantages of this method are more stable operation on mineralized soil, since due to the low-frequency powerful pulses of the sensor, the electromagnetic permeability is high and, as a result, the depth of detection of metal objects is greater. The selectivity function allows to configure the device to search only for a certain type of metal, to find out what metal the object is made of, and various defects and impurities in metal materials, etc. The sensor of such a device is less sensitive to shocks and temperature changes. The metal detector can be used in various industries for the following purposes: 1) in medical institutions to search for foreign metal objects in the body of patients; 2) as an inspection device at customs, security posts; 3) in archaeology to search for ore-enriched rocks; 4) for public utilities to search for emergency pipelines, electrical cables, foundation slabs, etc.; 5) in food industry to search for small metal objects in products; 6) in treasure hunting; 7) in the search for explosive devices; 8) in industry for automatic shutdown of agricultural machinery when a metal object enters the crusher, for determining the distance to a metal object, for checking the composition of manufactured alloys and profiles on the conveyor, etc. Figure 1 is a diagram that displays the main functional components of the metal detector. The current-limiting resistor (2) connected to the winding is constantly supplied with positive polarity power. When a signal is applied from the microcontroller (12) to the gate of the field key (4), the key opens, connecting the second end of the winding to the ground for the duration of the pulse. In this case, the signal taken from the resistor (3) connected in series with the winding is transmitted through the diode assembly limiting the voltage level to the input of the operational amplifier (6). The inverted amplified signal enters the variable resistor (7) and allows to adjust the output of the variable signal at the output of the operational amplifier (10), when setting the minimum well before the appearance of noise of the falling edge of the signal, the sensitivity of the device is maximum. This setting is used to adapt sensors that differ in resistance and inductance from the standard one. The differential capacitance (8) introduces a delay in the feedback signal of the operational amplifier when there is a potential between the inputs, and the element (9) is the pole of the amplifier. The resulting useful signal passes through the voltage divider (11) and enters the input of the controller (12), where the time value from the falling edge of the supply signal to the key (4) to the falling edge of the incoming signal is recorded and calculated. The controller repeats these actions for n periods of signals with a small borehole and n periods for signals with an increased borehole, during mathematical calculations and filtering of values, the results of the signal level from the metal and the number of metal discrimination are obtained. All these data are displayed on the display (14). An additional function of informing about the found target is performed by an LED indication and a speaker (15). The keyboard (16), consisting of two buttons, makes it possible to adjust individual parameters according to the sensitivity and threshold of the instrument signal, as well as the sound volume. Element (13) represents a voltage converter for powering the microcontroller. A selective impulse eddy current metal detector, including an inductor, current-limiting resistors, a voltage limiter, a comparator as an inverting signal amplifier, a configurable signal filter based on a comparator, a key based on a field-effect transistor controlled by another low-power bipolar transistor, a computational microcontroller, a keyboard, a graphic display, a sound indication, a light indication, a voltage stabilizer to power the device; the controller sets the frequency applied to the gate of the transistor key, if we take the number of pulses for 0.02-0.2 s as N, then N/2 pulses are supplied with a small well and N/2 pulses with an increased well; the controller receives the incoming signal back and processes it as an interrupt, making time measurements between the signal edges to obtain values of the current state of the residual inductance on the sensor; due to the difference in the change in the pulses of incoming signals from one and the other well, we get a number by which, if we divide the result of the change in the incoming signal from a larger well, we get a constant number for each metal characterizing its magnetoinduction characteristics and conductivity characteristics.

EFFECT: accurate determining the type of metal, easy assembly of the device and the coil to it, low power consumption relative to other pulse metal detectors, more stable operation with electromagnetic interference, high permeability of the signal emanating from the coil.

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