Metal detector device. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Metal detector device. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / metal detectors

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Components of a metal detector

Metal detector device

Rice. 1.1. Components of a metal detector

Armrest. It is located at the top of the main bar and fixes the elbow of the operator's hand. Attaches to the bar with bolts.

Main, upper stem. It usually has an "S" profile, as shown in fig. 1.1. A spongy handle is placed on the bend of the main shaft, by which the operator holds the metal detector. An armrest is attached to it with the ability to adjust the distance.

The ideal distance between the armrest and the handle should be the length of the operator's hand. This provides ergonomics through the best balance of the system, while the operator is less tired.

Блок управления. Contains electronic circuits that allow the generation and processing of searchcoil signals. Most often, the control unit is mounted on the main rod on a detachable connection, but there are models in which the main rod and the control unit are a single unit.

Reinforced plastic lower stem. On one side, it is inserted into the main rod, where it is fixed with a connector with a clamping ring. The use of this type of clamp allows you to adjust the total length of the device at any time, choosing the most optimal for the operator.

search coil. It is attached to the lower rod with a plastic bolt and nut. It turns out a connection with the ability to adjust the angle between the plane of the coil and the rod. From the coil to the control unit there is a cable that has a connector plug and is connected to the connector.

Usually, at the end of the search, incomplete disassembly of the metal detector For transportation purposes into two parts:

lower rod with coil;
top bar with control unit and armrest.

Metal detector coil configuration

Coils of metal detectors (metal detectors) can have a different configuration. The most practical and technological considered:

coils with a "wide" grip;
coils with "point" capture.

Currently, the second version of the design with a "point" capture is most often used.

In a number of cases, a part of the transmitting coil is wound around the receiving coil, which is turned on anti-phase-main (large diameter). The number of turns of such anti-phase coil is selected in such a way that the field around the receiving coil is balanced. And the magnetic flux of the large transmitting coil, which enters from one side, is balanced by the magnetic flux of the small coil, which enters the receiving coil from the other side.

There is a certain proportion in the ratio of the diameters of the transmitting and receiving coils. In this case, the best tuning of this system is achieved, as well as the possibility of obtaining a small level of residual signal in the receiving coil.

Residual signal level depends on many factors:

on the signal power in the transmitting coil;
from the location of the coils;
on the number of turns of the receiving coil;
from goodness;
on the quality of workmanship;
from the shape of the coils;
from their mutual position.

Therefore, it can have a significant spread from units to hundreds of millivolts.

If the receiving coil is included in a parallel oscillatory circuit (which is done quite often), the level of the residual signal can increase tens or hundreds of times due to resonance.

In this case, it is impossible to obtain a significant preliminary amplification of the signal of the receiving coil in terms of alternating voltage. This, in turn, requires significant DC voltage gains after the useful signal has been detected. But then the problem of "drift" is exacerbated, leading to unstable operation of the metal detector.

Residual signal level (R.S.) can to some extent affect the sensitivity of the metal detector. After all, after detecting a useful signal in the successor, the signal-to-noise ratio at high levels of O.S. decreases.

Comparison of the properties of coils with large and small widths

Which coil is better for searching - with a "wide" or "narrow" grip? There is no single answer.

According to the experience of using "point" capture better, since coils with a "wide" grip:

have a small ability of point orientation;
have a tendency to receive false signals from iron objects that are located on the outskirts of the search area.

But "wide" coils do not allow for such a dense scanning of the examined area of the earth, as coils with "point" capture.

This allows you to view large areas for a fixed period of time, and if the area is also not too saturated with metal, you get a decent time saving.

When working with a coil with a "point" capture, it is necessary to monitor the scanning density. Each subsequent stroke of the coil should overlap the previous trajectory by no more than half a diameter. Otherwise, gaps are inevitable, especially at the maximum detection depth.

Reels with point grip have benefits:

good when working in heavily littered areas;
they make it easier and faster to establish the exact location of the find (target).

Few search engines follow the rules for working with coils that have a "point" capture.

The trajectory of movement of their coil resembles a wide zigzag in the areas covered, as a result, many omissions of finds are obtained. As a result, during the repeated "ringing" of such sites, the finds they missed were often found.

Be careful, do not rush, remember, just one thing you missed can be more valuable than all the others put together.

Author: Dubrovsky S.L.

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