Depth of detection of objects by a metal detector. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Depth of detection of objects by a metal detector. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / metal detectors

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"How deep does he take?" - this question is most often asked by those who see a metal detector for the first time. A specific answer cannot be given, since many different factors affect the depth of metal detection. That is why in any advertisement of metal detectors you will not find a mention of the depth of the device.

Of the factors that determine the depth of detection of an object, only the electromagnetic field and the electronic circuit that interprets the change in the field are functions of the device itself. Other factors depend on the object itself and on the environment.

First of all, the larger the object, the deeper it can be detected (but up to certain limits). For example, most modern devices can detect a silver fifty at a depth of 20-30 cm, while a beer can can be found at a depth of 40-60 cm. However, if the ground is highly mineralized, then the detection depth can be significantly reduced, especially for objects of small size . The humidity of the pound also affects. It usually increases the depth of detection, but not in all cases. Sometimes dry soil gives the best results.

The duration of the presence of objects in the ground also plays a role. Thus, copper and bronze coins that have lain in the ground for centuries and covered with a crust of oxides can be found at a greater depth compared to modern coins. The fact is that copper oxides conduct electric current and, spreading around the coin, seem to increase its size. Corrosion of silver often produces sulphides, which reduce the depth of detection of such silver coins.

The shape of the object also affects the depth of detection. Objects with holes, such as a ring, can be found at greater depths than a coin of the same size. Difficult (in terms of detection) are very thin gold and silver chains. Of great importance is the orientation of the object in the ground. A coin standing on its edge can sometimes not be detected even at a depth of 10 cm. Fortunately for us, most coins lie flat.

The next important factor is the composition of the metal from which the object is made. Some metals have a fairly high electrical conductivity, but often in alloys they lose this property, and it becomes more difficult to find them. An example is an alloy of gold and silver. Both metals are good conductors, but electrum alloy (50% Au-50% Ag) is already a poor current conductor.

The level of discrimination that is used also affects the depth of detection. At low levels, the difference is not so noticeable, but with increasing discrimination, there is a significant loss of depth, especially for small objects and the use of static instruments. For dynamic metal detectors, the effect of discrimination on the detection depth is less pronounced

The level of sensitivity, of course, also affects the depth. As a rule, everyone wants to set the sensitivity knob to the maximum, however, with a strong mineralization of the soil, this leads to false signals and unstable operation of the device. Therefore, at high sensitivity, the depth of detection may actually be noticeably lower than at lower sensitivity. In addition to poor ground, it is often necessary to reduce the sensitivity in case of various electrical interferences (power lines, powerful generators, radars, etc.). In these cases, often reducing the sensitivity will help increase the depth of object detection.

Modern metal detectors determine the object not by its volume (mass), but by the surface area facing the search coil. If you already have a metal detector, you can see for yourself by moving a large coin near the coil with its flat to the coil, and then edge to the coil. In the second case, the detection depth is almost two times less.

Thus, summarizing the above and taking into account other circumstances, the following factors influence the depth of detection of objects:

1. The degree and type of soil mineralization.

2. Soil moisture.

3. The size of the object.

4. The shape of the object.

5. The composition of the metal of the object.

6. Orientation of the object.

7. Type and degree of corrosion of the object.

8. The presence of electrical interference.

9. Type of metal detector.

10. Operating frequency of the metal detector.

11. Size and type of search coil

12. Level of discrimination.

13. Level of sensitivity.

14. The quality of the metal detector settings.

15. Battery status.

16. Operator experience.

17. Speed of movement of the coil.

Special deep metal detectors can detect large objects at a depth of several meters, but they do not detect small objects the size of a coin.

Below are the approximate depths at which various objects can be detected in normal soil using modern metal detectors.

Car, tank - 4-6 m

Iron barrel 200 l - 2-4 m

Canister 20 l - 1,5-2 m

Soldier's helmet - 0,7-1,3 m

Rifle sleeve - 0,2-0,4 m

Copper coin - 0,15-0,3 m

Pipe with a diameter of 50 mm - 1-1,5 m

Author: Bulgak L.V.

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