III Parameters dependent for the use of the metal detector

To traverse the fields, wood, the meadows, etc... is a thing. To detect and all to detect is another thing. Indeed, c?est a demanding and rigorous detection which requires patience, perseverance and practice.

Consequently and it is in the sense that this part will tend, it is multiple risks which re-enter concerned and which are significant from the point of view of the good knowledge of detection.

These parameters, to be usable and reproducible, were studied on plane surface so that the apparatus is perfectly handy in places not presenting any irregularity (trees, bushes, rocks, etc...). The analysis which follows was carried out in a harrowed field, it is thus also valid in close-cropped meadows.

Data relating to the use of Fisher 1265-X with head of detection spider 27 cm in diameter.

It seems useful to determine the surface traversed by the user and that really probed in a given time. In a field, two stakes are distant one of the other of 100 meters. Let us measure time necessary to detect the best possible one in straight line between these two sticks. Ten parallel ways were timed. One will not hold account for the moment of the potential holes. On these 100 meters l?utilisator could probe a tape of 1,5 meters width (constant measurement with a margin of 3 cm). Speed of functioning of the individual: 1,62 km/h 3 min. 43 are necessary to make 100 meters length. One hectare (100 meters out of 100 meters) can be detected in 66,67 tapes of 100 meters out of 1,5 meters of width. To detect a hectare correctly, 4 should be passed. 07 min. on the ground. That if no hole is made. The average number d?allers and returns (A. & R.) successive the wafer (head of detection) to traverse 100 meters is 150. For one hectare one needs 10 000 outward journeys and returns. With reason of a way of twice 1,5 meters for an outward journey and return, the wafer of detection traverses 30 kilometers to detect one hectare! The head of detection has an average ground speed of 2 m/sec or 7,2 km/h Concept of loss of surface It is almost impossible to detect a great surface without there being a certain loss. Even while trying to cover the ground perfectly it always occurs of the risks (grass tuft, stones, irregular ground, tiredness, carelessness...) which create zones less better probed. - There are 150 A. & r. for 100 meters. Therefore 1,5 A. & r. or three passages of wafers per meter. The diameter of the head being of 27 cm, out of one meter 80 cm, are really prospected by wafer. In spite of the goodwill of the user only 81% of surface is detected, we thus have a loss of 19%. This loss can be checked by other approaches. One hectare is been overcast into 4. 07, weather during which the wafer should have traversed 10 000 m². With reason of 7200 m./h., the head 27 cm in diameter really explored 8009 m². The loss is 10 000 - 8009 = 1991 m²are 19,9% of surface. We have 10 000 A. & r. for 10 000 m²is 1 A. & r./m². An outward journey corresponds to 1,5 meter (bandwidth) on 0,27 Mr. (diameter of the head). The surface detected for 1 m²is of: (1,5 Mr. X 2) X 0,27 Mr. = 0,81 m². The loss is 0,19 m²is 19%. By three different means we arrive at same the conclusions each time: 19% of detected surface are ineluctably forgotten! However this phenomenon can be explained and minimized. The overlapping of the passages of the head cannot be completely uniform because of the quoted risks and the possible forgeries signals requiring checks and temporary interruption of sweepings. However, these losses can be compensated insofar as the objects rather close to the head without in being with the balance emit an aural beep nevertheless.

Concept of loss in-depth

For a part the maximum depth of detection does not exceed about thirty cm Essayons to determine the volume of ground probed according to sweepings carried out.

Roughly, half of volume is ignored. Let us consider that 15 cm only are taken into account.

For your curiosity, the volume of ground probed for one hectare is of: 10 000 m²X 0,15 Mr. = 1500 m3

Let us estimate, by an experiment carried out, that 1 m3 of ground weighs 1072 kg. There are thus a weight of 1608 tons prospected per hectare.

Data relating to the extraction of the objects:

The study would not be complete if one did not take account of time to make the holes.

The following data take into account all the stages necessary to recover an object: localization of the signal, the extraction, fast cleaning for the identification, the setting out of pocket and stopping.

Timed times:

• Various waste: on 27 holes, the average is 29 dryness.
• Kept objects and parts: on 11 holes, the average is 1 min.

We note without surprise that the " noble " objects require twice more attention.

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