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Departement of international trade:
reaction on hot rocks is to use the DHR algorithm (Disc. of hot rocks).
The risk from using discrimination settings to eliminate an audio re-
sponse to hot rocks is this. Due to effect of the ground valuable targets,
whose vector angle is close to that of hot rocks, can being missed. This
risk is virtually eliminated by using the algorithm DHR instead. But the
best and the most reliable way is to learn to identify such stones by ear
,
b
y a specific elongated signal.
Advice of an experienced searcher:
Having unearthed a similar stone, put it on the ground, and next to it, dig
a large copper coin. Scanning a stone and a coin in turn, listen to the dif-
ference in the signals - they are very different. The signal of a metal object
(both RT and ST) seems to be concentrated at the point of location of the
object. At the same time, the stone is distinguished by a long elongated RT
and belated ST signal after the coil is carried over it. “As if they pulled (RT)
and released (ST) the elastic”
As you know, a particular problem for induction metal detectors is the
identification of flat ferromagnetic objects such as steel caps/stoppers,
lids, cans, etc., objects with a relatively large diameter of the eddy cur-
rents. This is largely helped out by using our proprietary development –
The Hodograph Display (see Fig. 17).
In the interaction of such objects with the coil (assuming that the level
of the signal is above 20) then time curves of these objects, as a rule, are
twisted or looped in nature and “scattered” around the screen depending
on the direction of the scan. Fig. 17 shows the travel times of these types
of signals from an iron bottle cap/stopper.
For the given case, a sign that the ferromagnetic object is the loop-like
character of the hodographs and their scatter depending on the scanning
direction.
Normal operating mode
Fig. 17
