Search Coils for Metal Detectors, page 16
Pinpoint Metal Detected Targets: Coins On Edge, Audio Responses & Pinpointing Technique
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Pinpointing Coins On Edge
Coins standing on edge or perpendicular to the search coil's bottom emit audio responses similar to nails or short pieces of wire. Also, these coins will not be detected as deep as coins lying flat at the same depth.
The coins on edge will produce two audio responses in one direction of sweep and one response in the perpendicular direction. If the orientation of the coin's edge is perpendicular to the "toe to heel" (north to south) direction of sweep, the audio response will be two beeps close together and one beep in the east to west direction.
This effect will be exactly opposite when the coil's orientation is rotated 90 degrees. In one beep direction of coil movement, visual ID metal detectors may produce false readings of lower conductivity on coins.
Pinpointing in the double beep direction will require estimating center between the beeps. If a trash target resides in the same proximity, additional signals may confuse you.
To eliminate the confusing double response, the "edging" technique is used. The search coil itself is placed on edge, and when the target is pinpointed by "X-ing" the area, the audio responses will be singular in each direction.
The target will still be located respective of the search coil center, but you will not have the easy view of this center compared to the conventional coil orientation. Before trying this pinpointing method in the field, it is recommended to practice in a test garden environment first.