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Coping with electrical interference
The primary reason metal detectors provide a sensitivity (gain and/or threshold) control,
is so that users can reduce sensitivity in order to eliminate response to electrical
interference. Some users are reluctant to reduce sensitivity out of fear of losing depth.
At reduced sensitivity settings, you may lose same depth, but at least you can still
search. The Gain and Threshold knobs control the sensitivity and are your first line of
defence against electrical interference.
Electrical interference is usually more controllable in the ALL METAL Mode than in the
DISC Mode. On the TX-850, setting the discrimination level between 60 and 70 will
usually reduce electrical interference. In the DISC Mode, the detector may chatter if the
search coil is not in motion, but once you start sweeping it over the ground, the signal
from the ground will usually suppress the electrical interference chatter, except for an
occasional pop or click which will not sound like a real target.
IF you are conducting an indoor demonstration, you may find that changing the
orientation of the search coil will reduce the pickup of electrical interference.
If you carry a cell phone or other high-tech electronic equipment while metal detecting
and you encounter electrical interference, try turning the device off and see if that solves
the problem. Turn such devices completely off, not just into standby mode.
When working near overhead power lines, you may get the best results right under the
power line and the worst results when standing at 30° to 45°angle to the power line.
Many sources of electrical interference are intermittent. You may find that an area which
is difficult to search at one time of day may be easier after 5 PM, or on weekends. Power
lines are usually quietest late at night, and on weekend mornings.
Small search coils usually pick up less electrical interference that larger search coils. On
a site with severe electrical interference, a small search coil is often a better choice than
a large one.
Distinguishing electrical interference from other problems
Electrical interference will often vary as you walk around from place to place, and it will
also vary with changes in the orientation of the search coil. This is almost never the case
if there is a functional problem with the metal detector itself.
The most common cause of a noisy metal detector, where the problem is not electrical
interference, is a defective search coil. If striking the search coil with your hand causes
the noise to start or stop, the problem could be a defective search coil. Also, a defective
search coil often causes noise of a more intermittent nature than electrical interference.
The second most common cause is a loose search coil connector. The noise from a loose
connector will usually be very erratic or intermittent in nature. Try unplugging the search
coil and then reconnecting it to ensure the connector is firmly installed.
If you use a search coil cover, dirt or water can accumulate inside it, and movement of
those materials can cause false signals while sweeping the search coil. Search coil covers
must be periodically removed and cleaned.
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