By
Steve Herschbach
The waterproof pulse induction field is very limited at this time. It divides into two classes. Pulse induction metal detectors that ground balance, and those that do not.
A pulse induction (PI) detector by its nature tends to ignore mineralization, so much so that in milder conditions a PI works fine without a ground balance circuit. As I noted above however a PI is not immune to mineralization. A non-ground balancing PI detector will sound off when raised and lowered over true black sands. The more concentrated the magnetite, the more intense these signals will be. The bottom line is that on real bad black sand beaches even a basic pulse induction will sound off if the coil height is varied too rapidly over the beach. In the water with troughs and depressions false signals are all but impossible to avoid. The most extreme situations require a ground balancing pulse induction (GBPI) metal detector.
Pure white non-magnetic coral beaches - most any detector will work well
Even a hint of mineralization - a multifrequency detector has an edge over single frequency VLF where there are both saltwater and magnetic minerals.
Moderate mineralization - you want multifrequency or pulse induction.
Severe mineralization - at some point a ground balancing PI (GBPI) is required.
The above conditions grade from one into the other seamlessly. Hot rocks are a wild card as hot rocks in a normally mild beach can cause false signals on a PI detector that lacks ground balancing capability.
Finally, I should note that PI detectors with ground balancing capability have a crude sort of tone discrimination that can be used to advantage.
Fully submersible pulse induction metal detectors
Here are the current mainline waterproof PI detector offerings:
Bounty Hunter - no PI
Garrett - Sea Hunter Mark II (PI) and ATX (GBPI)
Fisher - Impulse AQ
Minelab - SDC 2300 (GBPI)
Nokta/Makro - no PI
Teknetics - no PI
Tesoro - Sand Shark (PI) (Discontinued)
White's - Surfmaster Dual Field (PI) and TDI BeachHunter (GBPI)
XP - No PI
Finally, here are the key specifications for comparison:
Fully submersible pulse induction metal detectors
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