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Date Posted: 11:31:46 06/28/02 Fri
Author: Steve Herschbach
Subject: Re: GB Numbers (Mineral Type)
In reply to: trapper 's message, "Re: More first impressions of new "Mini DD" coil from White's" on 22:21:24 06/27/02 Thu

Hi trapper,

You've hit one of my favorites gripes... metal detector ground balance numbers are backwards!

Low numbers indicate "hot" or "positive" ground, ground where the signal increases as the coil goes towards it.

High numbers indicate "cold" or "negative" ground, ground where the signal decreases as the coil goes towards it.

Here is one way to think of the ground balance numbers. You have two numbers, the ground number, and the detector setting. For the machine to "balance" the total of the two numbers must equal 100 on the GMT, or 10 on most other detectors.

So if on your GMT the Ground Balance (Mineral Type) number reads 70, then the ground is 30 (cold ground). If the GB number is 20, then the ground is 80 (hot ground).

Personally, I'd like to see the system changed to where the zero point for the GB is ferrite (non-conductive iron). Negative numbers would indicate negative ground, and positive numbers indicate positive ground.

The "Follow Black Sand (Amt Of Mineral) number is interesting, as unlike the GB number it starts at zero and increases with the black sand content. Black sand ground is usually "negative" ground, and so again we have increasing numbers indicating increasingly negative ground. But in this case they want you to think of higher numbers as indicating increasing amounts of black sand.

I hope I've helped and not confused the issue more. Personally, I think the whole system is backwards, and has been that way so long that it's accepted as the way it is. I've made the suggestion to White's that since the GMT is becoming somewhat of a "Ground Analysis" tool, that the readout should directly indicate the nature of the ground as compared to ferrite, instead what the machine is set at. Then we could all much easier collect and compile ground reading settings from our respective areas.

By the way, if I recall correctly, ferrite balances out on the GMT at about 77. So the zero point is really in the 70's. You may want to test your machine and find it's exact "zero point" as compared to ferrite, because it can vary a bit per machine. Knowing this "zero point" can be extremely helpful when bench testing ore samples for conductive mineral content.

Steve Herschbach

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