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Date Posted: 18:15:08 06/05/02 Wed
Author: Ralph
Subject: Some thoughts on mineralization and "ground balancing"

Soil conditions vary so much from place to place, there is no way to determine exactly what kind you're dealing with until you DO put the coil to the ground.

While most factory pre-set machines are set for a wide variety of ground conditions, it's important to remember that no matter how they are tuned, whether manually or internally, or even auto-tracking units, the worse the ground conditions get, the more effect they will have on your detectors performance. Ground mineralization, per se, is never really "eliminated" by the tuning of any detector. All that is really being accomplished is that the detectors "response" (or lack thereof) is being tuned to a point where you as the operator do not perceive any response by the detector, although the detector always "knows" or "sees" the mineralization. This applies, at least, to VLF Induction Balance type detectors. PI is a different animal altogether where ground response is concerned.

A good example of what I'm talking about here is how the discrimination circuits of the White's Classic I.D. and IDX machines work. You can operate the machine where the ID screen still displays basically "everything" (target wise) as it passes under the coil, although the "audio" reads only a desired level of discrimination and higher, while everything below the chosen level of discrimination remains silent while still displaying on the screen. You are effectively operating in "all-metal" mode while "tuning out" a certain level of conductivity by the "addition" of the discrimination "function".

I think alot of the confusion of late regarding ground balancing has alot to do with how most perceive the "separation" of all-metal and discrimination modes in most machines. The fact is that simply flipping the switch from all-metal mode to discrimination mode does not work as you might expect, turning "off" one mode and turning "on" the other. Switching to a discrimination mode actually ADDS the discrimination "function" to the all-metal mode, rather than changing "from one to the other". The all-metal mode is always a necessary function, in either mode of operation, because the all-metal function serves as a "reference" for the discrimination circuits to work from.

You might think of it as pulling 10 cards out of a deck, and trying to "guess" what they are with no reference to work from. A near impossibility, right ? But take the "REST OF THE DECK" (the all-metal function) using it as a reference point, and then there is very little problem in determining what those 10 cards are.

When I first heard that explained by a detector design engineer, things started to become much more clear to me about how these things actually operate, and the relationship between ground balancing between the all-metal and discimination "FUNCTIONS" (not "modes") of the various machines. To some extent, the all-metal mode will ALWAYS effect the discrimination function..... unless of course the design involves completely separate all-metal and "discrimination reference" functions.

Ground "balancing" is really a misnomer, and a point of confusion I suspect, in that you are not "balancing" anything within the meaning of the word when you ground balance. You are simply tuning the lowest levels of discrimination to "react" in a desired way to the ground mineralization (phase shift) so that the audio circuits can then be adjusted to NOT give an audible signal to that same ground. So although the detector still knows
the ground mineralization is there, it's just not "telling you" that it's there.

There's alot going on in these little boxes that is more intriguing as you learn more about their inner workings.

Ralph

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