"Sum of Exponentials Eliminator"

Hi Panther

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Xavier

Corbyn used a written construct to define an analog feature that is well known and incorporated into every PI detector ever made. Before the days of digital computers, the work was done using analog computers and the operational amplifiers, comparators and phase shifters in combination are what gets us the basic output. This is why even today adding a digital signal analysis is both difficult and considered a waste ot time and effort. The PI machine detects metals and does it well. It can be designed to ignore metal oxides in the ground and that is what he is talking about. The fact that we don't need a ground balance circuit is a key characteristic of a PI machine.

Today, instead of using discrete components for the design, we use high efficiency comparators to locate metal objects based on the residual eddy currents on the surface or the interior of metal objects in the ground. The level of hysteresis in the metal oxides is so very low that it can easily be ignored while allowing the ferrous and non-ferrous metals to be sensed based on the residual magnetic fields that remain after the TX pulse dies down. Those extremely tiny signals are amplified as much as 500,000 times in several stages, compared to the original pulse and the result is that beep you hear indicating that metal is present.

Posted on: May 13, 2013, 02:35:36 PM

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		Quote:			Posted by Panther
	Has anyone or  any manufacturer been successful in incorporating this technique into a modern PI detector?

Yes. All of them. The PI detector counts on it. See the above explanation.

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First of all, a DD coil is for separate TX and RX coils, not for a PI machine which uses the same coil for both functions. Secondly, if your PI failed in mineralized soil, then there was more to the story or the kit was built wrong. Sometimes there is metal there when you don't even know it. Carborundum, for example, does not look like metal but your PI machine correctly identifies it as such.

I'm really not sure you got what I was saying. His words are old fashioned words used to describe circuitry which was new and innovative at the time. We have different ways to describe it now but the function is the same. Stop quoting it back as if it were a magic spell. It's not. ALL operational amplifiers are capable of exponential differentiation. ALL of them. Digitizing the received signal is pointless because, unlike VLF/TR signals, they are not different enough to analyze. You get a beep. That's it. In the attempts that people have made to incorporate discrimination, every time they insert a marker in the TX signal that, if properly timed (as a function of quiescent time versus time it was received) can be loosely interpreted as defining the type of metal. Not much more than that, I'm afraid.

On to the mineralization issue now. Ground balance and mineralization are not the same. You can ground balance but not eliminate minerals from detection. Black sand is a mineral collection of iron oxides - not the red oxides. Sometimes, black sand is actually carborundum which cannot be eliminated. Rust in quartz probably wasn't the issue where you had your failure. Most likely it was jasper or hematite mixed in with the quartz. Both of them can foul up the best detector in the right quantity.

Ground balance issues in a real situation are more likely to be caused by water, rotting vegetation, root masses, grasses or combinations of all these things. Most mineralization which people believe they are eliminating is actually organic rather than metallic.

To answer your question more to the use of a machine, turn down your sensitivity. It will not affect your depth one iota, contrary to popular belief. It affects only your audio development inside of your machine. Turn it down by half at first. Then go back up or down until you reach a good balance point. As to your quartz, I sure hope you didn't toss some foil gold out.

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We've had discussions here about a DD coil but the end result is not a DOUBLE D but a folded figure 8 instead. One coil, twisted into an 8 shape and then made into an overlapping set of ovals.

The results were far less than good.

You seem to have this notion in your head so pursue it. Don't take this design engineer's word for it. Go and try it on for size. I'll be right here cheering you on to success. Seriously. Just because I've never gotten it to work doesn't mean I'd be excited if someone else did it. When I rain a little on your parade here, it's only to describe what I KNOW, not what I wish for.

My last failed experiment? A monopulse PI coil arrangement. DISMAL is not a strong enough word to describe my results. Even with a 60Mhz processor clock, the coil would be too far past the target to do any good even on a super slow sweep rate. That idea? Tossed out with Saturday's garbage. I saved the wire though. Copper, don't you know.

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PI detectors work just fine with a Single mono Coil.

Yes Enough Iron Oxide will effect a PI.

Just ask the kind folks in Australia.   LOL

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