PI with discrimination

[Ganesh]

Dear experts,
the PI projects here (Hammerhead and Gary's PI) have no diskrimination of ferrous and non ferrous metal.
Is there an analog way to filter or amplify the received currents to get discrimination ? Or to adjust the timing in such a way that discrimination can be achieved?
I heard that on a german PI machine (PulseII) the discrimination works only well on bigger objects.
An american machine combines the PI with a magnetometer to work around the problem.
So far I havn't even build my first PI but I would like to know if it could be done.
I assume it is not easy otherwise we would already have a hammerhead discriminator module.
Greetings
Ganesh

[schatzsucher]

i think, analog no!

[kt315]

No?? how about this info? did your opinion not crash down on it?

Re: Pulsed IB-VLF Detector instead of PI-Detector.



Posted by: Dave Emery (---.sip.clt.bellsouth.net)
Date: March 3, 2005 07:13PM

Aziz,
Eric Foster made a true PI with a balanced searchcoil which could discriminate over twenty years ago. The problem is that the reactive component suffers from ground effect. Using filters such as a motion VLF will result in a major reduction of depth over a regular PI. In short it has been done and may well prove to be a method for the future once the problems involved with such designs are solved. The dream is to find a reliable method of making a regular PI discriminate like a VLF using only a mono coil.

http://www.findmall.com/read.php?34,...061#msg-137061

[Unregistered]

P.I. Discrimination

Erics machine was called the P.P.D.1 (Pulse Power Discriminator 1 ?). The whole top shaft was full of D cells to provide power.
There was also the Protovale Pulse Analyst which was built into the Whites Beachcomber plastic case. Similar principle with a ferrous/non ferrous indicating meter but only used AA cells (think it was claimed to have a battery miser circuit) and had a iron mask switch.
Brian (in the U.K.)

[goldfinder]

PI w/ discrimination

In doing some experiments w/ 2 coils on a PI breadboard version I managed to get some discrimination between ferrous and non-ferrous. the coils overlapped but the overlap was extremely touchy. One coil was the transmitter and the other was the receive coil. Depending where the object was, i.e. under xmit or receive or overlap the output was different. The difference seemed to go from + to - depending on location. Thus a truth table would be a way to decide what the target material was. Give it ia try and let us know.
Goldfinder

[Reg]

Hi Goldfinder,

The two coils overlapping where one is the transmit and one is a receive is a DD coil. Yes, when used on a PI, it will discriminate iron objects to a point. When you pass a non ferrous object over the overlap zone, you will get a nice positive response if the polarity of the coils is correct. Now, when you pass a piece of iron close to the coils over the overlap zone, the signal will be negative. So, one can tell the difference as long as the iron trash is shallow.

A piece of gold, silver, copper, lead, or other non ferrous object will produce a nice smooth and somewhat narrow positive signal regardless of depth. A piece of a tin can, nail or other iron object will produce a double blip, much like a nail does when passed over with a VLF in the all metal mode if the object is shallow. Now, if the iron object is deep, then the double blip feature disappears and the object appears as a much wider positive signal.

One can use the delay feature to distinguish iron objects from gold nuggets. Normally, when the delay is turned up significantly, maybe to 50 usec or so, most gold objects such as nuggets less than 1/2 oz, and most rings will not produce a signal or if they do, it will be very weak.

At 50 usec or more, most larger iron objects will still produce a strong signal. Some smaller iron objects, such as small boot tacks, bobby pins, small pieces of wire or small piece of a tin can may act much like the gold signal and also disappear at the 50 usec point. So, this method can be used to distinguish much of the larger iron.

The difficulty lies in determinining the smaller iron objects more than anything.

Reg

[Guest]

Adonis

In France, there is a detector dealer who developed a new PI detector with discriminating abilities:
http://www.titanium-system.com

NB: There had been some delay in bringing this new maschine to the market.

[Ganesh]

Cool detector for 0 Euro

Site looks good but not all pages are working. Cool detector for 0 Euro!
This shopping system is from pre Euro times! I hope your machine is better than the shopping system. Good luck for your sales.

Interesting that France has also a Metalldetector hobby market.
I am from Germany and here detecting is in some states vorbidden without license but I heard in France things are much more delicate. Police confiscates your detector and charges a nice sum or even worse if they find you unearthing the rich history of this country with the help of a detector. Only beach hunting is tolerated.
Dear Adonis is that true or is it posssible to search in your country at daylight too with a detector?

Greetings from Berlin

Ganesh

[Sean Goddard]

Adonis, put my name on one, I want one of these!