ferrous discrimination on PI

[Unregistered]

Hi,
Does anyone have a description of how they do discrimination between high conductive and low conductive targets on PI detectors? I know some detectors output a high or low tone depending on the metal detected and I seem to recall a write up of how it is done but I can't find it. Also a schematic of such a detector would be appreciated if it is available.
Thanks,
Fred

[Reg]

Hi Fred,

Your heading and your questions in your post are basically two different issues. As to your main question about discrimination between low and high conductive objects, this can be done by simply adjusting the delay of the PI. Increase the delay and most low conductive objects disappear. When trying to separate most small gold objects, one can set the delay for about 40 to 50 usec and eliminate most of them, or at least reduce their signal to a very low value. At 50 usec, many gold rings and most gold nuggets 1/4 oz or less will disappear. A few larger gold rings will have a reduced signal, while most larger iron objects will still generate strong signals.

Higher conductive objects such as copper and silver will still produce nice strong signals also.

Now, as for iron objects, this is a whole different ball game. Fortunately, a lot of iron objects will follow the high low conductive disc technique and will generate nice strong signals even at the later delays.

On the down side, small iron objects and a lot of the thin metal trash such as small pieces of old rusty tin cans act considerably different and will "disappear" right along with low conductive objects at the later delay. Such objects are by far, the most difficult to "distinguish".

Now, as for a schematic, I am not sure just what you are looking for or how complex you would like to get. As an example, you can do a search for the Goldscan schematic on this forum and look at that schematic. The circuitry is such that some iron is discriminated. this detector has the potential of allowing an expanded form of iron discrimination by using the ground balance as a disc control also.

As for a simple delay type adjustment, then simply look at the Hammerhead schematic and note how the delay is accomplished. Once that is understood, then it is possible to switch resistors in and out to make quick adjustments of the delay. This would allow for a quick test of an object.

Reg