Bricks, goldscan IV and pulse induction

[Max]

Hi everybody,
I remember that when I had my first homemade pulse induction (the mark stuart's pic controlled one) working some years ago I had problems with shielding the coil to avoid static charges (ground capaciatance) but then another big issue was with red-bricks (and not only red) that sometimes are present in field in small fragments.
I experienced a lot of response with the stuart pi coming from small bricks fragments e.g. say big as a cigarettes box that sound like a small gold ring and so I was really confused at first becouse of the hi-resistivity of ceramics and other artifacts respect to metallic targets of any kind.

Anyway, I investigate, also on other forums, the problem and found that it was maybe don't from eddy currents in the target but due to magnetic materials inclusions generated in a transformation due to the hi-temperature in ovens that create maghemite crystals on ematite crystals present in the brick matrix. I know the "hot rock" cause false signals but a brick or other ceramic material has generally a much lower content of magnetic grains.

Does anyone know if the original (commercial) goldscan IV suffer of false signals on bricks like other PIs ? Does anyone know how (if it is possible) to avoid false signals generation due to small ceramic fragments ?

Best regards,
Max

[Reg]

Hi Max,
Yes the GS4 does suffer just like the other PI's and detect the bricks or pieces of them. I have a GS 4 and have other units that are very similar in design and they will detect red bricks as targets also.

Now, The GS 4 does have a ground balance adjustment which should be able to be adjusted sufficiently such that many of the bricks give little or no signal. The ground will now generate a slight negative response, so a slow even coil motion will work best.

One problem you will run into is the fact that all bricks are not the same so some will generate a stronger response than others, so if you adjust the ground balance such that one brick does not produce a signal, another brick just might cause a response.

Unfortunately, there is no easy solution to your problem.

Reg

[Max]

bad luck

Hi Reg,
thank you for the infos about the goldscan IV. When finished I'll try to use the ground balance to minimize the brick fragments signals. Yes , it's true that different fragments of different kind could have a completely different response. I remember that one kind of those (yellow to orange on surface) gives an incredible response on my first PI (the Stuart's one) that I was very surprised about how strong it was. I hold a piece of that brick and other kinds at home and should try it on the finished goldscan I'm building at now.

Best regards,
Max

[Reg]

Hi Max,

The Stuart PI is a good unit but has some limitations. One thing that would help on this PI was to reduce the pulse length. Since the Stuart PI didn't take a second sample and subtract it, targets having any magnetic lag could respond quite strongly. A simple second sample and a form of autotune would have helped that unit greatly.

Cheers,

Reg