Bricks again (it'll become an obsession?)

[Max]

Hi Reg and everybody here,
I'm building the goldscan IV (and it is, with no dubt, a very good project) but it seems that I must deal with the brick response problem of false detection of targets like I had before with another (simple) PI design,

BUT I have a few questions for you (please let me know what do you think about):

1. what's the best compromise to minimize ceramic fragments to be detected mantaining a good penetration depth ?
2. I mean, what's the best also between different kind of detectors (PI, VLF, TR, IB and ibrids) ?
3. And so, maybe say a white classic sl III or a tesoro or a PLL or other kind of detector could be better than a powerful (and expensive) PI in ceramics hi-contaminated environments ?

Best regards,
Max

[Reg]

Hi Max,

You will probably have to provide more info as to what you are looking for and what other problems might exist before a decent answer is possible.

Personally, if what I was looking for was important enough, I would try several different detectors, but again, it depends upon the "target" also.

As an example, if one were looking for non ferrous objects such as coins or maybe brass or silver items, then a good VLF might work better if you used the discrimination mode. This mode would "ignore" the ceramic objects and still find metal items at a very reasonable depth, providing they weren't right under or next to a ceramic fragment of any size. The reason being the disc mode would reject the ceramic and such rejection may be strong enough to cause the metallic item to be ignored. So, the key to such searching would be to search slowly to assure the rejection of a piece of brick was as done as much as possible before another target is encountered.

A ground balancing PI might work also, providing the desired targets were distinct enough. Generally, it doesn't take much adjustment of the ground balance to cause the detector to ignore brick type items. At least, it doesn't when testing the bricks I have available. So, one could simply adjust the GB to see if the object disappears. Again, this is much like the disc mode on a VLf in the fact the strongest signal will most likely prevail.

Now, here is a trick that helps reduce the effects of a ceramic type signal. The trick is to simply raise the coil a little. Signals from bricks, pieces of basalt and similar items will reduce significantly with just a little additional distance between the coil and the object. This reduction is much greater than what happens with a metal object of any size. This is the case on a PI and should be the case on a VLF also, but it has been a while since I tried it on a VLF.

Now, as for VLF instruments, you might want to try different ones but make sure they operate at different frequencies. As an example, a lower frequency such as a 6K frequency should do better on silver objects, while a 15K should do a little better on gold type items.

Well, I have tried to toss out some general ideas. Again, it would help to know more about what was being hunted and just how many of the ceramic pieces are in the area and the average depth of them. I would think most ceramic items would be near the surface. If so, then simply raking them out of the way may be a better idea than trying to build a detector that ignores them.

Cheers,

Reg

[Max]

Hi Reg,
I've just read your message and would like to thank you for the useful informations about the strategy to avoid false signals due to ceramic fragments , bricks and also minarelized stones.
Belive me when I say that sometimes there are a lot of disturbing fragments in the fields where I search in week-ends ! I was so worried of bricks kind of false target becouse in a session of md last summer I had to dig a lot of them and well I was using my first pi and also a whites sl III. The fragments were mostly ignored using the sl III disc control but I lose sensitivity and then switch back to the PI unit, digging about 40 fragments and only 2 good targets (silver small coins), then I have to give up (too hard work).

I'll use vlf machines on these fields in future, try different models.

Best regards,
Max

[Reg]

Hi Max,

One of the problems with the newer VLF's is they add an offset in the ground balance to minimize false signals from certain ferrite rocks. This offset does cause some depth loss which can be a problem.

Now, the Tesoro Bandido can be adjusted so the ground balance offset is adjusted out by adjusting the ground balance. The problem is, the all metal mode doesn't work then.

One can modifiy the Bandido to minimize this offset if they so desire.

Other problems with VLF's are strange at best. As an example, on the older Whites such as the Eagle, one can program in the last 5 to 7 negative numbers and minimize the offset problem. I haven't tried this with the newer models but it is worth a try. Generally, this will add an inch or two to the depth capabilities.

The point I am trying to make is about every detector has a quirk or two that can be overcome with a little experimenting.

Reg

[Max]

Hi Reg,
I never tested Tesoro's detectors but I'll do it pretty soon. I'm interested in small targets detecting (silver, gold, brass) and have to deal with some interesting fields full but with huge contamination. Some other fields where I go can be explored using both PIs and VLF types with minor differencies.
I'm really interested in the Bandido feature you told me in the previous post becouse it can be a good solution for many of my problems.

Best regard,
Max