Black sand meter

[Tim]

Can anyone please describe or indicate at which point in the circuit a black sand meter would be connected, using a block diagram or schematic example? Thank you.

[homefire]

??? Coming off the Phase detection would be my thinking. That would depend on the circuit being used. Black sands would be in the Ferrite region. Best detector for Black Sand I know of is a simple BFO.

[tony_av]

In case of VLF it would be the rectified preamp output. If PI - the end of flyback.

[Tim]

Thank you both. I have studied the Raptor schem, but without further study cannot be certain. U1a or U2a output? Referenced to ? End of flyback should be easy enough to sample for PI...if this is the correct measurement.

Please still I would ask some experts here for a diagram.

[Davor]

BFO or an off resonance would be good choice. Also you may try a magnetometer as a somewhat more sensitive instrument for magnetic materials. Point is that all other detectors were developed to reject materials like black sand.

[Tim]

Thanks Davor, but I am looking for information regarding black sand indicator like on the Whites GMT, Makro Gold Racer, Gold Bug Pro, etc. I should be able to work out connection for an analogue (or other) black sand meter to the Raptor...when I finally get time to make it.

[WM6]

..... black sand indicator ....

.

To be more clear, it is about relative " % " of Fe3O4 content indicator presented on display in bars:





It can be approximate converted to soil (probably useful in agriculture experiments) magnetic
susceptibility indicator, according to this conversion table I made for some 1st Texas models:



You ask where in schematic such Fe3O4 indicator circuit is attached an what is its electronic solution.

[Melbeta]

I believe that the Ground Balance (Cancel) control tunes out MAGNETIC black sand, not non-magnetic black sand. It is because the magnetic black sand shifts the targets phase AND if it is not removed from the detectors processing circuits. If the target is shifted out of phase by the magnetic black sand, the TID meter does not work correctly, nor does the tone ID work correctly. So if you are trying to connect a black sand meter, it would have to be prior to the Ground Balance control pot.

Now if you are trying to find black sands, which would consist of both magnetic black sand and non-magnetic black sand, the best detector to use would be Garretts BFO, the ones that run with a crystal controlled frequency. Find the black sands, and the possibility of placer gold and placer platinum could be achieved...

If you are trying to spot it before you tune it out with the Ground Balance control pot, it would have to be after the rectified Pre-Amplifier. Once it goes through the Amplifer it is now amplified.

WM6, that is quite a detailed study of magnetic ferrous material.
Melbeta

[Tim]

Excellent analysis Melbeta. This is what I wanted to know. After the pre-amp and prior to GB.
Thanks WM6 also for the graph. You will be aware of the heavy mineralisation here in Oz, so low Fe3O4 levels will not neccessarily indicate possibility of gold, so sensitivity to low levels would not be essential.
Thank you both.

A schematic diagram for circuit or connections would also be appreciated if anyone has the inclination.

[Melbeta]

Tim
I am going to make your day. I knew that Oz had heavy minerals called mafic conditions, and George Payne, when he was with Discovery Electronics, came out with a base unit Discovery metal detector. With a Pro Hunter Module, you can stick into the rear of it, what George called a Black Sand Module. Now if you can find one, with the base Discovery Baron unit, plus a Pro Hunter Module, and the Black Sand Module, just use it and hope it takes care of everything.

Now it did not have a meter, but you had a slide switch, which selected either medium black sands or heavy black sands. If you manage to draw out the schematic, send me a copy would you?

Now other manufacturers, before Minlab, used to send engineers to OZ, to try and come up with an alternative, these were Whites Electronics, Garrett Electronics, Compass Electronics, and a few more. There was even a company in OZ, who used to modify various brand metal detectors, for the local prospectors, but I do not know how well they worked.
Melbeta

[Tim]

Great backgrounding thanks Melbeta. I have never seen a Discovery Baron advertised. I am sure many here would be interested should a schematic arise by whatever means.

I appreciate your ongoing and valuable input that reminds us of the evolution of our world, and that we should not become complacent and contemptible towards past technologies.

With many manufacturers having this function nowadays, I am sure the generic information must be available...?

[Tim]

Found the guff on it in a for sale ad from 2010 on Tnet. There's also a base unit on Ebay for AU$1K with 4 coils Pro-hunter module,and an "ESP" unit (not black sand module) 19hrs left.
I am all for universal and modular design, but these thing take the cake. I honestly think that taking the original adjustment parameters, then adding more options, is absolute design overkill. Obviously these things were the ducks guts, but sheesh....
Gain, SAT/thresh, auto/manGB, maybe disc, 2 tone/centre meter, plus VCO and Black sand meter should suffice.

All these things are do-able, just need a black sand meter schem......

[Melbeta]

There is a schematic for a BASE BARON floating around the internet, but remember this, Discovery Electronics had the father of the VLF, GEORGE PAYNE working there as the Chief Engineer, and he created the mother of all metal detectors at that time, employing a microprocessor chip as the microcontroller unit, and with a boost on the motherboard, and without the code for the large chip, you are in the ship without the engine. I have not seen any schematic for the Black Sand Module so far.

My suggestion, pick up the pieces, and put them together, the Bass Unit is the main detector, stick in the Pro Hunter in the front, stick in the Black Sand Module on the rear, and you are running with the chip program version that was programmed into the microprocessor at the time.

Beyond that, I have never seen any schematic for any black sand module or black sand anything.

Now you can look for a Compass AU2000 Scanner metal detector, which was the cats butt at the end of the life of Compass Electronics, and it ran at either 52 KHz or 13.77 KHz frequency, a dual frequency machine, created to find gold nuggets as small as a 1/16th of something or other, using a oval DD coil, no meter to ID the gold nuggets, but gold nugget hunters swear by it. Its smaller brother, found the smalls speck of gold, in some ore, and is on exhibit in a museum in Nevada. They say the speck of gold was around the size of a fly's poop. Now if you have not seen a fly's droppings, it is so small you will need a magnifying glass. Not being sarcastic, just being honest and forthcoming. When Compass first came out with both the AU52 (single frequency) and the AU2000 (2-frequencies), they had a round DD coil, later the coil changed to a oval DD coil. Very very rare units to find if you can find them. Even scarcer then Discovery Baron units! Here below is some additional information:
Melbeta

And here is the family of the four Gold metal detectors, and the one on the lower right is the Gold Scanner Pro model...

[waltr]

Isn't Black Sand just iron rich?
https://geomaps.wr.usgs.gov/parks/co...blacksand.html

This is what the Ground Balance control is for- eliminates the effects of Mineralizer soils including Black sand.
Therefore just just the GEB circuit of a detector as the indicator of Black Sand. Or add a meter for measuring where the GEB control gets set.

[Melbeta]

And for your Australian knowledge, this information that Phil is referencing about, came from Compass Electronics representative telling how the Australian AU52 and AU2000 were changed from the American versions, to cope with the highly mineralized ground. Compass at the time had a Australian Compass Service Center, which experimented with various Compass models to see if this worked or if that worked, and they found what did work.... So if you can find an Australian Compass AU52 or AU2000, it will find the gold nuggets, maybe some mineralized areas might be a bit too hot or not.
MELBETA

Quote:
I was able to varify some information about the AU-52 variant with the variable auto-tune speed.
I spoke with Allan Cannon today and he relates that the three speed auto-tune was one of the modifys done in Australia to improve performance in overcoming the extreme ground conditions there.

The circuit is a simple selectable resistor interfaced with a switch as Melbeta mentioned he saw on another model Compass unit circuit drawing.

Because of the wacky ground down under (OZ), the AU requires a faster tuning speed in much of the OZ gold areas. There were other attempts to train the AU52/AU2000 to hunt in OZ but the AU never caught the attention of the nugget hunters there. They like their machines Blue (Minelab).

Compass RX coils were wound on the "on the cold side" for the Australian market to prevent the super hot ground from overdriving the RX. (that was the main problem from the mafic ground minerals in Australia). Maybe the AU model that we are talking about had one of those coils AND the circuit had been "set-up" for that style coil and the Australian ground using slightly different component values and trimmer settings. This could explain why the machine "never worked right" for Mike or Paul here in the USA. It's just something I wonder about. Allan did not mention it and I never thought to ask him.

The faceplate labeling is most likely created by cutting out the words slow, fast, normal from another faceplate and gluing them onto faceplate being used. If you take the picture and open it in a photo editor and then invert the colors of the image you can see the cutouts that are glued in place. Phil
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