ground balancing

[Unregistered]

So with the hammerhead .. how does one "ground balance" this machine
am familiar how to do it with sd and gp machine but how to with this hammerrhead .. please someone
thank y ou
george

[Carl-NC]

It does not have a true ground balance. HH was intended more for beach hunting than for gold fields.

- Carl

[Qiaozhi]

It does not have a true ground balance. HH was intended more for beach hunting than for gold fields.

- Carl

I thought that by their very nature P.I. detectors do not need to be ground balanced, and that they almost completely ignore ground mineralization and saturated salt. Is there a different setup for beach and nugget hunting, or it simply a matter of the sample delay time?

[Unregistered]

ground balance

yes .. i thought with all the controls and different settings one might have been able to ground balance .. is there some changes to be made in the up comming new version for this mode ? And I think that ground balancing is just basicly stepping back the sensitity and thresholds to accept the new ground settings at the sacrifice for sensitivity on the selected target(s).
Is there a modus operandi for basic search with all these knobs ??
thanks in advance
george

[robby_h]

I thought that by their very nature P.I. detectors do not need to be ground balanced, and that they almost completely ignore ground mineralization and saturated salt. Is there a different setup for beach and nugget hunting, or it simply a matter of the sample delay time?

I wish this was true. The fact is that the ground here in Australia can give a ground signal measured in volts at the first sampling output and a nugget micro volts. This is why Minelab can charge $5500 Oz dollars for a pi detector.
Rob.

[Qiaozhi]

I wish this was true. The fact is that the ground here in Australia can give a ground signal measured in volts at the first sampling output and a nugget micro volts. This is why Minelab can charge $5500 Oz dollars for a pi detector.
Rob.

I assume you're referring to Minelab's Multi-Period Sensing (MPS) technology?
Although I understand how ground balancing works for an VLF I.B. detector, it's not clear to me how this achieved with a P.I.

[Carl-NC]

I thought that by their very nature P.I. detectors do not need to be ground balanced, and that they almost completely ignore ground mineralization and saturated salt. Is there a different setup for beach and nugget hunting, or it simply a matter of the sample delay time?

In most regions, soil mineralization is mild enough that its response decays out quickly, and doesn't get detected. But some soil, especially in Australia, is severe and gives a long response.

yes .. i thought with all the controls and different settings one might have been able to ground balance .. is there some changes to be made in the up comming new version for this mode ? And I think that ground balancing is just basicly stepping back the sensitity and thresholds to accept the new ground settings at the sacrifice for sensitivity on the selected target(s).
Is there a modus operandi for basic search with all these knobs ??
thanks in advance
george

I don't think ground balancing is that simple. This is an area I haven't done much research in, but I think you want to run a seperate "ground" channel with a much longer integrator time constant, and subtract its results from the main channel. Eric, Reg, or other experts would know.

- Carl

[Unregistered]

ground balance

Hi again
Hi Reg / eric would you have some input into this thanks
:-)
thanks in advance

[Reg]

Hi,

The most common way to create a ground balance (GB) is to take a later sample, amplify it and then subtract that signal from the main sample signal. This requires more timing circuits that will allow for the additional samples.

Now, as an example, if the main sample is taken at 15 usec and is 15 usec long, then the secondary ground sample could be taken at maybe 35 or 40 usec. This second signal would have an adjustable amplification as a means of ground balance adjustment. This later sample would then be subtracted from the main sample signal and if the GB signal is equal to the ground signal in the main sample, the ground signal is eliminated.

One can look at the Goldscan 4 schematic to get an idea of how it is or can be done.

Reg

[Qiaozhi]

Hi,

The most common way to create a ground balance (GB) is to take a later sample, amplify it and then subtract that signal from the main sample signal. This requires more timing circuits that will allow for the additional samples.

Now, as an example, if the main sample is taken at 15 usec and is 15 usec long, then the secondary ground sample could be taken at maybe 35 or 40 usec. This second signal would have an adjustable amplification as a means of ground balance adjustment. This later sample would then be subtracted from the main sample signal and if the GB signal is equal to the ground signal in the main sample, the ground signal is eliminated.

One can look at the Goldscan 4 schematic to get an idea of how it is or can be done.

Reg

Thanks Reg.
Now I've read your description, I can understand how this works.

In an IB / GEB detector, the ground balance is used to adjust the sampling point so that only phase-shifted signals produce a response, but any purely resistive target (i.e. the ground) does not. Since PI detectors (in general) do not provide discrimination, then the method used here needs to be fundamentally different. I hadn't really thought about the requirement to ground balance a PI before, but in areas like Australia I can see that this would be a problem. It's funny how a solution can appear so obvious when you know the answer.

[gef12]

ground balance requested

Hi Reg , Carl
I live and prospect in Australia.
I have built the option 2 HH and have only used it with a mono at this stage.
I will be experimenting with some minelab dd coils that i have purchased on ebay and modifying the circuit to suit dd coils. I was hoping this would be the answer for our mineralised ground, but something tells me i may need something else to deal with the ground here and our hot rocks ( a heavily mineralised bit of rock that is abundant on our goldfields) quite an anoying piece of nature they are.
Carl is there a solution to ground balancing in your next model or is there can there be an add on "fix" for this minor problem.
cheers
gef

[Reg]

Hi Gef,

You might try reducing the power into the coil some by simply adding a 25 ohm resistor in series with the FET. At first, one will worry about a possible depth loss, but you will be surprised how little is lost.

By doing this, you should see much less ground signal than you see with full power. This will allow you to operate a DD coil much easier.

Drop me an email when you get a chance. I can be reached at rgsniff@comcast.net

Reg

[1843]

Hi Gef,
You might try reducing the power into the coil some by simply adding a 25 ohm resistor in series with the FET. At first, one will worry about a possible depth loss, but you will be surprised how little is lost.
Reg

Can we decrease the PW instead of adding a resistor in series with the MOSFET? Reducing the PW, will reduce the coil current...
I don't know what is the difference between them?!

Regards

[Reg]

Hi 1843,

Reducing the current still allows the remaining current to produce a field that will fully saturate the object. This will allow for a reasonable signal back from the target, whatever that might be.

Now, if you reduce the pulse width, then you do not get full saturation, which can result in less depth by itself.

I suspect there is a difference, but I haven't actually tried the two techniques to see just what difference there is. It would be an interesting project.

Cheers,

Reg

[1843]

Hi Reg

Ok!
So we can use a thinner wire for reducing the current and long PW for fully saturation.

But why reducing the current causes less ground signal?

Best regards