Dual Channel Ground Balance

[Daves]

Hi,
What does "Dual Channel Ground Balance" mean?

[Carl-NC]

In what context?

[Detectorist#1]

Maybe some like SD2000 with two "ground balance" pots?

[Detectorist#1]

Any ideas?

[Carl-NC]

In a simple ground balanced PI detector there are 2 signal channels. I call them the "target" channel and the "ground" channel. They are subtracted to null the ground, but that also creates a target hole. We can consider that these two signal channels, when subtracted, form a single ground balanced channel (GB1).

Another pair of signal channels can be used to create a second GB channel (GB2) with a second target hole. It's possible to place the target holes of GB1 and GB2 at different places so that, when they are combined, you end up with a ground balanced detector with no target hole.

[Detectorist#1]

Hi Carl,
Thank you for this clear explanation!

[boilcoil]

Hi Carl,

Thank you for all the explanations and efforts you make in the forum, but can you explain a little more about this hole removal process in PI metaldetectors.
Isn't it true, that by the ground balance, a rejection of the unwanted target (soil or hot rock reaction) is expected. To accomplish this, it is necessary to cut off targets with such or similar time constants, so it is imperative that there is a hole in the characteristic of the device. Even if we balance with more than one pair of samples (two, three, etc), there must be a target hole for the balance to be made. Even if we reduce the width of the hole with later sampling of ground (greater gain),or we make two holes, they need to overlap each other for this timeconstant in order to have a balance of the device, so the hole is there.
How can we make the hole disappear, when balancing. Could you explain (as much as possible) the real process.
Thank you again.

[Carl-NC]

You make 2 GB channels where the target holes are at different taus. Then you combine the channels like this:

[boilcoil]

Ok, but in this diagram where should be the time constant of the rejected object ?
How will the response from the object be reset after summing the signals from both channels ?

[Carl-NC]

The location of target hole is determined by timing, so you just use different timings on the two channels. You can place the holes wherever you want. The channels are summed together and signals are reset in the usual way in a PI system.

[boilcoil]

Thank you Carl again.

Sincerely, Vangel