Ground Balancing...What is happening inside the detector

[landman]

Hi All,
I understand what ground balancing is and does.
What I don't understand is what the machine is doing inside it.
What electronic adjustments it's doing to compensate for bad or good ground.
Is it just the threshold and RX gain being adjusted or something else?

Thank you!

 

[Southwind]

In a basic attempt.

The ground generally contains iron & or salt minerals which cause the detector to receive a signal from the ground. The problem is under bad conditions this signal can be stronger than the targets signal. The ground minerals signal is more of a gentle change from one location to another so the "phase shift" seen by the detector is gradual and can be ignored as ground minerals. A sharp change in the phase shift the detector interprets as a metal target and gets processed. So I would say inside the detector is being set to the mineral output of the ground as a zero point that it monitors for sharp changes in the zero number while ignoring gradual changes as changes in the ground minerals.

It is important to get a good GB in bad ground because a deep weak coin signal could be mistaken as a change in the ground minerals and ignored. Correct me if I'm work, but I believe the Sensitivity setting adjust how much of a change in the phase shift is requires before the detector see it as a possible target and not just a change in ground mineral and ignored. That is why when you have the Sensitivity high it is noisy because the detector sees changes in the minerals as possible targets and does not ignore them. Same happens when you power balance.

As far as what is going on inside I'd say the GB circuit is set to a zero point and will not process any gradual changes to that zero point.

 

[ArizFlash]

The ground canceling circuit is basically a discrimination circuit that works in the lower ranges of ground minerals. When you bob the coil up and down and an adjust the circuit to the level of the ground minerals present you are rejecting (discriminating) they ground minerals up to that point.

 

[metalpopper]

In a basic attempt.........Matt....adding a little 'mumbo-jumbo' to Southwind's good post.....


The ground contains MANY minerals, of which, those in the ferrite group are the ones which most adversely affect a detector.

Generally, such minerals are well dispersed throughout the soil.

So the resulting 'signals' are of a continuous manner, and of 'slow' amplitude variation. (RELATIVELY speaking)

Relative because.....it does depend BOTH your SWEEP SPEED and 'SLOPPINESS, besides THE DISPERSION DENSITY of the ferro mineralisation, per metre of ground in your sweep/ per second....and lastly...the UN-EVENNESS of the ground's surface.

SOooo....You must learn / determine / decide...at what rate to sweep-search,...such that the resulting 'FREQUENCY' (=1/ TIME) ground variation signal, is LOWER than the GROUND FILTER pass-band.

The simples way of describing the need for ground effect limitation, is so that your detector can then hopefully distinguish / sense, the faster 'rate-of-change' caused by any potential

artifact, from the slower amplitude changes of ground mineralisation, densities, or undulations.

In other word....provide as smooth an average base-line as is possible for any discrete target signal to ride on.

The Whites V3's give you a choice of 5Hz., up to about 12Hz in stepped frequency filtering......Your Minelab's Ground pre-filtering is 'fixed'....

So despite such pre-filtering, some ground variation can 'get through', especially if you sweep TOO FAST (Whatever rate that is?) and (ground dependency.)

The second stage of attacking the problem is done by 'timed-sampling' or synchronous phase sampling.......again, an example is whites 'ground-tracking' which in simple

terms, monitors the the residual ground variations getting through, and varies the sampling 'time/phase' to optimise ground effect limitation.

Fishers give you a manual method, whereby you choose when to 'up-date' the sampling gate's phase/timing, whenever the indicated ground phase changes significantly.

So that's a brief attempt to 'not too technically' describe what's involved, and why.

There are other ways to 'mathematically' process 'ground contaminate/good target signals', that's another more complex process.....micro processing digitised target

data etc., .....but that requires a Little more prior knowledge of some basic maths ....and sufficient interest to learn about what makes your detector 'tick'......Matt

*******************************************************************8****​

over to Southwind again.........

the to receive a signal from the ground. The problem is under bad conditions this signal can be stronger than the targets signal. The ground minerals signal is more of a gentle change from one location to another so the "phase shift" seen by the detector is gradual and can be ignored as ground minerals. A sharp change in the phase shift the detector interprets as a metal target and gets processed. So I would say inside the detector is being set to the mineral output of the ground as a zero point that it monitors for sharp changes in the zero number while ignoring gradual changes as changes in the ground minerals.

It is important to get a good GB in bad ground because a deep weak coin signal could be mistaken as a change in the ground minerals and ignored. Correct me if I'm work, but I believe the Sensitivity setting adjust how much of a change in the phase shift is requires before the detector see it as a possible target and not just a change in ground mineral and ignored. That is why when you have the Sensitivity high it is noisy because the detector sees changes in the minerals as possible targets and does not ignore them. Same happens when you power balance.

As far as what is going on inside I'd say the GB circuit is set to a zero point and will not process any gradual changes to that zero point.