Understanding Ground Balance

[B^C]

I came across this site http://jb-ms.com/Baron/gb.htm & wanted to get opinions on what is said about the ground balance technique.

Simple solutions to problems are always the best, anyone have a simple solution for ground balance, i may have one.

[Tinkerer]

I came across this site http://jb-ms.com/Baron/gb.htm & wanted to get opinions on what is said about the ground balance technique.

Simple solutions to problems are always the best, anyone have a simple solution for ground balance, i may have one.

Hi B^C,

George Payne's article refers to phase shift as in VLF. I don't know of a PI that reads phase shifting.
The TINKERERS IB-PI, hopefully will get us a step closer to be able to read phase shift in PI.

I would be very interested to hear your opinion and ideas about ground balancing methods.

Tinkerer

[B^C]

Gday Tinkerer,

Yeah i get what your saying with the phase shift from Mr Payne, i just wanted to see if anybody else had an opinion about what he wrote.

I have some idea's about ground balance with PI, i think the thing to remember also is that any ground balance is surely going to take away sensitivity to small targets.
If anybody disagrees along the way, have your say, debate is good!

Just off the point for a minute:
Small Targets, Gold in particular is what we all should be chasing---in my opinion anyway, because there is HEAPS of it--people just walk straight over it all the time & wouldn't know it's there waving there wheel size coils around or a ground balance that cancels everything out..
Sometimes people say boy i got this thing running quite & i think to myself --GOOD--, that means there missing everything hahaha.
If she ain't making a noise then there's no sensitivity, on the edge is where it needs to be so only general ground noise is cancelled but not all of it. Most people want a quiet detector for some reason but i want targets.

Some people also want the big boomer coils that pulse to CHINA so they can try to find horse head size nuggets, that's fair enough also but i do this for a living & big nuggets can be Few & Far between. Medium size coils are just right, up to about 16".
Any bigger & you may as well just put a radio antenna on it & listen to the music, because by the time you ground balance the big aerial most of the targets are cancelled out anyway.
So for me sensitivity to small gold is paramount, i would rather dig a thousand holes each with a 1grm nugget in the bottom than to just try to find the big 1kg nugget & wait a lifetime to do it & if then.

Back to the point:

Ground balance needs like i mentioned to be on the edge for the ground type your in, if it's not your missing targets.
Then to have a good enough ground balance in some ground means you take away sensitivity.

I believe the ground balance on the GPX4500 does in fact cancel out smaller targets unless you set the detector for on the edge running.
You can get it to run quiet all right but to quiet for me.



I'll let someone else have there say instead of me dribbling on any further at this stage, it's after midnight.

It would be interesting to hear what other people would like for a ground balance & why they they would want it like that.

[Qiaozhi]

As has already been stated, the George Payne article refers to VLF-IB operation and not to PIs. The ground balance in a VLF relies on the fact that the ground will only produce changes in amplitude, and very little or no phase-shift. That's why the GEB channel samples at the zero-crossing point of the received signal. The amplitude can move up and down as much as it likes, but without phase-shift the output will still be zero. However, along comes a metal target, and the RX signal shifts in phase, so that the GEB channel is no longer sampling at the zero-crossing. Thus a target is detected. When the ground is highly mineralized the sampling point has to be moved away from the ideal position ... and you are correct ... this reduces sensitivity to both small and deep targets.

PIs usually rely on the fact that the ground matrix cannot sustain eddy currents for any appreciable time. So, by the time you start sampling, any ground effects have died away ... unless you live in Oz.

[simonbaker]

I came across this site http://jb-ms.com/Baron/gb.htm & wanted to get opinions on what is said about the ground balance technique.

Simple solutions to problems are always the best, anyone have a simple solution for ground balance, i may have one.

Using TGSL as my reference, part of his argument doesn't make sense to me.

I agree when he says motion detector helps solve problem, but then he seems to contradict himself.

My belief is that the TGSL circuitry ignores any constant phase of the RX signal and just responds to changes in intensity of signals that have a phase within the discrimination range. This implies that nulling of the coils is not so critical as other people believe, I have not proved this and others do not hold my opinion, so take what I say with grain of salt.

G Payne says "As you move the coil over the ground, the internal detector signals are continually being driven negative. Any weak positive target signal is easily over-ridden by the huge negative ground signal."

I don't see that. The TGSL responds to changes in the signals, so a bump in a target signal should emerge fine from the overall negative signal.

A constant ground should not be a problem. It is fluctuations in ground mineralization that produce spacial "noise" that is hard to tell from targets. Ground balance ideally should suppress the fluctuation signals, not the overall level.

The harm that ground balance does in the TGSL (I believe, I need to reexamine to confirm) is that it shifts the detector phase windows off-center from the targets of interest, causing the target signals to be weaker than they would be otherwise.

I tend to agree with B^C (someday I'll figure out what that means) that you want to work with a noisy signal and use your ears and brain to do the final filtering, if you can tolerate it.

I suspect there is a similar effect with PI detectors, but I'm not up-to-speed with them yet.

Cheers,

-SB

[Tinkerer]

As has already been stated, the George Payne article refers to VLF-IB operation and not to PIs. The ground balance in a VLF relies on the fact that the ground will only produce changes in amplitude, and very little or no phase-shift. That's why the GEB channel samples at the zero-crossing point of the received signal. The amplitude can move up and down as much as it likes, but without phase-shift the output will still be zero. However, along comes a metal target, and the RX signal shifts in phase, so that the GEB channel is no longer sampling at the zero-crossing. Thus a target is detected. When the ground is highly mineralized the sampling point has to be moved away from the ideal position ... and you are correct ... this reduces sensitivity to both small and deep targets.

PIs usually rely on the fact that the ground matrix cannot sustain eddy currents for any appreciable time. So, by the time you start sampling, any ground effects have died away ... unless you live in Oz.

You just gave me an idea. On my IB-PI, I have what I call the PIVOT.
See: http://www.geotech1.com/forums/showp...18&postcount=3
It is a point where there is no movement in the signal wave shape. I wonder if I can find the PIVOT of the ground signal. That would be the ideal ground balancing sample.

Tinkerer

[Tinkerer]

Gday Tinkerer,

Yeah i get what your saying with the phase shift from Mr Payne, i just wanted to see if anybody else had an opinion about what he wrote.

I have some idea's about ground balance with PI, i think the thing to remember also is that any ground balance is surely going to take away sensitivity to small targets.
If anybody disagrees along the way, have your say, debate is good!

Just off the point for a minute:
Small Targets, Gold in particular is what we all should be chasing---in my opinion anyway, because there is HEAPS of it--people just walk straight over it all the time & wouldn't know it's there waving there wheel size coils around or a ground balance that cancels everything out..
Sometimes people say boy i got this thing running quite & i think to myself --GOOD--, that means there missing everything hahaha.
If she ain't making a noise then there's no sensitivity, on the edge is where it needs to be so only general ground noise is cancelled but not all of it. Most people want a quiet detector for some reason but i want targets.

Some people also want the big boomer coils that pulse to CHINA so they can try to find horse head size nuggets, that's fair enough also but i do this for a living & big nuggets can be Few & Far between. Medium size coils are just right, up to about 16".
Any bigger & you may as well just put a radio antenna on it & listen to the music, because by the time you ground balance the big aerial most of the targets are cancelled out anyway.
So for me sensitivity to small gold is paramount, i would rather dig a thousand holes each with a 1grm nugget in the bottom than to just try to find the big 1kg nugget & wait a lifetime to do it & if then.

Back to the point:

Ground balance needs like i mentioned to be on the edge for the ground type your in, if it's not your missing targets.
Then to have a good enough ground balance in some ground means you take away sensitivity.

I believe the ground balance on the GPX4500 does in fact cancel out smaller targets unless you set the detector for on the edge running.
You can get it to run quiet all right but to quiet for me.



I'll let someone else have there say instead of me dribbling on any further at this stage, it's after midnight.

It would be interesting to hear what other people would like for a ground balance & why they they would want it like that.

On my old PI I used to have a VCO with a frequency of 1 to 250Hz. My preferred threshold setting used to be about 3Hz, so I could listen to any change in the audio, UP OR DOWN. With the threshold at no sound, one never knows how much one looses.

Tinkerer

[Qiaozhi]

Using TGSL as my reference, part of his argument doesn't make sense to me.

I agree when he says motion detector helps solve problem, but then he seems to contradict himself.

Everything that George Payne says in the article is correct.

My belief is that the TGSL circuitry ignores any constant phase of the RX signal and just responds to changes in intensity of signals that have a phase within the discrimination range. This implies that nulling of the coils is not so critical as other people believe, I have not proved this and others do not hold my opinion, so take what I say with grain of salt.

As far as the TGSL is concerned, it responds to the rate-of-change of the sampled RX signal. If it was responding the DC level of the sampled signal, then it would be a non-motion detector, and you would need to occasionally adjust the threshold to account for DC drift. The GEB channel samples at the zero-crossing point. Which means that a change in amplitude can only be detected if the coil passes over a target which produces a phase-shift. Normal ground only causes a decrease in amplitude, but no phase-shift.
You are correct that nulling of the coils is not so important for the TGSL, I have already stated this numerous times, but it seems to fall on deaf ears, and several constructors are still trying to reduce the residual RX voltage to nV. The most important physical coil adjustment is the initial phase offset between TX and RX.

G Payne says "As you move the coil over the ground, the internal detector signals are continually being driven negative. Any weak positive target signal is easily over-ridden by the huge negative ground signal."

I don't see that. The TGSL responds to changes in the signals, so a bump in a target signal should emerge fine from the overall negative signal.

The George Payne aticle makes the assumption that ferrous targets cause the RX signal to phase-shift left, whereas non-ferrous targets cause the RX signal to phase-shift right. This is true for some detectors, but not for the TGSL. In the TGSL all signals cause a phase-shift to the left. (Some coil configurations can give phase-shifts to the right, and these will still work with the TGSL, but this is another story that I don't want to get into here.)
What GP is saying is that mineralized ground will keep pushing the RX signal to the left. In this case you need to offset the sample point in the GEB channel. Of course, if the ground mineralization changes rapidly you will get some false signals, so you then need to integrate the ground signal over time, and idealy provide some sort of automatic ground tracking. Detection of desirable targets can therefore be drastically reduced by the presence of highly minerlized soil.
The ground also causes a decrease in amplitude, which will likewise reduce the signal from any non-ferrous targets. Even though, in GP's article, the non-ferrous target causes a phase-shift to the right, and an increase in amplitude, it still has to overcome the amplitude reduction causes by the ground. Hence sensitivity is reduced.

A constant ground should not be a problem. It is fluctuations in ground mineralization that produce spacial "noise" that is hard to tell from targets. Ground balance ideally should suppress the fluctuation signals, not the overall level.

Agreed.

The harm that ground balance does in the TGSL (I believe, I need to reexamine to confirm) is that it shifts the detector phase windows off-center from the targets of interest, causing the target signals to be weaker than they would be otherwise.

The TGSL is not a good detector for highly mineralized soil. The amount of false signals would make it unusable in Oz. The TGSL is designed to have a preset ground balance, and there is no automatic GEB.

I tend to agree with B^C (someday I'll figure out what that means) that you want to work with a noisy signal and use your ears and brain to do the final filtering, if you can tolerate it.

I like the Tesoro range of detectors for that reason. Some background noise is more "comforting".

I suspect there is a similar effect with PI detectors, but I'm not up-to-speed with them yet.

Without discrimination, a PI is only good for relic, gold nugget, or beach hunting. Maybe one day PIs will become popular for inland coin shooting. Who knows?...

[Fred]

You are correct that nulling of the coils is not so important for the TGSL, I have already stated this numerous times, but it seems to fall on deaf ears,...

Not always

[Qiaozhi]

Not always

That's true in your case my friend - but, although most people listen, they don't hear the words.

Maybe you would be so kind as to reaffirm my statement.

[Fred]

Maybe you would be so kind as to reaffirm my statement.

I do , by all means

[ZED]

Gday Tinkerer,

Yeah i get what your saying with the phase shift from Mr Payne, i just wanted to see if anybody else had an opinion about what he wrote.

I have some idea's about ground balance with PI, i think the thing to remember also is that any ground balance is surely going to take away sensitivity to small targets.
If anybody disagrees along the way, have your say, debate is good!

Just off the point for a minute:
Small Targets, Gold in particular is what we all should be chasing---in my opinion anyway, because there is HEAPS of it--people just walk straight over it all the time & wouldn't know it's there waving there wheel size coils around or a ground balance that cancels everything out..
Sometimes people say boy i got this thing running quite & i think to myself --GOOD--, that means there missing everything hahaha.
If she ain't making a noise then there's no sensitivity, on the edge is where it needs to be so only general ground noise is cancelled but not all of it. Most people want a quiet detector for some reason but i want targets.

Some people also want the big boomer coils that pulse to CHINA so they can try to find horse head size nuggets, that's fair enough also but i do this for a living & big nuggets can be Few & Far between. Medium size coils are just right, up to about 16".
Any bigger & you may as well just put a radio antenna on it & listen to the music, because by the time you ground balance the big aerial most of the targets are cancelled out anyway.
So for me sensitivity to small gold is paramount, i would rather dig a thousand holes each with a 1grm nugget in the bottom than to just try to find the big 1kg nugget & wait a lifetime to do it & if then.

Back to the point:

Ground balance needs like i mentioned to be on the edge for the ground type your in, if it's not your missing targets.
Then to have a good enough ground balance in some ground means you take away sensitivity.

I believe the ground balance on the GPX4500 does in fact cancel out smaller targets unless you set the detector for on the edge running.
You can get it to run quiet all right but to quiet for me.



I'll let someone else have there say instead of me dribbling on any further at this stage, it's after midnight.

It would be interesting to hear what other people would like for a ground balance & why they they would want it like that.

Getting rid of ground noise is a must have,and i mean all of it !!!

Hot rocks are a pain in the but and the more sensitive your detector is the more hot rocks there are.
Did my own timings on a 2200 on many occasions and made it very sensitive to flysh!t [5 3/4 inchs on a 0.1 grammer] but the hot rocks made me give up after a couple of hours,noisey ground wears you out.
Its easy to say that you dont mind some ground noise when chasing tiddlers because digging false signals doesnt go much beyond six inchs,but when going after the biggin`s down deep false signals can take you down a foot or two and after you have done that six times your stuffed and fed up!

Ground balance systems generally subtract out to much target signal and perform poorly when trying to null out big shifts in the ground matrix.GB designs are a compromise,its very hard to have it all but it is doable.
M/lab have done it and so have i[not quite as well as m/lab though]but GB designs are presious and to be kept under lock and key !!!
Having two channels is a good start,one channel to cover the losses in another channel,also one channel can be set up for targets with a short TC while the other channel used for longer TC targets.
This is one of the approaches that m/lab use,you can see it in the 2000 schema.
GB designs while subtracting out some target signals will usually do so with certain TC targets while other TC targets will have very little in the way of signal subtracted out.Sampling is one of the keys to the characteristics of a GB cct,sampling that you see in genaral PI ccts is very basic to say the least.Consider m/labs large and 3 small transmit routine that one sees in there latter models,they sum the samples from the small transmit up against the samples from the large transmit to remove most of the ground response then they use a seperate GB channel to take care of the varibilitys that arise as one moves the coil over the ground,now.. it must be understood that the above example actually absorbes big shifts in the ground matrix even before the requirment of a GB cct to clean up the leftovers.

Zed

[B^C]

Gday Zed,

I understand about false signals & digging, a foot or two is niether here nor there though in reality, it's part of the game. I think a lot depends on how you actually detect that first response & then what you do with it.


I set my machines so there on the edge as mentioned, which of course picks up highly susceptible ground, hot rocks, clay etc.

The reason for this is that the metal detector is far better than me at picking up what soil matrix or substrate i am walking over--giving the first indication if i am on gold bearing ground or not to begin with, to me this is a first big positive sign that i'm on the right track, with a good ground balance i have no clue as to what's under my feet.
A detector picks up far more than just targets, it reliably relays information to the user that we can either take notice of or ignore, it can even pick up storms coming your way from many miles away.

Once your on the right ground with an on the edge ground balance the detector will be more erratic of course. Setup like this it will detect far bigger nuggets deeper than will something with a good ground balance, the downside is what you mentioned distingiusing false signals from the real thing. With a good ground balance to start with chances are your walking over gold & the big fella's down deep are cancelled out to.

If you set your detector on the edge for the ground type your on, any target signals boom back at you.
Now your on top of the seemingly good target now is the time for a more substantial ground balance from the suroundings to try to identify if it is infact a target worth digging, lets face it most things will balance out if there not good targets.

Some just easily will cancel out by sweeping at different angles

If your down a foot & the targets strength is not increasing chances are, keep moving.
If the signal from the original surface level over the hole decreases with depth of hole, move on.

If your down a foot & still getting a nice response & your not sure, ground balance on the dirt you have dug out & make sure the detector doesn't pick it up with the balance. More times than not this will cancel out most things except for a target when tested over the hole. Most times though if it isn't increasing in strength with depth it ain't a good target.

A trick i use works very well, carry a very small test target with you at all times.
If your unsure if your target signal is genuine from the above, next to the hole your digging dig another quick small 6" hole or so depending on your test target, two swings with the pick & place your test target in it cover it over with the soil out of the the main target hole & ground balance on this so you just get a very small indication that it's there.
If then if then you sweep the target hole & have a good response there's a very good chance that you keep swinging the pick.

The target response from a deep target sometimes isn't very strong & easy to balance out with a good ground balance, everybody has there own ways but i like to find most of what i walk over be it small gold or the far & few between bigger stuff down deeper.

At the end of most days prospecting is see a handfull of smaller gold & maybe the odd big one, at the price of gold today, them smaller bits up to 10oz sure do help the bank account.

I'm sure everybody has read this http://www.ncmd.co.uk/docs/how%20a%20detector%20works.pdf

Anybody see any flaws in the way Mr Candy looks at things?

[ZED]

Gday Zed,

I understand about false signals & digging, a foot or two is niether here nor there though in reality, it's part of the game. I think a lot depends on how you actually detect that first response & then what you do with it.


I set my machines so there on the edge as mentioned, which of course picks up highly susceptible ground, hot rocks, clay etc.

The reason for this is that the metal detector is far better than me at picking up what soil matrix or substrate i am walking over--giving the first indication if i am on gold bearing ground or not to begin with, to me this is a first big positive sign that i'm on the right track, with a good ground balance i have no clue as to what's under my feet.
A detector picks up far more than just targets, it reliably relays information to the user that we can either take notice of or ignore, it can even pick up storms coming your way from many miles away.

Once your on the right ground with an on the edge ground balance the detector will be more erratic of course. Setup like this it will detect far bigger nuggets deeper than will something with a good ground balance, the downside is what you mentioned distingiusing false signals from the real thing. With a good ground balance to start with chances are your walking over gold & the big fella's down deep are cancelled out to.

If you set your detector on the edge for the ground type your on, any target signals boom back at you.
Now your on top of the seemingly good target now is the time for a more substantial ground balance from the suroundings to try to identify if it is infact a target worth digging, lets face it most things will balance out if there not good targets.

Some just easily will cancel out by sweeping at different angles

If your down a foot & the targets strength is not increasing chances are, keep moving.
If the signal from the original surface level over the hole decreases with depth of hole, move on.

If your down a foot & still getting a nice response & your not sure, ground balance on the dirt you have dug out & make sure the detector doesn't pick it up with the balance. More times than not this will cancel out most things except for a target when tested over the hole. Most times though if it isn't increasing in strength with depth it ain't a good target.

A trick i use works very well, carry a very small test target with you at all times.
If your unsure if your target signal is genuine from the above, next to the hole your digging dig another quick small 6" hole or so depending on your test target, two swings with the pick & place your test target in it cover it over with the soil out of the the main target hole & ground balance on this so you just get a very small indication that it's there.
If then if then you sweep the target hole & have a good response there's a very good chance that you keep swinging the pick.

The target response from a deep target sometimes isn't very strong & easy to balance out with a good ground balance, everybody has there own ways but i like to find most of what i walk over be it small gold or the far & few between bigger stuff down deeper.

At the end of most days prospecting is see a handfull of smaller gold & maybe the odd big one, at the price of gold today, them smaller bits up to 10oz sure do help the bank account.

I'm sure everybody has read this http://www.ncmd.co.uk/docs/how%20a%20detector%20works.pdf

Anybody see any flaws in the way Mr Candy looks at things?

Well P/W !! thank you for the detecting tips,i will be sure to give it a try next time i go detecting.

Zed

[B^C]

Zed, not sure on the ---Well P/W !!


Bit slow on the uptake with all the abreviated stuff these days?