Ground balance

[ZED]

Auto GB can be done with an additional signal channel,which would be used for mathematical purposes or for determining coil direction,tracking on the other hand (ground balancing while walking) has a tendency to balance out very weak target signals.Alternatively it can be done without an extra signal channel but it would be limited to the lowering or the raising of the coil,not both...this is within the context of using an mcu.

[Bayu]

How about automatic ground balance ? Is not something that I believe has been discussed.

Can this be installed on Pi? and what ic is used because there is no ic number information ,, thanks

[6666]

Can this be installed on Pi? and what ic is used because there is no ic number information ,, thanks

There is a bit more to it.

[ZED]

You could use that circuit but as 6666 says,theres a lot more to it,you would add caps to the circuit,particularly the mixer amp,you would need to duplicate the signal channel for the GB signal then pulse circuits for the extra demods,its a job and a half,plus each detector design has its own circuit topology and GB circuit,there is no one circuit fits all.

[eclipse]

Hey ZED I'm looking at a circuit that has ground balance and there's a 100nF cap on the mixer amp as you say. If you look at TDI/GS5 designs you won't find any.
What is the benefit of the cap in there?

The circuit above is similar to what's described in ITMD book but honestly it came off Whites TDI circuit I have (there's a bunch of these TDI/GS5 floating around the forum have a look but watch out for errors).

[Orbit]

Hey ZED I'm looking at a circuit that has ground balance and there's a 100nF cap on the mixer amp as you say. If you look at TDI/GS5 designs you won't find any.
What is the benefit of the cap in there?

The circuit above is similar to what's described in ITMD book but honestly it came off Whites TDI circuit I have (there's a bunch of these TDI/GS5 floating around the forum have a look but watch out for errors).

Yes there are a lot of mistakes!Otherwise I do not notice that once set geb if we change location searches it must again be adjusted here in Serbia! Otherwise auto geb could be done on the TDI it came to my mind to take the signal from the exit from the comparator that signal I lead in mcu where it is checked whether the signal is o-volts if it is positive or negative over the mcu moves the digital potentiometer where adjustment is made that is, to bring the output to zero by pumping but without turning the analog potentiometer like before, I don't know how clear I was..Automatic tracking think it's wrong because of what Zed stated!I also have an idea of how it is done to device in the first thirty seconds automatically he chooses the frequency himself to avoid interference!

[Bayu]

master, because in my country the majority of red soil is high in mineral, so it really needs GB, many relics of royal residues made of gold, for MD here the popular type of pi is our local product mimiti, and the very qualified product is nokta, and there some who use minelab, it is very financially draining for most people, there are Chinese products tx850 but many are easily damaged, I have made pi polones with my modification that is cheap enough for the community, but constrained by the Gb, for that I ask for help from the master at this forum.

[ZED]

eclipse the noise from both channels will combine,it was a generic suggestion to keep the noise to a minimum,im always playing with filters,i cant speak as to the reasons why or why not the other circuits do or dont use them,i just see it as an opportunity to reduce noise.

Also if one lives in a region of the world where the ground mineralization is mild and ground balancing is not so frequent then i suppose auto GB is not as much of a necessity.

[ZED]

Bayu you could make a separate pulsing circuit for your sampling and run a sample through a circuit that changes the phase of the sample and run that to your demods as a means of ground balancing,i did exactly that on a SD2200 and it worked a charm.

[6666]

master, because in my country the majority of red soil is high in mineral, so it really needs GB, many relics of royal residues made of gold, for MD here the popular type of pi is our local product mimiti, and the very qualified product is nokta, and there some who use minelab, it is very financially draining for most people, there are Chinese products tx850 but many are easily damaged, I have made pi polones with my modification that is cheap enough for the community, but constrained by the Gb, for that I ask for help from the master at this forum.

You could also look at the MPP project by KRinAZ. This is an MPP that has been further modified to operate in high iron mineralization of the gold bearing areas of Arizona (or Australia).
you would have to carefully read the threads and see if its something you would want to do, I have not done any of the mods.

https://www.geotech1.com/forums/show...586#post206586

https://www.geotech1.com/forums/show...-build-the-MPP

[Elliot]

I’m currently working on designing a ground balancing Pi machine. My initial research identified that the standard Ground Balancing formula for a four sample design is:

X = A1 (S1 – S4) – A2 (S3 – S2) [Formula 1]

Where X = the resultant signal to be integrated
A1 and A2 are the gains for different sample groups
S1 = Target sample
S2 = Ground earth field effect (EFE) sample
S3 = Ground sample
S4 = Target EFE sample

As the EFE samples are reasonably static, you are meant to be able to take two different (albeit consecutive) EFE samples, and they should be the same, therefore the S2 and S4 will cancel out, leaving just the target and ground samples to process.

When A1 (S1 – S4) > A2 (S3 – S2) it gives a positive response (i.e. When the target has a high time constant (TC), or in other words, the target response decays slower than the ground response).

From a practical implementation perspective, under formula 1, when you change the gain (A2) in order to ground balance the machine, it also affects the gain of S2, resulting in an EFE imbalance. Additionally, there are resistance tolerances in real world circuits which means that one of the EFE samples would ideally be adjustable separately (and permanently locked in) to fully cancel out the other.

To overcome these issues, I’m proposing a more usable/practical formula for consideration. I’m also proposing to flip around the formula so that High TC targets (relative to the Ground Balance set point) give a negative pulse response (like on the Whites TDI etc.), and Low TC targets give a positive pulse response, as follows:

X = (A2 (S3) – A3 (S2)) – A1 (S1 – S4) [Formula 2]

The gain of A3 would be independently adjusted to fully cancel out EFE from the equation, regardless of the GB gain setting (A2).

An example schematic of formula 3 is as follows:

Elliot

[waltr]

Yes, that is a way to fine tune the gains and balance Gnd EFE with signal EFE.

Another that simplifies the circuits is the three Sample method. This is what I use in my HH2. Info in thread starting in Post #14.
https://www.geotech1.com/forums/show...ake-on-the-HH2

The advantage of the 3-sample is it is all done in the processor code and there is only one EFE sample that varies with the GEB timing control.

This also produces a high signal for high conductors and a low for low conductors (the GEB timing sets the break point but also creates a 'hole' at a particular conduction.
In my HH2 the output from the integrator/SAT goes into a VCO (PIC12F1501) for high/low tones (like the TDI).

[Elliot]

Hi Waltr.

My idea was mainly for implementation in an un-coded (ie discrete component) design. It can also handle a three sample method just as readily (by sending the one same EFE sample to both S2 and S4), but you still need to be able to adjust the gain of one of the duplicate EFE samples (even though S2 = S4) because of the differences in circuit path gain (e.g. resistor tolerances, and Jfet /4066 switch resistance tolerances).

Maybe I'm being too picky about unbalanced EFE effects, but it's just too easy to do it properly the first time, then you don't have to worry about it again.

Are you aware of any other potential imbalances that should/could be catered for?

[waltr]

The three sample method removes the issue of different component values since there is only the inverting and non-inverting sampling switches. It then is only the sample pulse timing (widths) that contribute.

In the discussion in my HH2 thread it was brought up that 'gain' (A1, A2, A3) verse 'pulse sampling width' is not the same, sampling width is not as linear. That makes the math difficult. However, we have a pot to adjust GB in the field so any non-linear effect is nulled due to simply turn the pot to obtain a non-response to 'hot ground'.

I am thinking that you are putting to much of balancing the EFE samples.
EFE is a very slow effect which is why they are taken far from the target & GEB samples. I do the EFE sample just before the next TX pulse. I haven't seen any indication that a slight un-balance of EFE sample to the target & GEB sample has any effect.

[6666]

Hi Waltr
you say in your thread that the sample timing.sequence is:

EFE sample : delay3 : TX pulse : delay1 : Target sample : delay2 : GEB sample

Would you mind saying which sample goes to which input of the intergrater (inverting-non inverting) thanks