Ground Balance

[WM6]

Thanks to deal with us your inventive toughs Davor.

Probably you can help us with some PI block diagram to show how to incorporate your GB solution in some of classic analog PI design (like Surf PI par example).

Is V2/555 input related to the output of pulse generation stage in PI? Some sort of how-to incorporating block diagram in classical analog PI design could be very helpful.

[Davor]

Yes, that's the idea. My way of designing mods is with a target device in mind, and in this case it is a minipulse. Other rigs may follow.

I figured out the way of decoupling GB and time base, so it is still on.

[greylourie]

wm6 in post 46, "Probably you can help us with some PI block diagram to show how to incorporate your GB solution in some of classic analog PI design (like Surf PI par example)."

I thought you could, using the Hammerhead as an example, send the output of Q1/Q8 to IC7b. And the output of Q2/Q3 to IC7a.

And for Surf P.I, could send Q1/Q8 (aka Plus) to U7B, and Q2/Q3 (aka Minus) to U7A.

[greylourie]

Just the opposite... mineralization decays rather quickly. Here is how the TDI does it (this is all public knowledge, so NBD):

Turn TX on for 100us
Shut off, enter flyback
Wait 10us, take the Target sample
After the end of the Target sample, wait a short delay, take the GB sample
After the end of the GB sample, wait a long delay, take the two EF samples
Use a diff integrator to subtract Target-EF1
Use another diff integrator to subtract GB-EF2
Subtract A1*(Target-EF1) - A2*(GB-EF2)
Adjust A2 for ground balance

In TDI, all the samples have identical widths. I could tell you what to use, but you would learn more trying a range of settings, say 5us up to 25us. The delay between Target and GB samples as well; try 5us to 25us. Technically, this same delay should be used to space the two EF samples. The spacing between GB and EF1 samples should be 50us or more.

There are other ways to do GB, even simpler, but this one has particular advantages that TDI uses to produce distinct audio responses.

- Carl

Hello Carl,

I'm looking at ground balance on the goldscan IV, which appears at first sight very similar to what you have described above. I'm having a difficulty (not uncommon for me) in understanding the way the GB channel aka Iron channel value is inverted before being fed to the balance pot connecting to the output of both channels.

A1 = Target - EF1
A2 = GB signal - EF2, but becomes (GB -EF2)^-1, as it is fed through an additional inverting opamp with no gain.

So in this instance, x = A1 - (A2)^-1

Or have I got it wrong ? I have attached an image to try show what I see ?

[Carl-NC]

The "inversion" stage doesn't invert as in x^-1, rather it makes it negative so the output at the pot is a subtraction instead of addition.

- Carl

[Davor]

As mentioned before, here is the solution with independent initial delay and the time base, by virtue of a clamp. Also is attached a LTspice project folder in a zip file.

For the time being I'm only concerned about GB for minipulse. This is not tested, but math says it should work. There is no practical reason why this approach would fail on other devices.

The math also implies a way of removing the problem of a "hole" in response typical to the PI machines with GB. It is only slightly more complicated. With increased number of samples in a geometric series duration and alternating polarity, the hole-less range of useful tau targets vs. sample duration becomes larger, and without harmful influence on target response. That would be point-on with Aziz' FFT solution, but to realise this one should go a bit deeper into FFT theory. In a way it truly is a WBGB system as he often advertised. Too bad he got banned.

[greylourie]

Cheers Carl,

I guessed I made a fundamental error. By using the expression (^-1), was trying to show the inverting opamp would multiply by a negative to what ever it sees on its input.
As a rule, what is coming out of the differential integrator (iron), before hitting the inverting opamp is a positive value ? As simple as that ? I complicated everything by assuming too much.

How could I translate the formula to use a single channel (with differential integrator at the front ), but continue to be able to exploit the means to see or balance to different metals like the original does ? Is it possible ?

[greylourie]

As mentioned before, here is the solution with independent initial delay and the time base, by virtue of a clamp. Also is attached a LTspice project folder in a zip file.

For the time being I'm only concerned about GB for minipulse. This is not tested, but math says it should work. There is no practical reason why this approach would fail on other devices.

The math also implies a way of removing the problem of a "hole" in response typical to the PI machines with GB. It is only slightly more complicated. With increased number of samples in a geometric series duration and alternating polarity, the hole-less range of useful tau targets vs. sample duration becomes larger, and without harmful influence on target response. That would be point-on with Aziz' FFT solution, but to realise this one should go a bit deeper into FFT theory. In a way it truly is a WBGB system as he often advertised. Too bad he got banned.

Oh wow, another implementation. Thanks a lot Davor. Bet Aziz would like it.

I'm still trying to pick Carls brain. I frequently watch a downloaded copy of Jose's youtube video of his homemade goldscan4 facsimile. It would great to be able to implement (if possible), the traits of that type of balancing in a hammerhead/minipulse type machine. Imagine the hours spent balancing out various items. Fun ! Maybe I'm just being stupid again, and missing the obvious.

[Davor]

The only thing you need to balance out is viscous soil. What remains are the targets, and perhaps a hot rock or two.

[Carl-NC]

Cheers Carl,

I guessed I made a fundamental error. By using the expression (^-1), was trying to show the inverting opamp would multiply by a negative to what ever it sees on its input.
As a rule, what is coming out of the differential integrator (iron), before hitting the inverting opamp is a positive value ? As simple as that ? I complicated everything by assuming too much.

How could I translate the formula to use a single channel (with differential integrator at the front ), but continue to be able to exploit the means to see or balance to different metals like the original does ? Is it possible ?

As a rule, in a simple PI everything (ferrous, nonferrous, salt, ground) responds with a positive value. The difference is the curvature of the response (1/t vs exp) and the time constant of the exponential response.

A 2-sample subtractive GB can be adjusted to exactly cancel ground, but that setting will also exactly cancel a particular exponential tau. If you take 3 samples then you can exactly cancel a 1/t response but not cancel any exponential taus because they have a different curvature. Regardless of the method, subtractive GB on the decay always reduces target depth.

You can use a single differential integrator by appropriately sampling on the inverting and non-inverting sides and adjusting either the gains or the sample widths. You can also do all this with a non-differential integrator by running some of the sample switches off an inverted preamp signal.

When I get some time I'll try to post some drawings of all this. Work has me hopping right now.

[greylourie]

Thanks Carl.

Really interested in the single differential integrator, and adjusting the sample widths. Will have a closer look at the example equations Qiaozhi posted up in another thread here (http://www.geotech1.com/forums/showt...ROL-PI-CIRCUIT), and see if I can figure out how to plug in the original goldscan pulse widths/sequences to come up with an alternative.

[greylourie]

The only thing you need to balance out is viscous soil. What remains are the targets, and perhaps a hot rock or two.

Your timing/generator circuit looks like a good candidate for experimentation with many platforms. Quite a list of possible projects could use this as a substitute or basis for their sampling regime. Very tempting. Thanks for taking the time to share. I'm going to study it.

[6666]

As mentioned before, here is the solution with independent initial delay and the time base, by virtue of a clamp. Also is attached a LTspice project folder in a zip file.

For the time being I'm only concerned about GB for minipulse. This is not tested, but math says it should work. There is no practical reason why this approach would fail on other devices.

The math also implies a way of removing the problem of a "hole" in response typical to the PI machines with GB. It is only slightly more complicated. With increased number of samples in a geometric series duration and alternating polarity, the hole-less range of useful tau targets vs. sample duration becomes larger, and without harmful influence on target response. That would be point-on with Aziz' FFT solution, but to realise this one should go a bit deeper into FFT theory. In a way it truly is a WBGB system as he often advertised. Too bad he got banned.

Good work Davor, where do you plug it into the mini pulse ?

[Davor]

At the FETs gates. Timing circuit must be powered with 0 and -5V for FETs to work properly, same as originaly in minipulse.

I'm considering scribbling an overview of ground balance with this approach in mind.

[Qiaozhi]

As mentioned before, here is the solution with independent initial delay and the time base, by virtue of a clamp. Also is attached a LTspice project folder in a zip file.

For the time being I'm only concerned about GB for minipulse. This is not tested, but math says it should work. There is no practical reason why this approach would fail on other devices.

The math also implies a way of removing the problem of a "hole" in response typical to the PI machines with GB. It is only slightly more complicated. With increased number of samples in a geometric series duration and alternating polarity, the hole-less range of useful tau targets vs. sample duration becomes larger, and without harmful influence on target response. That would be point-on with Aziz' FFT solution, but to realise this one should go a bit deeper into FFT theory. In a way it truly is a WBGB system as he often advertised. Too bad he got banned.

It would be a good idea if you could provide a block diagram of your proposed GB method, plus a simplified (executive overview) explanation of how it's supposed to work. At the moment I'm failing to understand the concept, even though I've downloaded and successfully run the simulation.