DEEPER PI DETECTION DEPTH

[Davor]

Well. that would be a whole idea of ballance. If a same mechanism works here and the same mechanism works there and everywhere, it is balanced out. Only in case of various perversions, e.g. golden nuggets, you'll get a broken balance. That's my idea.
Single balance should work with homogenous medium or a decent discontinuity with no gradient. Double balance should work with a linear gradient too. I'm afraid nothing will ever work with non-linear gradients, Barkhausen, saturation, or real targets. No way you will ever cancel that.

BTW I noticed that the majority of IB MD-s have unbalanced front ends (bad), and some of them have shielding (better). Also majority of IB MDs have asymmetric Tx with THD controlled only by the tank Q and samples timing is derived from there, hence it is prone to PWM and false ground problems - due to the proximity a tank Q is changed, oscillation average value and THD is changed and consequently timing criteria are shifted (PWM style). Knock-knock, the ground (proximity).

PI designs tend to suffer from high Z problems that shorten useable sampling period, and too much gain at front end that prolongs recovery. Frankly, you are orders of magnitude beyond the ground effects anyway.

I'd say that many design problems are attributed to ground and a whole story is blown up beyond its real proportions. Once you fix a first approximation problem, e.g. balance your coils properly, only then you'll be able to grasp the second. IMHO ground proximity is a first approximation to GB.

[Tinkerer]

Like double balance coils? I'm concentrating on this possibility.
Maybe Barkhausen effect? With TEM magnetisation it is sure to happen.

With 4 coils and 3 different value inductance interacting and having different coupling coefficients, it is already quite complex. But this is not where the major problems with ground balance are.

Tinkerer

[Davor]

Like double balance coils? I'm concentrating on this possibility.

.. (forgot probably more effects)

Maybe Barkhausen effect? With TEM magnetisation it is sure to happen.

[Tinkerer]

Ground balance

So has anyone got any ideas how to implement a ground balance system using the TEM transmitter ? Not that I fully understand it but I get the impression the ground balance system implemented on Whites half sine pulse system relies on taking two samples around the symetrical sine pulse. ie. identical dI\dt rising and falling. I imagine the un-symetrical TEM method is going to complicate that somewhat.

In this thread, we have explored the TX methods in search of deeper detection depth.
another very important factor for deep detection depth, is the ground balance.

I suggest we move to a new thread for the ground balance. I will name the new thread:

THE PERFECT GROUND BALANCE

Tinkerer

[Aziz]

BTW,

a dual-frequency VLF GB system can be simplified (approximated) by a simple linear equation (of form f(x) = a1*x + a0 ) .

Aziz

Now, hurry up and run to the patent office patent troll.

[Aziz]

The Holy Grail

Hi Midas,

the ground balance (GB) is the holy grail of the game.

We have more effects to cope width:
- induction balance change (coil coupling coefficient change due to ground mineralisation) (if an IB system is used)
- time constant change of the transmitter/receiver coil (inductivity changes over mineralized ground)
- static magnetisation M (of the ground/hot rocks, geo-magnetic field included)
- complex dM/dt (magnetisation change behaviour of the ground/ferrous-target, magnetisation decay and magnetic viscosity effects)
- TX energy losses due to magnetisation process (magnetic polarisation energy losses)
.. (forgot probably more effects)

As we know, the typical basic RLC circuit (i.e., TX circuit) is a two order circuit. It can mathematically be described with second order differential equations. Every energy storing element/part (L and C) contributes an order to the complex equation.

Energy storing elements:
L (inductivity) stores current/magnetic field energy (temporary, it can't store it permanently however)
C (capacitor) stores charge (it can store the energy permanently if we neglect the leakage energy losses)
Magnetisation process as well (short/long time constant)

If we add the target (inductivity) to the model, the order increases to three.
If we add the magnetisation process to the model, the order increases more.

It's going to be mind blowing now.

The whole process has a complex system memory (state of each energy storing element in the system, i.e., it's energy content dependent on time t). These dynamic systems can be modelled with differential equations only.

We want to detect the state of each energy storing element in the system to be able to remove all the disturbing effects at the end.

As we can not describe the complex system accurate enough, we have to make simplifications (approximations), which give us reasonable results with less cost and effort (but not perfect).

The art of setting the sampling time position is dependent on the systems state (what has been done with the system previously) and whether a disturbing effect is changing its state. You obviously need at least two samples to detect such a changing state.
But we have a lot of variables in the system, which require more samples to solve it.

If a disturbing effect isn't changing it's state at the sampled two time positions, that's easy as we can easily subtract it out. But we can not detect it.

We have lot's of superposition of effects, which doesn't make it trivial to solve it however.

You see, it's a big challenge. Even for a guru.


Cheers,
Aziz

[Midas]

So has anyone got any ideas how to implement a ground balance system using the TEM transmitter ? Not that I fully understand it but I get the impression the ground balance system implemented on Whites half sine pulse system relies on taking two samples around the symetrical sine pulse. ie. identical dI\dt rising and falling. I imagine the un-symetrical TEM method is going to complicate that somewhat.

[Carl-NC]

OK, now I remember... thanks!

[Aziz]

Great, thanks.

In a way, it's a lot like buck-boost regulator, sortof kindof.

-SB

This little circuit is simple but genius. It has it's own step-up converter while stimulating the target during charging and recycling phase too. Note, that charging and recycling phase use a single TX-on pulse gate.


Aziz

[simonbaker]

Ok guys,

found another TEM source. In this thread (post #51):
http://www.geotech1.com/forums/showp...3&postcount=51

Look at TEM1 and TEM2 variants.

Aziz

Great, thanks.

In a way, it's a lot like buck-boost regulator, sortof kindof.

-SB

[Aziz]

Ok guys,

found another TEM source. In this thread (post #51):
http://www.geotech1.com/forums/showp...3&postcount=51

Look at TEM1 and TEM2 variants.

Aziz

[Aziz]

I'm looking too... is this it?

http://www.geotech1.com/forums/showp...&postcount=819

I'm lost too! Good find.

It is based on this principle:
http://www.zonge.com/PDF_Papers/TEMposterAs.pdf

Aziz

[simonbaker]

OK, I'm lost in my own damned forums... can someone point me to the original thread on the TEM dev?

I'm looking too... is this it?

http://www.geotech1.com/forums/showp...&postcount=819

[Carl-NC]

OK, I'm lost in my own damned forums... can someone point me to the original thread on the TEM dev?

[Carl-NC]

So it seem John left White's. Hopefully for something even better.

I doubt it, he just left my office again. Hopefully for something even better.