Ground Balance Theory

[Aziz]

1A Premium Service

BTW guys,

I've got a lot of field test measurement data sets from Australia yesterday. I got it from the infamous Australian forum, which shall not be named here (obviously). But I'll publish the results only there, where I got the data (my fair rule).

If ya wanna make me busy, just upload some real measurement data here.

Aziz

[Ferric Toes]

There seems to be a lot of wheel reinventing going on here; chariot wheels mainly. My wheels are the best on the block so far and run in a true (1/t) straight line.

Eric

[Davor]

Good to see you back

[Aziz]

There seems to be a lot of wheel reinventing going on here; chariot wheels mainly. My wheels are the best on the block so far and run in a true (1/t) straight line.

Eric

Hi Eric,

now tell to the people, when the 1/t law gets true.
Aziz

[Tepco]

All this is just “academic”, about decay curves and measurements, theoretical behavior of soil samples... Who care for that, really, subtraction method GB will work anyway, no matter how decay curve actually looks like. Now, let's invent “chariots of fire” wheels. (WARP capable, if possible).

[Aziz]

All this is just “academic”, about decay curves and measurements, theoretical behavior of soil samples... Who care for that, really, subtraction method GB will work anyway, no matter how decay curve actually looks like. Now, let's invent “chariots of fire” wheels. (WARP capable, if possible).

Wouldn't you want to know the real truth?
Aziz,
WARP 7 engaged

[Tepco]

Wouldn't you want to know the real truth?

Actually no, I can live quite happily without it.

[moodz]

What makes all this talk about "the curves" so entertaining is that in the end, the curve you get depends on the apparatus you use to generate the curve. A practical ground balancing PI has to be balanced empirically.

The Fish Equation goes straight to the physics of the superparamagnetic-singledomain transition, I'm a bit surprised that Aziz is still discombobulated about the matter.

--Dave J.

...hmmm the statement that a PI has to be balance empirically is like saying that "distance has to be measured" ..... very illuminating to the subject at hand. A simple combination of ratiometric samples will balance your PI every time ....similiar techniques used to linearize thermocouples been used for the last 40 years at least ... yawn.

[Aziz]

Busted

Hi all,

I have the permission to post (some) results of the Mick's (user Mechanic) detector field test measurements on varying Oz mineralized ground. (Hooked the ground response at the pre-amp output of the F1A4 detector. )

Have a look at the results (see below). Can you imagine, that some hot ground response can cause a phase offset timing of >4 µs??? Well, we can measure and prove this phase offset p.

Pulse Diagram (Overview):


Ground response modelling parameters of various field measurements:


We haven't finished the analysis yet. More to come on the other forum.

Who's got busted now?

Cheers,
Aziz,
the "Armchair (Data) Prospector"(c)(r)(tm) *LOL*
Oh yeah!, eat this: G(t) = a*(t+p)^b

[Aziz]

BTW, I forgot to mention, that the unit of G(t) and all the related parameters refer to mV (milli Volt). The time variables refer to µs (micro seconds).
Aziz

[PiTec]

New measurement data

Hi,

from Aziz’ post # 476 in this thread:

VRM decay measurements require precise and accurate timing records.

Indeed … I should have noticed the time offsets when I copied the measurement data to the excel sheet. Thanks for clarifying!

G(t) = a*(t+p)^b

This formula can detect such unknown offset time shifts in the measurement data. Provided that, there is no significant physical effect in the early decay times. We haven't figured this out yet and we would require very precise data for this issue to solve. But it is very likely, that p either doesn't exist or can be totally neglected due to not significant effects (p < 1 µs). Note that every TX and RX combination of the front-end may cause p to exist even there might no physical effect.

I can confirm that there is no offset and no need to add p – at least as long as you’re not using my crappy data

Below are some new log-log graphs from the same samples I used before, plus two new ones. Setup similar to last time:
Small cylindrical TX coil, above that a differential RX coil, samples are in film containers inside the coil, standard PI waveform with 50 µs on and 2 µs off. But this time all decay curves start exactly 20 µs after the 2 µs pulse. Again, the TX coil decay curve (air signal) was removed in the oscilloscope by subtraction, i.e. the plots show the pure decays of the samples. The initial amplitudes are similar, but not equal this time (could be normalized in the Excel sheet, of course). The signal from the volcanic rock is a bit noisier as the sample is not as concentrated as the MV soil sample, so I used an extra x2 amplification here.

Samples:
1) Hematite powder (alpha-Fe2O3, could also contain some amount of gamma-Fe2O3/maghemite):
http://www.kremer-pigmente.com/en/pi...ght-48100.html
2) Magnetic viscosity soil from my area (concentrated with a magnet)
3) Magnetite powder (Fe3O4)
http://www.kremer-pigmente.com/en/pr...html?info=4988
4) Volcanic rock (crushed lava from the Eifel area in Germany, also concentrated with a magnet)
5) A thin gold ring with one TC of 13.8 µs
6) A thick silver ring with at least two TCs of approx. 15 µs and 120 µs

Very straight lines now for 1) to 4) in the log-log plots BTW, not only time, but also amplitude measurements must be precise and without offsets, otherwise the curves will be distorted.

"b" and "TC" have been calculated by using only two pairs of values at 20 µs and 40 µs. The accuracy could be increased by averaging several results.

The last graph shows that it is quite easy to simulate a viscous response with two simple rings by adjusting their distance and angle.

Here is the Excel file with all graphs and measurement data (new xlsx file format to avoid the log axis scale problem pointed out by Aziz):
decay_curves_02.rar

Thomas

[Tepco]

Few issues with this: First, dynamic range available is very limited, only around 20dB or so, things will pop out on larger vertical log scale. Another problem is irregular response from ring, most probably caused by interaction between target and test coil. Putting ring sized object inside small test chamber is something like putting beercan right inside normal sized coil. Containing more metal than coil itself, interference is unavoidable, producing irregular composite waveform. Also, interesting effects can be observed in early time, starting from first 5 or so uS.

[PiTec]

I do not see any irregular response from the rings, just typical graphs for a ring with one TC and for a ring with several TCs. I forgot to mention that they were measured above the coils as their response is by magnitudes higher than the weak signals from the minerals. See attached photo that shows distances and angles to achieve a response similar to MV soil.

The dynamic range is of course limited by noise and the vertical resolution of the scope, although this was increased considerably by averaging over 1024 samples. There is still room for improvements, of course.

I am planning to make more measurements with a shorter delay.

[Dave J.]

Haven't tried it, but seems to me that the "two rings" method of simulating nonconductive magnetic viscosity ought to be able to approximate pretty well a typical magnetic viscosity curve on a given piece of experimental apparatus.

--Dave J.

[Aziz]

...
I am planning to make more measurements with a shorter delay.

[ATTACH]27069[/ATTACH]

Hi Thomas,

I am looking forward to your new measurements. Thanks for putting up the latest decay curve data.

I also plan to make a VRM measurement instrument with super high dynamic range (5-6 decades) and resolution (24 bit).
Cheers,
Aziz