Ground Balance Theory

[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]

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/pigments/iron-oxide-pigments/iron-oxide-red-110-m--light-48100.html

2) Magnetic viscosity soil from my area (concentrated with a magnet)
3) Magnetite powder (Fe3O4)

http://www.kremer-pigmente.com/en/product.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

[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

[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

[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.

[Tepco]

Wouldn't you want to know the real truth?

Actually no, I can live quite happily without it.

[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]

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]

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

[Davor]

Good to see you back

[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

[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

[Aziz]

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.

Fine Dave. You're going to calculate the number of magnetic domain changes. But you still have to know the rate of change in a time interval before you can calculate the probability of the successive/other time intervals. And the rate of change must be stable (const).
But we know these processes like the radioactive decay.

Where is the logic link to the VRM decay now? Oh yeah!, the exponent b.
But we cannot say, that the exponent b stays constant. It may stay constant for one sample but for a different sample it is varying. And it is completely pulse history state dependent too. And other factors do change exponent b as well.

Well, I'm not reading always off-topic stuff. That's is probably the reason, why I didn't understand you and your fish example. So I got very confused and have tried to make the link to the related stuff. But I got more confused. You have to be more precise in your wording next time.

Cheers,
Aziz

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

[Dave J.]

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.

[Aziz]

I'm playing with metal detectors to try and learn something. Some of my measurements don't match other posts. Why I don't know, probably doesn't mater. If my curves are wrong or don't make sense say so. I'm sure the curves have been plotted many times, but I haven't seen them. Entertainment might be the best reason for doing it.

Please Mr. green,

just go on and ignore Dave. He is trying to troll and to strangle the GB topic.

His "fish equation" is a good example to make the thread off-topic. That had no reference to our GB here and has confused more members (including myself - oh yeah!, I've learned the Poisson distribution function along with Gaussian distribution, Bernoulli process etc. etc. and I could even calculate his fish example - but that is very off-topic here).

Just troll back (like I do it: G(t) = a*(t+p)^b ).

Aziz