ground signal

[green]

Looking at ground signals again this morning. I have ground from the back yard and some hot ground from California in zip lock bags. The California ground appears to have twice the signal strength of the Alabama ground when Tx on(X signal ?), lot more Tx off(R signal ?). Scope traces were taken with bag laying on one end of fig8 coil. Integrator was saturated, so some measurements were made with bag spaced about 2 inches from coil. Integrator out(California ground .83V)(Alabama ground .16V). What in the ground causes X/R signal for the California ground to be higher.

[6666]

Thanks for doing these experiments.
When you remove the bags of dirt does the integrator out voltage drop completely to zero ?

[Carl-NC]

What in the ground causes X/R signal for the California ground to be higher.

Higher concentrations of iron oxides. For TX-off, Cal dirt may also have more viscous material.

[green]

Thanks for doing these experiments.
When you remove the bags of dirt does the integrator out voltage drop completely to zero ?

Some offset. Measurement values were change in integrator output.

[Ferric Toes]

Looking at ground signals again this morning. I have ground from the back yard and some hot ground from California in zip lock bags. The California ground appears to have twice the signal strength of the Alabama ground when Tx on(X signal ?), lot more Tx off(R signal ?). Scope traces were taken with bag laying on one end of fig8 coil. Integrator was saturated, so some measurements were made with bag spaced about 2 inches from coil. Integrator out(California ground .83V)(Alabama ground .16V). What in the ground causes X/R signal for the California ground to be higher.

Hi Green,

There are a couple of things going on here. 1) The presence of magnetically susceptible material in one of the figure8 coil lobes will unbalance the system, so during Tx on, what you see is the derivitive of the Tx current growth in the coil. 2) At Tx off the response you get is due to the percentage of superparamagnetic particles (SPM) in the sample versus stable single domain (SSD) particles. SPM particles have time constants in microseconds; SSD is rather larger at many thousands of years. The California soil has a higher percentage of SPM than Alabama ground. The boundary between a particle being SPM rather than SSD is very small. At room temperature the boundary for a spherical grain of magnetite or hematite is 0.03 micrometres. Below that it is SPM and above, it switches to SSD. This boundary is also shifted by temperature and external magnetic fields. I did a test on a soil from Red Hill, Virginia, and found that an external field of 3.5 milliteslas caused the amplitude of a sample at Tx off to drop by nearly 50%. Similarly, higher temperatures will cause the amplitude to drop. If you pass a ferrite magnet within an inch of so of your samples, you should see the amplitude drop.

Eric.

[green]

Thanks for the replies. Need to do some reading.

[ZED]

While your at it Green,see if you can come up with a GB scheme that GB's both bags of dirt at the same time.

[6666]

Some offset. Measurement values were change in integrator output.

Hi Green would you mind showing the circuit before the integrator please, I have been trying a similar experiment but I must have something wrong.

[green]

While your at it Green,see if you can come up with a GB scheme that GB's both bags of dirt at the same time.

Some data with my bipolar circuit. I think the two grounds were closer with my unipolar Tx. 6us delay is the fastest I remember trying to ground balance the unipolar Tx. Need to try unipolar with the 133mm fig8 at 4us delay. The figure 8 coil does reduce the ground signal when both coils see the same ground. Any suggestions or additions for future testing.

Ground readings are integrator out .1mV resolution

[green]

Hi Green would you mind showing the circuit before the integrator please, I have been trying a similar experiment but I must have something wrong.

Not certain what you want. For Rx, I wind two round spiral coils the same(test for inductance and resonance, calculate a Rd for each coil[1.5 to 2 times pi x L x Fr]), lay them side by side and connect the outer windings together. Inner windings are Rx coil ends. Connect the Rd resistors across each Rx coil. For Tx I wind a oval coil over Rx, about 3/16 inch space between Rx and Tx. Complete the coil. Rx coil is connected to a differential amplifier. Coil is not perfectly balanced so a ferrite core is positioned on the coil for final balance(amplifier zero output when Tx on and no target). Circuit before the integrator is the amplifier and Rx coil. Are you asking for the amplifier schematic?

[6666]

Circuit before the integrator is the amplifier and Rx coil. Are you asking for the amplifier schematic?

Hi Green, yes, could you please show me the schematic, I think you showed it some time ago (hand drawn)
Thanks for the description of your coil connections.
I am using a standard mono coil PI amp and coil and the responses from my soil samples are horrible
and I must have some problem.
Your diff amp seems to work well for soil samples.

[green]

Hi Green, yes, could you please show me the schematic, I think you showed it some time ago (hand drawn)
Thanks for the description of your coil connections.
I am using a standard mono coil PI amp and coil and the responses from my soil samples are horrible
and I must have some problem.
Your diff amp seems to work well for soil samples.

schematic I use except base resistors are 1k. Think 2k might be better. Probably need IB coil, not sure why IB coil doesn't zap the amplifier.

[Ferric Toes]

Thanks for the replies. Need to do some reading.

Here is a very good paper which describes how soil magnetism develops, and how it is useful in archaeology. For metal detecting of gold nuggets, coins and other metallic items, it is something we usually want to eliminate, so it is good to know what causes it. I am sure that the GB methods used today can be improved considerably.

Eric.

https://iopscience.iop.org/article/1...6/17/1/019/pdf

[EL NINO]

short test of the PI type detector on 97% magnetite ... I tested the work of the Detector from the setting of the sensitivity level..and the reaction to the silver coin and also to 1 gram of 24k gold ...

https://www.youtube.com/watch?v=pkOZ54egQWo


Later I will do a similar test using a change in timing vs a change in detector sensitivity ...


..... and as for the tests of the coil of shape 8 / big foot/in the mineralization test, I recommend to keep the whole surface of the coil parallel to the surface of the mineralization ...with a stronger deviation you can lose IB balance. ... in strong mineralized terain...

[green]

Some data with my bipolar circuit. I think the two grounds were closer with my unipolar Tx. 6us delay is the fastest I remember trying to ground balance the unipolar Tx. Need to try unipolar with the 133mm fig8 at 4us delay. The figure 8 coil does reduce the ground signal when both coils see the same ground. Any suggestions or additions for future testing.

Ground readings are integrator out .1mV resolution

Tried unipolar circuit, similar results. Larger difference at 4us delay with Alabama timings same as California timings. Cancel close when delay is 6us or greater.

Ground readings are integrator out .1mV resolution should read change in integrator out (reply#9)