Best DIY PI detector for mineralized ground

[Wessex warrior]

Hi,

I built a Surfmaster PI (Silverdog), and it works fine, the thing is that I live in an area where there is quite a lot of iron (mineralization) in the ground, for this reason it is very difficult to actually use 'in the field', even when adjusting the delay before target sample is taken.

Was wondering what you guys thoughts are on what is best DIY PI solution for mineralized ground.

I am considering modifying the Surf PI kit so that it takes sample of ground (after target sample but before EFE sample) and subtracts it from signal in the way that some PI detectors achieve ground balance.

But there might be other options, perhaps a modification of Baracauda,Hammerhead etc. , or maybe using bipolar pulse, or maybe using two coils ? Obviously want to compromise depth of detection as little as possible.

Many Thanks

[waltr]

Take a look at how I do GEB on a modified Hammer Head II.
It does work.

This method can be adapted to other PI detectors, particularly ones that use a processor to generate all the timing pulses (TX coil and sampling).
This method has be discussed and analyzed in various other threads. I have links to these other threads in my thread.

A bi-polar pulse eliminates Earth Field not Ground.
Two coils also do not eliminate Ground but I feel have other advantages.

Link:
http://www.geotech1.com/forums/showt...ake-on-the-HH2

[Qiaozhi]

Hi,

I built a Surfmaster PI (Silverdog), and it works fine, the thing is that I live in an area where there is quite a lot of iron (mineralization) in the ground, for this reason it is very difficult to actually use 'in the field', even when adjusting the delay before target sample is taken.

Was wondering what you guys thoughts are on what is best DIY PI solution for mineralized ground.

I am considering modifying the Surf PI kit so that it takes sample of ground (after target sample but before EFE sample) and subtracts it from signal in the way that some PI detectors achieve ground balance.

But there might be other options, perhaps a modification of Baracauda,Hammerhead etc. , or maybe using bipolar pulse, or maybe using two coils ? Obviously want to compromise depth of detection as little as possible.

Many Thanks

You cannot exclude iron with the Surf-PI (or Baracuda, or Hammerhead) by adding a ground balance channel.
A PI is only capable of discriminating by conductivity using the delay (reject) control. The first targets to be rejected will be foil, followed by pulltabs. Iron cannot be rejected.

You may have heard that the TDI ground balance control can be used to exclude small iron nails, but this is effectively creating a hole in the response that matches the small nail response. In that particular case, the TDI gives a low tone for high conductivity items, and a high tone for low conductivity. However, I don't think that's what you're looking for.

[Wessex warrior]

Take a look at how I do GEB on a modified Hammer Head II.
It does work.

This method can be adapted to other PI detectors, particularly ones that use a processor to generate all the timing pulses (TX coil and sampling).
This method has be discussed and analyzed in various other threads. I have links to these other threads in my thread.

A bi-polar pulse eliminates Earth Field not Ground.
Two coils also do not eliminate Ground but I feel have other advantages.

Link:
http://www.geotech1.com/forums/showt...ake-on-the-HH2

Thanks waltr,
I read through that thread and it was interesting, I was impressed by your detector and things you found with it.
It is encouraging to see that ground balance can be achieved this way.


The method using two coils to eliminate ground I was thinking of, is actually this way: http://www.geotech1.com/cgi-bin/page...loop/index.dat

I believe this is a method that hasn't been done much. Sounds like it should work OK. You have two coils, overlapped somewhat, pulsed at same time and for same pulsewidth, and the output from one coil goes into non-inverting input of pre-amp, the other coil goes into inverting input. This way the ground signal is subtracted from itself. When there is a target, output from one coil differs from other coil causing signal. As I say Idon't think this method has been done much so hard to know how effective it is.

[Wessex warrior]

You cannot exclude iron with the Surf-PI (or Baracuda, or Hammerhead) by adding a ground balance channel.
A PI is only capable of discriminating by conductivity using the delay (reject) control. The first targets to be rejected will be foil, followed by pulltabs. Iron cannot be rejected.

You may have heard that the TDI ground balance control can be used to exclude small iron nails, but this is effectively creating a hole in the response that matches the small nail response. In that particular case, the TDI gives a low tone for high conductivity items, and a high tone for low conductivity. However, I don't think that's what you're looking for.

Not sure but think you might have misunderstood, I don't mean discriminating out iron in the form of nails etc, but eliminating the response caused by the soil itself when the soil contains tiny amounts of metal minerals as a lot of soils do.

[waltr]

The method using two coils to eliminate ground I was thinking of, is actually this way: http://www.geotech1.com/cgi-bin/page...loop/index.dat

Yea, I forgot about that one but as you said not much experimentation done.
Would be interesting to try and if you do Please make a thread and post what you did and the results.

The way I did GEB is totally in the Sampling so I didn't need to add circuits for a Ground channel.

[Wessex warrior]

Yea, I forgot about that one but as you said not much experimentation done.
Would be interesting to try and if you do Please make a thread and post what you did and the results.

The way I did GEB is totally in the Sampling so I didn't need to add circuits for a Ground channel.

Yeah I have often thought about making the 'Twin Loop', in a way it seems a more "elegant" way to achieve ground balance. I do worry that the detection distance might not be fantastic, because of powering two coils at same time, but maybe not.
I have wondered if it might work OK or better with a DD shape coil, it would certainly be less cumbersome.
The other thing about it, is it dosen't seem to have any EFE circuitry (only target sample is taken), I don't know enough about science to know but maybe the twin coils/subtraction provide EFE.

[waltr]

I think that twin coil should also eliminate Earth field also.
Earth field falsing is caused when moving the coil through the earth's magnet field which produces a current in the coil. This current should be the same in both coils and is then canceled with the differential measurement.

[green]

My attempt at making a detector with GEB. http://www.geotech1.com/forums/showt...845#post209845