Recent TDI Discovery

[Mark Gillespie]

Recent discovery of the conductivity switch on my White's TDI SL.
The video shows what I've found.
It also works the same with the 7 1/2" dual field coil.
Just the opposite happens if you run the machine with the conductivity switch to high, low conductors are also heard.

These results are the same as in ground targets to about 4" deep.

More information to follow......
 

 

[Steve Herschbach]

Hi Mark,

What you have rediscovered is that the conductivity switch on the TDI is nothing of the sort. That is just the name slapped on a control that appears to most people to separate low conductors from high conductors. It's real function is too complicated to boil down into a couple words and conductivity switch is as close as you can get but does not tell the whole story.

The TDI has a ground balance control. Where that control normally is set is determined by any ground response. You set the control to eliminate the ground response. The ground signal is first dictated by where you have set the pulse delay control and the gain control. Lower pulse delays enhance ground signals as do higher gain levels. So in general you decide where you want to set the pulse delay and gain controls first, then set the ground balance such that any ground response is eliminated.

The ground balance setting, wherever it ends up, creates two classes of targets. Those that read above (high) the ground balance setting, and those that read below (low) the ground balance setting. Experimentation reveals these are not high conductive versus low conductive targets, though there is a general trend in that direction. What the really are is "long pulse delay/slow decay" targets versus "short pulse delay/fast decay" targets. The key thing is which side of the dividing point targets fall varies and is determined mainly by the ground balance setting as modified by the pulse delay setting. Because the TDI generally ignores low mineral ground anyway, you can often vary these controls with a wide range without enhancing the ground signal to vary the target responses, converting these controls into a crude discrimination system.

The depth items may be found at also varies wildly depending on the settings. The ground balance control creates a "black hole" that sucks target responses down the closer the targets are to the ground balance setting. Targets that fall directly where the ground balance setting is will be completely eliminated. Purposefully offsetting the ground balance control away from certain target responses can greatly enhance the depth those targets may be detected at. The correct combination of the pulse delay and ground balance is the basis for my TDI coin settings.

Long story short, the response you are observing is directly related to where you have set the gain, pulse delay, and ground balance controls. Varying those control settings will change the responses you are observing.

There are some great 2009 test charts on Geotech at http://www.geotech1.com/forums/showthread.php?16010-TDI-Test you can access if you are a member of that forum showing how depth varies on a wide range of targets with different pulse delay and ground balance combinations.

A chart showing TDI responses on bullets, button, and nails at various settings https://www.mytreasurespot.com/main/read.php?49,578762,585756#msg-585756

White's Pulsescan TDI controls

[Mark Gillespie]

Steve anyway to send you a PM on this subject?

 

[Steve Herschbach]

Sure, just click on my name or any other persons name to send a personal message.