Eric....HELP

[Anonymous]

Hi Eric,
Maybe you are the only person in this forum who could help me.
My question is that where can i find a PI machine that can penetrate deep using a large cable coil let us say 1m"x1m" for extremely deep buried object.Anybody build this machine? I saw this deep instruments in various websites but they are very expensive.Can you recommend to me where i can find a low cost or homebuilt deepseeking PI? I want to build one..your help is highly appreciated...

 

[Anonymous]

Hi Errel,
I would think that Carl Moreland's Hammerhead design could be adapted to run on a 1m square coil. You would need to slow things down and change some of the pulse timings.
I would start as follows - Assuming a coil of 300 to 500uH and 1.5 - 2.0 ohms total resistance, set the transmitter pulse width to 500uS. The transmitter frequency would need to be dropped to 100 pulses per sec or less to avoid too much current drain.
Have a pulse delay that is adjustable between 60 and 100uS for starters. The sample pulse width could be 45-50uS for both this and the reference pulse. The reference pulse delay could be about 1mS.
You would need to slow the integrator down with larger capacitors, as you don't need a fast response. Maybe 4 - 5 times the value that is there now.
With additional heatsinking on the IRF740, you could run the TX output stage and drivers at a higher voltage to get more pulse current; say 24V. You would need to uprate the 1000uF reservoir of course, and put a higher wattage damping resistor across the coil. What I did once on a similar circuit, was to use a 12V negative regulator between the TX output supply and the rest of the circuitry that runs off 12V. On the Hammerhead, the 24V goes to the minus voltage at the bottom end of R9 and the -12V output to the 7660 circuitry.
The autotrack time constants may need to be changed, but it looks as though all the elements are there in the Hammerhead to make a deep seeking detector for larger objects and caches.
Shielded coils are not really needed with this type of detector.
Eric.