Sample Delay Question

[Anonymous]

I need some advice regarding the sampling delay range for a PI to get rid of ground mineral signals. Here in North Carolina I can get rid of ground signals by using a delay of 10uS on the beach and about 20uS inland. Right now I am using a digitaly controlled delay which is variable between 5uS and 99uS. I am wondering if this is enough? What about the Austalian gold fields? Does anyone have an idea as to the sample delays which are needed there? Thanks in advance, Dave. * * *

 

[Anonymous]

Hi Dave,
The problem with the response from magnetic minerals is that it goes on for a long time and can't be eliminated in the same way as a conductivity signal. As you increase the pulse delay time, the magnetic signal certainly decreases, but even at 100uS, it is still quite strong. One way of reducing the ground signal is to use a DD coil instead of a mono. However, for the best result, you need to combine this with multiple sampling and subtraction as I did in the Goldscan, and Minelab do in their SD series. This way, you can eliminate the magnetic ground signal while retaining the sensitivity to small objects.
Eric.

 

[Anonymous]

Thanks Eric, looks like I will need the ground balance circuit. I am using a PIC16F84 microcontroller to load and control a counter. This allows me to generate a plurality of seperate sample pulses of different delays for each transmit pulse. The present range is 5 - 99.9uS in increments of 100nS. I have not tried the ground balance circuit yet, but I will be including it this week. All the best, Dave. * * *