Hi bbs,
Depends what you want the detector to do, or more fundamentally, what object time constants do you want the detector to respond efficiently to. The Goldquest SS runs with a 30uS TX pulse, and a 10uS minimum delay. Sample pulses are 10uS wide with 40uS between the first and second; then the next TX pulse starts. This all works out to a pulse repetition rate of 10,000 per sec. This timing is good for medium/small rings and nuggets. Try a copper penny, or a silver quarter and you wont get the best range as the TX pulse is too short for the object time constant, and the sample pulse spacing will also give some signal cancellation.
For the silver and copper coins you would be better with a TX width of 300uS and wider sample pulses with more space between them. This would mean that the repetition rate would drop considerably, maybe by a factor of 10.
On the other hand, my textile detector which can locate broken off needle tips 1mm long, runs at 100,000 pulses per second. The TX pulse is 3uS wide, then a 1uS delay and 1uS samples. Great for tiny metal fragments, but poor range on larger targets. It will readily detect "invisible" gold nuggets though. See previous posts on that subject.
You can see that the 5uS unit I built fits the pattern by running at 20,000pps.
A lot of earlier PI's had a long waiting time after the last sample, before the next TX pulse began. My preferred technique now, is to start the next TX pulse as soon as possible after the last sample.
Eric.
Eric.
