Optimal PI timings

[Max]

Pulsestar isn't my design, but Deepstar is and runs at 3kHz. PulseStar is TB Electronics in Germany. My Goldquest SS runs at 10kHz pulse rate and 10uS delay and sampling. This is very good for small targets and fast response, but 10uS delay is about as fast as you can go on a saltwater beach. The fastest PI I have made runs at 100kHz and 1uS delay, 1uS samples. It has industrial uses for finding broken off needle tips in fabric, but you could not use it for ground searching. Some PI mine detectors run at a few hundred Hz and are still sensitive to small metal, so pulse frequency is of rather less importance than fast switch off of the TX and short delay. High pulse rates are better for integrating out random noise and low frequency noise. Detectors with low repetition rates have more problems with power line noise and its harmonics. A frequency shift control is always a good idea to prevent the beat note effect when interference and the pulse rate are near sychronism.

Eric.

Hi Eric,
sorry... I wrote pulsestarII but was thinking at your deepstarII actually.


Maybe I was thinking at PulsePower brand ...who knows !?

Big mistake I know ! PulsestarII is for depth searching running at lower frequency than yours.

Kind regards,
Max

[1843]

Pulse Frequency

High pulse rates are better for integrating out random noise and low frequency noise. Detectors with low repetition rates have more problems with power line noise and its harmonics.

Hi Max,
What do you think about Eric's opinion? Is he right?
As we know low pulse rates are better for random noise issue...

Regards,
1843

[Max]

Hi Max,
What do you think about Eric's opinion? Is he right?
As we know low pulse rates are better for random noise issue...

Regards,
1843

Hi,
Eric is right about everything ... cause he knows too well his machines !
So about deepstarII no dubts that integrators action is like he stated.

Depends much on differential integrator params.

I've noticed that other machines, with different integration params act different way. But in any case is possible shifting a bit the frequency to overcome similar problems due to intermodulation with 50/60 Hz... and that's what there is in some Eric's designs... some small frequency regulation that's enough to solve such problem with power lines interferences etc.

I noticed that some designs like much more lower frequencies than higher so they will run happy with 100 or 400Hz and not with 1.5Khz or 3Khz. Depends on integrators but also on coupling of various stages and e.g. tx pulse duration... if repetiton rate is high and tx pulse is large the duty cycle could become a stress for some switching devices... thus contributing to drift and then false signals... instability.

Also if TX pulse is wide and voltage spike with great energy the breakdown phase in mosfet could warm device, similar problem happens with large Rds-on... device warm-up to a point that then cause Rds-on variations detected by amplifiers etc that's why so often duty cyle is around 10% and extension of tx pulse is over-limited to keep device under SOA limits... otherwise will be a problem due to device params variations caused by increased internal semiconductor temperature.

Noticed that on e.g. XR-71 then I've experimented with other devices different than IRF740 and I reach a good compromise...but what a waste of time! Took too many time stabilizing a PI using tricks when you try to push it to the limit... that I don't know if it's worth or not...cause so often on real e.g. inland soil you have much bigger problems (this is my case).

Kind regards,
Max