Which pulse sequence would be best for small targets?

[GeoMax]

The question arose as to which of the two pulse sequences is better for small targets. This assumes that the search coil and electronics can process the signals. The two short pulses with the pause in between are exactly the same length as a single pulse.

[boilcoil]

For small targets it is necessary to take early samples. This means that at the moment of the sample, the eddy currents generated by the target must be maximum. Which brings us to the CCPI. This depends on many things, including the time constant of the coil.
In this line of thought, if you can achieve a satisfactorily constant current through the coil at the end of the pulse - good, if not - a longer pulse is better.

[Op04]

Coil Ampere Turn is priority
Coil TXon time - better is flat - before TX pulse ended, example like tx on in 85us while tx pulse 100us
Coil TXoff time - faster mean better 0.75us or less for small gold
Coil current after TXoff - also related with R damping

[Carl-NC]

The question arose as to which of the two pulse sequences is better for small targets. This assumes that the search coil and electronics can process the signals. The two short pulses with the pause in between are exactly the same length as a single pulse.

Assuming only the two choices offered and assuming a "small" target (tau = 10us or less), if the short pulses have no sampling between them then the first short pulse does nothing. By the time the second pulse starts the target's eddies have mostly died out and you are starting over from scratch. Therefore, the longer pulse will win.

[GeoMax]

Thank you for all your input. For very small targets with a tau <= 10µs, I agree that a longer pulse is better in the described situation. But what if the tau of a small target is, for example, 30µs or 40µs? Would two short pulses then be better than one long one?

[Carl-NC]

I can't think of a situation where 2 short pulses with no intermediate sample would be better.

[GeoMax]

Thanks Carl.

[pechkata]

Here is a circuit with short pulses.
1 or 2 or more pulses can be turned on - the timer determines the frequency.

[GeoMax]

Hello Pechkata,

thank you very much for showing the CS6PI schematic here. I'm familiar with the schematic. This schematic is almost identical to the one used for the PI Uniprobe from DetectorPro. Both circuits were developed by Eric Foster. Specifically, in this PI UniProbe PinPointer from DetectorPro (older version), only diodes 1 and 3 are driven by the gap between pulses 1 and 3 generated by the CD4017, which then controls the MOSFET.