PI TX Settling

[green]

I think the testing I've done suggests the flat Tx is no better than the ramp Tx. Maybe the test methods. Has anyone done tests that show different?

[daverave]

ive been reading with interest your postings on here concerning time constants...and it seems like the larger copper and silver coins and larger gold rings have a longer tc than say low conductive items...ive been asking several people on youtube about their whites tdi pro's and larger heavier items and they all use delay of 10 uS for low and high con ductive items...surely their pulse delay should be around the 20-30 uS setting....bearing in mind people on this thread say the larger coins and rings have a longer tc.

[Ferric Toes]

ive been reading with interest your postings on here concerning time constants...and it seems like the larger copper and silver coins and larger gold rings have a longer tc than say low conductive items...ive been asking several people on youtube about their whites tdi pro's and larger heavier items and they all use delay of 10 uS for low and high con ductive items...surely their pulse delay should be around the 20-30 uS setting....bearing in mind people on this thread say the larger coins and rings have a longer tc.

Hi Dave,

A short delay, such as 10uS, will always give more signal on both long and short TC objects so those people on youtube are correct. You are sampling higher up the curve on both types of object, but if you then go to a longer delay, say 20uS or even 50uS, you will find that your short TC objects have disappeared but your long TC objects remain. No thin rings, but plenty of copper coins and the odd silver coin; pound coins too.

In the 1970's PI's were renowned for their ability to ignore foil from sweet wrappings and cigarette packets. That is the reason; they used delays of 20uS and upwards. An adjustable delay is still a useful feature as you can set it to minimise the sea water signal on a beach, ignore some foil and bits of pulltabs, lead shot etc. On the dry sand however, you can run 10uS, or even less, with no problem, but you have to be prepared to dig plenty of small rubbish items.

Eric.

[daverave]

hi eric

Hi Eric....i understand now from what you said...i noticed the mirage pi uses a switchable sample pulse width for small and larger gold rings/coins...is that good for getting extra depth on larger gold/coins using wider sample setting ????? im using a very narrow sample pulse and i seem to find more low conductive items but not the bigger rings and coins..good targets in my area are now very deep and even the old large pennies are not much being found...so i just need to get my detectors better for larger deeper targets...ive seen on youtube people getting over 20" on coins using the white's tdi pro...i guess its because it uses app rox 500-600 ma giving it more tx power.

[Ferric Toes]

Hi Eric....i understand now from what you said...i noticed the mirage pi uses a switchable sample pulse width for small and larger gold rings/coins...is that good for getting extra depth on larger gold/coins using wider sample setting ????? im using a very narrow sample pulse and i seem to find more low conductive items but not the bigger rings and coins..good targets in my area are now very deep and even the old large pennies are not much being found...so i just need to get my detectors better for larger deeper targets...ive seen on youtube people getting over 20" on coins using the white's tdi pro...i guess its because it uses app rox 500-600 ma giving it more tx power.

Hi Dave,

There are a few things that if done together will improve the depth on larger objects. 1) More TX current 2) Wider TX pulse 3) Wider sample pulse 4) slower response on motion mode to prevent deeper and wider signals tuning out.

I use proportional timing on most projects now. i.e 50uS TX, 10uS delay, 10uS sample 1, 50uS delay to sample 2, 10uS sample 2, then next TX. The next switch position would be all of those previous numbers x2; The next position x3, and so on. Everything goes up in proportion except the pulse frequency which goes down in proportion. Using a constant current supply for the TX and the battery drain is the same in all settings.

If you have extra sample pulses for GEB the beauty is that there is virtually no adjustment needed in the GB setting whatever delay etc you are using.

Eric.

[Altair]

Hi Dave,

There are a few things that if done together will improve the depth on larger objects. 1) More TX current 2) Wider TX pulse 3) Wider sample pulse 4) slower response on motion mode to prevent deeper and wider signals tuning out.

I use proportional timing on most projects now. i.e 50uS TX, 10uS delay, 10uS sample 1, 50uS delay to sample 2, 10uS sample 2, then next TX. The next switch position would be all of those previous numbers x2; The next position x3, and so on. Everything goes up in proportion except the pulse frequency which goes down in proportion. Using a constant current supply for the TX and the battery drain is the same in all settings.

If you have extra sample pulses for GEB the beauty is that there is virtually no adjustment needed in the GB setting whatever delay etc you are using.

Eric.

Are you integrating together the samples mixed from different setup or have you multiple integrations, one for each setup?

[Qiaozhi]

Are you integrating together the samples mixed from different setup or have you multiple integrations, one for each setup?

I think Eric means that these different settings are switch-selectable, not that they run in sequence.

[daverave]

[QUOTE=Ferric Toes;222214]Hi Dave,

There are a few things that if done together will improve the depth on larger objects. 1) More TX current 2) Wider TX pulse 3) Wider sample pulse 4) slower response on motion mode to prevent deeper and wider signals tuning out.

I use proportional timing on most projects now. i.e 50uS TX, 10uS delay, 10uS sample 1, 50uS delay to sample 2, 10uS sample 2, then next TX. The next switch position would be all of those previous numbers x2; The next position x3, and so on. Everything goes up in proportion except the pulse frequency which goes down in proportion. Using a constant current supply for the TX and the battery drain is the same in all settings.

If you have extra sample pulses for GEB the beauty is that there is virtually no adjustment needed in the GB setting whatever delay etc you are using.

Eric.

Hi Eric....I think your idea of three way switching is very good !!! can the sample delay stay at 10 uS for all three switch settings or does the delay have to double at each setting ????i have a buck voltage drop converter with presets for current and voltage and i wonder would this be ok if i use this for my constant current power supply....maybe 24v input to buck voltage converter and say 15v output.

[green]

Hi Dave,

There are a few things that if done together will improve the depth on larger objects. 1) More TX current 2) Wider TX pulse 3) Wider sample pulse 4) slower response on motion mode to prevent deeper and wider signals tuning out.

I use proportional timing on most projects now. i.e 50uS TX, 10uS delay, 10uS sample 1, 50uS delay to sample 2, 10uS sample 2, then next TX. The next switch position would be all of those previous numbers x2; The next position x3, and so on. Everything goes up in proportion except the pulse frequency which goes down in proportion. Using a constant current supply for the TX and the battery drain is the same in all settings.

If you have extra sample pulses for GEB the beauty is that there is virtually no adjustment needed in the GB setting whatever delay etc you are using.

Eric.

What is the timing sequence with the extra sample pulses for GEB?

[green]

Hi Dave,

There are a few things that if done together will improve the depth on larger objects. 1) More TX current 2) Wider TX pulse 3) Wider sample pulse 4) slower response on motion mode to prevent deeper and wider signals tuning out.

I use proportional timing on most projects now. i.e 50uS TX, 10uS delay, 10uS sample 1, 50uS delay to sample 2, 10uS sample 2, then next TX. The next switch position would be all of those previous numbers x2; The next position x3, and so on. Everything goes up in proportion except the pulse frequency which goes down in proportion. Using a constant current supply for the TX and the battery drain is the same in all settings.

If you have extra sample pulses for GEB the beauty is that there is virtually no adjustment needed in the GB setting whatever delay etc you are using.

Eric.

Charted three coins with 50, 100 and 200usec flat Tx. US nickel(10usec TC) US quarter(130usec TC after 100usec delay) 1 troy oz. 99.9% pure copper coin(500usec TC after 100usec delay). Each coin was taped to a spacer for about a 2 volt signal at 5usec delay with 200usec Tx to give repeatability when removing and placing the coins on the coil. Charted log amplitude, easier to see the difference at lower amplitudes. Charted target recording-no target recording. Rx(two 1.5 inch round, figure eight) Tx(oval surrounding Rx). Better S/N with the smaller coil. Don't know if the larger coil would chart similar. Don't know why the copper coin amplitude is closer at 5usec delay than the US quarter with the different Tx times. No difference with the US nickel(10usec TC)as expected. About 10usec ramp to flat Tx current.

[green]

Charted three coins with 50, 100 and 200usec flat Tx. US nickel(10usec TC) US quarter(130usec TC after 100usec delay) 1 troy oz. 99.9% pure copper coin(500usec TC after 100usec delay). Each coin was taped to a spacer for about a 2 volt signal at 5usec delay with 200usec Tx to give repeatability when removing and placing the coins on the coil. Charted log amplitude, easier to see the difference at lower amplitudes. Charted target recording-no target recording. Rx(two 1.5 inch round, figure eight) Tx(oval surrounding Rx). Better S/N with the smaller coil. Don't know if the larger coil would chart similar. Don't know why the copper coin amplitude is closer at 5usec delay than the US quarter with the different Tx times. No difference with the US nickel(10usec TC)as expected. About 10usec ramp to flat Tx current.

Wondered what effect the different flat Tx times have on ground response.

[Tinkerer]

Wondered what effect the different flat Tx times have on ground response.

So it would seem that the CA ground has a TC of more than 200us

[green]

So it would seem that the CA ground has a TC of more than 200us

Charted the copper coin reply #47 and California ground reply #51 on three different charts(lin.-lin., lin.-log, log-log). Don't know how to determine the ground TC. The coin charts a straight line on a lin.-log chart after a 200usec delay. Ground charts a straight line on a log-log chart. Ground charted a slope of -1 with a 16000usec Tx, with Tx times 500usec and less the decay was steeper.

[Tinkerer]

Charted the copper coin reply #47 and California ground reply #51 on three different charts(lin.-lin., lin.-log, log-log). Don't know how to determine the ground TC. The coin charts a straight line on a lin.-log chart after a 200usec delay. Ground charts a straight line on a log-log chart. Ground charted a slope of -1 with a 16000usec Tx, with Tx times 500usec and less the decay was steeper.

Thank you for the interesting charts and thank you for doing all these tests that give us a better understanding of how PI detectors work.

The following comments are more of a guess than anything else. It would be good if more knowledgeable people would give their comments.

Looking at the lin.-lin. traces, one can see that the ground decay is considerably faster than the copper. The copper decay has not yet reached 0 at 1100us.

Looking at the lin.log traces, the slope of the copper shows 435us, that seems to correspond to the decay or TC of the lin.-lin. traces.

Looking at the log-log traces, we see different behavior of the ground and the copper. This seems logical since the copper response is resistive, while the ground response is permitive.

It is interesting to see that in the lin.-lin., both traces look very similar, except for the TC, no indication of or difference between resistive target and permissive target.

Will samples taken at the beginning of the TX ON time (first 500us) show a difference?

[green]

Tried charting target decay during coil current on and off. Tx(100usec CC) about 10usec ramp before constant current(90usec). Current is in a servo loop. The loop was to control constant rate during coil on time for ferrous non ferrous indication. To noisy for looking at amplifier out during coil on constant current. Good enough for what I'm charting. Charted absolute value(target signal recording- no target signal recording). 1 troy oz. 99.9% pure copper coin. I would be interested in what ground decay would look like during the constant current on time. Would need to improve constant current loop to chart it. Maybe someone could say what to expect and how it would effect GEB. Tx(1000pps)