I didn't need another project -

[WM6]

Delay range 20 - 118uS

Eric.

According your experience, Eric, is this delay range still sufficient to detect sub-gram gold nuggets?

Or from another point of view, what would be most adequate delay range (using fast 18-22cm coil),
to detect sub gram gold nuggets?

Asking this I hope to correlation between sub gram gold nuggets and syringe injection needle lost in
parks and playgrounds of schools and kindergarten, made from medical grade stainless steel which
is here my main goal of interest.

[green]

According your experience, Eric, is this delay range still sufficient to detect sub-gram gold nuggets?

Or from another point of view, what would be most adequate delay range (using fast 18-22cm coil),
to detect sub gram gold nuggets?

Asking this I hope to correlation between sub gram gold nuggets and syringe injection needle lost in
parks and playgrounds of schools and kindergarten, made from medical grade stainless steel which
is here my main goal of interest.

Nupi started a thread on hypodermic needles a few years ago. I tried recording decay back then without much success. https://www.geotech1.com/forums/show...564#post196564

[Vadim18]

Nice progress !
What about STP14NK60ZFP for RFP8N18 replacement?

Rds 0.45 Ohm (vs 0.5 Ohm)
Vds 600V (vs 200+v)
Coss 240pf at 25v (vs 250pf)
Gate treshold 4.5 V max (vs 4V)

Price around $1.5
I dont know how, but I was lucky to get it for free as it came from salvaged tv board. Fate)

If Coss after installing isolation diode play no role, SPA17N80C3 may be superior in Vds and Rds

[bbsailor]

To detect small things, do this mental model.

1. Identify the time constant of the target.
2. Assume it takes 5 time constants of that targets time constant to decay to zero.
3. Any Pulse Induction detector delay beyond the full decay of the target will not allow that target to be detected.

What are the things that will allow me to attempt to detect this small target.
1. Let us assume that the needle time constant is 0.25 micro seconds (uS).
2. Now we know that the energy in this target will decay to zero in 1.25uS.
3. Can I make a Pulse Induction detector that can sample a little faster than 1.25 uS so I can detect this low TC target?
4. What size coil would be optimum for detecting this small target?
5. What distance should my coil be from the desired target?

Once you think about this detecting challenge in the above terms, you may begin to find a solution.

Joseph J. Rogowski

[6666]

I still have a way to go with all the updates that I would like to see, and when it is done then the full information will be made available. I'm not sure how much interest there is, but since 1983 and 1991 a lot of XL500 and XL200's must have been sold.

Hello Eric I am interested in your work thank you.

[WM6]

To detect small things, do this mental model.

1. Identify the time constant of the target.
2. Assume it takes 5 time constants of that targets time constant to decay to zero.
3. Any Pulse Induction detector delay beyond the full decay of the target will not allow that target to be detected.

What are the things that will allow me to attempt to detect this small target.
1. Let us assume that the needle time constant is 0.25 micro seconds (uS).
2. Now we know that the energy in this target will decay to zero in 1.25uS.
3. Can I make a Pulse Induction detector that can sample a little faster than 1.25 uS so I can detect this low TC target?
4. What size coil would be optimum for detecting this small target?
5. What distance should my coil be from the desired target?

Once you think about this detecting challenge in the above terms, you may begin to find a solution.

Joseph J. Rogowski

Thanks for interesting insight bbsailor.

According your calculated specification, I cannot see such available technology in hobby sphere.

Our devices sampling capability end up at 5μS at best.

In my view this remain unsolved problem, not only with PI but with VLF/IB tech also. I tested a lot of
prospecting VLF detector, but no one is able to detect hypodermic needle. Empty hand yes, but not needle.

Nupi started a thread on hypodermic needles a few years ago. I tried recording decay back then without much success.
https://www.geotech1.com/forums/show...564#post196564

Thanks green, it is known to me, but I was in hope, that maybe technology advanced somewhat in meantime.

As I see state of the art, it is only PI technology capable to solve this problem. So I ask Eric, first authority in
field of PI solutions.

[ivconic]

...But without schematic it will be again numerous textual posts diluted by various distractive questions and opinions from others.
What we need here is solid ground. The schematic...

You must give me a credit for this Eric.
Just as i finished my latest post; it happened again.
See what happens when we don't have schematic to focus on?
Next 124 pages we'll talk here about pins and needles and "i did this ... i did that."
I am afraid i will not live long enough to finally see the schematic of your upgrades.
The heck with it!
I am not getting any younger here!
There must be better things to do in life, than this.

[Ferric Toes]

Thanks for interesting insight bbsailor.

According your calculated specification, I cannot see such available technology in hobby sphere.

Our devices sampling capability end up at 5μS at best.

In my view this remain unsolved problem, not only with PI but with VLF/IB tech also. I tested a lot of
prospecting VLF detector, but no one is able to detect hypodermic needle. Empty hand yes, but not needle.




Thanks green, it is known to me, but I was in hope, that maybe technology advanced somewhat in meantime.

As I see state of the art, it is only PI technology capable to solve this problem. So I ask Eric, first authority in
field of PI solutions.

When I was involved in industrial metal detectors, one of the areas we were asked to investigate was that of detecting surgical instruments, including needles. These are invariably made of high grade stainless steel which is non-magnetic and low in conductivity. Even recently, I have been asked if it is possible to detect titanium bolts that are used to secure artificial joints. The latter I can do at several inches range, but only at a delay of 4uS. Hypodermic needles can't be detected even using a 1uS delay due to them being hollow. Some other technique needs to be used and UHF radio waves may be a possibility as the needles must have a resonant frequency, depending on their length. Attached is a block diagram on one such arrangement.

Eric.

[ivconic]

NEXT 1245 pages...

[Ferric Toes]

Nice progress !
What about STP14NK60ZFP for RFP8N18 replacement?

Rds 0.45 Ohm (vs 0.5 Ohm)
Vds 600V (vs 200+v)
Coss 240pf at 25v (vs 250pf)
Gate treshold 4.5 V max (vs 4V)

Price around $1.5
I dont know how, but I was lucky to get it for free as it came from salvaged tv board. Fate)

If Coss after installing isolation diode play no role, SPA17N80C3 may be superior in Vds and Rds

Thanks Vadim, I have a couple on order although they are STP14NK50ZPF. 500V is enough.

Eric.

[Ferric Toes]

According your experience, Eric, is this delay range still sufficient to detect sub-gram gold nuggets?

Or from another point of view, what would be most adequate delay range (using fast 18-22cm coil),
to detect sub gram gold nuggets?

Asking this I hope to correlation between sub gram gold nuggets and syringe injection needle lost in
parks and playgrounds of schools and kindergarten, made from medical grade stainless steel which
is here my main goal of interest.

Hi WM6, No, that delay range is not good for sub-gram nuggets. the XL500 is designed for shallow and deep water searching mainly in the sea. Sea water starts to give a large signal once you get below 30uS and in water depths greater than a couple of metres you have to retard the delay even further. For sub gram nuggets you need to be at 10uS delay or even less. The problem there is that mineralised ground gives more signal at shorter delays and a good GB system is needed.

Eric.

[eclipse]

Is there a way to test sea water effect on delay say in a bucket of water?
Something like adding a graphite powder /something else - higher conductive is going to be needed I guess/ step by step will give similar result as sea water /just for testing purposes of course/.

I have a JW Fishers 8X underwater PI and I want to see how it performs if conditions are not ideal /air - regular ground etc/.
Or just go with a bucket full of dirt and black sand /Magnetite/.

[eclipse]

BTW a circuit that monitors where the preamp has settled to a specific voltage level and adjust the delay to start from that point can work in no matter what sea water depth and advantage on the park/fields (sample at 10us etc). What do you think?

[WM6]

Hypodermic needles can't be detected even using a 1uS delay due to them being hollow.

Some other technique needs to be used and UHF radio waves may be a possibility as the needles
must have a resonant frequency, depending on their length.

Attached is a block diagram on one such arrangement.

Eric.

Interesting remark, Eric.

I never think about UHF solution with hypodermic needle problem, cause UHF antennas are usually
lead over surface at greater distance from soil, than PI or VLF coils.

So we need to rethink near to soil UHF antenna movement and possible exclusion near soil impact.

Your suggestion could be real solution, cause dangerous discarded hypodermic needle in play
and park lots around schools and kindergarten are by rule not buried in soil, but only hidden in
grass and sometimes very shallow covered by sand in sandboxes.

Hi WM6, No, that delay range is not good for sub-gram nuggets.
the XL500 is designed for shallow and deep water searching mainly in the sea.
Sea water starts to give a large signal once you get below 30uS and in water depths greater than
a couple of metres you have to retard the delay even further.

For sub gram nuggets you need to be at 10uS delay or even less.
The problem there is that mineralised ground gives more signal at shorter delays and a good GB
system is needed.

Eric.

Thanks. So Pi technology is practically excluded, same as VLF/IB in searching for hypodermic needle
detecting solution.

I will rethink suggested UHF way. You mentioned here needle resonance and not GPR like reflection.
Hypodermic needles are of different lengths, which lead to conclusion that UHF antenna should emit
sweeped frequency spectrum to resonate with needle about 3 to 7cm body length.
Here we are talking about 5 to 10GHz frequency sweep to catch most needle resonances.

[ivconic]

... Sea water starts to give a large signal once you get below 30uS and in water depths greater than a couple of metres you have to retard the delay even further...Eric.

This is indicative info.
My digital attempt of Barracuda can sample starting at 27-30uS with pretty steady behavior.
I am using ancient Roman brick (IV century) to mimic hard soil and minerals.
...
Still no schematic?
This topic will bust!