Competition!

[ivconic]

specify a low, medium and high target size, shape, weight and time constant

Very well said

ivica, it is your turn to specify the precise purpose you desire for your detector. Without precise specifications, we are walking blind.

FelezJoo PI, whoever made it so far will remember the claim from the author how it is roughly based on Minelab patent.
Later on I realized it is kinda true claim.
In the patent they talk (sorry for rough interpretation, long time, I don't remember well) about 3 "vectors" aka 3 time constants.
And in FelezJoo PI code there is a function to "calibrate" to the attached coil, by measuring 3 "numbers" which actually are the 3 time constants.
So the author gave the best ranges of those 3 numbers so diyers to know how good their diy coil is matched.
There is "debug" screen you get on detector, displaying those 3 numbers and one can check the coil with them.
This is related, but it took me years to realize that!
Having said that; I think is good to return to that patent and read it with bit more attention.

[ivconic]

3 time constants?
I don't know how relevant this is; with such detector and coil I will hunt only for described targets.
I am not interested in any different and larger targets then what I described already.

[GeoMax]

Hi Thinkerer,

thanks for the pictures. [COLOR=inherit !important]


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[Tinkerer]

Hi Thinkerer,

thanks for the pictures. [COLOR=inherit !important]


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Here is the KW_1 detector on a shipwreck. If I remember right, it was about 1996 on the wreck of a French galeon that wrecked in 1678 on the reefs of Aves Islands, off the coast of Venezuela.
This is the small coil, about 20 cm diameter. I could also change to a 32cm diameter coil for deeper targets.

[Tinkerer]

With the KW detector detector we have a very simple PI for beginners to experiment with.

For a higher level experience, I propose the attached project.
I could not upload the whole document, as it is about 10Mbites, so I have printed out the first 6 pages.
If there is no way to upload the whole document in one go, I can split it into chapters that are small enough to upload.

Very little has been done to look at the target return signals of PI detectors during the ON time. This document could be a primer for that.

I spent myself a considerable amount of time investigating ON time signals. I would be happy to share what I know about it.

[GeoMax]

Here is the KW_1 detector on a shipwreck. If I remember right, it was about 1996 on the wreck of a French galeon that wrecked in 1678 on the reefs of Aves Islands, off the coast of Venezuela.
This is the small coil, about 20 cm diameter. I could also change to a 32cm diameter coil for deeper targets.

Nice to see the actual device in use!!! I like it. Thanks again for posting the picture(s)

[GeoMax]

Hi Thinkerer,

I have a question in regards to the coil of the KW-1. From the circuitry, I would guess the search coil has about 200-220uH. What coil inductance/specification has the actual search coil of the KW-1?
Can you still remember?

[Tinkerer]

Hi Thinkerer,

I have a question in regards to the coil of the KW-1. From the circuitry, I would guess the search coil has about 200-220uH. What coil inductance/specification has the actual search coil of the KW-1?
Can you still remember?

The small coil had about 300uH and 20cm diameter. 20AWG wire. Best to use 300V or 600V plastic insulated, tinned, 1x19 or even finer stranded wire, but for a cheap quick and dirty trial, magnet wire will work.
This detector was for underwater use, so it did not need shielding on the coil. For use on land, shielding will reduce EMI noise.
This circuit ran at about 3000 cycles per second. I think about 30us TX on - 30us delay to first sample- 30us sample time - second sample same 30us just before TX on again.
If you change the clock capacitor to a smaller value, the clock will run faster and all timings will be shorter, but remain relative.

[Tinkerer]

[ATTACH]n417773[/ATTACH] The MiscEl app is a good tool to calculate almost everything on a PI detector. It is old and I can not open the homepage, but the app in the Zip file should work. It does here. It starts giving some error messages, but just ignore these.

[GeoMax]

The small coil had about 300uH and 20cm diameter. 20AWG wire. Best to use 300V or 600V plastic insulated, tinned, 1x19 or even finer stranded wire, but for a cheap quick and dirty trial, magnet wire will work.
This detector was for underwater use, so it did not need shielding on the coil. For use on land, shielding will reduce EMI noise.
This circuit ran at about 3000 cycles per second. I think about 30us TX on - 30us delay to first sample- 30us sample time - second sample same 30us just before TX on again.
If you change the clock capacitor to a smaller value, the clock will run faster and all timings will be shorter, but remain relative.

Thanks for the coil info....

[bbsailor]

[ATTACH]n417773[/ATTACH] The MiscEl app is a good tool to calculate almost everything on a PI detector. It is old and I can not open the homepage, but the app in the Zip file should work. It does here. It starts giving some error messages, but just ignore these.

The UXO research that the military did was about optimizing the detection of small metal parts found in recovered UXOs. Their main point was that they tried to stimulate many different size and time constant metal parts and found that if they kept increasing the coil discharge slope, there was no better full stimulus of a particular time constant target beyond five times faster than the target time constant. This sets a reasonable goal for specified targets.

The PI coil performance is a real challenge for small low time constant targets. When a fully stimulated target signal decays to 2 target time constants it has lost about 86 percent of its induced charge. At 3 target time constants the target has lost about 95 percent of induced charge. This is why making a pulse induction coil to operate a very low delays requires a higher damping resistor value to make fully stimulating small targets possible. Then reducing the delay so the RX circuit can turn on as quickly as possible to capture the small target signal before it dies out and cannot be detected.

The optimization of detecting low time constant targets then becomes a balancing act between these things.
1. Coil diameter and distance from target
2. Coil inductance governed by the number of coil turns.
3. Coil current governed by coil wire size and voltage.
4. Coil seen capacitance which affects the damping resistor value.
4.1 MOSFET and other circuit capacitance.
4.2 Coil turn to turn capacitance governed by coil wire insulation dielectric constant value and thickness.
4.3 Coil to shield capacitance governed by the thickness and dielectric constant of the spacer between the coil and the shield plus the area of the shield either being solid or a thin wire mesh.
5. Damping resistor value which governs the coil discharge slope and ability to fully stimulate a low time constant target as well as reducing the delay between the coil TX mode and RX mode.

This is why we need some commonly available targets to specify so the final Pulse Induction performance can be more easily and accurately compared too each other.

Joseph J. Rogowski

[ivconic]

Joseph, I thought about it, what I could suggest as a common target that could be found easily anywhere in the world.
It seems that we have no choice but to cut squares of several dimensions with sheet metal scissors.
Squares or circles... or both. 2mm,5mm, 10mm etc

[pito]

[bbsailor]

Joseph, I thought about it, what I could suggest as a common target that could be found easily anywhere in the world.
It seems that we have no choice but to cut squares of several dimensions with sheet metal scissors.
Squares or circles... or both. 2mm,5mm, 10mm etc

ivconic,

Aluminum foil and masking tape is commonly available. Just cover the aluminum foil with masking tape and mark the tape with lines that match a specified size and cut the foil to be specified targets. You can even use thicker aluminum targets such a soda can that is cut to the same size targets. The main point is that everyone who submits a design has access to specified targets and provides information about their coil such as coil diameter, inductance, resistance, pulse length, current, coil discharge time constant, damping resistor value, target size and time constant and target distance to coil.

Just pick the things that most people can agree to submit with their circuit and coil design.

Joseph J. Rogowski

[ivconic]