IB Rx coil at Tx off

[green]

The more samples you integrate, the better SNR gets. We can only integrate so many samples without slowing down the sweep speed too much. High repetition rate helps.
with a TC of about 0.7us, 15us is enough time for the signal to decay.

Today I got to 26mm for the #9, by narrowing the pass band of the filters.

What is your delay and sample time or is it different from a normal PI?

With pulses every 15us, what is your Tx on time?

[Tinkerer]

Today I made tests with a #9 lead shot. I tried with pulses every 30us, then 25us then 20us then 15us. That is, one TX flyback every 15us. This worked best, but I only got 18mm distance from the 200mm concentric coil. I have seen way better than that, so the latest changes to the circuit obviously are not good. from reply #145

Any thoughts why you got more distance before? Sampling #9 lead shot with a TC of .68us 1.5us sooner should increase the signal 10 times, maybe 90mm increase in detection depth with 200mm coil(hadn't noticed you were using a concentric coil, should make it easier to detect the shot but wouldn't get as large of increase in detection distance with 10 times the signal). What else could increase detection depth?

Sampling faster should decrease the noise. Is there a formula for expected decrease in noise? Did sampling faster make much difference for you?

The more samples you integrate, the better SNR gets. We can only integrate so many samples without slowing down the sweep speed too much. High repetition rate helps.
with a TC of about 0.7us, 15us is enough time for the signal to decay.

Today I got to 26mm for the #9, by narrowing the pass band of the filters.

[green]

Today I made tests with a #9 lead shot. I tried with pulses every 30us, then 25us then 20us then 15us. That is, one TX flyback every 15us. This worked best, but I only got 18mm distance from the 200mm concentric coil. I have seen way better than that, so the latest changes to the circuit obviously are not good. from reply #145

Any thoughts why you got more distance before? Sampling #9 lead shot with a TC of .68us 1.5us sooner should increase the signal 10 times, maybe 90mm increase in detection depth with 200mm coil(hadn't noticed you were using a concentric coil, should make it easier to detect the shot but wouldn't get as large of increase in detection distance with 10 times the signal). What else could increase detection depth?

Sampling faster should decrease the noise. Is there a formula for expected decrease in noise? Did sampling faster make much difference for you?

[green]

Did you mean FLATTENING?
Eric.

I meant to make thinner. Same weight.

[Ferric Toes]

Fattening a nugget would decrease the TC and increase the peak signal so depending on delay time fattened might be easier or harder to detect?

Did you mean FLATTENING?
Eric.

[green]

The static sparks only bother me in the lab. Otherwise I find them funny.

If you have some small nuggets that I could use as reference, I would be glad to buy them. I know that you found them yourself. The lead shot is fine for testing, but it leaves me wondering how the nuggets would do. Lead shot is perfectly round, while nuggets come in all sort of shapes.

I'm glad I purchased the 1gram of nuggets because I had no idea what their TC's would be. 7/gram or about 2grains each, signal difference at least 10 to 1. Like Carl posted, Gold nuggets vary wildly. I have a 2-grain that's more difficult than my 1-grain. Lead shot is far more uniform. If you can detect a #9 pellet then you can detect most 1/2 grain nuggets. If a 2grain nugget could have a 1us TC, wondering what the TC is for a typical 1/2grain nugget. Fattening a nugget would decrease the TC and increase the peak signal so depending on delay time fattened might be easier or harder to detect?

[Tinkerer]

Hello Tinkerer

I may be suggesting the obvious here,have you tried putting a flexible conductive strap on the undercarriage of the car so it maintains a conductive path to ground.

Also have you thought about buying a small nugget from ebay,you can get them for less than $20 AU.

The static sparks only bother me in the lab. Otherwise I find them funny.

If you have some small nuggets that I could use as reference, I would be glad to buy them. I know that you found them yourself. The lead shot is fine for testing, but it leaves me wondering how the nuggets would do. Lead shot is perfectly round, while nuggets come in all sort of shapes.

[Tinkerer]

Wondering what we are doing different that you can detect a 15x15mm piece of space blanket. I see a change at integrator out with the 225x300mm piece, opposite polarity I would expect. Don't see a change at amplifier out during sample time, maybe some - change during coil decay. The 15x15mm foil has a TC of about 1us and can easily see a change during sample time at amplifier out.

Don't have a piece of #9 shot but did chart some #8 shot with a couple other sizes. https://www.geotech1.com/forums/atta...6&d=1556470610 Couldn't see a piece of #8 shot with the circuit I'm using with a 8in figure Rx coil. Maybe outside with less noise pickup. Decay(.78us TC), sample sooner or use a smaller coil would help.

Purchased 1 gram of 8mesh gold nuggets awhile back and charted their decay using a smaller coil. https://www.geotech1.com/forums/atta...2&d=1547586775 Tried detecting each one with the 8in figure coil that I used for the 15x15mm aluminum foil above. All could be detected at 16mm, some a lot easier than others. Nugget pictures were taken on paper with 1/4in squares(hard to see).

Shot and nugget charts copied from https://www.geotech1.com/forums/show...835#post252835 reply #287 and #293.

"wondering what we are doing different" Well, everything. Your PI is fairly conventional. Your tests are excellent. The data that you publish is very useful and I always look at it and appreciate all the good work you put into it. I use it as reference.

My own PI is still experimental. It is radically different from any other PI I know of. That is my goal. To design a PI that is totally different. Completely new.
To know if my PI design is any good I need to compare with other PI. I am really grateful that you share your data so that I can compare.
When you mentioned a space blanket as test target it made me wonder if I could detect it. So I tried a 15x15mm piece.
Today I made tests with a #9 lead shot. I tried with pulses every 30us, then 25us then 20us then 15us. That is, one TX flyback every 15us. This worked best, but I only got 18mm distance from the 200mm concentric coil. I have seen way better than that, so the latest changes to the circuit obviously are not good.

I don't have any nuggets to try. There are none to be found in this country. I could try to buy nuggets on Ebay, but have no faith of getting reat natural nuggets. If you could spare a few of your nuggets, I would be glad to send you the money in advance, by PayPal.

[green]

Sweeping and holding the hand over spacer and removing quickly are good tests. Looking at the amplitude of the target signal of about 400mV? peak to peak and no target response with shielded coil suggests that the shielding is very good.

The question now is how much is the target response affected by the shield, with your smallest target?

I feel the large space blanket test is not much use. My small space blanket test with 15x15mm is close to the minimum I can detect with this 200mm coil. I don't know what natural target to compare it with though.
My smallest target is usually a #9 lead shot, supposed to be comparable with a small gold nugget. I don't have any gold nugget to play with.

I suspect that the environmental static situation might strongly affect all static test and also the hand tests. A big fat hand might respond quite differently then a small skinny hand. Just guessing.

When living near the ocean, I never saw static sparks. Up here in the mountains in winter there is static everywhere. One gets electric shocks when putting a foot on the ground when stepping out of a car, touching a door knob etc.

Wondering what we are doing different that you can detect a 15x15mm piece of space blanket. I see a change at integrator out with the 225x300mm piece, opposite polarity I would expect. Don't see a change at amplifier out during sample time, maybe some - change during coil decay. The 15x15mm foil has a TC of about 1us and can easily see a change during sample time at amplifier out.

Don't have a piece of #9 shot but did chart some #8 shot with a couple other sizes. https://www.geotech1.com/forums/atta...6&d=1556470610 Couldn't see a piece of #8 shot with the circuit I'm using with a 8in figure Rx coil. Maybe outside with less noise pickup. Decay(.78us TC), sample sooner or use a smaller coil would help.

Purchased 1 gram of 8mesh gold nuggets awhile back and charted their decay using a smaller coil. https://www.geotech1.com/forums/atta...2&d=1547586775 Tried detecting each one with the 8in figure coil that I used for the 15x15mm aluminum foil above. All could be detected at 16mm, some a lot easier than others. Nugget pictures were taken on paper with 1/4in squares(hard to see).

Shot and nugget charts copied from https://www.geotech1.com/forums/show...835#post252835 reply #287 and #293.

[Carl-NC]

Also have you thought about buying a small nugget from ebay,you can get them for less than $20 AU.

Gold nuggets vary wildly. I have a 2-grain that's more difficult than my 1-grain. Lead shot is far more uniform. If you can detect a #9 pellet then you can detect most 1/2 grain nuggets.

[ZED]

Hello Tinkerer

I may be suggesting the obvious here,have you tried putting a flexible conductive strap on the undercarriage of the car so it maintains a conductive path to ground.

Also have you thought about buying a small nugget from ebay,you can get them for less than $20 AU.

[Tinkerer]

Another test. Recorded differentiator output. Amplifier, integrator then differentiator. Used a spool of thread or a new roll of Duck masking tape for spacer. About 2inch spacer between coil and hand. Think increased signal with Duck tape spacer is due to increased dielectric(more area and maybe higher dielectric)?

Spacer was centered over one of the 8in fig8 Rx coils. Hand was swept over spacer. Didn't see a signal change when sweeping hand over shielded coil.

Sweeping and holding the hand over spacer and removing quickly are good tests. Looking at the amplitude of the target signal of about 400mV? peak to peak and no target response with shielded coil suggests that the shielding is very good.

The question now is how much is the target response affected by the shield, with your smallest target?

I feel the large space blanket test is not much use. My small space blanket test with 15x15mm is close to the minimum I can detect with this 200mm coil. I don't know what natural target to compare it with though.
My smallest target is usually a #9 lead shot, supposed to be comparable with a small gold nugget. I don't have any gold nugget to play with.

I suspect that the environmental static situation might strongly affect all static test and also the hand tests. A big fat hand might respond quite differently then a small skinny hand. Just guessing.

When living near the ocean, I never saw static sparks. Up here in the mountains in winter there is static everywhere. One gets electric shocks when putting a foot on the ground when stepping out of a car, touching a door knob etc.

[green]

Another test. Recorded differentiator output. Amplifier, integrator then differentiator. Used a spool of thread or a new roll of Duck masking tape for spacer. About 2inch spacer between coil and hand. Think increased signal with Duck tape spacer is due to increased dielectric(more area and maybe higher dielectric)?

Spacer was centered over one of the 8in fig8 Rx coils. Hand was swept over spacer. Didn't see a signal change when sweeping hand over shielded coil.

[green]

The time scale is 2 second division.

The coil is stationary, the hand and targets sweep across the coil at a measured distance controlled by a spacer.

Although this setup is definitely a PI, it is not conventional at all. I would call it a very advanced technology PI, with many innovative features.

The TX includes 8 mosfets and the timing is very tricky. It took me years to find somebody who could write the firmware.

The coil is also very unconventional. There is really not more else at the frontend, I mentioned a single opamp stage with a gain of 10.
All the rest is done in digital processing. We use a STM32F446 for the processing.

Thanks. My error, (10 sweeps)isn't static. I included the space blanket because it's something I tried. Don't think space blanket is a good test. Think hand test might be good because shielding reduces the effect a lot and shielding doesn't seem to effect target signal strength? Wondering how much different the signal would be for a non shielded coil if 5 different persons swept their hand over the coil. Been trying foam without success so far.

[Tinkerer]

There are Static meters but they are a bit expensive. I have used them at places I work to test/measure work stations for ESD compliance.
Probably could build something that gives good relative measurements.
simple metal plate to a JFET and op-amp meter drive would do it.

FET and op-amp could certainly capture the static level. But how do we get the coil/field relationship with static defined? With the metal plate we will have eddy currents in the metal plate, that is a different story than the static field.

The human body is a really strange structure. How does it conduct the static charge from a carpet to the ends of the fingers to discharge to whatever we touch? The body is conductive, OK, but more often that not it is non conductive objects like styrofoam or a synthetic carpet, that show a static charge.