minimum sample delay

[6666]

Interesting about detecting a 3usec TC target with a 50usec delay. I'll have to try and understand how it does it.

I'm curious to.

[KingJL]

Interesting about detecting a 3usec TC target with a 50usec delay. I'll have to try and understand how it does it.

The reason is the TX/coil current waveform... The detector is the Fisher Impulse which I believe was designed by Dave Johnson (Dave J). That is the problem I have with referencing sample time relative to TX-off. In my opinion, sampling needs to be referenced to the trailing boundary of the coil current waveform envelope. If you reference the sample timing to the trailing boundary of the coil current waveform enveope, the sample time for the Impulse becomes ~15 usec.

[green]

TX current waveform (triangular, half sine, trapezoidal, etc.).

What you are doing is commendable and worthy of continued efforts. However, I would also think of your frame of reference... "minimum sample delay". In reference to what? In reference to removal of TX input pulse, actual MOSFET current shut-off (can be in excess of 2 usec after removal of gate signal), after coil current achieves some threshold level, etc. What is the objective? To achieve a fast coil or to detect a specific minimum TC target goal? To achieve the later does not necessitate the former... it is one means to achieve the result, but is not the only one. In fact I know of one detector that has excellent performance against a 3-5 usec TC target and samples at 50 usec after TX turn-off with a sample width of 50 usec... it really does not care about "how fast" the coil is (it has a TON of capacitance in the TX). What really needs to be thought about during observations of target responses is what is actually happening with target eddy currents within the context of the exciting TX current waveform (like Carl keeps saying "coil current waveform, not voltage"). Then you can implement a suitable solution to obtain the desired result. But that is probably suitable for a separate thread and discussion.

As food for thought about the above discussion, I give you a link to an article to tickle your brain cells.
http://iieta.org/sites/default/files..._A/54.2_02.pdf

would like to chart AWG28 solid that I have been using to make my coils to see if it charts a TC just over .3usec projected on the chart. At 5TC's, 1.5usec AWG28 would lose 99% of it's peak signal .http://www.geotech1.com/forums/attac...4&d=1526683069
Interesting about detecting a 3usec TC target with a 50usec delay. I'll have to try and understand how it does it.

[Mdtoday]

Have a read of this article. It changed my thinking on using expensive Litz wire.

https://engineering.dartmouth.edu/inductor/papers/stranded.pdf

Eric.

Very good read with practical applications, thanks for sharing Eric.

Cheers

Mdtoday

[Mdtoday]

TX current waveform (triangular, half sine, trapezoidal, etc.).



As food for thought about the above discussion, I give you a link to an article to tickle your brain cells.
http://iieta.org/sites/default/files..._A/54.2_02.pdf

Now that is is a great little read... thanks for sharing.

Cheers

Mdtoday

[6666]

What the H#!!, bought it anyway. If anyone needs some, let me know!

Maybe , would like to see a picture of the wire when you receive it thanks

[KingJL]

I can't justify purchasing 5000', otherwise this would be GONE!!!
https://www.ebay.com/itm/5000-FEET-S...gAAOSwnHZYj5by

What the H#!!, bought it anyway. If anyone needs some, let me know!

[KingJL]

Have a read of this article. It changed my thinking on using expensive Litz wire.

https://engineering.dartmouth.edu/inductor/papers/stranded.pdf

Eric.

I can't justify purchasing 5000', otherwise this would be GONE!!!

https://www.ebay.com/itm/5000-FEET-SEA-WIRE-CABLE-WIREMASTER-COPPER-24-AWG-SINGLE-CONDUCTOR-AIRCRAFT-NEW/183227870959?hash=item2aa93b6eef:g:NigAAOSwnHZYj5by

[Ferric Toes]

Have a read of this article. It changed my thinking on using expensive Litz wire.

https://engineering.dartmouth.edu/inductor/papers/stranded.pdf

Eric.

[KingJL]

... maybe something else?

TX current waveform (triangular, half sine, trapezoidal, etc.).

What you are doing is commendable and worthy of continued efforts. However, I would also think of your frame of reference... "minimum sample delay". In reference to what? In reference to removal of TX input pulse, actual MOSFET current shut-off (can be in excess of 2 usec after removal of gate signal), after coil current achieves some threshold level, etc. What is the objective? To achieve a fast coil or to detect a specific minimum TC target goal? To achieve the later does not necessitate the former... it is one means to achieve the result, but is not the only one. In fact I know of one detector that has excellent performance against a 3-5 usec TC target and samples at 50 usec after TX turn-off with a sample width of 50 usec... it really does not care about "how fast" the coil is (it has a TON of capacitance in the TX). What really needs to be thought about during observations of target responses is what is actually happening with target eddy currents within the context of the exciting TX current waveform (like Carl keeps saying "coil current waveform, not voltage"). Then you can implement a suitable solution to obtain the desired result. But that is probably suitable for a separate thread and discussion.

As food for thought about the above discussion, I give you a link to an article to tickle your brain cells.

http://iieta.org/sites/default/files/Journals/AMA/AMA_A/54.2_02.pdf

[green]

Some of the reasons I want to sample at or near 1usec. I have charted TC vs AWG wire size. http://www.geotech1.com/forums/attac...4&d=1526683069 have tried AWG24, charts about .8usec(projected on chart), would like to chart AWG28 that I have been using to make my coils to see if it charts just over .3usec projected on the chart. At 5TC's, 1.5usec AWG28 would lose 99% of it's peak signal. I'm hoping if I understand what is required to sample at 1usec I can make a better coil to sample at 5 or 6usec. Eric posted in another thread he has sampled at 1usec, challenge to see if I can do it. I'm thinking coil inductance, wire size,Tx circuit resonance, peak current and amplifier response have an effect, maybe something else?

[KingJL]

"We like to call this the "Heisenberg Effect..."

I know... I apply it to life in general... not just electronics (and physics in general). That way, I eliminate a lot of conflict in my thought processes that would affect understanding vs. knowing.

[waltr]

I am of the opinion that you never really KNOW that what you are observing is what is really happening when you are not observing it. In other words, when you observe anything, the result you see is an artifact caused by simply observing it in the first place! Think about it...!

Yep, been there many, many times. Scope and meter probes have capacitance which alters the circuit operation. I've have circuits not working until a scope probe is connected, then the circuit works. Makes for very frustrating troubleshooting.

We like to call this the "Heisenberg Effect" (Although technically this is actually the "observer effect").

[KingJL]

... My point was, it can matter where the measurement probe is connected. I wanted to record coil decay so I measured resonance with the probe across the coil.Agree With the probe removed Rd increases from 1345 to 1530 ohms...

I am of the opinion that you never really KNOW that what you are observing is what is really happening when you are not observing it. In other words, when you observe anything, the result you see is an artifact caused by simply observing it in the first place! Think about it...!

[rickb]

Using litz wire where individual strand radius is smaller than skin depth at the highest frequency of interest, means that the detector will no longer detect its own coil, i.e. no eddy currents. Then you pick an overall strand count that will support the current you need to put through the coil. Then pick the next largest standard strand count that is available. You cannot achieve that with uninsulated twisted strands. Then and only then do you work out the coil topology for the lowest SRF. That will be the plan for my PI.