Coil Saturation in a PI?

[Carl-NC]

Read your formula and wondered if it was correct, then remembered decay is twice as fast if critical damped?

Yes, for critically damped RLC the tau is 0.5*L/R = 2*RC = sqrt(LC).

[deemon]

We've been discussing this for many years:
https://www.geotech1.com/forums/show...025#post143025
https://www.geotech1.com/forums/show...226#post256226

And here is about "coil saturation" and "target charging" effect too ... https://www.geotech1.com/forums/show...QUESTION/page3

[ivconic]

Problem with forum is in fact that it is too large, massive.
Many similar topics, many similar thoughts. Often stopped and broken, than repeated in a while on another topic.
It's the mosaic. One have to search and collect the pieces together to round up the picture on wanted issue.
I was always rather a "practician" than "mathematician". I never wanted to go deeper in the theory and math on PI's.
Now i see the drawbacks of such behaving. Most of the time i don't have a clue on what people are talking about here.
I guess it is time to start learning some things. This topic opened new appetite for that.
I am confused though. Do we have consensus about some questions here or not?
What is the final answer on current role in coil? Important or not? Limits?
One thing is clear to me even now; you can't saturate the coil, you can saturate the target only.
"Saturation" of coil would be wrong interpreting of situation where skin effect is reached to 100%, at given wire gauge.
What happens than? (no idea how to measure such states, so obviously only math can give some answers)
etc

[Carl-NC]

Problem with forum is in fact that it is too large, massive.
Many similar topics, many similar thoughts. Often stopped and broken, than repeated in a while on another topic.
It's the mosaic. One have to search and collect the pieces together to round up the picture on wanted issue.

Heh, no kidding. Geotech forums are now over 20 years old and so much has been discussed and re-discussed it's impossible to keep track of it all.

https://www.geotech1.com/forums/showthread.php?7033-Welcome!

I decided long ago it is what it is. Each thread is a conversation, often re-hashing the same information, but with different audiences. But perhaps some of the more re-hashed information could be compiled into white papers similar to Joe R's fast coil paper.

[dbanner]

I see, so that flat topping the coil current period (just sufficiently long pulse width) allows for eddy currents in the target to dissipate such that it doesn't counteract the flyback discharge eddy currents with a subtractive element. All having to do with the target TC versus the coil TC. Seems an exceptionally thin corridor within which to optimize a PI front end.
So it's really the eddy currents produced by the collapsing field which are paramount to target detection.
That's why I suppose the coil parameters are so important to the overall design, it's integral to the entire calculas.

[dbanner]

Also, I'm unsure about the term "coil saturation", is that really a valid term? What is the defintion?

[green]

Also, I'm unsure about the term "coil saturation", is that really a valid term? What is the defintion?

Carl's reply #4 Saturation means "can't get any higher." It's ok for this, because it's the point where the TX current can't go higher (5tau).

[Qiaozhi]

Carl's reply #4 Saturation means "can't get any higher." It's ok for this, because it's the point where the TX current can't go higher (5tau).

Rather than use the term "saturation", it would be more correct to say that the coil current has reached "steady state". i.e. it is no longer changing.
The term "saturation" is more commonly used when referring to magnetic flux density.

[dbanner]

Steady state? HUH? Well ok, yes, the current has momentarily reached a plateau, but in the context of a pulse, I prefer the term "flat topping".
"Coil saturation" may not be an appropriate term to be used in this context at all. Here is a definition I pulled from the net:
"Saturation current in an inductor is, to use layman's language, the current at which the core is completely filled with magnetic flux and it can't take any more. More scientifically, it's the current at which all the magnetic domains in the core are aligned and there are no more available."
So since we are dealing with air core coils, well what does it really mean? In our case, the copper wire will melt and evaporate long before the coil saturates.

[green]

Rather than use the term "saturation", it would be more correct to say that the coil current has reached "steady state". i.e. it is no longer changing.
The term "saturation" is more commonly used when referring to magnetic flux density.

One thing is clear to me even now; you can't saturate the coil, you can saturate the target only. from reply #48

Can the target be saturated? What does saturate the target mean? The target does charge to a steady state value in 5TC's with a constant rate Tx?

[dbanner]

Green, I think you are on to something. Experts here often refer to imperitives, but never really explain how they got there. I'm not saying that they don't know(and perhaps it's all there scattered in bits and pieces on the forum), all I'm saying is that perhaps it's better to nail down the fundamentals first, so that when someone says a monkey's nose, everyone else knows what he means.
WE NEED A PAGE OF EMPIRICAL DEFINTIONS when it comes to PI methodology

[Carl-NC]

You can saturate
a magnetic core
a dielectric
a bipolar transistor
a MOSFET
an opamp
a CCD
and probably a whole lot more.

My preferred term for coil charging is flat-topping. Steady-state is a more common textbook term.

Target saturation is an unclear term to me. The eddies can flat-top (if the B-field is a linear ramp) but I don't think that's a good application of the term.

[dbanner]

I propose the following defintion for target saturation:
"A target is said to be saturated when all the magnetic domains in the target are aligned and there are no more available."

[dbanner]

[Carl-NC]

I see, so that flat topping the coil current period (just sufficiently long pulse width) allows for eddy currents in the target to dissipate such that it doesn't counteract the flyback discharge eddy currents with a subtractive element. All having to do with the target TC versus the coil TC. Seems an exceptionally thin corridor within which to optimize a PI front end.
So it's really the eddy currents produced by the collapsing field which are paramount to target detection.
That's why I suppose the coil parameters are so important to the overall design, it's integral to the entire calculas.

Yes, yes, and yes.

Most PI designs do not attempt to flat-top the current, but it's nice to have an understanding of what's going on if, for example, you want to detect Atocha bars.