What is the best equipment to obtain the correct I and V of an RC Circ
What is the best equipment to obtain the correct I and V of an RC Circ
(OP)
This is an ongoing question I have for which I still have not found a satisfactory answer. This concerns measurements with oscilloscopes in general and to understand it I am considering one of the simplest model circuits -- the RC circuit. Suppose you have a 10Ohm resistor and a 100pF capacitor in this RC circuit and you apply 800kHz of 8ppV amplitude. I have asked a question regarding this circuit earlier in this forum and I remained with the impression that studying such model circuit even with the state of the art equipment is so unreliable that the I and V data obtained hardly reflect the real I and V that would be expected theoretically. Is that the case? Is it really true that there is no equipment at present that would provide true I and V? If it isn't then what exact equipment (oscilloscope and probes) would you recommend that would yield true current and voltage of the said sine curves measured across the capacitor and the resistor, with all parasitic effects (capacitances and inductances) at a negigible level?





RE: What is the best equipment to obtain the correct I and V of an RC Circ
In the real world, one would not often have cause to require the sort of data in your question. Prototyping an RC circuit would typically rely on modeling. Trouble-shooting would be looking for gross failures, perhaps by comparison to parallel-channel circuits. Is this for school?
RE: What is the best equipment to obtain the correct I and V of an RC Circ
As for modelling, I've dropped it altogether after I saw how sloppy PSpice (which is at the basis of all else having to do with modeling) is. So, at this point it seems that there is no reliable apparatus that can measure correctly even the simplest of circuits. Hard to believe.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
TTFN
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
That's why EE:s are there to fix your problem. There's always a way. And it is usually easy to follow. But you seem to concentrate more on how difficult things are. Go find a qualified EE. He will sort this out for you.
Gunnar Englund
www.gke.org
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
It's not like RCs are complicated or mysterious, so why is there a need to obtain "correct I and V of an RC Circ?"
TTFN
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
Thing is, is it my problem or that's an inherent problem in measuring circuits. If it's the latter EE can't help, won't you agree?
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Just curious. It appears that while theoretically a, say, RC circuit in its ideal state is well understood, experimentally it is quite a challenge to obtain the current and voltage which theory requires. This may have unforeseen ramifications, don't you agree?
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Is this something personal? Why the whining?
Heisenberg told us long ago that you cannot observe without influencing the observed object. And resistive and capacitive loading effects on a circuit has been known for centuries and those effects can be handled with great success.
So, the answer is that an EE can help. Believe it or not. If you want to make a philosophical statement, just do so. But do it in some other forum. This is for practicing engineers.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Look at it another way... consider a circuit with a 1 ohm resistor and a 1F cap. That scope probe isn't going to affect the measurement one whit. Theory will match up with actual spot on. As you approach your circuit with much lower capacitance, the measured will start to roll away from theoretical... but you know why it's rolling away, the effect of the measurement tool is getting larger. Theory tells us how it will effect the measurement and to what degree, so a good scientist will account for those changes in his data (or at least know where the measurement limits are). I don't see a problem with that.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Happy now?
Why supercaps? They are in an entirely different capacity range. Some ten billions or more higher capacitance value. I really cannot see your problem. And why you are so persistent. Are you designing power supplies for guitar amplifiers?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
We're getting close to a hundred years past the point where testing the (R-C) theory is necessary, or even interesting.
I'll give you a couple of typical situations where one could tune capacitors to pF precision without even raising a sweat.
Let say you had several channels in a circuit that all had to be matched as identical as possible (hey, I've got this T-shirt). One can sort through the components, measuring them out-of-circuit using a $10,000 4-wire instrument with lots of digits, and bin them into exact measured value values. Then build the circuit (carefully), and all three channels WILL BE exactly the same (unless you've done something wrong).
Another example. Presumably the real-world circuit has an output. Presumably these components have some real-world measureable effect on the output in some circumstances (otherwise, why not remove them). So one can arrange for the circumstances to be true (bench test), and then measure the husky output to see if it's what you want.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
There's no science to be discovered here; only the frustration of uncontrolled strays.
You might wish to look-up 4- and 5-wire measurement techniques. That's exactly where you're headed if you are serious.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
See "Google".
Or buy a book. I strongly recommend this one:
http:
Or rent an EE to tutor you.
Mike Halloran
Pembroke Pines, FL, USA
RE: What is the best equipment to obtain the correct I and V of an RC Circ
4-wire OR 5-wire measurement technique
I even see 6-wire technique mentioned in the results, something I've not done.
We have 4-wire Wayne Kerr RCL meter here that's fantastic. It can reliably measure components with very small values. I think it even gives the equivalent circuit for parallel or series mixed circuits (R and C, or R and L).
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
You _would_ pick the book we used as a text for Aero lab class! :) Though I'm pretty sure it would tell how to build an op amp circuit to pick up the signal desired. I could even sell my copy to the OP, but that would just guarantee that I'd need to wire an op-amp the day after I posted it.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Is it safe to assume that the test cap is capacitance, the whole capacitance and nothing but capacitance? Same goes for the test resistor.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
How do you proposed to directly measure the current?
...And do so without affecting the voltage?
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
I wasn't going to attempt elucidation re Heisenberg.
pybb3ezv, if you wish for someone to point you to a particular line of a particular paragraph of a particular book to answer your particular question as phrased, how much money are you willing to pay for that information?
Mike Halloran
Pembroke Pines, FL, USA
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Mike Halloran
Pembroke Pines, FL, USA
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
"...cite a peer-reviewed paper..." Such a demand implies that it matters to the regulars on this forum. It doesn't.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Why is he discussing ohms and pF? There are techniques to measure microohms and femtofarads - and less than that. I see no point whatsoever in discussing a trivial case like his.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Oh this is a work related engineering problem. I intend manufacturing and marketing the solution and I am not a student nor am I preparing a thesis about a theoretical problem that in practice does not really exist as workarounds are common practice and effective.
I reject the forum rules about not hijacking threads so don't bother criticising me in that regard either.
Oh I have been kicked off here before for cheating on my homework, so now I make sure my
homeworkumm job is work related before I post.Regards
Pat
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
At these frequencies nothing is simple. I doubt that you have a pure 10 nF or a pure 10 ohm device.
RE: What is the best equipment to obtain the correct I and V of an RC Circ
Take it to the extreme. I suspect that internal corrosion may be affecting the resistance of a piece of 500 MCM cable ten feet long.
I have been testing it with my $25 multimeter but have not been able to determine whether the cable is good or faulty.
Similar problem at the other end of the scale.
Why am I wasting my time?
Bill
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"Why not the best?"
Jimmy Carter
RE: What is the best equipment to obtain the correct I and V of an RC Circ
I mean, we're talking about 0.8 AMPs of current, for crying out loud. People have been able to make even more difficult measurements involving 100 AMPs, with even less headroom.
TTFN
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
TTFN
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
TTFN
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RE: What is the best equipment to obtain the correct I and V of an RC Circ
RE: What is the best equipment to obtain the correct I and V of an RC Circ
If the theory didn't work, there would be many devices that do work that wouldn't. Can't you accept that?
Why not worry about chemical problems instead of trying to reprove well established electrical principals?
RE: What is the best equipment to obtain the correct I and V of an RC Circ