measuring impedance

Dec 31, 2011 71 Replies
P

50ohm..
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frequencies:

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All the ones I knew left on account of Bill 22. :(

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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G

=A0 =A0 =A0 =A0 =A0 =A0 =A0scope tip here

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=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 ---

=A0 =A0 =A0 =A0 =A0 =A0 --- 3.3 uf np

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0C| 330uh

=A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 GND =A0scope common/grd.

where

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Are you asking a question of me?

I live near Buffalo, NY.

At resonance a parallel LC looks like a high impedance... (and looks like a low impedance far off of resonance). So if you drive it from a source with relatively high impedance (a big R in series) you see a rise in voltage at resonance.

A series LC circuit looks like a low impedance on resonance. (and high impedance off of resonance). So if you drive it from a low impedance source, you see a dip in the voltage (when looking across both L and C) at resonance.

Maybe try the parallel resonance first. Stick, say, a 1 k or 10 k ohm resistor between your signal source and the LC in parallel. With on channel of the 'scope look at the generator signal, and the other across the LC.... (after the resistor.)

Make a plot of the peak to peak voltage of both signals as a function of frequency.

Report any observations about the relative phases of the signals.

George H.

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J

Not really true from the point of view that if you drive the series LC with a voltage source (low Z) , the voltage across the LC will remain constant below, through, and above resonance. At resonance, however, the current out of the source will be limited only by the DC resistance of the L and the ESR of the C. Perhaps you meant a high impedance source?
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G

Opps! Quite right John my mistake! (Thanks for pointing it out.)

I had to bodge something together on the bench....

Ahh well I do get a peak at resonace, with a parallel LC.

Here's a FFT 'scope shot of parallel LC (L=3D3.3mH, C=3D1nF) driven through 10 k ohm's from a zener noise source. (It just happened to be sitting on the bench too.)

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I guess it's all a question of the relative impedances when you are on resonance.

George H.

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J

Yes, of course; silly me... Thanks for the reality check. :-) Version 4 SHEET 1 880 680 WIRE -128 48 -288 48 WIRE -128 80 -128 48 WIRE -128 192 -128 160 WIRE -32 192 -128 192 WIRE -288 208 -288 48 WIRE -32 224 -32 192 WIRE -128 240 -128 192 WIRE -288 336 -288 288 WIRE -128 336 -128 304 WIRE -128 336 -288 336 WIRE -32 336 -32 304 WIRE -32 336 -128 336 WIRE -288 384 -288 336 FLAG -288 384 0 SYMBOL voltage -288 192 R0 WINDOW 123 24 124 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMATTR Value "" SYMBOL cap -144 240 R0 SYMATTR InstName C2 SYMATTR Value 1n SYMATTR SpiceLine Rser=1 SYMBOL ind -48 208 R0 SYMATTR InstName L2 SYMATTR Value 3.3e-3 SYMATTR SpiceLine Rser=100 SYMBOL res -112 176 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R1 SYMATTR Value 10k TEXT -280 360 Left 2 !.ac oct 1024 1000 500000
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C

m a

ohm

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HI,

I did an experiment with the following 5uF 0.213mH and different resistor size.

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Sig Gen---Resistor---Cap---Inductor---Gnd The scope reading is with a 1kohm resistor when I put a 5ohm or 1ohm resistor the output is the same as the input. Three pictures are shown. They are self explanatory. is this the correct setup for a tank LC circuit ? ken

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C

=A0 =A0 =A0 =A0 =A0 =A0 =A0scope tip here

+

=A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 ---

=A0 =A0 =A0 =A0 =A0 =A0 --- 3.3 uf np

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0C| 330uh

=A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 GND =A0scope common/grd.

p where

ctor.

voltage drop

parts.

peaking.

gain.

p://www3.sympatico.ca/captoro/upload/204KHz.jpghttp://www3.sympati...

m

me

Thats a bit far for a drive :(

k
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A

Try finding the self resonant frequency of the inductor all by it's self. Use the biggest resistor you can that still allows you to see a signal on your scope.

sig gen----- 1 Meg-----inductor----ground l l ground

Watch the voltage across the inductor with your scope. You should find a peak at some frequency, although I think that big bolt is going make it a weak peak. What frequency is the peak? Mikek

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G

_ =A0 =A0 =A0 =A0 =A0 =A0 =A0scope tip here

--+

=A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 ---

=A0 =A0 =A0 =A0 =A0 =A0 =A0 --- 3.3 uf np

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0C| 330uh

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0C|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+

=A0 =A0 =A0 =A0 =A0 =A0 =A0 GND =A0scope common/grd.

dip where

ductor.

e voltage drop

ve parts.

ee peaking.

e gain.

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orm

same

Hmm is there no one there to help you? Do you have any connections to a college or University? Someone doing HAM? Maybe one of these "Makers" places that I heard about on the radio.

George H.

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C

.htm

."

, Ok so from my first post with pictures, there is no gain.. unless somebody is saying otherwise right? this is what I wanted to see. I read this link a while ago , take a look at page 18,

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K
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E

Don't know which post you have in mind when you say your first post. The pictures I commented on had no gain, which is correct.

Correct.

Gain doesn't depend on what anyone says - it is either there or it is not there. Your pictures show no gain, and that is what you should see with your setup.

Where is says "RESONANCE IS THE KEY TO OVERUNITY" ? It's my guess that you'll get confused reading that page. I took one look at the title and left - I've no desire to indulge in that fantasy.

Ed

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J

Yes, I am, as opposed to someone like you who thinks that "no school" is better and is rude enough to interrupt a discussion he can't possibly understand on the grounds that it's "boring" and that his diversion is important. Nothing could be further from the truth.
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