effective capacitance measurements

[Peter_Bham]

I am probably overlooking something simple, but here goes.

How do I take simple capacitance measurements?  I have an actual circuit and used an RLC meter with 1000Hz and 1V excitation.  Probed the circuit in various spots and recorded the values.  Now I want to see if they are close to the theoretical.  Yes I could do this on paper but the loading network is complex and I would like to take the easy road.  TIA.

Peter A.

[lacy]

You will have forgive my lack of understanding here. You say you have an actual circuit and you want to simulate that in Multisim. Is this correct?  Do you have all the component values of the real circuit that you can plug into Multisim or is this what your looking for?

I am sorry that I am not understanding this well enough to provide you with a suggestion right now. If you could elaborate just a bit I may be able to help.

[Peter_Bham]

Yes,

I have an actual circuit in which all the values are known.  The circuit is assembled and being used as a loading network.  I would like to simulate the exsiting circuit in multisim.  I will use the simulation values to validate the exsiting circuits integrity.  Thanks.

Peter A.

[lacy]

If you have a circuit with known component values then you will have to place these components on the sheet and then using the original circuit trace out the wiring/traces and just run the corresponding wires in Multisim. After your done you will probably have to straghten it up a bit to make it look tidy. Then run your signals into it and you should be able to simulate it and see your results i.e Voltage, Current etc.

To answer another part of your question, Multisim does not have an LCR meter that I am aware of. All the parts are labeled and there would be no use of an LCR meter as far as I can tell.

I hope some of this answers your question. If not let me know.

[Peter_Bham]

I have the circuit in Multisim already.  Because there are so many parallel and series cap's in the circuit mixed in with resistors I was hoping for a quick method of evaluating the capacetence.  It seems like I am going to have to excite each section and then calculate out the C portion by hand.  I have already done this for a few values.  Was hoping there was an easier way.

On the same subject.  How would you evaluate an RC circuit to validate that it has not degraded in performance?  I was considering using an RLC meter and taking several measurements at different points in the circuit.  Then compare those values to the theoritical ones obtained in Multisim.  In liu of Multisim not being able to take these same measurements I was considering a frequency response analysis.  I could use a worst case simulation to account for the tolerances and then find an acceptable pass band.

Thinking out loud. Thanks fo the help.

[lacy]

I understand your situation, but I would have to actually see the circuit and see what I could come up with. I don't know if you can post it or not, but if you can I would love to try and see what anaylsis that could arrive at the results you are looking for.

I am sure there would be voltage or current measurements as well as frequency measurements that could isolate a bad capacitor even in a circuit complex as you describe without going through all the mathmatics.

Let me know if you wish to persue this.