calibration capacitor

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peter g

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hi, i've completed the construction of an esr meter.and need to calibrate it. to do this i need someone who has access to a really accurate cap value reader. i need someone to test the actual value of a 470mfd. cap. and send it to me. i will gladly pay for any expense. thanks all.
 
Why?? - the tolerance on 470uF capacitors is HUGE!!! - probably +25%/-50% or something along those lines.

An ESR meter doesn't need to have any degree of accuracy on the capacitance value, it's totally unimportant - it's only the ESR which matters, and that's easily calibrated, if indeed there's any requirement to?.
 
One way of doing this yourself by doing a simple RC oscillator or ramp generator
with a current source, and measure trip points, time and V and calculate the C. Use
a current source, opamp/comparator and reference or a LM334 type of part. Needless
to say if using a scope and / or a DVM those have to be caled.

It all depends on the accuracy you want to achieve. Electrolytics are very imprecise
C's, with strong T dependence. Generally the low % accuracy measurements adequate.
Example, ramp approach Q = C x V, or I = C x dV/dT, C = (I x dT) / dV

Obviously in above your accuracy is dependent on accuracy of each equation element,
dV, dT, and current, so do an error budget to see if you are meeting your goals.

Lots of info here : https://en.wikipedia.org/wiki/Electrolytic_capacitor

You can use some ESR meters for C measurement, and they can be reasonably accurate.
1 - 2% kinds of accuracy for the cheap ones., for large C values, << 1% for sub 1 uF types
of caps. Accuracies similiar to many low cost DVMs. Some esr meters even give you the
vector values :



Other approaches : https://www.youtube.com/results?search_query=capacitance+measurment




Regards, Dana.
 
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i know the tolerance is large (20%) in modern electros. there are occasions when the esr is good, but the capacitance value is much lower than it should be. these are the caps that are missed when relying on esr only. its 470mfd.
 
i know the tolerance is large (20%) in modern electros. there are occasions when the esr is good, but the capacitance value is much lower than it should be. these are the caps that are missed when relying on esr only. its 470mfd.

Again, there's no need for any great accuracy, if it's way out of tolerance then it will be obvious.

The correct abbreviation for microfarad is uF - where the u would preferably be the greek letter 'mu' (µF).
 
i know the tolerance is large (20%) in modern electros. there are occasions when the esr is good, but the capacitance value is much lower than it should be. these are the caps that are missed when relying on esr only. its 470mfd.

Actually you can get electrolytics in +/- 3% tolerance, but one cannot consider them as miniature.



Regards, Dana.
 
For future :





Note for all the above, some do not show any sound card input protection, just google
"sound card input protection) for circuits. Or use an external sound card dongle.


Regards, Dana.
 
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Actually what you need is a standard capacitor (capacitance standard) or several standard capacitors. A LCR meter is calibrated using standards of Inductance, Capacitance and Resistance.

If you have access to a really good LCR meter you can measure the values of a few capacitors and note their actual values. Then use those capacitors as what is called a simple transfer standard for your unit under test.

A Google of ESR Meter Calibration should give more ideas.

Ron
 
I think that what the OP is asking is for someone who has a good LCR meter to take a generic capacitor, measure it to some reasonable precision, and record that number. That would create a transfer standard.

Then send that capacitor and it's measurement to him for use as a reference standard to calibrate his meter.

The capacitor chosen should be one with good stability.
 
OK, if you are in the US or even North America give me a range, I'll measure a cap in the range and be happy to mail it to you. Heck, I'll even pay the postage and you can keep the cap. Will that work for you? I have sent parts to members in Canada and Mexico in the past without a problem and anywhere US is simple. That what you want?

Ron
 
wow! thats great. i live in s.florida. address information deleted by moderator the capacitor range is 470 to 1000mfd. thanks, again.
 
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peter g

I think that posting personal details in an open forum is a bad idea, and suggest you edit your post to remove them.

It would be better to send this information to Ron by private message.
 
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