Cable capacitance measurement / calculation

Why can't you connect the three cables together and then measure the capacitance to the screen?

I forgot to mention that the cables are terminated with connectors and we are talking about the final test for such assemblies in big quantities. Of course there would always be the possibility to create an adapter to short all three wires for this test but this would require user intervention during an automated test adding to the test time plus the QA control of this adapter.

Capacitance measurements are notoriously inaccurate. Even in a laboratory they are iffy. Capacitor maunfactuters spends much money trying to design test equipment used to test their product and still have problems. Ask yourself what is this data to be used for? Just stuck in some record somewhere and never looked at again? Fugetaboutit!

I beg your pardon Guest!!

Capacitance measurements are extremely accurate and repeatable if measured correctly!!

I have an old General Radio capacitance bridge that will accurately measure capacitance to within 0.01% absolute value...

And if used to compare capacitance values against a known reference capacitor will measure to within a few parts per million!!!

The total range of measurement is from 10 attoFarads (0.00001pF!!!) to 10 microFarad with resolution to 0.1 ppm

Now say again why you think capacitance measurements are "...a bit iffy..."

John.

Hello Guest,

capacitance measurements of components that have significant parasitic impedances can be indeed a challenge. I have my experiences with varistors and suppressor diodes. High dependance on the measurement voltage, temperature, etc. Also cable capacitance varies with measurement frequency. There are some variables that have to be controlled for repeatable measurements.

Capacitors themselves are built to minimize the parasitic components and maximise stability. If they are built accordingly, they can be measured very accurately as Electroman states.

The capacitance spec of the cables I have to measure is safety related (medical equipment). That´s why I need the records. I know there is a lot of variables that have to be controlled for repeatable measurements.

I will check with some cable manufacturers next to see if they can help.