Measuring Interconnect Electrical Characteristics of Interconnects

Ron Resnick

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Jan 24, 2015
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I want to compare the capacitance and the loop inductance of two XLR terminated interconnect cables using a B&K Precision Model 880.

How do I measure the capacitance of each cable?

How do I measure the loop inductance of each cable?

To what part of the cables do I connect the meter’s probes for these measurements?

Which prongs on the cable do I short to create the loop to measure loop inductance?
 

Folsom

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Oct 25, 2015
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For capacitance you don't need to short anything. They directly connect at the same end.

Inductance requires you to short the end of each cable.



You would short pin 2 & 3 for inductance measuring. They are also the pins you connect to in order to measure capacitance and inductance (but not at the same end they are shorted).

Your readings may not be wholly accurate because they would calculate them with ground (shield), so they may not compare to a datasheet. Also don't forget to calibrate the meter. Also ratings are either on 1ft or 1000ft typical, so you'll have to do some math to try and compare to spec sheets.
 

Uk Paul

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Hi Ron,

Inductance probably nothing to worry about in IC's, but as Folsom says, just hold the probes on male end pin 2&3 of the xlr, (nothing connected at other end!) for C. Set frequency as low as meter will go, probably 100Hz. 1meter will most likely be 100-200 pf. You can use this to match pairs if you like too..

Rgds,
Paul
 
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Folsom

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I think the meter does 1khz, which I think is a typical measurement for cables. But it also tends to be a resonate frequency for other measuemt equipment.
 

Ron Resnick

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Jan 24, 2015
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For capacitance you don't need to short anything. They directly connect at the same end.

Inductance requires you to short the end of each cable.



You would short pin 2 & 3 for inductance measuring. They are also the pins you connect to in order to measure capacitance and inductance (but not at the same end they are shorted).

Your readings may not be wholly accurate because they would calculate them with ground (shield), so they may not compare to a datasheet. Also don't forget to calibrate the meter. Also ratings are either on 1ft or 1000ft typical, so you'll have to do some math to try and compare to spec sheets.

This is just what I needed! Thank you very much, Folsom!
 

Ron Resnick

Site Co-Owner, Administrator
Jan 24, 2015
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Hi Ron,

Inductance probably nothing to worry about in IC's, but as Folsom says, just hold the probes on male end pin 2&3 of the xlr, (nothing connected at other end!) for C. Set frequency as low as meter will go, probably 100Hz. 1meter will most likely be 100-200 pf. You can use this to match pairs if you like too..

Rgds,
Paul

Will do! Thank you, Paul!
 

Ron Resnick

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Jan 24, 2015
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I wonder how much something like sound-staging is affected if interconnects have insufficiently similar electrical characteristics?
 

DonH50

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Jun 22, 2010
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Be sure to zero the meter with the probes in place but not touching the cables. What I have done in the past was to create a little jig using a shorting plug for the far end to measure inductance and a pair (M/F) of jacks at the near end with short wires to test points for the meter probes. I would attach the meter probes to the jack of interest without the cable connected, make sure the meter's wires were fixed and away from everything possible (including me), then zero the setup. After that I would plug in a cable with the other end open to do the capacitance measurement, then stick in the shorting plug at the other end of the cable to get inductance. It sounds harder that it was -- easier to see and do than to describe.

Fo XLR I would measure hot to shield, cold to shield, and hot to cold capacitance. Inductance was hot to cold loop and sometimes the ground loop (had to do hot/cold/shield and solve the set of equations to extract shield inductance, or measure it at one end).

Note "insufficiently similar" is pretty vague -- they'd have to be pretty unrealistically mismatched IME/IMO.

There is a little book by a guy named Walker that has all sorts of wire/plane configurations with equations plus a bunch of experimental data. Not sure it is still available and of course it is pricey but it is one of those little gems for this kind of stuff.
 

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