Question About Cable Capacitance In Intrinsically Safe Systems
I'm trying to understand some of the requirements for choosing an intrinsically safe diode barrier to be used with an intrinsically safe sensor. I think I understand the concepts pretty well with the exception of one key item. The thing I'm struggling with is how to determine the cable capacitance (and inductance) to be added to the sensor parameters to make sure the requirements of the barrier are met.
Specifically, I am having trouble understanding what cable capacitance to use. Manufacturers typically give two capacitances on their spec:
CC : Conductor to conductor CS : Conductor to all other conductors and shield
I'm tempted to say that it would make the most sense to interpret the cable capacitance as: CT = CC + CS
Where CT : Cable Capacitance Total
However, I can't find a single reference that nails this down. I was wondering if you could either give me some guidance on how this is typically calculated or estimated in industry or point me to a reference that might explain how to approach this? I do understand that in absence of other information, a capacitance of 200 pF/m can be used, but I'd really like to better understand the application when the two standard cable capacitance parameters are known.
Also, any in-depth literature or standard which covers this would be welcome as well.
The application I'm using this for is a residential propane tank liquid level sensor. (Rochester R3D type.)
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