Electronics > Metrology

Replacing Teflon cable with CAT6 in metrology

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mmagin:

--- Quote from: DiligentMinds.com on May 05, 2016, 04:39:25 pm ---Polyethylene is a very good insulator-- not as good as PTFE, but close, and it does not have some of the bad characteristics of PTFE [dielectric absorption].  Similar to the fluorocarbon family, polyethylene does not absorb water very much [<0.01%], so is relatively unaffected by humidity.

--- End quote ---

I see some plenum-rated Cat 6 cable has FEP insulation.  Would this be better than PE?

ManateeMafia:

--- Quote from: DiligentMinds.com on May 06, 2016, 11:12:49 pm ---
--- Quote from: mmagin on May 06, 2016, 11:07:06 pm ---
--- Quote from: DiligentMinds.com on May 05, 2016, 04:39:25 pm ---Polyethylene is a very good insulator-- not as good as PTFE, but close, and it does not have some of the bad characteristics of PTFE [dielectric absorption].  Similar to the fluorocarbon family, polyethylene does not absorb water very much [<0.01%], so is relatively unaffected by humidity.

--- End quote ---

I see some plenum-rated Cat 6 cable has FEP insulation.  Would this be better than PE?

--- End quote ---

FEP is in the Teflon family and has very good electrical characteristics.  The only thing to watch out for is to not use the cable at 1000V, and then immediately use it for a low voltage-- (the "charge" will need time to dissipate).  If you are not using it at higher voltages, then this is a non-issue.  FEP handles much higher heat than PE, and like PTFE will not absorb water vapor.

--- End quote ---

Thanks for the warning. It is good to know before hooking up to a HV source.

Belden makes a FFEP insulated cable model 82688 . I ended up getting a "small" quantity of it. Haven't had time to test it yet. It is not CAT6 but token ring so this is only two pair.
http://www.belden.com/techdatas/metric/82688.pdf

I am not sure how high of a resistance it actually will measure out to based on the >16000 Megaohms spec.

Cerebus:

--- Quote from: DiligentMinds.com on May 06, 2016, 11:12:49 pm ---FEP is in the Teflon family and has very good electrical characteristics.  The only thing to watch out for is to not use the cable at 1000V, and then immediately use it for a low voltage-- (the "charge" will need time to dissipate).  If you are not using it at higher voltages, then this is a non-issue.  FEP handles much higher heat than PE, and like PTFE will not absorb water vapor.

--- End quote ---

Are you saying it's got horrible dielectric absorption, or just saying it makes a good capacitor and 1/2CV2 at 1000V needs respect even if it is only a few 10s of pF?

Cerebus:

--- Quote from: DiligentMinds.com on May 07, 2016, 12:40:59 am ---
I'm not certain if "dielectric absorption" is the right property-- I'm getting old, and my memory is not so good... 

--- End quote ---

Um, yes, now what did I come in here to comment about? Oh yes...   :)

From the rest of what you say, it sounds as if you are talking dielectric absorption - or "soakage" in old money for those of us who remember ten bob notes and threepenny bits.

Talking about terrible soakage, I was searching on ebay the other day for a cheap kit of poly-whatever capacitors and encountered boxes of newly manufactured paper and wax capacitors obviously targeted at audiophool electric guitarists. I conclude the latter because the kit was for a named guitar and consisted of 1 (one) 50 nF cap and 1 (one) 100 nF cap for, drum roll, £51.00 GBP! At 25 sobs a capacitor I fully expect those to come with a photograph of each individual capacitor being hand rolled on the thighs of naked virgins by the ghost of Bob Pease.

Edwin G. Pettis:
"I fully expect those to come with a photograph of each individual capacitor being hand rolled on the thighs of naked virgins by the ghost of Bob Pease."

Good line, I think Bob might have gotten a good laugh out of that himself and then tore into them for being stupid.

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