Any suggestions on protecting RS422/485 when using CAT5 cable? explanation here
Most 422 line drivers seem to have a max common mode Voltage of +-12V.
These days everbody seems to be using CAT5 for almost every conceivable signal.
Just wondering what you do for protection (insert condom jokes if reqd.)?
martin
Void the warranty of your device when connected to an improper cable or source.
Rene
-- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net
LOL, I agree
Thanks
martin
Does RS-422 have the signature 25K resistance? (IIRC there is also a capacitance check.) i.e., the -48v is not applied to the cable unless the signature is present, to prevent damaging non-PD devices. Early non-standard implementations were hard-wired on, and they quickly learned of the incompatibilities.
The discovery process applies a low current-controlled voltage to probe for the "signature" before the power is enabled. I don't know the characteristics of this signal, but I'd expect it to be closer to 5v than 48v for exactly this reason.
Richard
Practical, but I doubt customers will see it that way.
Corporate cable plant is RJ-45 jacks for everything, and the telephony gear is less friendly than PoE. A very real hazard is a digital phone jack or a modem line, which will have up to 48v on the center pair and possibly the others, depending on the system.
Richard
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