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Unread December 2nd, 2019, 01:13 PM   #8
GaryS
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Join Date: Aug 2003
Location: Lancaster Pa.
Posts: 1,134
For the reference to ethernet most PLC's today communicated using ethernet so I presumed they were using ethernet if not then things would change
Normally RS485 would be an excellent choice for this the length for copper RS485 is 5,000ft it can easily make the 400ft. but most PLC's can't communicate directly over RS485 you will need a converter on both ends then you have to convert the protocol
you would need some device to pole and read both devices and convert the data that would really add to the hardware and software cost.
to go directly with the 4-20ma you will need a splitter to feed both devices and you still have the questionable reliability if running it over that distance. I just think its a poor choice in this application
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