Red Lion Hmi failures

I have some red lion g306A Hmis connected to a Dh485 network with 4 slc 5/03 and 1747-aic modules and I keep burning out comm ports on the screens. there are slc 500s connected 2 at a local station and the other 2 are at a remote station with areial comm line in between. the engineer that installed the screens originally recommended some phoenix contact rs485 isolation repeaters to isolate the comm line. So I installed the siemens equivalent (my wholesaler is a siemens dealer) rs 485 repeater they seemed the same except the siemens didn't have a spot for the common wire. so I ran the wire through a 24V surge protector and installed the new HMI which lasted only a day or so before the comm port was toast again. Does any one have any ideas on testing to see what is going on or ideas for products that could help me get these hmis to last.


Thanks

That's very weird. So multiple G306A got hosed already? I like to see a physical diagram of the wiring. Wonder if some crazy ground loop is going through the 485 network? Are you able to measure any kind of currents?

maybe go all out and isolate everything?

https://iotmart.advantech.com/Seria...solators-and-Repeaters/ABB_13496.products.htm

they seemed the same except the Siemens didn't have a spot for the common wire.

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Are you sure they're ordinary RS485 isolators, or are they for Profibus DP ?

DH485 is a true isolated differential RS485 circuit, so it really does use an isolated signal common wire, as well as two differential signal wires. It does not use ground or chassis ground as the reference to the RS485 signal like Profibus DP does or like some RS485 devices can.

Get a meter on those RS485 terminals and see what kind of voltages you're seeing between the common and the signal, and between those and actual earth ground.