Scadapack RS485 comm issues

Kevinroland · ‎2022-04-10

I am having issues communicating to a valve on an RS485 network. There are a total of 10 valves and the RS485 is daisy chained starting from the PLC to the first valve, and onwards to the last valve. The issue is I can see all of the valves utilizing modscan, except the first one the PLC is daisy chained to. I am not sure if there are termination resistors wired. Is there any reason I cannot see the first valve in the daisy chain but all others?

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Joel_Weder · ‎2022-04-11

Hi Kevin,

Attached is an old document I sometimes refer to when dealing with an RS-485 issue. Please dig into that and check all the various issues discussed. One other item to consider is "What's different about that first valve?" Maybe different firmware, maybe a different switch setting, maybe a poor terminal connection, could be any of many different things...

Joel

Joel Weder
Remote Operations Specialist
Schneider Electric

See Answer In Context

Joel_Weder · ‎2022-04-11

Hi Kevin,

Attached is an old document I sometimes refer to when dealing with an RS-485 issue. Please dig into that and check all the various issues discussed. One other item to consider is "What's different about that first valve?" Maybe different firmware, maybe a different switch setting, maybe a poor terminal connection, could be any of many different things...

Joel

Joel Weder
Remote Operations Specialist
Schneider Electric

insideau786 · 4 weeks ago

i used to get same issue as well.