hello dears
I have a modbus and modbus plus network in my plant with Schneider Modicon quantum 114 series ( i know they are so old) CPUs, currently i face an issue with my modbus plus communication, i removed all node connectors and tested pin 2 and 3 and 60 ohms resistance was there and between pin 1 and 2 and pin 1 and 3 open circuit is ok, my problem is that one of my node in SCADA is faulty and it is very weird, the addresses are 1,2,3,4,18,20 when all node connected to modbus node address 18 is red and data update is not OK, when I remove Node address 3 connector, node 18 become ok and data updates normally, i removed all cables and connect Node 3 to PC ( SA-85) the CPU seems fine but some delay of alarms and tags.

Anyway to know how to solve the issue?

Thanks in Advance,

 

Are you using the MB+ Taps and drops? You may email me directly at [email protected]

 

This sounds very similar to a problem we had on a different network. Our trouble turned out to be that we were pushing the network distance too much and we solved the issue by adding a repeater.

Out of curiosity, what changed on your installation from when it was working correctly until now?