Nole
Member
So I am attending a site next week that is reporting PLC communication issues between its three SLC 5/03s (PLC1, PLC2, PLC3). PLC2 communicates with PLC1, and PLC3 via a DH485 network, and then sends all the required PLC data to an RTU via Modbus. PLC2 is communicating properly with the RTU, but only the values for PLC2 (not PLC1 or PLC3) are updating. Apparently this issue has existed for years, and other engineers have tried to fix it with no luck.
This leads me to believe that there is an issue with the DH485 network. I attended site yesterday, but could not connect to any of the PLCs as Chan. 0 (RS232 port) was configured as shutdown in the program, and I didn't bring my DH485 programming cable. (rookie move
)
My question is, what is the best way to get online and troubleshoot the DH485 Network? My current plan is to go online with PLC2 through the DH485 port, take an upload of the program, reconfigure the program's Channel Configuration to allow Chan. 0 to communicate DF1 Full Duplex, then download the program back in. After this is complete, I should be able to connect to PLC2 while the DH485 cable is plugged in to allow me to troubleshoot the network, right?
Two other points:
- There will be an operator on site who can put everything in manual while the download takes place.
- The SCADA PC on site has been down for 7 years according to operations.
If anyone has any better ideas of how to troubleshoot this issue, it would be greatly appreciated.
Sorry if this isn't a great question, I usually deal more with electrical issues, and Ethernet communications and am just learning about Allen Bradley Comms.
Thanks,
This leads me to believe that there is an issue with the DH485 network. I attended site yesterday, but could not connect to any of the PLCs as Chan. 0 (RS232 port) was configured as shutdown in the program, and I didn't bring my DH485 programming cable. (rookie move
)My question is, what is the best way to get online and troubleshoot the DH485 Network? My current plan is to go online with PLC2 through the DH485 port, take an upload of the program, reconfigure the program's Channel Configuration to allow Chan. 0 to communicate DF1 Full Duplex, then download the program back in. After this is complete, I should be able to connect to PLC2 while the DH485 cable is plugged in to allow me to troubleshoot the network, right?
Two other points:
- There will be an operator on site who can put everything in manual while the download takes place.
- The SCADA PC on site has been down for 7 years according to operations.
If anyone has any better ideas of how to troubleshoot this issue, it would be greatly appreciated.
Sorry if this isn't a great question, I usually deal more with electrical issues, and Ethernet communications and am just learning about Allen Bradley Comms.
Thanks,
