Hi,
We are using a redundant serial interface (RS-485 Half Duplex) to communicate the Temperature Multiplexer supplied by GM International with DeltaV using redundant serial card. The MUX has following units.
D2010M Analog Input Field Unit
D2050M Power Supply & Gateway
As per the device manufacturer the D2050M is capable of providing redundant serial interface using MODBUS RTU protocol. We observed that the communication between DeltaV and D2050M works fine with occasional BAD status. Disconnecting the secondary/backup serial link resolves the issue.
The GMI response on this issue is that "The two ports on the MUX are tied together. It is possible to use both simultaneously, BUT the host (DCS) must ensure that the one port completes its poll/response cycle before the other port attempts a poll/response". My questions are as below:
1) Is there any way in DeltaV to control the poll sequence as indicated by GMI?
2) Is it possible to delay the poll on secondary serial link so that the MODBAD alarm frequency can be delayed?
3) Has anyone experienced the similar issue with redundant serial link? If yes then was there any resolution to the issue?
Thanks and appreciate your help on this.