[foxboro] Redundant Cabling for Modbus Integrator 30s

Hey List,

I have a question about Foxboro Modbus Integrator 30s........


Equipment:
1. Redundant Modbus Integrator 30's with redundant Modbus cabling (not
Modbus+).
2. One Modbus Slave device, with one serial input (configurable as either
RS232 or RS485)

Problem:
1. If the Modbus slave device you are communicating to only has one Modbus
serial connection, how do you "merge" the two redundant cables from the
Integrator 30 to this device?
2. Can you convert both of the RS232 serial lines from the Integrator to
RS485 so you can electrically tie them together?
3. Are there times where both cables from the Integrator communicate
simultaneously, which would cause double requests for data from the Slave,
and also cause confusion for the return path of the Slave's reply?
4. If you can make the Slave device redundant (for example, use two Prosoft
Modbus modules, and both would be configured to use the same slave address
and have the same data), would there be any issues with connecting each
cable from the Int 30 to each slave device individually?  That is, connect
one cable to the first slave device, and connect the other cable to the
"backup" slave device.

The Foxboro documentation dances around a solution for this problem (doc
B0193RL, Figure 2-15).  The document merely shows redundant wiring as two
independent inputs to the Modbus device; it assumes the Modbus slave device
has two serial inputs that work as one slave address.  Since Foxboro MDSCAN
and ECBs do not allow for a backup/alternate slave addresses, the two Modbus
serial inputs would both have to be the same Modbus slave address, which is
not a common feature for Modbus devices to have.


Any help or insight would be greatly appreciated.

Thanks in advance,
Mark Dumond
FeedForward, Inc



 
 
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