BM85 bridges in a Hot Standby System

U

Thread Starter

Ute Swetlle

In a HSBY configuration 2 Quantums connected to a 2 BM85C002 bridges.
The Primary Quantum sends messages through a BM85 if this bridge fails then the Quantum shall use the second BM85.

I read the BM85 User's guide. I couldn't find a way to identify a failure in the bridge to code the switching to the backup BM85.

I know that failures in Modbus ports are shown in the indicators in front of the bridge....

But How to code BM85 switching?

I'll appreciate any help
 
If this is a redundant MB+ network then the switching is between the Modbus Plus A and Modbus Plus B cables that the communication switched between. The Mux's (BM's are not bridges) are the same address on both cables.

Unless I misunderstand your description, the 2 BM85's have different addresses and don't change.
 
J
Ute,

The Quantums are talking to Modbus slaves that
are connected to the BM85's serial ports, right ?

As far I know, you will only be able to detect that a Modbus slave does not respond to an MSTR instruction after so many timeouts and retries. If its just one slave that does not respond, then that slave is broken (probably), if all slaves
fail then the BM85 is broken (possibly) and it is time to switch to the other BM85.

Coding the switchover is simply a matter of changing the first route in MSTR's routing table, this can be done on the fly. It may be best to perform the swithover on the basis of BM85 port failures, rather than on the whole BM85, since the problem may be with the comm link on just one port.

BTW, the BM85 has a pretty high MTBF. The quote I
received from Modicon a few years ago put it at 16
years. You might end up causing more failures by writing this backup communication logic than you would ever see by just using one bridge mux ( and keeping the other for a spare ).

Does this BM85 have RS232 or RS485 ports ? If you are using RS232, how are you joining the port-pairs back together ?

JK
 
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