800XA controller power failure
We are running ABB PM865 800XA based ESd system at our facility. The current architecture calls for connectivity of Two controllers controlling two different station. But both are connected to common F&G system via MMS tags.
Day before yesterday due to damage of electrical cable Controller#2 power failure occured and no alarms were generated regarding F&G system by Controller#1. MMS tags retained their last known values, this is a concern as cetain tripping are also shared via MMS as cuses are on controller 2 and trip action are initiated by controller 1.
can somebody guide me as to how to lookup this matter and resolve the isuue.
Voted best answer
This is expected behaviour. When MMS communication stops, the MMS variables retain the last value - ie they do not receive updates.
There are 2 ways around this ....
1. Dont use MMS. Hardwire critical signals. Be sure to configure the correct fail state for the IO channels.
2. Monitor the MMS "Connected" status on the MMS_Connect blocks. If the "Connected" status is lost, wait a reasonable timeout value, then mark the communications as failed and perform the appropriate actions in your application code. Note that downloading and warmstarting a controller will cause MMS comms to halt briefly and the Connected status will be lost. You need to allow a sensible timeout.
Rob is 100% right we got same issue on ESD system Last year, we had tripping signals on MMS Communication and dring plant abnormality MMS didn't pass the tripping signal. and it was real mess for us.
Best way is to use the hardwire signals specially for SIL2 and SIL3 level applications where safety is most improtant. Also ABB recommened to use hardwire Signals for trippings in Saftey Applications.
Source: SIL2 and SIL 3