3

Hot Standby Mode

Individual blocks can be included in the output subsystem as GMR blocks, Hot Standby blocks, or non-GMR blocks. There are significant differences in block operation between these three operating modes.

Operation of GMR output blocks and non-GMR blocks is explained elsewhere in this chapter. Hot Standby mode is a type of Genius redundancy that can be used with or without GMR.

Basic Hot Standby Mode Operation

In basic Hot Standby mode (without GMR), blocks receive outputs from two PLCs, but they are normally controlled directly by the PLC at serial bus address 31. If no output data is available from bus address 31 for a period of three bus scans, the outputs are immediately controlled by the PLC at bus address 30. If output data is not available from either 30 or 31, outputs go to their configured default or hold their last state. The PLC at bus address 31 always has priority, so that when 31 is online, it always has control of the outputs.

Bus Controller

31

Bus Controller

30

outputs '''

Selection of Hot Standby mode is made during block configuration.

Hot Standby Mode in a GMR System

If a block is set up for Hot Standby mode in the GMR configuration, its Hot Standby operation is automatically expanded to include three PLCs: 31, 30, and 29.

PLC 31

PLC 30

PLC 29

outputs '''

The manner of operation is the same. The block uses outputs from PLC 31 if they are available. If not, it uses outputs from PLC 30. If outputs from both PLC 31 and PLC 30 are not available, the block uses outputs from PLC 29. If output data is not available from any of the three PLCs, outputs go to their configured default or hold their last state. The PLC at bus address 31 always has priority, so that when 31 is on±line, it always has control of the outputs.

As mentioned, this assignment of an additional Hot Standby PLC happens automatically for a Hot Standby block that is included in the GMR configuration.

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GeniustModular Redundancy Flexible Triple Modular Redundant (TMR) System

GFK-0787B

 

User's Manual ± March 1995

 

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GE GFK-0787B user manual Basic Hot Standby Mode Operation, Hot Standby Mode in a GMR System