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3-4 Genius Modular Redundancy Flexible Triple Modular Redundant (TMR) System
User’s Manual – March 1995
GFK-0787B
The following three tables compare voting results for a block group receiving outputs
from all three PLCs with results when one of the three PLCs is offline.
Results of Block Group Voting with Three PLCs Online
For comparison, this table shows how a block group votes on outputs received from
three PLCs when all three are online. The block group doesn’t use the Duplex Default, so
it is shown as an X (don’t care).
PLC A Output
State
PLC B Output
State
PLC C Output
State
Duplex Default
Setting in Block
Output State
0 0 0 X 0
0 0 1 X 0
0 1 0 X 0
0 1 1 X 1
1 0 0 X 0
1 0 1 X 1
1 1 0 X 1
1 1 1 X 1
Results of Block Group Voting with Two PLCs Online, and Duplex Default Set to 1
If one PLC is offline, the outputs from both online PLCs must be 0 for the voted output
state to be 0. The voted output is 1 if either of the online PLCs outputs a 1.
PLC A Output
State
PLC B Output
State
PLC C Output
State
Duplex Default
Setting in Block
Output State
0 0 1 0
0 0 1 0
0 1 1 1
0 1 1 1
1 0 1 1
1 0 1 1
1 1 1 1
1 1 1 1
Results of Block Group Voting with Two PLCs Online, and Duplex Default Set to 0
If one PLC is offline, the inputs from both online PLCS must be 1 for the voted output to
be 1. The voted output is 0 if either of the online PLCs outputs a 0.
PLC A Output
State
PLC B Output
State
PLC C Output
State
Duplex Default
Setting in Block
Output State
0 0 0 0
0 0 0 0
0 1 0 0
0 1 0 0
1 0 0 0
1 0 0 0
1 1 0 1
1 1 0 1