GE GFK-0787B Noise Reduction Machine User Manual


 
6
6-54 Genius Modular Redundancy Flexible Triple Modular Redundant (TMR) System
User’s Manual – March 1995
GFK-0787B
For output blocks set up for GMR redundancy, the duplex default state
is used when a block determines that only two PLCs are online. The
Duplex Default state of On or Off is used by the 2 out of 3 voting
algorithm in the block, instead of the state that would have been
supplied by the third PLC.
The Duplex Default state determines whether voting will be 1 out of 2
or 2 out of 2 in the On or Off state when only two PLCs are providing
outputs. This is explained below.
The following three tables compare voting results for a block receiving
outputs from all three PLCs with results, and with one of the three
PLCs is offline.
Results of Block Voting with Three PLCs Online
For comparison, this table shows how a block votes on outputs received
from three PLCs. In this case, the block 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
Duplex
Default