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4-20 Genius Modular Redundancy Flexible Triple Modular Redundant (TMR) System
User’s Manual – March 1995
GFK-0787B
D). PLCC executes the autotest and detects the fault, then starts its 8-hour shutdown
timer. The message “Shut down in 8 hours” is logged in the fault table. The autotest
master function passes to PLCA.
E.) The message “Shut down in 1 hour” is logged at PLCA.
F.) The shutdown timer expires in PLCA. The message “I/O Shut Down” is logged in
fault table of PLCA. PLCA shuts down the I/O of the affected I/O group. Real I/O is
not yet affected because of the 2 out of 3 voting mechanism, although output
discrepancy errors may be generated.
G.) The message “Shut down in 1 hour” is logged at PLCB.
H.) The shutdown timer expires in PLCB. The message “I/O Shut Down” is logged in
fault table of PLCB. PLCB shuts down the I/O of the affected I/O group. Real I/O IS
NOW affected because of the 2 out of 3 voting mechanism.
This example shows the I/O Shutdown sequence when the autotest interval is 8 hours.
0
Hours
A B C D
124
F
16
9
E
15
23
A.) A fault occurs just after the autotest interval at PLCA begins.
B.) PLCA executes the autotest and detects the fault, then starts the 8 hour shutdown
timer. The message “Shut down in 8 hours” is logged in the fault table. The “I/O
Shut Down in Progress” status bit (%M12244) is set in each PLC. The autotest
master function passes to PLCB.
C.) The message “Shut down in 1 hour” is logged at PLCA.
D.) The shutdown timer expires in PLCA. PLCA shuts down the I/O of the affected I/O
group. The message “I/O Shut Down” is logged in fault table of PLCA. Real I/O is
not yet affected because of the 2 out of 3 voting mechanism, although output
discrepancy errors may be generated. PLCB executes the autotest and detects the
fault, then starts its 8 hour shutdown timer. The message “Shut down in 8 hours” is
logged in the fault table. The autotest master function passes to PLCC.
E.) The message “Shut down in 1 hour” is logged at PLCB.
F.) The shut down timer expires in PLCB. “I/O Shut Down” message is logged in fault
table of PLCB. PLCB shuts down the I/O of the affected I/O group. Real I/O IS
NOW affected because of the 2 out of 3 voting mechanism.