4

D). PLCC executes the autotest and detects the fault, then starts its 8-hour shutdown timer. The message ªShut down in 8 hoursº is logged in the fault table. The autotest master function passes to PLCA.

E.) The message ªShut down in 1 hourº is logged at PLCA.

F.) The shutdown timer expires in PLCA. The message ªI/O Shut Downº 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 ªShut down in 1 hourº is logged at PLCB.

H.) The shutdown timer expires in PLCB. The message ªI/O Shut Downº 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.

Hours

 

 

 

0

1

9

15 16

23 24

A

 

B

C D

E F

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 ªShut down in 8 hoursº is logged in the fault table. The ªI/O Shut Down in Progressº status bit (%M12244) is set in each PLC. The autotest master function passes to PLCB.

C.) The message ªShut down in 1 hourº 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 ªI/O Shut Downº 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 ªShut down in 8 hoursº is logged in the fault table. The autotest master function passes to PLCC.

E.) The message ªShut down in 1 hourº is logged at PLCB.

F.) The shut down timer expires in PLCB. ªI/O Shut Downº 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.

4-20

GeniustModular Redundancy Flexible Triple Modular Redundant (TMR) System

GFK-0787B

 

User's Manual ± March 1995

 

Page 58
Image 58
GE GFK-0787B user manual Hours