GE GFK-0787B Output Faults that Cause I/O Shutdown, Programming for I/O Shutdown, Interval Until Shutdown in Each PLC

4
4-19GFK-0787B Chapter 4 PLC Subsystem
Output Faults that Cause I/O Shutdown
For discrete output groups there are also two types of faults which may prevent the
output autotest from continuing to execute for that output group and thus cause an I/O
shut down for the outputs in the group.
1.) Loss of a block within the group. (I.E. any failure which causes the block to no
longer communicate on the Genius bus such as loss of power.)
2.) Output autotest failure detected of a type which could potentially prevent a
normally energized output from being tripped off. An example is the short of a
source block output to +24 Vdc.
Programming for I/O Shutdown
To be made aware of a pending I/O Shutdown, the program can monitor this GMR
Status Bit:
%M12244 – (IO_SD) Any I/O Shutdown Timer Activated
To completely prevent an I/O Shutdown from occurring, the program can set this GMR
Control Bit:
%M12265 – (SD_CAN) Cancel I/O Shutdown
Interval Until Shutdown in Each PLC
The period of time before an I/O Shutdown occurs depends on the autotest interval
which is set for the system. The initial autotest interval is set by the autotest interval
value selected in the GMR configuration.
The configured autotest interval can be adjusted in each CPU through the application
program by varying the value in the autotest interval register. The system allows for a
total maximum time of 24 hours between a fault occurring and the resultant I/O shut
down when the autotest inter val is set to 8 hours.
Examples
The first example shows the I/O Shutdown sequence when the autotest interval is 3
hours.
0
Hours
A B C D
13 11 24
F
614
H
9
EG
10 13
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.) 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.