4

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 interval is set to 8 hours.

Examples

The first example shows the I/O Shutdown sequence when the autotest interval is 3 hours.

Hours

 

 

 

 

 

 

0

1

3

6

9

10 11

13 14

24

A

 

B

C

D

E F

G H

 

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.) 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.

GFK-0787B

Chapter 4 PLC Subsystem

4-19

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