3

Results of Block Group Voting with One PLC Online

If two PLCs are offline, the ªvotedº outputs are the same as the outputs from the PLC which is still online (x = don't care).

PLCA Output

PLC B Output

PLC C Output

DuplexDefault

OutputState

State

State

State

Setting in Block

 

 

 

 

 

 

0

 

 

x

0

0

 

 

x

0

0

 

 

x

0

0

 

 

x

0

1

 

 

x

1

1

 

 

x

1

1

 

 

x

1

1

 

 

x

1

 

 

 

 

 

PLC Logon Control

To prevent untripping of tripped block outputs, blocks do not use output data from a

PLC that has previously been offline until one of the following occurs:

A.all of the output data received from the newly-online PLC agrees with the voted output data of the block.

B.the user forces the PLC to log onto the output block(s) by turning on the GMR control bit FORCLOG (Force Logon).

For more information about PLC Logon control, please see page 7-17.

Output Fault Reporting

On detection of any block or circuit fault, a directed fault message is transferred to the three PLCs on an event-driven basis.

The PLC currently operating as the Autotest Master also monitors output blocks for discrepancies between the output values commanded by the PLCs. If a PLC is offline, its data is not considered ªdiscrepantº. But if a PLC is online and its data is discrepant, the GMR software logs a fault into the I/O Fault Table of the PLC that detects the discrepancy which is copied to the other PLCs. The appropriate fault references are also set in each PLC.

GFK-0787B

Chapter 3 Output Subsystem

3-5

Page 33
Image 33
GE GFK-0787B user manual Output Fault Reporting, PLC Logon Control