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MELSEC-Q
14 SYSTEM CONFIGURATION OF MULTIPLE PLC SYSTEM
POINT
A "MULTIPLE PLC DOWN" stop error will be occur for the PLC on which the error
was detected when a stop error occurs.
There are cases where the timing of error detection will search for the PLC on
which the stop error that has caused the "MULTIPLE PLC DOWN" error occurs, not
the first PLC on which a stop error occurs, and the entire system will assume the
"MULTIPLE PLC DOWN" status.
For example, if a stop error occurs in the PLC No.2 and the PLC No.3 is halted as a
direct consequence of this, there are cases where the PLC No.1 will be halted
because of the stop error on PLC No.3 depending on the timing of error detection.
Power s
u
ppl
y
PLC N
o
.1
Halted with an "OPERATION ERROR"
Halted with stop error detection on PLC No.2
(becomes "MULTIPLE PLC DOWN")
There are cases where the system will be halted
with stop error detected on the PLC No.3
depending on the timing of error detection.
(becomes "MULTIPLE PLC DOWN")
PLC N
o
.2
PLC N
o
.3
Owing to this, there are cases where a different PLC No. to the PLC that initially
caused the stop error will be stored in the error data's common information
category.
In this event, remove the reason for the error on the PLC that caused the stop error
in addition to the "MULTIPLE PLC DOWN" error when restoring the system.
In the illustration shown below, the cause of the PLC No.2 error that did not cause
the "MULTIPLE PLC DOWN" error is removed.
(c) Observe the following procedures to restore the system.
1) Confirm the cause of the PLC No.1 error with the PLC diagnostics
function.
2) Remove the cause of the error.
3) Either reset the PLC No.1 or restart the power to the PLC.
All PLCs on the entire multiple PLC system will be reset and the system
restored when the PLC No.1 is reset or the power to the PLC is restarted.