Mitsubishi Electric Melsec-QS Series Safety Application Manual page 4

[Design Precautions]
When a safety PLC detects an error in an external power supply or a failure in PLC main module, it
turns off all the outputs.
Create an external circuit to securely stop the power of hazard by turning off the outputs.
Incorrect configuration may result in an accident.
Create short current protection for a safety relay, and a protection circuit such as a fuse, and
breaker, outside a safety PLC.
If load current more than the rating or overcurrent due to a short circuit in the load has flowed in the
CC-Link Safety remote I/O module, the module defines it as a fault and turns off all the outputs.
However, if overcurrent flows in the CC-Link Safety remote I/O module for a long time, it may cause
smoke or a fire. To prevent it, create a safety circuit such as a fuse outside the module.
When data/program change, or status control is performed from a PC to a running safety PLC,
create an interlock circuit outside the sequence program and safety PLC to ensure that the whole
system always operates safely.
For the operations to a safety PLC, pay full attention to safety by reading the relevant manuals
carefully, and establishing the operating procedure.
Furthermore, for the online operations performed from a PC to a safety CPU module, the corrective
actions against a communication error due to a cable connection fault, etc. should be predetermined
as a system.
All output signals from a safety CPU module to the CC-Link Safety system master module are
prohibited to use.
These signals can be found in the CC-Link Safety System Master Module User's Manual.
Do not turn ON or OFF these signals by sequence program, since turning ON/OFF these output
signals of the PLC system may cause malfunctions and safety operation cannot be guaranteed.
When a safety remote I/O module has detected CC-Link Safety error, it turns off all the outputs. Note
that the outputs in a sequence program are not automatically turned off.
If CC-Link Safety error has been detected, create a sequence program that turns off the outputs in
the program.
If the CC-Link Safety is restored with the outputs on, it may suddenly operate and result in an
accident.
To inhibit restart without manual operation after safety functions was performed and outputs were
turned OFF, create an interlock program which uses a reset button for restart.
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