Design Precautions - Mitsubishi Electric MELSEC-Q Series User Manual

[DESIGN PRECAUTIONS]

● Configure safety circuits external to the programmable controller to ensure
that the entire system operates safely even when a fault occurs in the external
power supply or the programmable controller. Failure to do so may result in an
accident due to an incorrect output or malfunction.
(1) Configure external safety circuits, such as an emergency stop circuit,
protection circuit, and protective interlock circuit for forward/reverse
operation or upper/lower limit positioning.
(2) When the programmable controller detects the following error conditions,
it stops the operation and turn off all the outputs.
• Overcurrent or overvoltage protection of the power supply module is
activated.
• The CPU module detects an error such as a watchdog timer error by
the self-diagnostics function.
All outputs may turn on when an error occurs in the part, such as I/O
control part, where the CPU module cannot detect any error. To
ensure safety operation in such a case, provide a safety mechanism
or a fail-safe circuit external to the programmable controller. For a fail-
safe circuit example, refer to Chapter 4 LOADING AND
INSTALLATION in this manual.
(3) Outputs may remain on or off due to a failure of an output module relay or
transistor. Configure an external circuit for monitoring output signals that
could cause a serious accident.
● In an output module, when a load current exceeding the rated current or an
overcurrent caused by a load short-circuit flows for a long time, it may cause
smoke and fire. To prevent this, configure an external safety circuit, such as a
fuse.
● Configure a circuit so that the programmable controller is turned on first and
then the external power supply. If the external power supply is turned on first,
an accident may occur due to an incorrect output or malfunction.
● For the operating status of each station after a communication failure, refer to
relevant manuals for the network.
Incorrect output or malfunction due to a communication failure may result in
an accident.
WARNING
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