Mitsubishi Electric MELSEC iQ-R Series User Manual page 4

[Design Precautions]
WARNING
● In an output circuit, 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.
● Configure a circuit so that the external power supply is turned off first and then the programmable
controller. If the programmable controller is turned off 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 manuals for the network
used. For the manuals, please consult your local Mitsubishi representative. Incorrect output or
malfunction due to a communication failure may result in an accident.
● When connecting an external device with a CPU module or intelligent function module to modify data
of a running programmable controller, configure an interlock circuit in the program to ensure that the
entire system will always operate safely. For other forms of control (such as program modification,
parameter change, forced output, or operating status change) of a running programmable controller,
read the relevant manuals carefully and ensure that the operation is safe before proceeding. Improper
operation may damage machines or cause accidents. When a Safety CPU is used, data cannot be
modified while the Safety CPU is in SAFETY MODE.
● Especially, when a remote programmable controller is controlled by an external device, immediate
action cannot be taken if a problem occurs in the programmable controller due to a communication
failure. To prevent this, configure an interlock circuit in the program, and determine corrective actions
to be taken between the external device and CPU module in case of a communication failure.
● Do not write any data to the "system area" and "write-protect area" of the buffer memory in the
module. Also, do not use any "use prohibited" signals as an output signal from the CPU module to
each module. Doing so may cause malfunction of the programmable controller system. For the
"system area", "write-protect area", and the "use prohibited" signals, refer to the user's manual for the
module used. For areas used for safety communications, they are protected from being written by
users, and thus safety communications failure caused by data writing does not occur.
● If a communication cable is disconnected, the network may be unstable, resulting in a communication
failure of multiple stations. Configure an interlock circuit in the program to ensure that the entire
system will always operate safely even if communications fail. Incorrect output or malfunction due to a
communication failure may result in an accident. When safety communications are used, an interlock
by the safety station interlock function protects the system from an incorrect output or malfunction.
● To maintain the safety of the programmable controller system against unauthorized access from
external devices via the network, take appropriate measures. To maintain the safety against
unauthorized access via the Internet, take measures such as installing a firewall.
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