Mitsubishi Electric MELSEC iQ-R Series Migration Manual page 4

[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) Emergency stop circuits, protection circuits, and protective interlock circuits for conflicting
operations (such as forward/reverse rotations or upper/lower limit positioning) must be
configured external to the programmable controller.
(2) When the programmable controller detects an abnormal condition, it stops the operation and
all outputs are:
• Turned off if the overcurrent or overvoltage protection of the power supply module is
activated.
• Held or turned off according to the parameter setting if the self-diagnostic function of the CPU
module detects an error such as a watchdog timer error.
(3) All outputs may be turned on if an error occurs in a part, such as an 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 "General Safety Requirements" in the MELSEC iQ-R Module
Configuration Manual.
(4) Outputs may remain on or off due to a failure of a component such as a relay and transistor in
an output circuit. Configure an external circuit for monitoring output signals that could cause a
serious accident.
●
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.
●
For the operating status of each station after a communication failure, refer to manuals relevant to
the network. 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.
●
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.
WARNING
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