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[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. Incorrect output or malfunction
due to a communication failure may result in an accident.
(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 the output status is as follows:
• If the overcurrent or overvoltage protection of the power supply
module is activated, all outputs are turned off.
• If the self-diagnostics function of the head module detects an error
such as a watchdog timer error, all outputs are held unchanged or
turned off according to the parameter setting.
All outputs may turn on if an error occurs in a part, such as an I/O control
part, where the head 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 this manual.
(3) Outputs may remain on or off due to a failure of an output circuit relay or
transistor. 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.
WARNING
2
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