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xxiii
Safety Precautions 3
!WARNING Provide safety measures in external circuits (i.e., not in the Programmable
Controller), including the following items, to ensure safety in the system if an
abnormality occurs due to malfunction of the PLC or another external factor
affecting the PLC operation. Not doing so may result in serious accidents.
• Emergency stop circuits, interlock circuits, limit circuits, and similar safety
measures must be provided in external control circuits.
• The PLC will turn OFF all outputs when its self-diagnosis function detects
any error or when a severe failure alarm (FALS) instruction is executed.
As a countermeasure for such errors, external safety measures must be
provided to ensure safety in the system.
• The PLC outputs may remain ON or OFF due to deposits on or burning of
the output relays, or destruction of the output transistors. As a counter-
measure for such problems, external safety measures must be provided
to ensure safety in the system.
• When the 24-V DC output (service power supply to the PLC) is over-
loaded or short-circuited, the voltage may drop and result in the outputs
being turned OFF. As a countermeasure for such problems, external
safety measures must be provided to ensure safety in the system.
!Caution Execute online editing only after confirming that no adverse effects will be
caused by extending the cycle time. Otherwise, the input signals may not be
readable.
• Emergency stop circuits, interlock circuits, limit circuits, and similar safety
measures must be provided in external control circuits.
!Caution Fail-safe measures must be taken by the customer to ensure safety in the
event of incorrect, missing, or abnormal signals caused by broken signal lines,
momentary power interruptions, or other causes. Serious accidents may
result from abnormal operation if proper measures are not provided.
!Caution Confirm safety at the destination node before changing or transferring to
another node the contents of a program, the PLC Setup, I/O tables, or I/O
memory. Changing or transferring any of these without confirming safety may
result in injury.
!Caution Tighten the screws on the terminal block of the AC Power Supply Unit to the
torque specified in the operation manual. The loose screws may result in
burning or malfunction.