General Safety Requirements - Mitsubishi Electric LCPU-U-HW Safety Manuallines

5. GENERAL SAFETY REQUIREMENTS

When a programmable controller is powered on or off, proper output of
the control target may not function temporarily due to delay and startup
time differences between the power supply for the programmable
controller and the external power supply for the control target
(especially in the case of DC). Also, an abnormal operation may occur if
an external power supply or the programmable controller fails.
From the point of view of fail-safe circuit and to prevent any of these
abnormal operations from leading to the entire system failure, configure
external fail-safe circuits (an emergency stop circuit, protection circuit,
and interlock circuit) in the areas where incorrect operation can result in
mechanical damage or accidents.
This chapter shows a circuit example of system designs.
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