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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 a total network 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.
(1) Fail-safe measures against failure of head module
The self-diagnostic function can detect failure of the head module.
However, if an error occurs in an area such as I/O control part, the
head module may not detect failure.
In this case, all points may turn on or off depending on the failure,
and normal operation and safety cannot be ensured.
Although Mitsubishi programmable controllers are manufactured
under strict quality control, it is recommended to configure external
fail-safe circuits to prevent mechanical damage or accidents due to
failure of the programmable controller.
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