Appendix 9 General Safety Requirements - Mitsubishi Electric MELSEC-L SSCNETIII/H User Manual

Appendix 9
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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General Safety Requirements