Appendix 9 General Safety Requirements - Mitsubishi Electric Q26UD(E)HCPU User Manual

Appendix 9
When the programmable controller is powered on and off, normal control output may not be done momentarily due to
a delay or a start-up time difference between the programmable controller power supply and the external power supply
(DC in particular) for the control target.
For example, if the external power supply for the controlled object is switched on in a DC output module and then the
programmable controller power supply is switched on, the DC output module may provide false output instantaneously
at power-on of the programmable controller. Therefore, it is necessary to make up a circuit that can switch on the
programmable controller power supply first.
Also, malfunction may occur if an external power supply or the programmable controller is faulty.
To prevent any malfunction which may affect the whole system and in a fail-safe viewpoint, provide an external circuit
to the areas which can result in machine breakdown and accidents (e.g. emergency stop, protective and interlock
circuits) must be constructed outside the programmable controller.
The following page gives examples of system designing in the above viewpoint.
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General Safety Requirements