User`s manual
Safety guidelines Installation
MELSEC System Q, Hardware 9 – 1
9 Installation
9.1 Safety guidelines
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 con-
troller 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 mod-
ule 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.
Malfunction may occour 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. emer-
gency stop, protective and interlock circuits) must be constructed outside the programmable
controller.
The following page give examples of system designing in the above viewpoint.
P
DANGER:
● Outputs may remain on or off due to a failure of an output module relay or transistor.
Configure an external circuit for monitoring output signals that could cause a
serious accident.
● In an output module, when a load current exceeding the rated current or an
overcurrent caused by a load short-circuit flows for a long time, it may cause smoke
and fire. To prevent this, configure an external safety circuit, such as a fuse.
● Malfunction may occour 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.