FPΣ
Installation and Wiring
5-22
5.6 Safety Measures
This section explains the safety measures, momentary power failures and protection
of power supply and output.
5.6.1 Safety Measures
Precautions regarding system design
In certain applications, malfunction may occur for the following reasons:
Power on timing differences between the PLC system and
input/output or mechanical power apparatus
Responce time lag when a momentary power drop occurs
Abnormality in the PLC unit, external power supply, or other
devices
In order to prevent a malfunction resulting in system shutdown choose the adequates
safety measures listed in the following:
Interlock circuit
When a motor clockwise/counter-clockwise operation is controlled, provideaninterlock
circuit externally.
Emergency stop circuit
Add an emergency stop circuit externally to controlled devices in order to prevent a
system shutdown or an irreparable accident when malfunction occurs.
Start up sequence
The PLC should be operated after all of the outside devices are energized.To keep this
sequence, the following measures are recommended:
Turn on the PLC with the mode selector set to the PROG. mode,
and then switch to the RUN mode.
Program the PLC so as to disregard the inputs and outputs until
the outside devices are energized
Note
When stopping the operation of the PLC also, have the
input/output devices turned off after the PLC has stopped
operating.
Grounding
When installing the PLC next to devices that generate high voltages from switching,
such as inverters, do not ground them together. Use an exclusive ground for each
device.
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