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9 Input Wiring Procedures
74
FX3S Series Programmable Controllers
User's Manual - Hardware Edition
9. Input Wiring Procedures
DESIGN PRECAUTIONS
• Make sure to have the following safety circuits outside of the PLC to ensure safe system operation even during external power supply
problems or PLC failure.
Otherwise, malfunctions may cause serious accidents.
1) Most importantly, have the following: an emergency stop circuit, a protection circuit, an interlock circuit for opposite movements
(such as normal vs. reverse rotation), and an interlock circuit (to prevent damage to the equipment at the upper and lower
positioning limits).
2) Note that when the PLC CPU detects an error, such as a watchdog timer error, during self-diagnosis, all outputs are turned off.
Also, when an error that cannot be detected by the PLC CPU occurs in an input/output control block, output control may be
disabled.
External circuits and mechanisms should be designed to ensure safe machinery operation in such a case.
3) If an overload of the 24 V DC service power supply occurs, the voltage automatically drops, inputs in the PLC are disabled, and all
outputs are turned off.
External circuits and mechanisms should be designed to ensure safe machinery operation in such a case.
4) Note that when an error occurs in a relay or transistor output device, the output could be held either on or off.
For output signals that may lead to serious accidents, external circuits and mechanisms should be designed to ensure safe
machinery operation in such a case.
DESIGN PRECAUTIONS
• Do not bundle the control line together with or lay it close to the main circuit or power line. As a guideline, lay the control line at least
100 mm (3.94") or more away from the main circuit or power line.
Noise may cause malfunctions.
• Install module so that excessive force will not be applied to peripheral device connectors.
Failure to do so may result in wire damage/breakage or PLC failure.