FP2/FP2SHInstallation and Wiring4 − 364.6 Safety Measures4.6 Safety Measures4.6.1 Safety InstructionsPrecautions Regarding System DesignIn certain applications, malfunction may occur for the following reasons:Power on timing differences between the PLC system and I/O or motorized devicesAn operation time lag when a momentary power failure occursAbnormality in the PLC, external power supply, or other devicesIn order to prevent a malfunction resulting in system shutdown choose the adequatessafety measures listed in the following:Interlock circuitWhen a motor clockwise/counter-clockwise operation is controlled, provide an interlockcircuit that prevents clockwise and counter-clockwise signals from inputting into the mo-tor at the same time.Emergency stop circuitAdd an emergency stop circuit to controlled devices in order to prevent a system shut-down or an irreparable accident when malfunction occurs.Start up sequenceThe PLC should be operated after all of the outside devices are energized. To keep thissequence, the following measures are recommended:Turn on the PLC with the mode selector set to the PROG. mode, and then switch to theRUN mode.Program the PLC so as to disregard the inputs and outputs until the outside devices areenergized.NoteWhen stopping the operation of PLC also, have the I/O devicesturned off after the PLC has stopped operating.Alarm functionWhen an alarm occurs, the PLC turns off the output and stops operation. Even whilein this condition, take the appropriate safety precautions outside of the PLC to ensureno malfunction or damage is transmitted to anywhere else in the system.GroundingWhen installing the PLC next to devices that generate high voltages from switching,such as inverters, do not ground them together.
