Please design protection circuit at the external of PLC for entire system to operate safely because an
abnormal output or an malfunction may cause accident when any error of external power or malfunction
of PLC module.
(1) It should be installed at the external side of PLC to emergency stop circuit, protection circuit, interlock
circuit of opposition action such as forward /reverse operation and interlock circuit for protecting machine
damage such as upper/lower limit of positioning.
(2) If PLC detects the following error, all operation stops and all output is off.
(Available to hold output according to parameter setting)
(a) When over current protection equipment or over voltage protection operates
(b) When self diagnosis function error such as WDT error in PLC CPU occurs
In case of error about IO control part that is not detected by PLC CPU, all output is off.
Design Fail Safe circuit at the external of PLC for machine to operate safely. Refer to 12.2 Fail Safe
circuit.
(1) Because of error of output device, Relay, TR, etc., output may not be normal. About output signal that
may cause the heavy accident, design supervisory circuit to external.
In case load current more than rating or over current by load short flows continuously, danger of heat, fire
may occur so design safety circuit to external such as fuse.
Design for external power supply to be done first after PLC power supply is done. If external power
supply is done first, it may cause accident by misoutput, misoperation.
In case communication error occurs, for operation status of each station, refer to each communication
manual.
In case of controlling the PLC while peripheral is connected to CPU module, configure the interlock circuit
for system to operate safely. During operation, in case of executing program change, operation status
change, familiarize the manual and check the safety status. Especially, in case of controlling long
distance PLC, user may not response to error of PLC promptly because of communication error or etc.
Limit how to take action in case of data communication error between PLC CPU and external device
adding installing interlock circuit at the PLC program.
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