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Fail-safe Circuits Section 5-1
An external relay (CR1) is connected to the RUN output from the Power Sup-
ply Unit as shown in the following diagram.
Note When a Power Supply Unit without a RUN output is used, program the Always
ON Flag (A1) as the execution condition for an output point from an Output
Unit.
Interlock Circuits When the PLC controls an operation such as the clockwise and counterclock-
wise operation of a motor, provide an external interlock such as the one
shown below to prevent both the forward and reverse outputs from turning ON
at the same time.
This circuit prevents outputs MC1 and MC2 from both being ON at the same
time even if both CIO 000500 and CIO 000501 are both ON, so the motor is
protected even if the PLC is programmed improperly or malfunctions.
MCB1
MCB2
CR1
+
–
DC
PLC RUN
output*
input/output
CR1
CJ-series PLC
Power supply
Controlled system
DC voltage
regulator
Surge suppressor
Twisted-pair wires
Transformer
or noise filter
PLC
MC2
MC1
000501
000502
MC1
MC2
Interlock circuit
Motor clockwise
Motor counterclockwise
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