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Application Precautions 5
• Always turn ON power to the PLC before turning ON power to the control
system. If the PLC power supply is turned ON after the control power sup-
ply, temporary errors may result in control system signals because the
output terminals on DC Output Units and other Units will momentarily turn
ON when power is turned ON to the PLC.
• Fail-safe measures must be taken by the customer to ensure safety in the
event that outputs from Output Units remain ON as a result of internal cir-
cuit failures, which can occur in relays, transistors, and other elements.
• Fail-safe measures must be taken by the customer to ensure safety in the
event of incorrect, missing, or abnormal signals caused by broken signal
lines, momentary power interruptions, or other causes.
• Interlock circuits, limit circuits, and similar safety measures in external cir-
cuits (i.e., not in the Programmable Controller) must be provided by the
customer.
• Do not turn OFF the power supply to the PLC when data is being trans-
ferred. In particular, do not turn OFF the power supply when reading or
writing a Memory Card. Also, do not remove the Memory Card when the
BUSY indicator is lit. To remove a Memory Card, first press the memory
card power supply switch and then wait for the BUSY indicator to go out
before removing the Memory Card.
• If the I/O Hold Bit is turned ON, the outputs from the PLC will not be
turned OFF and will maintain their previous status when the PLC is
switched from RUN or MONITOR mode to PROGRAM mode. Make sure
that the external loads will not produce dangerous conditions when this
occurs. (When operation stops for a fatal error, including those produced
with the FALS(007) instruction, all outputs from Output Unit will be turned
OFF and only the internal output status will be maintained.)
• The contents of the DM, EM, and HR Areas in the CPU Unit are backed
up by a Battery. If the Battery voltage drops, this data may be lost. Provide
countermeasures in the program using the Battery Error Flag (A40204) to
re-initialize data or take other actions if the Battery voltage drops.
• Always use the power supply voltages specified in the operation manuals.
An incorrect voltage may result in malfunction or burning.
• Take appropriate measures to ensure that the specified power with the
rated voltage and frequency is supplied. Be particularly careful in places
where the power supply is unstable. An incorrect power supply may result
in malfunction.
• Install external breakers and take other safety measures against short-cir-
cuiting in external wiring. Insufficient safety measures against short-cir-
cuiting may result in burning.
• Do not apply voltages to the Input Units in excess of the rated input volt-
age. Excess voltages may result in burning.
• Do not apply voltages or connect loads to the Output Units in excess of
the maximum switching capacity. Excess voltage or loads may result in
burning.
• Separate the line ground terminal (LG) from the functional ground termi-
nal (GR) on the Power Supply Unit before performing withstand voltage
tests or insulation resistance tests. Not doing so may result in burning.
• Install the Units properly as specified in the operation manuals. Improper
installation of the Units may result in malfunction.
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