Omron CJ1M-CPU21, Operation Manual

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xxvi
Application Precautions 5
• 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.
• 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.
• 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.
• 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.
The Memory Card may become unusable if the power supply is turned
OFF or the Card is removed while data is being transferred.
• Confirm that no adverse effect will occur in the system before attempting
any of the following. Not doing so may result in an unexpected operation.
• Changing the operating mode of the PLC.
• Force-setting/force-resetting any bit in memory.
• Changing the present value of any word or any set value in memory.
• Install external safety measures against short-circuiting such as circuit
breakers in external wiring. Insufficient safety measures against short-cir-
cuiting may result in burning.
• Be sure that all the terminal screws, and cable connector screws are tight-
ened to the torque specified in the relevant manuals. Incorrect tightening
torque may result in malfunction.
• Mount Units only after checking terminal blocks and connectors com-
pletely.
• Before touching a Unit, be sure to first touch a grounded metallic object in
order to discharge any static build-up. Not doing so may result in malfunc-
tion or damage.
• Be sure that the terminal blocks, Memory Units, expansion cables, and
other items with locking devices are properly locked into place. Improper
locking may result in malfunction.