Safety Precautions - Omron DEVICENET Operation Manual

Safety Precautions

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Safety Precautions

!WARNING
!WARNING
!WARNING
!WARNING
!Caution Execute online edit only after confirming that no adverse effects will be
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Never attempt to disassemble any Units while power is being supplied. Doing
so may result in serious electrical shock or electrocution.
Make sure that the current or voltage input to the Unit is within the specified
ranges. Using a current or voltage outside of the specified range may result in
damage or fire.
Provide safety measures in external circuits (i.e., not in the Programmable
Controller), including the following items, to ensure safety in the system if an
abnormality occurs due to malfunction of the PLC or another external factor
affecting the PLC operation. Not doing so may result in serious accidents.
1. Emergency stop circuits, interlock circuits, limit circuits, and similar safety
measures must be provided in external control circuits.
2. The PLC will turn OFF all outputs when its self-diagnosis function detects
any error or when a severe failure alarm (FALS) instruction is executed. Ex-
ternal safety measures must be provided to ensure safety in the system in
case an error or FALS instruction causes all outputs to be turned OFF.
3. The PLC outputs may remain ON or OFF due to fusing or burning of the
output relay contacts or destruction of the output transistors. External safe-
ty measures must be provided to ensure safety in the system in case the
outputs fail and remain ON or OFF.
4. When the 24-V DC output (service power supply to the PLC) is overloaded
or short-circuited, the voltage may drop and result in the outputs being
turned OFF. External safety measures must be provided to ensure safety
in the system in case of a power supply problem that causes outputs to be
turned OFF.
The PLC's CPU Unit continues I/O refreshing even when the program is not
being executed (in PROGRAM mode). Before proceeding with any of the fol-
lowing operations, verify that it is safe to do so in case the operation changes
the status of output bits allocated to Output Units or the data allocated to Spe-
cial I/O Units or CPU Bus Units. It is possible for a load connected to an Out-
put Unit, Special I/O Unit, or CPU Bus Unit to operate unexpectedly.
• Using a Programming Device (Support Software in a personal computer)
to transfer data to the CPU Unit's I/O memory area.
• Using a Programming Device to change present values
• Using a Programming Device to force-set or force-reset bits
• Transferring an I/O memory file to the CPU Unit from EM file memory
• Transferring I/O memory from another PLC or host computer in the net-
work
caused by extending the cycle time. Otherwise, the input signals may not be
readable.
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