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3 Installation and Wiring
NA-series Programmable Terminal Hardware User’s Manual (V117)
3-2 Fail-safe Measures
3
3-2-1 Power ON Sequence
3-2 Fail-safe Measures
We recommend the following sequence for turning ON the power supplies.
(1) Ethernet switches and other network devices
(2) Connected devices
(3) NA Unit
If you turn ON the power supply to the connected device after you turn ON the power supply to the NA
Unit, an error may occur depending on system settings.
It takes up to approximately 30 seconds for execution of the HMI project to start after the power
is turned ON. External communications are also not performed during this period. Implement
fail-safe measures so that connected devices do not operate incorrectly, including measures to
check the execution of the HMI project.
Provide safety measures in external circuits to ensure safety in the system if an abnormality
occurs due to malfunction of the NA Unit or due to other external factors affecting operation.
Not doing so may result in serious accidents due to incorrect operation.
The circuits associated with safety measures, such as emergency stop circuits, interlock cir-
cuits, and limit circuits, must be provided in external control circuits.
External safety measures must be provided to ensure the safe operation of the system from
when the power supply is turned ON until execution of the project starts.
Unintended operation may occur when an error occurs in memory or other data. As a counter-
measure for such problems, external safety measures must be provided to ensure safe oper-
ation of the system.
Provide measures in the communications system and in the user program to ensure safety in
the overall system even if errors or malfunctions occur.
You must implement fail-safe measures to provide sufficient protection in the event that abnor-
mal signals or problems occur as the result of broken signal lines or momentary power inter-
ruptions. Not doing so may result in serious accidents due to incorrect operation.
3-2-1 Power ON Sequence
WARNING
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