ABB S800 I/O User Manual page 108

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Hardware and software in a S800 I/O system is provided with supervision against
system faults.
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Sometimes, you lack the information from the controller diagnostics, that tells you
where the fault is located. Suspicion about a fault is raised by the process behavior.
Experience indicates that approximately 85% of all faults occur in the process, 10%
in the control program and 5% in the control system hardware.
It is always advisable to localize the malfunction with these figures in mind to
minimize the down-time.
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In an electronics system which has given satisfactory service, most malfunctions
have external causes. It is therefore important, when tracing a fault, to determine if
any external factor such as incorrect handling of the equipment, short circuits,
welding work, lightning strike and/or power failure has caused the malfunction.
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– Green LED, RUN, indicates normal function.
– Yellow LED indicates an active signal, for example, status of digital input
(DI) or digital output (DO), OSP and Warning
– Red LED, FAULT, indicates malfunction
3BSE 020 923R101