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4-27
Supporting Functions
Self Supervision
The functions of the micro controller and the associated circuitry, as
well as the program execution are supervised by means of a separate
watchdog circuit. Besides supervising the device, the watchdog
circuit attempts to restart the micro controller in a fault situation. If
the restarting fails, the watchdog issues a self-supervision alarm
indicating a permanent internal fault.
When the watchdog circuit detects a permanent fault, it always
blocks any control of other output relays (except for the self-
supervision output relay).
In addition, the internal supply voltages are supervised. Should the
auxiliary supply of the device disappear, an alarm is automatically
given because the internal fault (IF) output relay functions on a
working current principle. This means that the IF relay is energized
when the auxiliary supply is on and no internal fault is detected.
Diagnostics
The device runs self-diagnostic tests for hardware and software in
every boot sequence and also performs runtime checking.
Fatal Errors
If fatal error has been detected, the device releases IF relay contact
and error led is set on. Local panel will also display an error message
about the detected fault. Fatal error state is entered when the device
is not able to handle protections.
Runtime Errors
When self-diagnostic function detects a fault, Selfdiag Alarm matrix
signal is set and an event (E56) is generated. In case the error was
only temporary, an off event is generated (E57). Self diagnostic error
can be reset via local panel interface.
Error Registers
There are four 16-bit error registers which are readable through
remote protocols. The following table shows the meaning of each
error register and their bits.
857-UM001A-EN-P – July 2009
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