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Technical Reference Manual, General
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If there are more auxiliary contacts available, an opening contact can be series
connected with the R -resistor. The shunt-resistor circuit is opened when the CB is
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closed. Therefore the supervision of the auxiliary contact is also possible.
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In order to avoid false operations due to relay faults and to maximize the overall
availability of the protection, a set of autodiagnostic circuit arrangements have been
implemented in the relay modules.
The different memory circuits, that is, the RAM and the non-volatile memories, are
continuously tested with different methods.
The microcontroller and the program execution are supervised by a watchdog once
every 100 ms.
The selector, the A/D converter and other measuring input electronics are tested by
checking a very accurate reference voltage once a minute. This is to ensure that a
measured signal is real and not caused by a fault or disturbance in some input circuit,
all to avoid false output signals.
Setting values are tested with the help of a checksum.
Furthermore, critical setting values are always checked to ensure that the values used
are within the maximum and minimum limits.
The internal supply voltages from the power supply module are tested once a minute
by measuring the voltages, +24 V, +15 V and -15 V.
The trip output paths, the output amplifiers and the output relay coils are checked
once a minute by injecting a 50
current flows through the output relay coils. Both short-circuits and open coils are
detected, since the rise time of the voltage pulse is measured.
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