Self-Supervision; 10.Calibration - ABB REF 54 Series Technical Reference Manual, General

1MRS750527-MUM
5.1.9.9.
5.1.9.10.
Feeder Terminal
Technical Reference Manual, General

Self-supervision

Each input sample is validated before it is fed into the filter algorithm. The samples
are validated by measuring an internally set reference voltage immediately after the
inputs are sampled. If the measured offset voltage deviates from the set value more
than 1.5% of the measuring range, the sample is discarded. If the fault continues
longer than for the set filter time, the invalid attributes of all inputs are set to TRUE
to indicate a hardware fault. Should the measurement succeed later, the invalid
attributes are reset to FALSE. This prevents most sudden hardware faults from
affecting the measured value before the invalid attribute is set. To ensure that the
specified measurement accuracy is met, a more thorough test of the hardware is
performed by the continuous recalibration procedure which will catch errors that
degrade the measurement accuracy.
Calibration
The RTD/analog module is calibrated at the factory. To be able to maintain the
specified accuracy in spite of aging and varying temperature, the card also includes
special hardware to allow self-recalibration on the field. This recalibration
procedure runs continuously, even when no measurements are activated, to ensure
that the card is always optimally calibrated. If the recalibration procedure fails, the
reason is a hardware failure. In this case the card's measurement accuracy is no
longer obtained, and the invalidity attributes of all inputs are set to TRUE. However,
the card continues updating the measured input values, and if the invalidity attributes
are not used in the feeder terminal configuration, the situation could go unnoticed.
Should the recalibration succeed later, the invalidity attributes return to normal
operation.
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