Casestudie Breakdown prediction Contell PILOT - Transumo

Moreover, the fridge’s filling level can vary the cooling-down time, so that form and
shape of the corresponding temperature sequence changes, although the technical
condition remains the same.
Beside these general existing sources of error, the current practice is faced with
additional problems that originate from the currently applied method, which was
introduced in section 2.3.
2.4.3 Methodological Problems
The presented graphs within section 2.2 already exemplified many different
behaviors of fridges and freezers. These examples were chosen to show the difficulty
of an accurate classification of different kinds of behavior as normal operation or
malfunction.
The currently applied method to predefine critical temperature limits only allows a
classification that is based on the actual temperature value. 9 Hence, as soon as
temperature rises above the predefined maximum or falls below the predefined
minimum, the cooling device is classified as malfunctioning. This method could
indicate a bad technical condition of a fridge. But due to the lack of information and
other possible error sources, it is impossible to prove a malfunction by using this
method.
Since an error of second kind has to be avoided in any case, H 0 has to be rejected
every time, temperature limits are exceeded. This leads to a very high number of
errors of first kind, because of the very low probability of a real technical
malfunction. 10
Beside this high number of false alarms, another methodological problem does exist.
As mentioned in section 2.2.5, most malfunctions occur slightly, so that they could be
recognized before temperature is exceeded. Such a change in form and shape of a
temperature sequence is not recognized by the current method. Hence, situations
like that lead to an error of second kind because H 0 is accepted, although the system
starts to malfunction.
Also the required recognition of changes in behavior on the long-run is only possible
to some extent with the existing method. Typically, a change is bound to significant
9 See section 2.3 for details
10 See section 2.2.5 for details
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