Casestudie Breakdown prediction Contell PILOT - Transumo

S
o
n
2
= ∑ Yi
−Yi
n −1
i=
2
−1
with :
S
o
= Outlier threshold value
Y = Measurement values
n = Number of measurement values
Formula 4-1: Threshold Value to Determine Potential Outliers
But an ignorance of every measurement value with a higher distance than S o would
lead to a neglecting of trends and other changes in behavior. That is why the number
of outliers in a row is counted. Every possible outlier is set to the current mean value
as long as less than three values in a row are classified to be outliers. In case of
three or more values in a row, no further elimination will take place. (Daßler95] p. 54-
55)
This approach is able to cut off single outliers. The only disadvantage is a delay of
trend recognition that is pictured in Figure 4-2. The green points represent the
measured values with an existing change in trend. The red points illustrate the delay
of trend recognition, because the first two higher values are classified as outliers and
set to mean value. (Daßler95] p. 55)
Figure 4-2: A Delayed Trend Recognition Due to Removal of "Outliers"
After eliminating outliers, the measurement data is stored to a ring memory. This kind
of memory has a fixed size. As soon as no sufficient memory is available to add an
additional measuring point, the oldest value is overridden. This organization is used
to avoid a high influence by too old values. The size of this ring memory is not
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