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Appendix A
HMI Function Reference
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A-25
Historical Trend Statistics
Use the Historical Trend Statistics VI to compute statistical data for a historical trend.
Statistics include minimum value, maximum value, average and standard deviations. The
statistics skip invalid input points (where value = NaN). The average and standard deviation
are weighted according to the time duration of each valid input point. The last point in the
historical trend is not included in the average and standard deviation because the time interval
associated with it is unknown.
Statistics include minimum value, maximum value, average and standard deviations. The
statistics skip invalid input points (where value = NaN). The average and standard deviation
are weighted according to the time duration of each valid input point. The last point in the
historical trend is not included in the average and standard deviation because the time interval
associated with it is unknown.
historical trend is the tag trend data upon which statistics are computed.
timestamp is the date and time for the value.
value is the value of the tag at the timestamp.
time ON (ETM) is the amount of time for which data has known values in
the trend. It is roughly the same as the amount of time historical logging
was turned on for the tag.
the trend. It is roughly the same as the amount of time historical logging
was turned on for the tag.
Qual is the ratio of time the trend has known values to the total time elapsed
in the trend.
in the trend.
max value is the maximum value in the historical trend. This output
ignores invalid points (value = NaN).
ignores invalid points (value = NaN).
min value is the minimum value in the historical trend. This output ignores
invalid points (value = NaN).
invalid points (value = NaN).
average is the average for the values in the historical trend. This is a
weighted average. Each point is weighted according to its time duration.
average ignores time intervals with invalid points (value = NaN). The last
point in the trend is not included in average, because there is no known
time interval associated with it.
weighted average. Each point is weighted according to its time duration.
average ignores time intervals with invalid points (value = NaN). The last
point in the trend is not included in average, because there is no known
time interval associated with it.
std dev is the standard deviation for values in the historical trend. This is a
weighted standard deviation. Each point is weighted according to its time
duration. Std dev ignores time intervals with invalid points (value = NaN).
weighted standard deviation. Each point is weighted according to its time
duration. Std dev ignores time intervals with invalid points (value = NaN).