Vaisala GMP343 - Manual (Page 43)

Chapter 4 ________________________________________________________________ Operation
VAISALA_______________________________________________________________________ 41
Measurement Data Filtering
The raw measurement values (measurement interval = 2 seconds) are an
input to a chain of three filters: a median, an averaging, and a smoothing
filter. The filters can be individually enabled or disabled by setting the
filter coefficient to 0 (zero) or by choosing CO
2
RAW instead of CO
2
for
the measurement output quantity (see FORM command).
Figure 8 Entering Measurement Values
Median Filter
Median filter is the first section in the filter chain, removing random peak
values caused by external interference. The output of the median filter is
the moving median of the values over the set number of measurements.
The median filter arranges the values in the order of magnitude and outputs
the middle value (not the average) if the number of the measurements is
odd. In case an even number is set, the output is the average of the two
middlemost measurements.
The lowest reasonable set number of measurements is 3. Note that if the
noise distribution is somewhat uniform the median filter does not give any
additional value.
The number of the measurements is set by the MEDIAN command.
Maximum number of measurements is 13. The default value is 0 (meaning
that the median filter is disabled).