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Appendix C: Algorithms
TVS600 & TVS600A Command Reference
C–33
2100,"CalculateN questionable; digital filter error - lowpass
filter cutoff invalid", or
2100,"CalculateN questionable; digital filter error -
highpass filter cutoff invalid", or
2100,"CalculateN questionable; digital filter error -
bandpass/notch filter start/stop invalid"
Note that for both major sources of error, errors are detected and reported when
the calculate block is executed, not when filter parameters are defined or when
the filter expression is defined. The errors are delayed because the sample rate
(which defines Nyquist) and record length (which sets the maximum number of
filter coefficients) may change after you define the filter parameters.
When these errors occur, the waveform analyzer CALC block copies its input
waveform to its output and performs no filtering.
Edge effects from the filter can set up to 5% of the data on either end of the
filtered record to NULL values: ASCII, 9.910000E+37 or binary, IEEE NAN. If
you are going to filter the data, make sure all acquisitions have a sufficient
number of points on either side of the data of interest.
If you apply a filter to a set of data and get an error, you can either specify a filter
with less stringent specifications or you acquire the data a second time using a
longer record length. The maximum length of the filter is 10% of the data record,
so if you use a longer record you have more points available in the filter and you
can use a higher specified filter.
To increase the number of points in your data, use the same sample rate but a
longer record length. See the commands SWEep:POINts and SWEep:TIME to
set the record length. Make sure you acquire additional points before and after
the data of interest. Do not try to obtain more points in your data record by
simply increasing the sampling rate. Increasing the sampling rate provides more
points but it also increases the Nyquist sampling rate which can make the desired
filter more difficult to achieve.
General Guidelines