Rockwell Automation 1440-DYN02-01RJ XM Dynamic Measurement Module - Manuel (Page 74)

74 Publication ICM-UM002F-EN-E - March 2013
Chapter 3 Configure XM Module in RSLogix 5000 Software
FFT Window Type Choose the type of window to be applied to the
waveform measurement prior to computing the
spectrum.
• Rectangular - Also know as Uniform (no window).
Use this only for transient signals that die out
before the end of the time sample, or for exactly
periodic signals within the time sample. Gives poor
peak amplitude accuracy, good peak frequency
accuracy.
• Hamming - A general purpose window that is
similar to a Hanning window. It provides better
frequency resolution but decreased amplitude
accuracy when compared to the Hanning window.
Use it to separate close frequency components.
Gives fair peak amplitude accuracy, fair peak
frequency accuracy.
• Hanning - A general purpose window that is similar
to a Hamming window. It is used on random type
data when frequency resolution is more important
than amplitude accuracy. Most often used in
predictive maintenance. Gives fair peak amplitude
accuracy, fair peak frequency accuracy.
• Flat Top - Also called Sinusoidal window. Use this
when amplitude accuracy is more important than
frequency resolution. In data with closely spaced
peaks, a Flat Top window may smear the peaks
together into one wide peak. Gives good peak
amplitude accuracy, poor peak frequency accuracy
for data with discrete frequency components.
• Kaiser Bessel - Gives fair peak amplitude accuracy,
fair peak frequency accuracy.
Number of Averages Enter the number of individual data sets to be
incorporated into the average calculation. Averaging
reduces the random errors and provides a more
reliable measurement. In asynchronous mode, the spectrum is
averaged. In synchronous mode, the time
waveforms are averaged.
Note: The averaged data is used only for
captured time waveform or FFT’s. All data
calculated from the FFT, such as bands, is
taken from each individual sample, not the
averaged sample.
In this field Values are Comments