Rockwell Automation 1440-SDM02-01RA XM-124 Standard Dynamic Measurement Module - Manuel (Page 70)

70 Rockwell Automation Publication 1440-UM001C-EN-P - May 2014
Chapter 2 Configure the XM-124 Standard Dynamic Measurement Module
Data Format Choose complex or magnitude data format. Complex data includes phase information but takes longer to
upload and requires more conversions before plotting.
Magnitude data is half the size and requires fewer
conversions before plotting but does not include phase
information.
See the description of the Spectrum/Waveform object’s
Get_Spectrum_Chunk/Get_Waveform_Chunk service for
more information.
FFT Window Type Choose the type of window to be applied to the waveform measurement
prior to computing the spectrum:
• Rectangular - Also known 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.
Important: The averaged data is used only for captured time
waveform or FFTs. All data calculated from the FFT, such as
bands, is taken from each individual sample, not the
averaged sample.
Tachometer Rotations Enter the number of teeth on the buried shaft gear. Set the value between 1…65,535.
Rotor Rotations Enter the number of teeth on the external shaft gear. These parameters are dimmed in asynchronous sampling.
Gear Ratio Displays the relationship between the Tachometer Rotations and the
Rotor Rotations parameters.
The Tachometer Rotations and Rotor Rotations are used to convert the
speed measured by the speed sensor to a shaft speed that is related by
this gear ratio. This is useful when the shaft of interest does not have a
speed sensor of its own.
When a gear ratio is configured, the synchronous measurements are
synchronized with the rotation of the buried (internal) shaft. This
includes the Vector, Not 1X, Sum Harmonics, and order-based Band
measurements. Synchronous averaging is also synchronized with the
internal shaft. However, the Speed measurement is not affected by the
gear ratio. The Speed measurement always reflects the speed of the
shaft with the speed sensor (raw tachometer speed divided by number
of pulses per revolution).
This parameter applies only to synchronous sampling.
In this field Values are Comments