
Rockwell Automation Publication 1440-UM001D-EN-P - September 2016
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Configure the XM-124 Standard Dynamic Measurement Module
Chapter 2
Frequency Maximum
The maximum frequency or order for the spectrum measurement.
The sampling mode determines whether the frequency
maximum is specified in Hz or orders. It also determines
whether you enter a value or choose a value from a list of
available values:
• If sampling mode is synchronous with tach, enter the
Frequency Maximum value. The frequency maximum
range for Synchronous sampling mode is 4…200 orders.
• If sampling mode is Asynchronous, choose the Frequency
Maximum value. Note you can enter a specific value if you
choose 10…5000 range. Supported maximum
asynchronous frequencies are dependent on sensitivity
units and full scale units you choose on the Channel tab.
When integrating, the Maximum Frequency is not always set
greater than the analog LPF that is applied to all integrating
measurements.
Number of Spectrum Lines
Choose the number of lines (bins) in the spectrum measurement:
• 100
• 200
• 400
• 800
• 1600
This number determines the frequency resolution of the
spectrum measurement.
IMPORTANT: When sampling mode is Synchronous, the
Number of Spectrum Lines must be evenly divisible by the
Frequency Maximum value (no remainder).
Period
Displays the total period of the waveform measurement in seconds.
Samples are accumulated into a time waveform of this duration before an
FFT is performed on the collected data. Period is provided to show the
effect various settings, such as Number of Spectrum Lines, have on the
update rate of measurements (Band and Vector) derived from the
spectrum.
The value is in seconds when sampling mode is set to
Asynchronous. The value is in cycles when sampling mode is
set to Synchronous.
Order of Sum Harmonics
Choose the starting order for the sum harmonics measurement:
• 1
• 2
• 3
• 4
• 5
The amplitudes of all harmonics from the specified harmonic
through the Frequency Maximum are included in the sum.
IMPORTANT: The sum harmonics measurement requires the
tachometer to be enabled (Pulses Per Revolution is set to 1 or
more), and a tachometer signal must be present.
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 excludes phase information.
See the description of the Spectrum/Waveform object’s
for more information.
FFT Window Type
Choose the type of window to be applied to the waveform measurement
before computing the spectrum:
• Rectangular - Also known as Uniform (no window). Use rectangular
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 flat top when amplitude
accuracy is more important than frequency resolution. A Flat Top
window can smear the peaks together into one wide peak, in data
with closely spaced peaks. 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.
Table 10 - Spectrum/Waveform Measurement parameters (Continued)
In this field
Values are
Comments
Summary of Contents for 1440-SDM02-01RA
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