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Table 30 - FFT (continued)
Parameter
Values
Measurement
Select from:
Units
• inch/s
• m/s
• mm/s
Speed Reference
Select from:
• Speed 0
• Speed 1
• Factored Speed 0
• Factored Speed 1
Number of
Select from:
Averages
• 1
• 2
• 3
• 6
• 12
• 23
• 45
• 89
• 178
Average TWF
Enable (checked) / Disabled (not
checked)
Comment
Select the engineering units for the TWF and FFT.
The rules for units selection, which are based on the transducer units (see the HW Configuration properties page),
are provided in this table.
CLASS
Temperature
Bearing Defect Units
Pressure
Flow
Current
Frequency
Power
Voltage
Acceleration
Velocity
Length
For any acceleration, velocity or displacement (length) units, the module can convert the measurement between
equivalent Metric and English units.
Displacement
m
mm
│
micron
inch
mil
Select the reference speed source.
When TWFs and FFTs are read from the module, the value of this RPM is included with the data.
Select the number of averages for the FFT or TWF (see Average TWF later in this topic).
• If you select Average TWF, the module performs in the average time domain (available when you define the
measurement to use synchronous sampling). Otherwise the module performs with an average on the linear
FFT data.
• When averaging, the module updates the individual TWFs (and FFTs) as quickly as possible. How fast updating
occurs depends on the overall processing demands on the module, which is a function of the module
configuration and the current load. This factor, along with the fact that the module always captures TWFs with
maximum overlap, makes it impossible to define precisely how long (in time) it takes for the module to
acquire any specific number of samples to use in the averaging.
• Averaging is exponential. Once the module has acquired the specified number of samples, then the averaged
sample (result) is available after each subsequent update.
Select the checkbox to perform the averaging in the time domain (on the TWFs). The module can average time
waveforms only if they are synchronously sampled. Set the Signal Source to Alternate Path, and set the Alternate
Path Processing Mode to Synchronous.
Clear the checkbox to average the FFTs instead of the TWFs.
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
CHANGE EU OPTION
No change allowed
Change in class only
Velocity
Acceleration
2
m/s
m/s
2
mm/s
mm/s
2
│
inch/s
inch/s
g
mg
Measurement Definition
Chapter 4
147
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