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Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 4
Measurement Definition
For standard dynamic channels, the dynamic measurement module calculates
FFT bands from a unique FFT that is calculated specifically for the band
measurements. This calculation enables optimization of the definition of the
FFT bands for this purpose. It provides a higher-performance solution than the
common FFT or gSE FFT measurement by configuring the band
measurements to update faster in most cases.
This page is presented when the channel is configured for dynamic or Spike
Energy (gSE) measurements (see Channel Type selection,
).
Number of Averages
Select from:
• 1
• 2
• 3
• 6
• 12
• 23
• 45
• 89
• 178
Select the number of averages for the FFT that is used in FFT Band measurements.
• When averaging, the individual FFTs are updated as quickly as possible. How
fast this update occurs is dependent on the overall processing demands on the
module, which is a function of the module configuration and, to some degree,
the circumstance of the moment. This, along with the fact that the waveforms
are always captured without respect to an overlap requirement (so always
“max overlap”), makes it impossible to define precisely how long (in time) it
takes to acquire any specific number of samples that are used in the average.
• Averaging is Exponential, meaning that once the specified number of samples
has been acquired that the averaged sample (result) is available, for FFT Bands
to be calculated, upon each subsequent update.
Band 0…7 Enable
Enable (checked) / Disabled (not checked)
Check the box if the FFT Band (0…7) is calculated from this channel.
The module (object) lets you define any of the 32 total bands to any channel. So
the “Channel Source” attribute specifies to the module on which channel this
band processes from (or = -128 if unused/disabled). The AOP however simply
applies eight bands per channel and automatically associates (when Enabled) the
bands to their respective channels.
Band 0…7 Measurement
Mode
Select from:
• Band Overall
• Band maximum pk
• Freq of Band maximum pk
Select the type of measurement to be provided by the band.
• Band Overall: Returns the calculated RMS value of the band.
• Band maximum pk: Returns the magnitude of the bin with the highest
amplitude within the band. This value is in Peak, Peak-to-Peak, or RMS value
as defined by the signal detection that is defined for the bands FFT.
• Freq of Band maximum pk: Returns the frequency (in Hz) of the bin that
contains the highest amplitude within the band.
Band 0…7 Band Limit
Begin and End
1. Begin limit must be less than the end limit.
2. The end limit is the value of FMAX presented at the top of the page.
3. If the calculated FFT bin for the band begin is greater than the processed FFT
FMAX, then the band returns a 0.0.
4. Based on selected samples per rev.
Band 0…7 Domain
Select from:
• Hz
• Orders
Select the domain that the limits are entered in.
If set to order domain, then begin and end limits are calculated with each sample.
Band 0…7 Speed
Reference
Select from:
• OFF
• Speed 0
• Speed 1
• Factored Speed 0
• Factored Speed 1
Select the source for the speed to be used in the band limit calculation if Do main
= Orders.
See the
for further information on speed sources.
Table 32 - Bands (continued)
Parameter
Values
Comments
Mode for
Selected Data
Source
Band
Domain
Begin
Limit
1
End Limit
2
Asynchronous
Hz
0.1
Selected FMAX
Order
0.5
40000
3
Synchronous
Hz
0.1
ADC-out FMAX
3
Order
0.5
Selected Orders
4