Rockwell Automation 1441-DYN25-Z Dynamix 2500 Data Collector - Manual (Page 80)

80 Rockwell Automation Publication 1441-UM001B-EN-P - September 2012
Chapter 3 Setting Up Measurements
If your Maximum frequency is specified in CPM, convert CPM to Hertz using
the following formula.
Next, find the total collection time for the time waveform measurement using
this formula.
Number and Type of Averages
The number and type of averages are part of the collection specification (Setup >
Collection). See
Collection Specification Dialog Box on page 75 .
Select the collection specification when you set up the measurement definition.
The Emonitor software and the Dynamix 2500 data collector support the
following number and types of averages for data collection.
Averaging is useful for reducing random errors. Random errors include
background vibration due to some source other than the machine being
measured. If you collect more averages, you have fewer random errors. However,
collecting more averages requires more time.
Overlap processing (Percent overlap) speeds up the averaging process. The
overlap amount determines how much of the time samples are overlapped for
successive averages. The greater the overlap, the faster the sample can be collected.
The disadvantage is that the greater the overlap, the less new data there is, and the
greater the influence of random errors.
EXAMPLE If you had a Maximum frequency value of 7200 CPM and a Number of
lines value of 400, you would:
1. Convert CPM to Hz.
2. Find the total collection time.
Averages Description
Linear Up to 4096 averages.
Time Synchronous Up to 255 averages, and requires a trigger.
Exponential Up to 99 averages. Uses exponential weighting. Use for measurements on a
continuous signal that may be slowly varying. Also use to obtain a uniform
statistical error over all frequencies.
Peak Hold Up to 99 averages. Holds the highest measured value in each bin (line).
Fmax (Hz)
Fmax (CPM)
60
------------------------------- =
collection time
spectral lines
Fmax (Hz)
------------------------------- =
7200 CPM
60
-------------------------- 120 Hz =
400 lines
120 Hz
--------------------- 3.3 seconds =