Rockwell Automation 441-PEN25 Enpac Ex Data Collector - Manual (Page 48)

Publication GMSI00-UM001A-EN-E - February 2005
42 Setting Up Measurements
Measurement Window Types
The measurement window type is part of the collection specification (Setup >
Collection). See Figure 3.4 on page 40. You select the collection specification
when you set up the measurement definition.
Emonitor and the Enpac Ex support the following measurement window
types. In general, the Hanning measurement window provides the best
compromise of frequency and amplitude accuracy for most predictive
maintenance measurements.
• Hanning - A general purpose window to use on random type data
when frequency resolution is more important than amplitude accuracy.
Use this setting for most of your machinery monitoring activities.
• Rectangular - The data collector does not apply a 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.
• Flattop - Use this when amplitude accuracy is more important than
frequency resolution. In data with closely spaced peaks, a Flattop
window may smear the peaks together into one wide peak. Use this
setting for sinusoidal or calibration signals.
• Hamming - A general purpose window that is similar to the Hanning
window. It provides better frequency resolution but decreased amplitude
accuracy when compared to the Hanning window. You can use it to
separate close frequency components.
Measurement Signal Detection Types
The signal detection is part of the collection specification (Setup >
Collection). See Figure 3.4 on page 40. You select the collection specification
when you set up the measurement definition.
Emonitor and the Enpac Ex support the following signal detection types.
• None - Use for numeric measurements. None defaults to RMS when
applied to magnitude or spectrum measurement definition.
• RMS - Use for detection of voltage and current. For the frequency
domain, the dynamic signal is measured as the square root of the mean
of the square of the signal. This is the RMS amplitude of a sine wave at
the frequency of interest. For the time domain, the dynamic time signal
is squared, integrated over some time period, and then the square root is
taken.
• Peak - Use for detection of acceleration, velocity, and high frequency
energy. This is the peak (0 to maximum) amplitude of a sine wave at the
frequency of interest and is calculated from the RMS value.