Rockwell Automation 1441-PEN25-Z Enpac 2500 Data Collector - Manual (Page 161)

Rockwell Automation Publication GMSI10-UM002D-EN-E - August 2012 161
Multi-channel Measurements Chapter 6
Figure 27 - 1X Orbit Plot
If the machine has unbalance only, the displayed orbit will be dominated by a
once-per-revolution signal and have a circular or elliptical shape.
To get a better impression of the actual shaft motion and to identify other
common machine anomalies, such as misalignment, shaft whirls, rubs, and
looseness, all signal frequencies are required up to several orders of shaft speed.
The orbit shape then becomes more complex, and it may be highly elliptical,
non-elliptical, or it may have several inner and outer loops.
Inner loops presented in a Lissajous orbit plot can indicate a hit and bounce type
condition. This phenomenon occurs when the shaft comes in contact with the
bearing surface and bounces off.
In early stages of contact, a flat spot in the orbit plot will be presented. As the
condition becomes more severe, the number of loops present will increase and
become tighter. Detailed analysis of the orbit plot can indicate exactly where the
shaft is coming into contact with the bearing in question. This figure shows a
non-filtered orbit plot of the same shaft as discussed above.
Figure 28 - Non-filtered Orbit Plot
In the Filtered plot, only 1X frequency information appears in the orbit. In this
case, the rub condition presented would have been overlooked if only a 1X orbit
was taken. In general, a filter of OVERALL in the Emonitor software specified
for the orbit plots will give the most useful information.
Inner Loops