Rules For Measuring Phase

Rule #1: Phase is a relative measurement. Readings at different locations on a bearing are analyzed relative to one another. Readings at the same angle (direction) on adjacent bearings are analyzed relative to one another. Readings at different times at the same exact location are analyzed relative to one another. These comparisons give us information on how the components behavior - namely how they are moving relative to one another.  There is only one use for a single phase reading which we will discuss shortly. Rule #2: Phase is collected at ONE frequency at a time. The analyzer must be told what frequency. This is done by tuning the analyzer with either a strobe light or a tach pulse from the shaft. Rule #3: The analyzer must be able to detect a vibration signal at that frequency. Since the angle is calculated based on the arrival of a sinusoidal peak from the vibrating component, there must be an amplitude peak to get a phase angle.

Simple Phase Analysis  Data Conventions

In order to discuss phase at the most basic level, we need a convention to use. Phase is represented by the 360° of a circle. Since a high degree of accuracy is not required in a simple, general phase analysis (what we will be discussing here), phase is most easily referred to in terms of clock face numbers: 1 o'clock through 12 o'clock. The phase "angle" is based on where the mark appears (the red key in the example shown here) on the clock face. It is shown here at 12 o'clock but could appear at any angular location. Applications requiring more precise detail (i.e. balancing or phase monitoring on a turbine) will require the use of specific angular references (0 - 359°).

Clock Face Numbers Use For Simple  Phase Analysis