“Understanding Amplitude and Phase in Rotating Machinery,”
E. J. Gunter, 2009.


The measurement of phase is essential in the balancing of single- or multi-plane balancing of rotating machinery. The rate of change of phase is important, as it may indicate the presence of a critical speed, and from the rate of change of phase one may be able to deduce the amplification factor or log decrement of a particular mode. Having a phase reference mark is particularly critical on complex machinery such as gas turbines and also the space shuttle oxygen and hydrogen pumps. Without the presence of a phase signal, it is impossible to determine what component of the total vibration is synchronous and what is due to external or subsynchronous vibrations. The use of the timing mark, therefore, allows us to track amplitude and phase to determine critical speeds, amplification factors, and balancing.


Phase; Bode Plots; Nyquist Plots; Amplification Factor; Critical Speeds; Log Decrement