Page 299 - Intro Predictive Maintenance

290 An Introduction to Predictive Maintenance

Figure 14–2 Multiplane imbalance generates multiple harmonics.

machine-trains varies, at least slightly, during normal operations. These vibration com-
ponents appear at the 1¥ frequency.

14.1.3 Mechanical Looseness
Looseness, which can be present in both the vertical and horizontal planes, can create
a variety of patterns in a vibration signature. In some cases, the fundamental (1¥) fre-
quency is excited. In others, a frequency component at one-half multiples of the shaft’s
running speed (e.g., 0.5¥, 1.5¥, 2.5¥) is present. In almost all cases, there are multi-
ple harmonics, both full and half.

Vertical
Mechanical looseness in the vertical plane generates a series of harmonic and half-
harmonic frequency components. Figure 14–3 is a simple example of a vertical
mechanical looseness signature.

In most cases, the half-harmonic components are about one-half of the amplitude of
the harmonic components. They result from the machine-train lifting until stopped by
the bolts. The impact as the machine reaches the upper limit of travel generates a fre-