Page 165 - Intro Predictive Maintenance

156 An Introduction to Predictive Maintenance

Figure 7–24 Types of coiled cables.

noncoiled cables can be more difficult to use in conjunction with a portable analyzer,
they are essential for low-speed and electromagnetic field applications.

7.7.2 Data Measurements
Most vibration-monitoring programs rely on data acquired from the machine housing
or bearing caps. The only exceptions are applications that require direct measurement
of actual shaft displacement to obtain an accurate picture of the machine’s dynamics.
This section discusses the number and orientation of measurement points required to
profile a machine’s vibration characteristics.

The fact that both normal and abnormal machine dynamics tend to generate unbal-
anced forces in one or more directions increases the analyst’s ability to determine the
root-cause of deviations in the machine’s operating condition. Therefore, measure-
ments should be taken in both radial and axial orientations.

Radial Orientation
Radially oriented measurements permit the analyst to understand the relationship of
vibration levels generated by machine components where the forces are perpendicu-
lar to the shaft’s centerline. For example, mechanical imbalance generates radial forces
in all directions, but misalignment generally results in a radial force in a single direc-
tion that corresponds with the misaligned direction. The ability to determine the actual
displacement direction of the machine’s shaft and other components greatly improves
diagnostic accuracy.