For many people, the interpretation of vibration signals for a machine at running speed is complicated and foreign, and is considered an art in many circles. Interpreting the rich characteristics of the raw signals during run-up and coast down requires even more skill and experience. For some, interpreting the signals at slow speeds (sometimes called slow roll speeds) is so difficult that the signals are often ignored and discredited as not useful data. This paper will communicate the author’s experience in using this valuable, yet sometimes difficult, data to correlate and corroborate with high-speed data. This data and interpretation are used to understand the dynamic behavior of the machine while the forces on the rotor are driving the response characteristics at run up, full speed and coast down. In the sports arena, good coaches often say that if you cannot execute skills in slow motion, you likely won’t be able to execute them at normal speeds and absolutely not in high-pressure game situations. This is also true for vibration diagnostics: if you don’t do correct slow speed analysis, full speed and transient (startup and coast down) analysis may be misleading or just wrong. In this instance, the analyses and diagnostic calls that were made by using slow speed signal analysis include: Selecting Slow Roll Values, Shaft Surface Quality, Direction of Rotation, Rotor Bow (Gravity), Rotor Bow (Thermal), Locked up Coupling, Non-Concentric Coupling, Reverse Rotation. This paper will describe the methodologies for collecting data and the analysis of the data to make the above calls on specific examples experienced by the author and his colleagues.

This content is only available via PDF.
You do not currently have access to this content.