[5F2] Shaft CL – A powerful diagnostic tool for FFB machinery part II: shaft CL and proximity probe
F Youssef
Misr Fertilizers Production Company (MOPCO), Egypt
Eddy current proximity probes are widely used for condition monitoring and diagnostics on large rotating machinery, including steam/gas turbines, centrifugal compressors, gearboxes and blowers. These non-contact sensors measure the distance between the probe tip and the shaft surface, allowing them to capture the shaft’s vibration and position relative to the bearing housing. Proximity probes directly monitor shaft motion within fluid-film bearings, providing sensitive measurements of rotor dynamics. This paper delves into the mechanical fundamentals of shaft centreline motion, explains how proximity probes capture and plot this motion and examines how to interpret centreline behaviour under various conditions. It also discusses the mathematical representation of shaft orbits and centreline displacement, proximity probe principle of operation, mounting, shaft material, location and shaft geometry, calibration, field wiring, environmental consideration, data acquisition principles, relevant industry standards (ISO 7919, ISO 10816, API 670), original equipment manufacturer (OEM) best practices (Bently Nevada) for probe installation and maintenance strategies to ensure long-term accuracy of the shaft. Proximity probe systems form the backbone of machinery protection and diagnostics, helping detect issues early and minimise unplanned shutdowns.
