Predicting Shaft Proximity Probe Track Runout on API Motors and Generators

Eddy current proximity probes are used extensively for monitoring shaft vibration of large motors and generators, especially those manufactured to American Petroleum Institute specifications [1] [2]. It is important to minimize proximity probe track runout, which is also known as slow roll runout, so as to minimize the measurement error when monitoring and diagnosing vibration. Customer specifications strive to reduce the slow roll runout in order to improve the reliability of the vibration signal. The slow roll runout specification is recognized as one of the more difficult requirements to meet on a consistent basis. If the runout specification is not met during final test of a machine, it can cause critical delays in delivery and impact project completion. Manufacturers are developing strategies to provide motors and generators with the lowest possible runout, consistently and on time. This paper describes a factory measurement method used during the manufacturing process that is able to discriminate the four major components of runout: journal surface out of roundness, proximity probe track out of roundness, lack of concentricity of the two surfaces, and electrical runout. With accurate knowledge of each of the components of slow roll runout, manufacturers have the ability to control and improve them. With today's aggressive project timelines, on-time delivery is vital. Diagnosing issues early in the manufacturing process allows steps to be taken to mitigate problems before machine assembly. This minimizes the likelihood of having to disassemble the machine to correct excessive runout and avoids the associated schedule delay. This is essential for critical machines and especially those that are schedule driven. Results from this in-process measurement method are also compared with final test stand results.