Analysis of total rotor runout components with multi-probe roundness measurement method

Several standards for vibration testing of rotating machinery define limits for relative shaft displacement during rotation. With requirements for relative shaft displacement, limits are given for combined electrical and mechanical runout, which is the eddy probe reading error and the error caused by geometry of the measured shaft. Some standards allow for compensation of the mechanical and electrical runout by vectorially subtracting them from the eddy current probe values. This paper presents a measurement procedure applying multi-probe error separation to accurately determine the roundness profile and center point motion of electric motor shafts. The roundness error and center point movement obtained from multi-probe measurement with tactile displacement probes are compared with eddy current sensor displacement measurements to separate the total displacement measured with an eddy current probe into three components: center point motion, roundness error and electrical runout. Additionally, a transform for the measured eccentric component is presented to obtain an estimate for permanent rotor bow regardless of the rotor support arrangement during measurement. The relevant industrial vibration testing standards were reviewed. Several issues were found in the measurement methods required by the standards. The requirements of the standards and the used terminology are assessed critically and improvement proposals are presented.