Separation of lateral and torsional shaft vibration via a multiple sensor time interval measurement system

A common torsional vibration sensing method for rotating equipment is the Time Interval Measurement System (TIMS). The method utilizes the time passage of discrete intervals from an incremental geometric encoder (i.e., gear) on a rotating shaft. Ideal measurement conditions consist of a constant shaft running speed, an encoder with identical segments and no transverse motion of either the shaft centerline or the encoder passage sensor. In practice, these ideal conditions are rarely achieved as the shafts of large rotating equipment can experience lateral vibration due to imbalance and/or misalignment. The lateral shaft vibration can affect the TIMS torsional encoder passage times and hence results in measurement errors. The work in this paper describes and evaluates a multiple encoder passage sensing and data processing algorithm to separate the torsion and lateral vibration. The multi-sensor TIMS method is then applied to an industrial pump to illustrate the separation capabilities of the method.