Analysis of Low Sampling Rate Time Interval Torsional Vibration Measurement System with Encoder Non-Uniformity Problem

The idea of developing a low sampling rate time interval torsional vibration measurement system has potential in expanding the capabilities of widespread lateral vibration monitoring systems. Such system, when used with a gear or zebra tape encoder system when operating at a lower sampling rate can experience problems regarding non-uniform encoder segment geometry. The problem is usually manifested in the presence of high-level order content in the frequency spectrum. Correction of encoder segment non-uniformity is performed by the use of normalized time passage ratio of encoder segments and basically corrects the reference time array. In order to determine the convenient combination of the sampling rate and the number of encoder segments, a series of simulations were performed as well as experimental testing with two different encoding devices, i.e. toothed wheel encoder with an eddy current sensor and zebra tape encoder with an optical reference sensor. Computer simulations and experimental results show that it is possible to measure torsional vibration at a low sampling rate with acceptable performance.