Instantaneous angular speed analysis, measurement errors and signal filtering

Recently, Instantaneous Angular Speed (IAS) is becoming an interesting measurement solution for condition monitoring of rotating machines. Various researchers are studying the measurement’s limits, new signal processing methods and new industrial applications. In Spagnol et al. (Proceedings of COMADEM2013, 2003) [1], IAS is compared to Torsional Laser Vibrometer (TVM) and to acceleration data. IAS is less affected by noise if compared with TVM and it is very informative in respect to acceleration. The current work focuses on the estimation of the IAS through the Elapsed Time (ET) method, using a counter to measure the time elapsed between the pulses of an encoder. From the variation of the IAS during the machine loads’ cycle it is possible to identify defects and faults. The data is acquired from an experimental test rig specifically designed for IAS evaluation. The setup is composed of an asynchronous four poles electric motor driven by a 380V 50Hz line current, a bearings’ test group and a variable brake system simulating different loads’ conditions. The paper reports on the results obtained with different data processing techniques and filtering approaches. The combined effect of the errors generated by the counter and the speed variation of the machines will be analyzed and commented, showing the advantages and drawbacks of the adopted IAS measurement.