Experimental Evaluation of a Novel Webcam-Based Tachometer for In-Situ Rotational Speed Measurement

Rotational speed measurement of industrial rotating machinery and mechanical parts is of great interest for process and system monitoring and control, process characterization and fault diagnosis. The estimation of motor load and pulley-belt transmission slip in induction motor driven systems are examples where the rotational speed measurement can be useful. In conventional systems, mechanical coupling of devices such as encoders and resolvers with the rotating shaft/part is required for continuous speed measurement. For short-time measurements, optical reflection or stroboscopic techniques can be used through noninvasive contactless optical tachometers. Reflective marks or strips in the rotating parts are usually required when using optical tachometers. In this paper, the results of several experimental tests under different light sources for an innovative nonintrusive, low-cost, webcam-based tachometer, previously proposed by the authors, are presented and discussed. For a motor shaft speed varying between 750 and 3000 rpm, the average error obtained with the proposed solution was lower than 0.2%. Such solution can be used to continuously measure the speed of a given rotating part during an in-situ energy audit or operation characterization period, with real-time data logging and without sticking reflective strips or introducing shaft-coupled encoders/resolvers, allowing the speed to be easily estimated/measured and recorded over time in, for example, electrical motors, pulleys, shafts and wind turbines.