Rotational speed measurement through digital imaging and image processing

This paper presents a rotational speed measurement system based on a low-cost imaging device with a simple marker on the rotor. Structural similarity and two-dimensional correlation algorithms are deployed to process the images. The measurement principle, structure design and performance assessment of the proposed system are presented and discussed. The effects of different markers, image processing algorithms and illumination conditions on the performance of the measurement system are quantified through a series of experimental tests on a laboratory test rig. Experimental results suggest that the system is capable of providing the maximum relative error of ±1% with normalized standard deviation less than 0.8% over a speed range from 0 to 700 RPM (Revolutions Per Minute).