Dual-mode digital revolution counter

Revolution speed measurement methods are analyzed. Three different measurement methods are presented and appropriate resolutions and relative errors are calculated The method which measures the time between two pulses gives the best results for slow rotation speeds. The method which counts the number of pulses in a fixed time window gives better results for high rotation speeds. Measurement optimization is done by measuring in two modes corresponding to the previous methods and the relative error is significantly decreased. A revolution counter is realized for measuring rotation speeds in the range 10-9999 r.p.m. with a sensor which gives one pulse per revolution. In the entire range the resolution of 1 r.p.m. is displayed. A microcontroller is used for switching between the measurement modes as well as for the rotation speed calculation and displaying.