High-Resolution Shaft Speed Measurements Using a Microcomputer

A Motorola 6800 microcomputer has been applied to the measurement of instantaneous angular velocity at one degree intervals on a pair of coupled shafts. Velocity is determined by accurately measuring the time intervals between pulses produced by shaft encoders. Variations in relative velocity can be detected when precision timing is available. Using an essentially software approach time can be measured in 30-μs increments. The number of instructions in the timing loop can be reduced by adding a small amount of hardware to permit parallel data acquisition. Time increments of 12μs were obtained using inputs from two shafts. The results of measurements on a pair of shafts coupled by noncircular gears is included as an example.