Accurate tachometry methods with electronic counters

High-speed electronic counters have become commercially available within the past few years which indicate by means of a display of neon-lighted figures, and can count from 20 to 100,000 events per second or more with an inherent accuracy of ±1 count in the measuring interval. By relatively simple modifications of the basic counting circuits in these instruments they can also be used for measuring short intervals of time to an accuracy of ± 10 microseconds. The measured time interval is displayed directly in figures indicating the decimal fraction of a second to the nearest hundred-thousandth. Tachometry is a fruitful application of these instruments. Three methods of using the counters in tachometry are described here, and the advantages and limitations of each method are discussed.