Unless the rotational speed of the shaft is very slow, and can be counted visually, there is little chance of estimating an accurate result. Shaft speed is measured in revolutions per minute, or rpm, using a tachometer. The ability to measure rpm is vital when designing machinery, tuning it for best performance, or fault-fi nding when something is not operating as it should. This month, we look at the various ways of determining shaft speed and some handy tools to help us.

View the PDF report here: Handy tools for counting the revs