What is a primary function of a photo tachometer?

A photo tachometer is an instrument specifically designed to measure the rotational speed of an object, typically in revolutions per minute (RPM). It operates by using a light source and a photodetector to detect the reflection or interruption of a beam of light by a rotating object. The device counts the number of times the object crosses the light beam in a given timeframe, allowing it to calculate the RPM accurately.

The primary use of a photo tachometer is in mechanical systems where monitoring the speed of rotation is critical for performance and safety. Many industrial applications, such as in motor testing or monitoring machinery, utilize this tool to ensure that components are operating within specified speed limits. This is vital for maintaining operational efficiency and preventing potential damage due to excessive speed.

The other options serve different purposes. For instance, temperature readings, air velocity, and pressure differentials focus on distinct measurements unrelated to rotational speed. This highlights why the correct answer emphasizes the role of a photo tachometer in measuring RPM.