Measuring RPM, Angle, and Speed Using Digital, Encoder and Counter Sensors

In this article, we will discuss how you can measure digital signals as well as digital encoders, tachometers, and RPM sensors with today’s best data acquisition (DAQ) systems, with enough detail so that you will:

Most engineers understand that data acquisition systems are used to measure time-history signals, such as voltages, temperatures, currents, vibrations sensed by accelerometers, strain sensed by Wheatstone bridge strain gauge sensors, and more. 

But often it is necessary to measure discrete events and angle of rotation signals which are synchronous with the more common time-history data. Discrete events are those events that have only two possible values, e.g. on / off switches, etc.

These are sometimes called “digital signals” since they are fundamentally composed of high-low (aka “on/off”) voltage states. In the sections that follow, we will present some examples of these additional signal types, and discuss how they are best measured and synchronized with the rest of the data.

Let’s take the case of a proximity switch or sensor, which outputs a low voltage (0 V in this example) when the unit under test (UUT) is not nearby, but then outputs a higher voltage (5V) when the UUT comes within range. It may be necessary to record this discrete state in sync with our measuring system in order to put the analog data into context. So how can we do it?

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