In modern terminology, these projects involved the creation of digital twins from IoT data. They began by collecting time series data around events such a change in operating speed. This is important because systems do not provide dynamically rich data under static operating conditions. Think of a lightbulb with a hairline crack in its filament. Unless you have incredible eyesight, it is impossible to tell if the lightbulb is work on not. However, if you gently tap the lightbulb, you will hear the filament vibrate. That is what reveals that the broken is bulb. In addition to the signal processing aspects, this diagnostic and testing process relies on our mental model of how filament lightbulbs work.
