I'm going to have a bit of a #tech#rant (less charitable people might say #whine) here. If you just want jokes and cute bunny pictures, feel free to skip this one.
Object of my #ire this week? #Furnaces. I'm not even going to rant about their main control boards; most of that's been said better than I could say it, by others with more knowledge than I.
From the timings of those back-EMF spikes, the #embedded#CPU can determine how fast the motor is turning. But even trickier is that by sensing the shape or magnitude of that back-EMF signal, it can determine how much #torque the motor is producing - and therefore how much air is actually moving.
This is useful; in an A/C setup, you want to know if air is actually moving past the #evaporator#coil, not just how fast the motor is turning, so you can detect the coil "#icing up".