How would one go about to implement accurate sensing of metal oxide varistor wear level?
Even cheapo surge protects come with a LED to indicate protection status, but I presume this is not based on actual sensing, but most likely a "time fuse" that simply prompts the use to replace the device, regardless of the amount of wear.
I've read that MOVs mitigate power surges by absorbing some of the energy and redirecting another portion to ground. And that they burn out when overloaded. In other words, the amount of thermal energy they generate is proportional to the amount of wear.
So one possibility might be to try and measure how much heat is displaced into the ambience, but it sounds kinda complex and course, and presumably most of the time the wear is rather subtle.
Maybe something else? I am interested in accuracy of measurement, not in economic viability, obviously MOVs are fairly cheap and typically do not merit sensing sensing circuitry that will be much more expensive.