|MadSci Network: Engineering|
Roger, the pics I can find won't be much help in understanding the gearing inside the watt-hour meter. As you say, the aluminum disk is essentially an induction motor whose speed of rotation about its central shaft conforms to the Hall Effect. The upper end of the disk-shaft has a spiral machined into it to act as the worm portion of a worm gear combination where the gear portion of the combination is a large gear on a horizontal shaft. At the other end of the shaft is a mating set of angle gears that drive the gear attached to the first needle. From there on out, the gears are all the same. A small gear on the previous shaft drives a large gear on the next shaft such that ten rotations of the previous gear causes one rotation of the next gear. If you look at one of those meters, you will see that the needles rotate in opposite directions because that's the simplest way to make such a meter, and after years of development and field use, they are reliable and accurate. Do they fail? Yes. Usually they come to a dead stop, but occasionally, they begin to read erratically. Today, that can be picked up by the billing computer. And, also, most utilities have a program of periodic replacement and recalibration for the metering of major customers.
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