MadSci Network: Engineering

Re: How does an electricity meter work?

Date: Mon May 7 00:45:33 2001
Posted By: Donald Howard, Staff, Nuclear Engineering, Retired
Area of science: Engineering
ID: 981582897.Eg

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 

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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