Re: [Phys-l] Wiki. is wrong?

["John Clement" <clement@hal-pc.org>]

Now an interesting question: Is it possible to have the meter run backwards?

The answer is: Yes!

We had a case of this.  In our barn the meter would normally go forwards,
but if you turned off all the lights except for one particualar light the
meter ran backwards.  We never found out why this happened, but that light
was left on all the time to save a little money.

This was in the 1950s, and it might be possible that the design was slightly
different, but would anyone know why this might have happened?

John M. Clement
Houston, TX


> "Electromechanical meters
> The most common type of electricity meter is the 
> electromechanical induction watt-hour meter.[15][16]
> The electromechanical induction meter operates by counting 
> the revolutions of an aluminium disc which is made to rotate 
> at a speed proportional to the power. The number of 
> revolutions is thus proportional to the energy usage. It 
> consumes a small amount of power, typically around 2 watts.
> The metallic disc is acted upon by two coils. One coil is 
> connected in such a way that it produces a magnetic flux in 
> proportion to the voltage and the other produces a magnetic 
> flux in proportion to the current. The field of the voltage 
> coil is delayed by 90 degrees using a lag coil.[17] This 
> produces eddy currentsin the disc and the effect is such that 
> a force is exerted on the disc in proportion to the product 
> of the instantaneous current and voltage. A permanent 
> magnetexerts an opposing force proportional to the speed of 
> rotation of the disc. The equilibrium between these two 
> opposing forces results in the disc rotating at a speed 
> proportional to the power being used. The disc drives a 
> register mechanism which integrates the speed of the disc 
> over time by counting revolutions, much like the odometer in 
> a car, in order to render a measurement of the total energy 
> used over a period of time."
>
> http://en.wikipedia.org/wiki/Electricity_meter#Electromechanic
> al_meters
>
> The above, which I missed,  follows.  Sui generis, it 
> measures the power, not he imaginary volt ampere power.   The 
> key is instantaneous -- no phase diff. if the PF is one.  
> This is the same (essentially) method that Watt meters of the 
> d'Arsonval method use.