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




On 2011, Jul 27, , at 09:31, chuck britton wrote:

I lost track of the 'Bottom Line' on this one.
Is the Wikipedia ok here?

Can anyone propose an improvement?


In addition to Bernie's quote, it includes

"Electricity meters operate by continuously measuring the
instantaneous voltage (volts) and current (amperes) and finding the
product of these to give instantaneous electrical power (watts) which
is then integrated against time to give energy used (joules,
kilowatt-hours etc.)."

I suspect that the rms scenario is closer to what's actually used
rather than the instantaneous scenario.

thanx
.


"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#Electromechanical_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.


bc thinks chuck has it backwards.