Re: [Phys-l] [tap-l] Energy Conservation?

[Gary Karshner <gkarshner@stmarytx.edu>]

Most watt-hour meter measures "real power" the product of volts time amps 
with phase taken into effect. The phase factor is thus included. But if you 
measure it with a volt and ammeter you ignore the phase. Since power 
companies are in the business of selling "Power" (energy) there meters 
should correct for it. This is one of the reasons that many power 
substations will have racks of big capacitors to adjust the average phase.
        In the old days watt meters had two coils one whose field is 
proportional to the current and the other the voltage. Thus correcting for 
the phase.
        Recently I bought a meter call a "Kill A Watt" that out performs 
the old watt meters. It will measure the sources voltage, current, power, 
VA, frequency, and power factor all in one unit. In addition It measures 
time and KWH as well. It was under thirty dollars, where as my power meter 
I bought over thirty years ago, cost me about fifty dollars not correcting 
for inflation.
        The KWH feature allows you to leave it plugged into to device your 
measuring and see how much total power it uses over time.
Gary

At 08:56 AM 12/3/2008 -0800, you wrote:
> As I suggested in my previous post, I think it unlikely the meters do
> not incorporate the power factor.  The watt meters I have do that
> inherently.  They are d'Arsonvals that use a series coil to supply
> "the" magnetic field while the moving coil is powered by a parallel
> connection (w/ a dropping resistor).  I easily imagine the meter's
> motor is constructed similarly.
>
> bc thinks likely Wiki. has an article on watt-hour meters.
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l