Re: Average, RMS and Power Factor made easy!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>



> > This is not true. These meters are true Wattmeters. They don't look
> > at power factors or RMS values, but measure the amount of energy
> > effectively consumed.

> I'm glad your power company forked out for better units than mine did =)
 
> > Old electromechanical units essentially integrate the force between
> > two coils, one with a sample of the current being consumed and another
> > with a current proportional to the voltage at the power line. This
> > force is proportional to the average power being consumed.
 
> Sounds like a variation of the electrodynamometer. I agree that it's not
> hard to measure real power but the statement made was based on my own area
> where they just use eddy currents to push a little aluminium wheel around.

	Same as is being described.  The mechanical ones are actually quite
	sop[hiticated, subject to legal requirements as to accuracy etc.

> The eddy currents are induced by an inductor in series with the supply
> (maybe shunted?) and I have been told by an A-class electrician whom I
> have respect for that they are usually like that in Australia, they don't
> even care what RMS voltage you get fed when they measure the integrated
> current. I'll ask him again though when I see him.

	Two coils.  One voltage coil (meaures the voltage).  One (or more)
	series coils (no shunt usually, for household work, industrial
	is anoither matter), for current.  The two coils are displaced
	90 degrees, mechanically.

	This provides two phaes of mag field (assuming, for the moment,
	unity power factor (resistive) load).  (OB Tesla: Like a Tesla two
	phase motor...).  If the power factor drops, the electrical phase
	shifts, the torque on the disk drops, since the electrical PLUS
	the mechanical phase difference is no longer the designed optimum
	90 degrees.

	Or so it is in the US...  In the electromechaniocal ones.

	best
	dwp