Re: Proposal: Wattmeter project

Tesla List wrote:

> There are two things that confuse simple meters:
> 1. Input current is phase-shifted due to inductive nature of load (so
> called cos-factor)
> 2. Input current is not pure sinuoid at line frequency.  This tends to be
> more or
> less complex waveform.

An old analog moving coil wattmeter is not expected to be affected by 
these characteristics of the signals.
They just measure the average force between two coils, one with
a current proportional to the current in the load, and another with a
current proportional to the voltage in the load.
The only problem with these meters is that their coils are inductive,
and eventually produce phase shifts in the signals that they are
measuring. These meters are accurate at a range of frequencies, from
DC to a certain limit, usually specified by the meter maker.
They work correctly with distorted waveforms, if there are no excessive
high-frequency content in both the voltage and the current waveforms.
Electronic wattmeters are also not affected by distortion, are
possibly faster, but more sensitive to RF interference.

Antonio Carlos M. de Queiroz