Kevtrane wrote:
John,

I have a question about power meters, I would like to do some
consumption monitoring at my house. I see the cheap plug in meters and
the $500 Fluke recording multimeters. Is there anything in between? I
would like to measure on some 220V appliances and I don;t think that
the plug in ones will do it. Any advice?

Thanks,
Kev

Quoted Text
"I purchased my own power meter but I understand that some utilities
have
such equipment for loan to their customers."


I use the cheapest model from Brand Electronics and it does the little I
need it to do although having the ability to monitor 240V loads might be
occasionally useful to me. Brand does sell a 240V meter but they call it
their "whole house" model and with the two current transducers required
for the job it costs about $300. There may be others out there and I'm
sure that a Google search would turn up something.

Measuring true power is a bit trickier than it might appear since it
involves monitoring current but without interfering or modifying the
circuit unnecessarily, monitoring the voltage, then calculating the true
power many times per AC cycle, then integrating and displaying the
result. Add to that the $ calculations and long-term integration of
results that most users want and the design quickly becomes non-trivial.
Of course if the load is purely resistive some shortcuts like using a
clamp-on ammeter and a decent RMS voltmeter and doing the calculation
for instantaneous power manually but most users would balk at that
amount of work.

--
John McGaw
[Knoxville, TN, USA]
http://johnmcgaw.com