On Friday 23 July 2010 11:04:59 Chris. Aubrey-Smith wrote:
> Any thoughts? Can these units give more than a general indication of
> consumption? Is there any point in recording the actual numbers?
>
> Incidentally, I had a 'phone conversation this morning with a
> representative of the organisation which runs this monitoring scheme on
> behalf of nPower. He tells me that one factor which distorts the readings
> is..... using low-energy, compact fluorescent lamps!
>
> Chris.
I have heard mention that fluorescent lights seem to draw "more" power. I
think it's just the phasing due to load, but it's a while since I did AC
phase theory. The easiest way to test the meter's accuracy is to get some
resistors (or resistive loads) which, when connected across the mains will
give currents of around 1 Amp to say, 10 Amps. Incandesant lightbulbs and
electric fires are ok, but the resistance will change as they heat up. So,
connect the resistance and measure the voltage across it (be clear whether
this is RMS or peak voltage). Make a note of this voltage, then turn off the
supply and measure the resistance, while the "resistor" is still hot.
Ohm's law states that V=IR (I is current) so I=V/R, so you can now compare
this with the reading from the current meter. Unless you have reasonably
sophisticated equipment, you'll only get an indication of the accuracy (and
only for resistive loads), but it should give you a ball-park accuracy.
Hope this helps, Googling for AC Power factor or AC Phase angle may also help.
Tim B.
* I accept no responsibility for electrocution or missing fingers resulting
from this post. Mains electricity is dangerous.
--
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