I was just confirming that we were both on the same page, as it were. ;-)
Woah! Hold your horses! Does your LAB meter take a series of samples,
square each value, sum them over a period of time, preferably over at
least one or more complete cycles, average the results then calculate the
square root of that average to accurately measure the RMS voltage?
It is called a "true RMS" reading AC voltmeter.(digital, not moving
coil)
Or, is it just an accurately calibrated moving coil meter with a
rectifier to produce an average voltage reading which is then calibrated
by the multiplier resistor to produce a deflection on the scale based on
the fixed relationship between average and RMS for a sine waveform?
Or, does the meter simply use the peak value of the mains voltage and use
a multiplier resistor 1.4 times larger than it would be for a constant DC
voltage to scale the peak to its corresponding rms equivalent (again, a
correction factor based on the assumption that the mains is a pure sine
waveform)?
Since that EM100 is already gathering such voltage signed sampling data
to be multiplied by the corresponding current signed sampling data to
calculate both positive and negative power values to be averaged then
summed to produce a net power flow reading, it seems highly likely that
this data and processing power is not going to go to waste.
I have 2 EM100s One agrees with my lab meter - the other does not.
Reads a full 3 volts less.
There's every chance, within the limits of sampling error, that the meter
is giving a more accurate RMS voltage reading than a simple moving coil
meter ever could since the mains waveform (at least in the UK) is quite
noticeably flat topped (if you have you ever looked at the mains waveform
on an oscilloscope, you'll know exactly what I mean).
Mains voltage pattern here in Ontario Canada is as close to a perfect
sine wave as you will find - no "clipping".
No, that just means it's 78VA which may or may not be 78 watts. In this
case, the real power figure is likely to be a lot less though not to the
same extreme you might see with a line interactive switching UPS such as
the SmartUPS 2000 that I've just been testing 3 digital meters and my
analogue Metrawatt power meter on[1].
The reading on the EM100 is KwH, Watts, and Amps. The KwH devided by
on-time in hours gives me the 40 watt reading (41.25 watts over 16
hours)- I agree with your 78 VA, rather than 78 watts, because either
the power factor is crasy or the meter is reading peak amps (not
sampling fast enough) and the input current to the UPS is switching at
a frequency that gives a wrong "average" current draw. I'm thinking
power factor, or a combination.
That does seem the more likely figure in view of the fact that the UPS is
float charging a battery with a steady inverter load on it. Incidently, it
would be useful to know what the UPS's model number is or it's basic
specifications.
UPS model is (formerly Excide)Powerware Prestige 650.( I thought it
was a 1000)
The sticker says 4.9 amp at 0.9PF at 120 volts, 50 or 60 hz.
[1] I've just spent about an hour in my basement collecting as much
measuring data on the four states of operation of the SmartUPS 2000. These
were rear panel switch in the off position (all functions disabled), rear
panel switch in the on position (charging only enabled, protected power
turned off, then activated from the front panel, enabling protected power
function without load then ditto with a 150W lamp load. I'll only detail a
couple of readings here and now which are relevant to yours (I'll post the
details in a later posting since it is now 4:48 AM BST as I type.
When I was testing the charging only mode (after allowing some 15 minutes
to let the battery return to its fully charged state) the 2000MU-UK (UK
version of the KAW P4400) I was getting a 26.5W and a 136VA reading
(averaged - there was a +/- variation of up to a watt/voltamp either way).
I would have recorded a PF figure but I forgot, however I did record a PF
value of 0.21 on the next stage of the test where I was getting readings
of 29.4W and 136.5VA. Assuming the 40 watt figure is correct that 78VA
figure you calculated implies a PF of just over 50%.
HTH & HAND
I have another Powerware Presige 1000 EXT that I will test too.
Right now (on the first UPS) I just turned the output off - leaving
thepower switch on - and I'm getting 0.72 amp, 13-60 watts at 117
volts.
Thw 1000EXT has been sitting, not plugged in, for several months.
It is drawing 84 watts and1.01 amps at 117 volts with the output
turned off, and the same with the output turned off with no load. The
wattage is fluctuating between 82 and 85. We'll see what it says after
the batteries have stabilized.
The first unit is a 36 volt DC battery pack unit, and this one is 42
volt - and has provision to use external battery packs. The tag on
this one says 11.5 amps input and PF of 0.95 -.
