power factor paradox

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frog
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power factor paradox

Post by frog »

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Hi,
I'm using a 3204 which is rapidly approaching its 20th birthday, and the noise performance is somewhat improved since I persuaded a visiting ant colony to move out. But that's not why I'm posting today.

I'm using some of the maths functions to calculate power and VA so that I can determine the power factor of a load:

I've created a math channel that converts the voltage across a sense resistor into current (a simple multiplication), and a power channel that represents the instantaneous current*voltage. So far so good.

I then look at the true RMS of the voltage, current and instantaneous power: the VA figure is (RMS voltage) * (RMS current) while the power figure is (RMS instantaneous power). The figures all look sane, and by inspection the RMS figures look plausible for the waveforms. However, the power is higher than the VA measurement, which should be impossible.

Any guidance as to what's going on would be very welcome.

Gerry
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Re: power factor paradox

Post by Gerry »

Hi frog,

Your measurement of Instantaneous Power is wrong, it should be DC Average, not True RMS.

Regards,

Gerry
Gerry
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frog
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Location: Nelson, New Zealand

Re: power factor paradox

Post by frog »

Yes of course, thank you very much.

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