He has a Raspberry Pi and a MCP3008 (Post #5)

Timing the zero-crossings will probably work in his case because the load is an induction motor, but if the current waveform is non-sinusoidal it won't.
Dividing the real power by the VA will work in all circumstances. A phase angle can be computed by taking the inverse cosine, but it will only be meaningful if the current waveform is a sinusoid.

Oh ok I was assuming a sine wave. If the wave is not a sine then all bets are off if that means just any random wave will be measured. Usually real power and apparent power are properties associated with sine waves. To get around that we'd probably have to move to something like RMS measurements where we take a lot of samples over the entire waveforms.

What else can work in analog is to multiply the two waves and then filter out the double frequency component. That leaves a term that can be used to calculate the phase angle.

So he already has a way to measure the power and the voltamperes?

 

Oh ok I was assuming a sine wave.

What else can work in analog is to multiply the two waves and then filter out the double frequency component. That leaves a term that can be used to calculate the phase angle.

So he already has a way to measure the power and the voltamperes?

A heat pump compressor is most likely an induction motor, so a sinewave is probably correct.

He started off with current and voltage transducers with DC outputs, confused us all by starting a second and very similar thread, now is using a Hall-effect current transducer with analogue output and a voltage transformer.

Multiplying V*I and averaging gives P
Then obtaining V and I separately as RMS values
That works for all waveforms.

 

Thanks to everyone for their great contribution and support. Really appreciate it.

 

Thanks to everyone for their great contribution and support. Really appreciate it.

Hi,

I hope this all helped you to get something reasonable working. Would be interesting to hear how you made out with it when you get to putting it all together.