"Sorry, but it seems you think the power factor is just cos phi, where phi is the angle that current is shifted in relation to the voltage."

Actually, no. We have some economy products for PF measurements, and in some of those, I use this method. For most capacitive and inductive loads, I get fairly good results.

The load current is expected to be symmetrical, but not at all sinusoidal. In the link you mentioned, you can see that I had commented about the right method to compute PF.

Here, I am looking for a cheaper solution. I already have RMS computing, and I add an extra parameter - PF. For PF, I use two methods.

1. First one is as mentioned. Find the peak of current and voltage. Find zero. Peak - DC offset is my zero. Now I can calculate rms and PF.

2. Use a precision rectifier. Get the zero crossings of V & I. Use zero crossing point to compute parameters. In this case, I don't need to track the peak. I blindly compute for a wave period. Wave period is = last computed value of period. ie: zero crossing to next zero crossing.

In the second method, If I can avoid the precision rectifier, I can cut costs. But without precision rectifier, at low sense voltages / currents, my rms computation error margin will go up, even though I manage this by adding an offset. Offset is derived from actual Fluke meter reading / my reading.

Regards, Raj