? on phase correction value for emon1.voltage

Thank you for the excellent resources you provide. I am grateful to be able to learn from them.
in the Arduino sketch when we provide parameters to calibrate voltage readings - emon1.voltage(2, 234.26, 1.7);

I do not have the experience / knowledge to know if 1.7 is a great settng for phase shift, even after reading the explanation.

My voltage (measured from Kill-A-Watt) is 123.7VAC. I “get” that due to just the limitation of measuring the voltage and then the current there will be a phase shift. However, I am not clear how much > 2˚ will be caused by the voltage phase error.

Practically, is 1.7 the best starting point?

thank you.

The explanation of the phase-correction algorithm explains the algorithm, not the reason for the phase correction in the first place. All transformers exhibit a phase error, most show a lead - meaning the output appears to happen before it should. I have measured the error only for the components sold via our shop, and you can read the reports in ‘Learn’. The good point is both errors go in the same direction, the bad is the a.c. adapter’s error is a lot bigger than the c.t’s. And separating the samples, as you say, is a time difference. (And before you point it out, it would be better to reverse the order of the samples.)

Unless you are using the ‘shop’ UK a.c. adapter and the 100 A c.t, and you’re on a 50 Hz supply, then 1.7 is but a starting point. I’ve only analysed the situation with those: the greatest component in the error and the most variable is actually the phase error of the a.c. adapter, which varies with the mains voltage. So whatever you set, it’s only right some of the time! I can’t tell you what the best value will be for you, you’ve just got to alter your sketch temporarily to print the power factor, then tweak the calibration to get as close to 1 as you can.