# Customizing EmonLib for Voltage and Current to read 2 separate systems

There is the grid Voltage and Current, then there is the pure sine wave inverter Voltage and Current. What I’d like to do is measure these parameters for both, then perform the math to find out just how beneficial this off grid system is, while I slowly expand it. I may be able to do it already, but one area of doubt is the line in EmonLib for Voltage and Current:

emon1.voltage(2, 234.26, 1.7); // Voltage: input pin, calibration, phase_shift

I am not sure what to put in for calibration and phase_shift.
Could the calibration be the UK line voltage? If it is then mine would be 118.50. Is that correct? As for the phase_shift, I know what phase shift is, but as for it’s context here, I’m at a loss, Stephen

There are articles in ‘Learn’ that give you the gory details of calibration theory and the procedures to follow. In the least number of words possible, the calibration constant is the voltage or current that gives you 1 V at the ADC input, so in the case you give, it’s close to but not exactly the line voltage (because we aim for 1.1 V at the ADC for better resolution).
There’s no easy way to calculate phase shift, you must do it empirically. It depends on the transformers you use, and line voltage and current, in non-linear ways.

Thank you Robert Wall. After I sent my last post, I discovered the page where the discussion on how the measurement method causes this phase shift and why it’s necessary to correct for it. I have ordered two wall wort step down transformers. I’ll take this topic up again once they arrive. Thanks again. Stephen