I would like to confirm whether or not it's mandatory to calibrate IxGAIN (and VGAIN), aka "channel matching", before attempting to calibrate for each channel's phase errors. To date I've always done it that way, and the datasheet recommends it:
Changing the content of the IxGAIN registers affects all calcu-
lations based off that channel, including the active and reactive
energy. Therefore, it is recommended that the channel matching
be performed first in the calibration procedure.
Currently I do several passes to get the meter calibrated:
- IxGAIN and VGAIN (aka channel matching)
- PCF at 50Hz
- PCF at 60Hz
- WGAIN and VARGAIN
I'm wondering whether I can combine the first two (or even three) passes. I use IxGAIN and VGAIN to force the device to output real-word values in the RMS registers and I realise changing IxGAIN and VGAIN has a big impact on the Active and Reactive energy readings. But I've noticed they don't seem to have any impact on tan-1(Reactive/Active) which is what matters when trying to calibrate for phase errors. I calibrate at a 60 degree phase shift, and when I calculate that tan-1, I typically get 58.5 degrees say, which tells me I need to calibrate away a 1.5 degree phase error. But I get that same answer regardless of whether I check it before or after the channel matching step (IxGAIN and VGAIN). When I stopped to think about it, that kinda' makes sense, because anything I do to IxGAIN or VGAIN should impact Reactive and Active by the same proportion, so their ratio will remain the same, and hence the tan-1 of their ratio stays the same. Is that a reasonable assumption?