I finally end the “hardware and soldiering” part of my system.
Is based on a Arduino mkr1000 + 1 SCT013-030 (30A/1V) + 1 SCT013-020 (20A/1V) + Voltage transformer 230V/9V Ac-Ac
High freq noises coming from sct sensors are filtered with a Sallen-Key Low-pass Filter system based on 1 Op Amp lm358 dual with one side CT30A and on the other side the CT20A.
Filtering noise I have less than 0.1A residual when CT are with “zero primary current state”. I’m happy about these first step resault…
Now I’m trying to calibrate the system with some real load. I chose a bath heater 3 power levels. on the box was write pow1 800W pow2 1200W pow3 2000W.
I have a Digital multimeter HT4014 with a good resolution to see real data VS Energymonitor data.
I’m surprise about resoults:
on one hand Voltage transformer is very very precise. I have error < 0.5%
on the other hand CT are not precise after a fraction of the total range.
with low primary current , readings are very precise
after 6/7 A (about 20%/25% the range of 30A CT) errors start to grow
at 20 A error is 2.5A/3A.
X values = REAL
Y values = EACH COLUMN
Can some one help me to understand why with “mid-hi” rmsI values error is big? I suppsed to find some kind of linearity on CT output
How can I do in order to improve my precision?
Thank you so much