emonTX 3Phase. Calibration points


I’ve been running the emonTx 3Phase by RW here, on an emonTxShield I built. I calibrated by checking the 5V reference, using the USB power supply it’s been installed with.

I used a 2.5kW electric stove for the next stage of calibration, which may have a little inductance, I’m not sure… It a old hot plate type heater.

The phase correction values I found looked a bit odd… To achieve +1, -0.5, -0.5 I had I1Lead = 4, I2Lead = 2.1, I3Lead = 4
I’m using the standard 100A CTs from the shop.

After one month the reading from the TxShield with the new 3Phase firmware the setup was reading 8% lower than the meter.

Apart from the (quite old looking) meter being dodgy what else could it be? I noticed on the ‘inputs’ page that the values would go negative if there was no load on a particular phase. Could the voltage offset of the resistor network, post-burden resistor, be creating a negative offset?