Phase Correction on emonTx V4


I have an emonTx V4 with 1x 100A, 3x 50A and 2x 20A CTs. All in use on a single phase system.

What should the value of ‘Phase Correction’ be for each CT in the serial configuration? It seems some want to be 3.20 but others are defaulting to 0. I suspect this was something to do with the issue pre firmware 1.5.4? I have set all to 3.20 but do not know if this is right. Is it documented somewhere?

Also I assume voltage calibration is pre-set and I don’t need to change it?

The only way to know if it is right is to check each c.t. at a “typical” system voltage and a “typical” load current, because the phase error of the emonVs and the c.t. will depend on the working values.

I have only been able to measure one sample of each: the 25 A and 50 A samples varied between 1 & 2° over the working range, while the 100 A varied between 0.6 & 1.8°. In his wisdom, Trystan uses the default of zero in emonLibDB for the phase error of the emonVs, so you need to subtract about 0.2° from the c.t’s phase error to get the overall error.

But these numbers come with a warning - they might not be representative because I had only one sample of each to measure. All I can suggest is you adjust each input on a purely resistive load to give you as close to unity power factor as possible. The configuration command c1 should turn on the power factor reporting (and c0 turns it off again).

Thanks for this…

So is calibration required? Is this process documented somewhere? I’d hoped the emonTx V4 is a case of connecting the CTs and off I go.

I don’t know why the phase error of the c.t. is thought to be approx 3.4°, but I repeat, I only have one sample available to measure.

If you want the best accuracy, then yes, calibration is required. Having said this, the ‘off the shelf’ calibration is very much better than the previous versions of the emonTx with the a.c. adapter and SCT-013-000 c.t., and most users seem to be happy with it.