Accuracy of emonPi ?


I've have a emonPi with 2 CT's so just out of interest I put them both on the same wire and I get different readings, usually between 7w and 30w different.

Is there any way of increasing the accuracy of this or is it just a limitation of this this type of setup?

Also just to see what would happen I left the CT plugged in but nowhere near any cables and I get a fairly constant reading of 30 to 32watts, is there a way of zero-ing this ?


Robert Wall's picture

Re: Accuracy of emonPi ?

I'd hazard a guess that the standing 30 W is power supply noise. For the scale factor error, if you can compile and reload the AVR sketch with adjusted calibration constants, you might get closer. You must of course tie the CT to its respective input, because calibration is affected by manufacturing tolerances in both the CT and the input components.

glyn.hudson's picture

Re: Accuracy of emonPi ?

Are you using an AC adapter to provide an AC voltage reference? It's highly recommended to increase the accuracy of the monitoring. 

pb66's picture

Re: Accuracy of emonPi ?

Have you tried swapping the CT's over to see if the "noise" changes with the CT or remains with the emonPi channel?

I run a "no current" test over a day or so by just having the CT's plugged in but not clipped to a cable and found the results pretty good concidering I made no effort to eliminate any outside influence just plugged them in and left them laid on the workbench.

The attached screen shots show power1, power2 and the sum of power1plus2 over the same 24hr period and as you can see they only very occasionally step out of the 0 to 3 or 4 watt range.

I haven't done the same test with a fixed load yet as I don't have a convenient "test circuit" right now.

Is it possible an outside influence is causing the difference ? a magnetic field of some sort? you try the same test in another location to confirm.


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