OpenEnergyMonitoring – Calibration

As the emon’s are now up and running, the next big thing needs to happen, calibrating the sensors..

There is a good wiki on how and what to do:


What do we need to calibrate?


  • AC Voltage, in combination to the AC-AC power adapter
  • AC current used, compared to what is read by the coil sensors

Following the guide, these number reflect the Node10:

The new calibration coefficient can be calculated by:

New calibration = existing calibration × (correct reading ÷ emonTx reading)
const byte Vrms=                  226;                               // Vrms for apparent power readings (when no AC-AC voltage sample is present)

const float Ical1=                86.96;                                 // (2000 turns / 22 Ohm burden) = 90.9
const float Ical2=                86.43;                                 // (2000 turns / 22 Ohm burden) = 90.9
const float Ical3=                87.01;                                 // (2000 turns / 22 Ohm burden) = 90.9
const float Ical4=                15.97;                               // (2000 turns / 120 Ohm burden) = 16.67
//const float Vcal=               260;                             //  Calibration for EU AC-AC adapter 77DE-06-09 
float Vcal=               242.2;

I used a heater which was using just about 6A (5.99A) constantly. Strange enough the power readings where at about 40W.. so there is still something strange 😉