emonTX - confused with calibration

Trying to use the emonTX_CT123_Voltage sketch as a starting point, but I'm confused with calibration.  The sketch includes:


  ct1.voltageTX(234.6, 1.7);                                          // Voltage: calibration, phase_shift
  ct1.currentTX(1, 113.4); 
​But the web site suggests 
  emon.calibration(238.56, 138.8,1.7);
Is the latter just a roll up of the first two?  Can someone explain a little more please?
TrystanLea's picture

Re: emonTX - confused with calibration

Apologies about the confusion about calibration, we have changed the calibration values several times recently as we switched different components. The latest CT calibration for the YHDC SCT-013-000 with a 18ohm burden resistor is: 111.11

If you have a 15ohm burden resistor it would be: 133.33

For the Voltage transformer the new calibration is: 234.26. I will be updating all the sketches with this change today.

For detailed information, including the potential error in the calibration due to component tolerances see here:


Lloyd's picture

Re: emonTX - confused with calibration

Thanks for that. Can you explain the difference between what appears to me to be two different set of function calls. Do I need to call emon.calibration?


TrystanLea's picture

Re: emonTX - confused with calibration

No sorry thats the old EmonLibrary function call.

The new calibration functions are on the emontx: (note that the voltage pin is preset and the ct is referenced by the emontx channel rather than the arduino input pin)


ct1.voltageTX(234.26, 1.7);           // Calibration coefficient, phase_shift
ct1.currentTX(1, 111.1);              // CT channel, calibration coefficient.

If your not using the emontx you can skip out the TX part and set the arduino pins directly:


ct1.voltage(2,234.26, 1.7);           // Voltage input pin. Calibration, phase_shift
ct1.current(1, 111.1);                // CT input pin, calibration coefficient.

Have you got the latest EmonLib and emonTXfirmware downloaded?

Polidano's picture

Re: emonTX - confused with calibration

so the old basic sketch with calibration is not good anymore??you are using the emonTx, but if I wish to continue on the old version it is still good?? since I worker all the way and all of a sudden I came back here and found everything renovated :)

glyn.hudson's picture

Re: emonTX - confused with calibration

There is nothing wrong with the old version, we have just been reorganizing the code to make it consistent and easier to follow. If the old version is working for you then don't worry about changing. We recommend you try and check the energy readings against another meter and further tweak the calibration if needed.

Polidano's picture

Re: emonTX - confused with calibration

many thanks :) I really appreciate

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