At http://openenergymonitor.org/emon/buildingblocks/ct-and-ac-power-adaptor-installation-and-calibration-theory
the theory about the voltage constant is described.
Here, a 230 to 9 voltage adapter is used and for the EmonTx V2 the voltage is further divided by 11.
So, in order to get the original voltage from the analog pin in the Arduino, you need to multiply the voltage by 11 and then multiply it by a ratio of 230/9.
However, on the page the formula is:
"voltage constant = 230 × 11 ÷ (9 × 1.20)"
Where comes the 1.20 from?
Re: Calibration theory voltage - formula voltage constant
Read the description. It is all explained there.
Re: Calibration theory voltage - formula voltage constant
I see "...and the voltage is approximately 20% higher...", missed that.
Thank you!
Re: Calibration theory voltage - formula voltage constant
It's called Transformer Regulation. 20% is a typical figure for devices of that size. And beware of the way it's specified: in low voltage isolating transformers, the voltage is specified at full load and it is the voltage rise at no-load ÷ full-load voltage. In power distribution transformers, it's the other way round, i.e. the voltage drop at full load ÷ the no-load voltage, and it's the no-load voltage that specifies the transformer.