On page 61 of the ADE7880 datasheet there is a statement regarding harmonic distortion:

The total harmonic distortion ratios computed using the rms of the fundamental components and the rms of the phase current and the phase voltage (see Root Mean Square Chapter for details about these measurements) are stored into the VTHD and ITHD 24-bit registers in 3.21 signed format. This means the ratios are limited to +3.9999 and all greater results are clamped to it.

I understand the 3.21 formating, but would like to know what he number is scaled to; tor example does 3.99999 mean 3.9999% or 399.99% or something else?

Hi roadrunner

The ratio of 3.99 would correspond to 399%.

Regards

hmani