The Sigma-Delta Converter has a fully differential input; therefore, no added dc offset is needed to precondition a signal, which is the case with most single ended converters.

The output of the Sigma Delta is a signed integer. Any stray dc offset value is removed independently for V and I by subtracting a long term dc tracking filter’s output from each ΣΔ sample. This long term dc tracking filter is synchronized to the mains cycle to yield a highly stable output.

The resulting instantaneous voltage and current samples are used to generate the following information:

• Accumulated squared values of voltage and current for V_RMS and I_RMS calculations.
• Accumulated energy samples to calculate Active Energy.
• Accumulated energy samples with current and 90° phase shifted voltage to calculate Reactive Energy.

These accumulated values are processed by the foreground process.