Patent ID: 7212931

Claim:
An electric energy meter for an AC mains supply providing an AC mains voltage, the electric energy meter comprising: (a) a current transformer with a primary conductor connected to the AC mains supply and to a load, and a secondary winding inductively producing a secondary voltage, in which a transformer phase shift exists between the current in the primary conductor and the secondary voltage; (b) an AC mains voltage sampler connected to the primary conductor; (c) a current sampler connected to the secondary winding; and (d) a microcomputer coupled to the AC mains voltage sampler and to the current sampler, the microcomputer operable to compute a frequency for the AC mains voltage, a correction for the transformer phase shift dependent upon the AC mains voltage frequency, and an integration of the products of samples of the AC mains voltage multiplied by the samples of the current and corrected for the frequency-dependent transformer phase shift; (e) whereby the integration provides a measure of electric energy provided to the load.