An 
intelligent electronic device, and in particular, an electrical power meter, featuring an internal calibration 
system capable of calibrating its measurement mechanisms for the integral nonlinearities introduced by the components which make up those mechanisms, in particular, the analog-to-
digital converter, is disclosed. The analog-to-
digital converter is coupled with at least one sensor which is operable to sense electrical energy in one or more conductors and output a corresponding electrical 
signal indicative thereof, the analog-to-
digital converter being operative to convert the electrical 
signal output by the sensor to at least one corresponding 
digital signal. Integral non-
linearity (“INL”) is a term describing the deviation between the ideal output of an analog-to-digital converter and the actual output (after offset and 
gain errors have been removed). The disclosed embodiments further relate to an electrical power meter having internal INL calibration using a relatively low cost, low accuracy internal 
signal source, obviating the need for costly external signal sources or measurement systems, which quickly calibrates the electrical power meter for such INL substantially across its entire measurement range and significantly improves the measurement accuracy thereby.