Sampling And Averaging Considerations For Measuring AC Input Power

There is a strong movement in the information technology (IT) industry to reduce the energy consumption of IT equipment. For managing energy consumption in data centers it is important to measure the power consumption of servers and other equipment. The most common approach is to require power supplies to report their input power to the host system. In the past, the input power was often calculated by dividing the output power by an approximate efficiency. The accuracy of such methods is not meeting current needs. Instead, power supplies often now include the ability to measure the input current and voltage and calculate the true rms input power. This kind of digital sampling, measurement, and signal processing is unfamiliar to most power supply engineers. This paper addresses several issues related to the sampling and averaging that can affect accuracy and hardware requirements.