AVR465

This application note describes a single-phase power/energy meter with tamper logic. The design measures active power, voltage, and current in a single-phase distribution environment. It differs from ordinary single-phase meters in that it uses two current transducers to measure active power in both live and neutral wires. This enables the meter to detect, signal, and continue to measure reliably even when subject to external attempts of tampering.

The heart of the meter is an AVR microcontroller. All measurements are carried out in the digital domain and measurement results are available in the form of frequency-modulated pulse outputs and as plain-text values, accessible over the USART interface. This enables the design to be used in cost-effective applications based on mechanical display counters. Alternatively, the design easily fits more computerized applications with features such as remote reading (AMR), demand recording, multiple tariffs, and other.

A prototype built for 230V and 10A operation showed better than 1% accuracy over a dynamic range of 500:1. With careful PCB design and following the guidelines given at the end of this document the accuracy can be further increased. The meter is easily configured to fit any other voltage and current settings.