May 2006

Rev 1

1/29

AN2288

Application note

Single-phase energy meter with tamper detection

based on ST7FLITE2x

Introduction

This application note describes the design for a single-phase power / energy meter with

tamper detection. The design measures active power, voltage, current, power factor and line

frequency in a single-phase distribution environment and displays active energy, voltage,

current, power factor, line frequency, current date and time. It differs from ordinary single-

phase meters in that it uses two current transformers (CT) to measure active power in both

live and neutral wires. This enables the meter to detect, signal, and continue to measure the

active energy consumed reliably even when subject to external tamper attempts.

ST7FLITE20 is the microcontroller used to perform all the measurements in the meter. As

the ST7FLITE30 is pin-to-pin compatible with ST7FLITE20, the ST7LITE30 can also be

used in this application (replacing the ST7LITE20) but a revalidation is required for finding

the accuracy class of the meter.

The active energy consumed is available in the form of frequency-modulated pulse outputs

and the accumulated active energy on an LCD display module. Additional features for both

consumer types can also be incorporated. These include multiple tariff rates and improved

communications, through which meter readings can be taken with less time and with higher

accuracy.

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