RM410ASEB Application Note:

Low-Cost Watt-Hour Energy Meter

SPEC-1621 (REV. 1)

1/16

PRELIMINARY

12-11-04

RM4104ASEB

FEATURES

n

Designed to meet IEC61036 requirements for class 1

active energy meters

n

Selectable rated conditions, LED pulse rates and

counter resolutions

n

On-board precision calibration

n

Direct drive capability for stepper motor or impulse

counter

n

Opto-isolated output for connection to measurement

equipment

INTRODUCTION

This application note addresses various design aspects of a

low-cost watt-hour energy meter based on the SAMES

SA4104A integrated circuit. The SA4104A is a single-chip

solution for accurate bi-directional energy measurement. It

incorporates an on-chip oscillator and has a direct drive

capability for a stepper motor or an impulse counter. The

emphasis for the design of this meter has been placed on

meeting the specifications whilst incurring the lowest

possible cost. The specification for this design is the

International Standards IEC61036 (Alternating current static

watt-hour meters for active energy). This meter is designed

to meet all class 1 sections of the IEC61036 specification

that relate to electrical characteristics.

METER SPECIFICATIONS

A basic meter block diagram using the SA4104A is shown in

Figure 1. The load current is sensed with a shunt resistor

and converted to the required input current via the current

input network. The scaled mains voltage signal is applied to

the SA4104A via a voltage divider circuit. Calibration is done

by means of a resistive network on the voltage sensing

network. Both the current and voltage input networks

incorporate

low-pass

filters

to

improve

the

meters

performance, especially the immunity to electromagnetic

disturbances. The measured energy is displayed on a

stepper motor or an impulse counter. An LED as well as an

optical isolator provide an electrically isolated connection to

measurement

equipment

during

calibration

and

performance verification.

The

most

important

IEC61036

class

1

accuracy

specifications to which the meter was designed are listed in

SA4104A

Energy metering

device

Differential Current

Sensing Network

IIN

IIP

Shunt

Resistor

LIVE OUT

LIVE IN

AGND

Voltage

Sensing Network

IVP

NEUTRAL

Power Supply

VDD

VSS

VDD

VSS

Reference

Resistor

VREF

Stepper

Motor

MOP

MON

Rated Condition

Setup

R3, R2

R1, R0

FMS

LED

Calibration

LED

Opto-

isolator

VDD

Isolated

Pulse

Output

Figure 1: Block diagram of a watt-hour meter based on the SA4104A