RM4301ASEA Application Note:

Low-Cost Three-Phase Watt-Hour Energy Meter

SPEC-2368 (REV. 1)

1/19

PRELIMINARY

25-04-07

RM4301ASEA

FEATURES

n

Designed to exceed IEC62053-21 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

n

Per phase mains voltage and energy direction indicator

LEDs

INTRODUCTION

This application note addresses various design aspects of a

low-cost three-phase watt-hour energy meter based on the

SAMES SA4301A integrated circuit. The SA4301A is a

single-chip solution for accurate bi-directional three-phase

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 exceeding the specifications whilst

incurring the lowest possible cost. The specification for this

design is the International Standards IEC62053-21. This

meter is designed to meet all class 1 sections of the

IEC62053-21

specification

that

relate

to

electrical

characteristics.

METER SPECIFICATIONS

A basic meter block diagram using the SA4301A is shown in

Figure 1. The three load currents are sensed with

current transformers and converted to the required input

currents via the current input networks. The scaled mains

voltage signals are applied to the SA4301A via three voltage

divider circuits. Calibration is done by means of a resistive

network on these voltage sensing networks. 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 IEC62053-21 class 1 accuracy

specifications to which the meter was designed are listed in

SA4301A

Energy

Metering

Device

Differential Current

Sensing Network

IIP

IIN

LIVE OUT

LIVE IN

AGND

Voltage

Sensing Network

IVP

NEUTRAL

Power Supply

VDD

VSS

VDD

VSS

Reference

Resistor

VREF

Stepper

Motor

MOP

MON

Device

Setup

RA, RB

FMS

MS

LED

Calibration

LED

Opto-

isolator

VDD

Isolated

Pulse

Output

4

Tamper LED

Array

PH1, PH2

PH3

PH/DIR

4

3X - Once for each phase

3

SA4301A

Energy

Metering

Device

Differential Current

Sensing Network

IIP

IIN

LIVE OUT

LIVE IN

AGND

Voltage

Sensing Network

IVP

NEUTRAL

Power Supply

VDD

VSS

VDD

VSS

Reference

Resistor

VREF

Stepper

Motor

MOP

MON

Device

Setup

RA, RB

FMS

MS

LED

Calibration

LED

Opto-

isolator

VDD

Isolated

Pulse

Output

4

Tamper LED

Array

PH1, PH2

PH3

PH/DIR

4

3X - Once for each phase

3

Figure 1: Block diagram of a three-phase watt-hour meter based on the SA4301A