FEATURES

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Exceeds the IEC 61036 accuracy requirements for class 1

active energy measurement

Uni-directional and Bi-directional power and energy

measurement

Selectable rated conditions, LED pulse rates and counter

resolutions

sames

RM2102DSE

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On-board precision calibration

Direct drive capability for both stepper motor and impulse

counters

Opto-isolated output for connection to measurement

equipment

INTRODUCTION

This application note describes the SAMES reference design

for a low cost, watt-hour energy meter based on the SAMES

SA2102D integrated circuit. It is advisable to use this

application note in conjunction with the SA2102D datasheet,

which provides detailed information on the functionality of the

SA2102D.

The SA2102D is a single chip solution for accurate bi-

directional power / energy measurement. It incorporates an

on-chip oscillator, and has direct motor drive capabilities for

stepper motors. A fast calibration LED output is made

available to the meter manufacturer to ensure convenient and

fast calibration of the meter. The normal calibration model at a

lower frequency provides for accurate and stable energy /

power measurement. The device can be configured to

measure either positive or negative energy, or to measure

energy irrespective of the direction.

The International Standards IEC 61036 (Alternating current

static watt-hour meters for active energy) was used as the

primary specification for this design.

The dynamic range of the meter is 800, and the meter not only

easily meets this specification but exceeds the IEC 61036

specification over this range.

A basic meter design using the SA2102D is shown in figure 1.

This design uses a shunt as the current sensing element,

while the voltage is supplied to the device by means of a

voltage divider circuit. Calibration is done by means of a

precision resistive network. The measured power is displayed

on either a stepper-motor driven counter, or a mechanical

impulse counter. An opto-isolator and LED is connected to the

output for visual inspection, or use with an optical pick-up or

measurement equipment.

METER SPECIFICATIONS

I

, I , V

as well as the pulse motor constants can be chosen

by the meter designer. Two examples are given later on in this

document for illustration.

The selection and positioning of the current and voltage sense

resistors, as well as the selection and positioning of the resistor

used for setting the bias are very important to ensure the

correct operation of the SA2102D.

The most important

external components for the SA2102D integrated circuit are the

current and voltage sense resistors, as well as the bias setting

resistors. These resistors must be of the same type as

specified in the parts list to ensure that the temperature effects

and noise susceptibility are minimized.

A signal of 14µA

must be applied to the voltage input of the

SA2102D for the nominal rated mains voltage. Please note that

this input will saturate with currents bigger than approximately

17µA

(25µA max), which translates into a 20% overdrive

capability. This also ensures that the device will not saturate

with a 10% variance in mains voltage. The mains voltage is

divided down via a resistor network (see Figure 2) to 14V. This

voltage is fed to a 1M

resistor (R18) to realize the 14µA

.

Ignoring jumpers J3...J10 results in the following equations:

RA = R1 + R2 + Rtrim

RB = R18 || R14

Where Rtrim = R4 + R5 + R6 + R7 + R10 + R11 + R12 + R13

Combining the two equations result in:

(RA + RB) / 220V = RB / 14V

Values for resistors R14 = 24k , R18 = 1M

are chosen.

MA

X

B

nom ,

RM S

RM S

RM S

VOLTAGE INPUT IVP

W

WW

CIRCUIT DESIGN

ANALOG INPUT

RM2102DSE Application Note:

Reference Meter

Watt-Hour Energy Meter Based on the SA2102D

1/16

SPEC-1015 (REV. 1)

29-10-02

PRELIMINARY