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.
MAX 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
