SA9903B
FUNCTIONAL DESCRIPTION
The SA9903B is a CMOS mixed signal integrated circuit,
which performs the measurement of active power, reactive
power, RMS voltage and mains frequency. The integrated
circuit includes all the required functions for single phase
power and energy measurement such as oversampling A/D
converters for the voltage and current sense inputs, power
calculation and energy integration.
( )
푝 푡 = 푣(푡) × 푖(푡)
( )
(
)
(
)
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휓
ꢀꢁ
ꢂꢁ
then
2
√
Let 휙 = 휃 − 휓, and 푉푅푀푆
=
and 퐼푅푀푆
=
2
√
( ) )
(
)
(
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휃 − 휙
( )
(
( ( ))
)
푝 푡 = 푉푅푀푆 푅푀푆
퐼
cos 휙 + cos ꢃ 휔푡 + 휃 − 휙
The SA9903B integrates instantaneous active and reactive
power into 24 bit registers. RMS voltage and frequency are
continuously measured and stored in the respective registers.
The mains voltage zero crossover is available on the FMO
output. The SPI interface of the SA9903B has a tri-state
output that allows connection of more than one metering
device on a single SPI bus.
where
p(t) is the instantaneous power,
v(t) is the instantaneous voltage signal,
i(t) is the instantaneous current signal,
VM is the amplitude of the voltage signal,
IM is the amplitude of the current signal,
is the phase angle of the voltage signal and
is the phase angle of the current signal.
Current
Sensing
SPI
Microcontroller
SA9903B
Active Energy
Reactive Energy
VRMS and
Frequency
Measurements
The instantaneous power is integrated in the active energy
registers. Over time this removes the double mains frequency
component cos(2(t+)-) to provide the average power
information
Voltage
Sensing
LEDs
LCD
Power
Supply
EEPROM
N
L
ꢄ
1
푃 = ∫ 푝(푡)푑푡
푇
ꢅ
Figure 5: Typical architecture of an energy meter using the
SA9903B
푃 = 푉푅푀푆 푅푀푆
퐼
cos 휙
where
In the typical meter architecture, a microcontroller is used in
conjunction with the SA9903B. In addition to communicating
with the SA9903B the controller is used to read/write
parameters to the EEPROM, output pulses for fast calibration
and to display the consumed active and reactive power, VRMS
and mains frequency information. Other parameters such as
IRMS, phase angle etc. can be accurately calculated.
P is the average power and
cos is the power factor.
Reactive power is calculated by applying a 90 degree phase
shift to the voltage signal before multiplication:
푇
( )
푞 푡 = 푣(푡 − ⁄ ) × 푖(푡)
4
휋
( )
푞 푡 = 푉푀 cosꢆ휔푡 + 휃 −
(
)
ꢇ × 퐼푀 cos 휔푡 + 휓
⁄
ꢃ
Theory of Operation
( ) )
푞 푡 = 푉푀 sin 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휃 − 휙
(
)
(
The SA9903B includes all the required functions for single
channel multifunction power and energy measurement.
Identical AD converters sample the mains voltage and current
input signals. The pair of digital signals, accurately
representing the voltage and current inputs, is used to
calculate active energy, reactive energy, VRMS and the mains
frequency. These quantities are stored in 24 bit registers that
can be accessed via the SPI bus. The energy registers
accumulate instantaneous energy.
( )
(
( (
)
))
푞 푡 = 푉푅푀푆 푅푀푆 sin 휙 + sin ꢃ 휔푡 + 휃 − 휙
퐼
The instantaneous reactive power is integrated in the reactive
energy registers. Over time this removes the double mains
frequency component sin(2(t+)-) to provide the average
reactive power information
ꢄ
1
푄 = ∫ 푞(푡)푑푡
푇
ꢅ
For given voltage and current signals the instantaneous
active power is calculated by:
푄 = 푉푅푀푆 푅푀푆 sin 휙
퐼
where
Q is the average reactive power.
SPEC-0051 (REV. 5)
29-09-2017
8/17
SAMES [ SAMES ]
