SA4106A
FUNCTIONAL DESCRIPTION
Theory of Operation
Analog Inputs
The input circuitry of the current and voltage sensor inputs is
illustrated in Figure 5. These inputs are protected against
electrostatic discharge through clamping diodes. The
feedback loops from the outputs of the amplifiers AI and AV
generate virtual short circuits between IIP and IIN as well as
IVP and AGND. The current sense inputs (IIP and IIN) are
identical and balanced. The AD converters convert the
signals on the voltage and current sense inputs to a digital
format for further processing. All internal offsets are
eliminated through the use of various cancellation
techniques.
The SA4106A includes all the required functions for single
channel single phase power and energy measurement. Two
AD converters sample the voltage and current input signals.
The two digital signals, accurately representing the voltage
and current inputs, are multiplied using digital multiplication.
The output of the multiplier represents the instantaneous
power, which is subsequently low pass filtered and integrated
over time to remove the instantaneous components forming
the averaged instantaneous energy. This energy is
accumulated over time to form the outputs of the device.
For given voltage and current signals the instantaneous
power is calculated by:
VDD
IIP
( )
푝 푡 = 푣(푡) × ꢀ(푡)
VSS
( )
(
)
(
)
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휓
CURRENT
CURRENT
SENSOR
CHANNEL
ADC
AI
INPUT
VDD
ꢁꢂ
ꢃꢂ
then
2
√
Let 휙 = 휃 − 휓, and 푉푅푀푆
=
and 퐼푅푀푆
=
2
√
IIN
( ) )
(
)
(
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휃 − 휙
VSS
VDD
( )
(
( ( ))
)
푝 푡 = 푉푅푀푆 푅푀푆
퐼
cos 휙 + cos ꢄ 휔푡 + 휃 − 휙
where
IVP
p(t) is the instantaneous power,
VOLTAGE
SENSOR
INPUT
VSS
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,
VOLTAGE
CHANNEL
ADC
AV
AGND
is the phase angle of the voltage signal and
is the phase angle of the current signal.
Figure 5: Analog input configuration
The instantaneous power is low pass filtered to remove the
double mains frequency component cos(2(t+)-) and is
then integrated over time to provide the average power
information
Digital Outputs
The calculations required for power and energy are
performed and converted to pulses on the LED, MON and
MOP outputs. The complimentary output pins MON and MOP
are provided for driving a stepper motor counter directly. The
output frequency on the LED output is, in both STANDARD
and FAST mode, proportional to the average active power
consumption measured. The FAST mode is intended for fast
meter calibration and verification purposes or for interfacing
the SA4106A to a microcontroller.
ꢅ
1
푃 = ∫ 푝(푡)푑푡
푇
ꢆ
푃 = 푉푅푀푆 푅푀푆
퐼
cos 휙
where
P is the average power and
cos is the power factor.
Anti-Creep Threshold
An integrated anti-creep function prevents any output pulses
on the LED output and the MON/MOP motor drive outputs
when the level of measured energy is below the anti-creep
threshold. This threshold is selectable between 0.01% and
Linearity
The SA4106A is a CMOS integrated circuit, which performs
power/energy calculations across a dynamic range of 500:1
to an accuracy that exceeds the IEC62053 specification.
SPEC-1587 (REV. 5)
29-09-2017
7/18
SAMES [ SAMES ]
