SA4104A / SA4104B
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 SA4104A/B 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
CURRENT
CHANNEL
ADC
CURRENT
SENSOR
INPUT
( )
(
)
(
)
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휓
AI
VDD
ꢁꢂ
ꢃꢂ
then
2
√
Let 휙 = 휃 − 휓, and 푉푅푀푆
=
and 퐼푅푀푆
=
2
√
IIN
VSS
VDD
( ) )
(
)
(
푝 푡 = 푉푀 cos 휔푡 + 휃 × 퐼푀 cos 휔푡 + 휃 − 휙
( )
(
( ( ))
)
푝 푡 = 푉푅푀푆 푅푀푆
퐼
cos 휙 + cos ꢄ 휔푡 + 휃 − 휙
IVP
where
VOLTAGE
SENSOR
INPUT
VSS
p(t) is the instantaneous power,
VOLTAGE
CHANNEL
ADC
AV
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,
AGND
is the phase angle of the voltage signal and
is the phase angle of the current signal.
Figure 5: Analog input configuration
Digital Outputs
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
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 SA4104A/B 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 set to 0.01% of FMAX on the
SA4104A and 0.004% of FMAX on the SA4104B, where FMAX
is the output frequency in FAST mode when the input currents
Linearity
The SA4104A/B 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.
are IVPMAX = 16μARMS and IIPMAX = 16μARMS
.
SPEC-1654 (REV. 4)
29-09-2017
7/18
SAMES [ SAMES ]
