SA4104ASAR datasheet(7/18 Pages) SAMES

7 / 18 page

SPEC-1654 (REV. 4)

7/18

29-09-2017

SA4104A / SA4104B

FUNCTIONAL DESCRIPTION

Theory of Operation

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

accumulated over time to form the outputs of the device.

For given voltage and current signals the instantaneous

power is calculated by:

��(��) = ��(��) × ��(��)

��(��) = �� cos(�� + ��) × �� cos(�� + ��)

Let

�� = �� − ��, and �� =

��

√2

and

�� =

��

√2

then

��(��) = �� cos(�� + ��) × �� cos(�� + �� − ��)

��(��) = ��(cos �� + cos(2(�� + ��) − ��))

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.

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

�� =

��

∫ ��(��)��

��

�� = �� cos ��

where

P is the average power and

cos

 is the power factor.

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.

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

various

cancellation

techniques.

Figure 5: Analog input configuration

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 SA4104A/B to a microcontroller.

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

are IVPMAX

= 16μARMS and IIPMAX = 16μARMS.

IIN

IIP

VDD

VSS

VDD

VSS

IVP

VDD

VSS

AGND

VOLTAGE

SENSOR

INPUT

CURRENT

SENSOR

INPUT

CURRENT

CHANNEL

ADC

VOLTAGE

CHANNEL

ADC

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