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sames

sames

SA2005F

Figure 3: Analog Input Internal Configuration

http://www.sames.co.za

FUNCTIONAL DESCRIPTION

The SAMES SA2005F is a CMOS mixed signal integrated

circuit, which performs three phase power/energy calculations

over a range of 1000:1, to an overall accuracy of better than

Class 1.

The SA2005F is functionally similar to the SA9105F. No

external loop capacitors are required and an precision

oscillator is integrated on chip.

The integrated circuit includes all the required functions for 3-

phase power and energy measurement such as oversampling

A/D converters for the voltage and current sense inputs, power

calculation and energy integration. Internal offsets are

eliminated through the use of cancellation procedures.

The SA2005F generates pulses with a frequency proportional

to the power measured. The pulse rate follows the

instantaneous power measured. The pulse frequency is

proportional to the total sum of the three phases.

POWER CALCULATION

In the application circuit (figure 5), the mains voltages from V1,

V2 and V3, are converted to currents and applied to the voltage

sense inputs IVP1, IVP2 and IVP3.

The current levels on the voltage sense inputs are derived from

the mains voltages (3 x 230VAC) being divided down to 14V

through voltage dividers. The resulting input currents into the

A/D converters are 14µA

through the resistors R8, R9 and

RMS

R10.

For the current sense inputs the voltage drop across the

current transformers terminating resistors are converted to

currents of 16µA

at rated conditions, by means of resistors

RMS

R1, R2 (Phase 1); R3, R4 (Phase 2) and R5, R6 (Phase 3). The

signals providing the current information are applied to the

current sensor inputs IIN1, IIP1, IIN2, IIP2 and IIN3, IIP3.

The output frequency of the SA2005F energy metering

integrated circuit at rated conditions is 64Hz on FOUT

(PGM0=0, PGM1=1).

One pulse (measured in Watt second) correspond to an energy

measured of 3 x I

x V

/ 64Hz.

RATED

RATED

For a more detailed description see the Input Signals section.

INPUT SIGNALS

Analog Input Configuration

The current and voltage sensor inputs are illustrated in figure 3.

These inputs are protected against electrostatic discharge

through clamping diodes, in conjunction with the amplifiers

input configuration. The feedback loops from the outputs of the

amplifiers A and A generate virtual shorts on the signal inputs.

I

V

Exact duplications of the input currents are generated for the

analog processing circuitry.

Voltage Reference Connection (VREF)

A bias resistor of 24k provides an optimum bias conditions on

chip. Calibration of the SA2005F should be done on the

voltage inputs of the device as described in Typical

Applications.

Current Sense Inputs (IIN1, IIP1, IIN2, IIP2, IIN3, IIP3)

At rated current the resistor values should be selected for input

currents of 16µA

. Referring to figure 5, the resistors R1 and

RMS

R2 on current channel 1, resistors R3 and R4 on current

channel 2 and resistors R5 and R6 on current channel 3, define

the current level into the current sense inputs of the SA2005F.

The current sense inputs saturates at an input current of ±25µA

peak. Resistors R25, R26 and R27 are the current transformer

termination resistors. The voltage drop across the termination

resistors should be at least 20mV at rated conditions. Values

for the current sense inputs are calculated as follows:

R = R = (I / 16µA

) x R / 2

1

2

L

RMS

25

R = R = (I / 16µA

) x R / 2

3

4

L

RMS

26

R = R = (I / 16µA

) x R / 2

5

6

L

RMS

27

Where:

I = Line current/CT-ratio

L

VOLTAGE

SENSOR

INPUT

IVP

DR-01288

SS

V

CURRENT

SENSOR

INPUTS

IIP

IIN

SS

V

VDD

SS

V

VDD

DD

V

GND