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SA9110AFA

MONOCHIP THREE PHASE BIDIRECTIONAL KILOWATT HOUR METERING IC

South African Micro Electronic Systems 

SA9110A

4. Device Programming

The SA9110A contains on-chip registers which enables the meter manufacturer to

store various data:

Slope Adjustment

The slope of the device may be adjusted by programming a slope constant (K ) into

S

the device during calibration. The output frequency at SDO (fP) is calculated by

means of the following formula:

f = 11.16

P

*

Where

FOSC

*

40062.5

*

(I

I1

*

I)

V1

+

(I

I2

*

I)

V2

+

(I

I3

*

I)

V3

3.5795MHz

KS

3 * IR2

FOSC = Oscillator frequency (2MHz ...... 4MHz)

II1, II2, II3 =

IV1, IV2, IV3 =

IR

=

K

=

S

Input current for current sensor input (16µA at rated line current)

Input current for voltage sensor input (14µA at rated line voltage)

Reference current (typically 50µA)

Slope constant (1025 ... 16384)

(The default value is 11389)

By changing the slope of the device the resolution of the LCD together with the pulse

rate on SDO may be changed by up to an order. The block diagram below illustrates

the display update rate.

Programmable slope divider

40062.5*

Pulses / s

1/K s

Display

1 / 64

Increment

DR-00956

fp

* At rated conditions

The display is incremented after every 64th pulse on SDO.

Display Resolution

From the above formula for fp it can be derived that the slope constant, Ks, is given

by the following expression:-

K

s

=

(626

*

3600

*

1000

*

E)

KWh

/

(

3

*

V

L

*

I)

L

Where EkWh =

VI L

=

=

L

energy for 1 Display increment in kWh

rated line voltage

rated line current

This formula is valid only if 16µA flows into each of the current sense inputs for rated

line current (I ) and 14µA flows into the voltage sense inputs for rated line voltage

L

(VL).

sames

9/18

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