sames

SA2002P

8/14

http://www.sames.co.za

PARAMETER DESCRIPTION

Refer to the EEPROM memory allocation map table 1 as well

as the Signal flow diagram figure 8, for a description of the

registers used in this section.

The Cor register divides the pulse-modulated signal with a

programmable value of 495 with a variation of ±3.2% (481 to

512). Only the 5 least significant bits are required for this

register. The Kr register is used to program the rated

conditions of the meter. This feature is required for correct

counter increments using the same meter design for various

meter ratings from less than 10A to several 100A.

The Kr register can have any integer value up to 128. The

pulse rate is then further divided down by the Cled register to

provide the required LED pulse rate. The Cled register

provides 3 different dividing factors namely 1, 0.5 and 0.25. In

addition using the Cled register the SA2002P can be set to fast

mode. In fast mode the LED pulse output is a programmable

high frequency output and is proportional to the instantaneous

power consumption. This mode is useful for faster calibration

times or can be used to interface to a micro-controller. Refer to

figure 5 for the LED output timing diagram.

The divider registers Cor and Kr are used for gain calibration.

These two registers used together with the LED pulse-rate

register (Cled) will generate the required meter constant

(pulses per kWh). The following formula can be used to

calculate Cor, Kr and Cled:

Pre-Divider (Cor), Rated Condition (Kr) and LED Pulse-

rate (Cled) registers

Where:

M

=

Meter constant (pulses per kWh)

Unom

=

Meters nominal voltage

Imax

=

Meters maximum current rating

Cor

=

495 default value, and can be varied by ±3.2%

(481 to 512, integer values only).

Kr

=

8 bit register having any integer value up to 128.

Cled depends on the two bits of byte D18:

D18[1] D18[0] Cled dividing factor

0

1

1

0

1

0

1

0

1

0.5

0.25

This sets the LED pulse rate to fast mode

of 641454/ Cor pulses per second. Default

would be 641454/495 = 1296 pulses/sec.

The initial value of Kr can be calculated from the above formula

using Cor's default value 495 as follows:

Krx

=

641454 / Unom / Imax / M x 3600 x 1000 / 495

The SA2002P's internal counter counts from zero so a one

must be subtracted from Kr:

Kr

=

Round (Krx) - 1

Krx is the real value and Kr is the integer value.

Once Kr has been established Cor can be calculated as

follows:

Corr

=

495 x (1 + (Krx - (Kr + 1) ) / Kr

Cor

=

Round (Corr) - 1

Where Corr is the real value and Cor the integer value.

Cor is made up of bits 0 to 4 of byte D12

Kr is made up of 1 byte (D16)

For further information see the example on calculating Kr and

Cor.

A 13 bit divider divides the pulse rate from the rated conditions

divider down to the desired counter resolution.

Cres can be calculated using the following formula:

Cres is made up of bits 0 to 6 o f byte D21 and byte D20.

Where:

Counter Resolution (Cres)

LED pulses / kWh

Cres

Counter pulses / kWh =

D21[4:0]

D20[7:0]

Counter Resolution

Counter Pulse-Width (Pw)

The pulse width for the mechanical counter driver output is

selectable to accommodate various step-motor and impulse-

counter requirements.

Pw is made up of bits 7 and 6 of byte D22.

D22[7]

D22[6]

Counter Pulse-Width

1

0

0

-

1

0

284 ms

142 ms

71 ms

Creep Current Threshold (Cs)

The creep threshold is expressed relative to the rated current

of the meter. The SA2002P will not meter currents below the

641454

CorxKr

3600

((Unom x Imax)/1000)

X

M=

X Cled