sames

SA2002P

9/14

http://www.sames.co.za

Example of calculating Kr and Cor values

Metering specifications:

Unom

=

230V

Imax

=

80A

Meter constant

=

6400 p/kWh

Calculate the Kr value:

= 40 (round Krx up to convert to integer)

The value 39 is stored in the Kr register. The pre-divider (Cor)

value is calculated next. Cor is programmable to divide

between 481 and 512. Only the 5 least significant bits need to

Krx = 641454 / Unom / Imax / M x 3600x1000/495

Krx = 641454 / 230 / 80 / 6400 x 3600 x 1000 / 495

Krx = 39.61549

Krx

Kr = Krx-1

Kr = 39

be programmed. During the Kr calculation the value was

rounded up and any rounding error is now taken into account. A

ratio of the rounding "error" is calculated relative to the center

of the variable range of Cor (481 - 512).

Store the calculated values in the EEPROM

Ensure that the device reload its registers from the EEPROM

by means of the RLOAD pin or power down the meter and

power up again.

The meter is now set up with the correct register values but not

yet calibrated.

Measure the %Error with a Watt hour standard

The %Error will be worked back into the calculations above.

For this example we will assume a 2.83% error between the

correct energy value and energy measured by the SA2002P.

Recalculate the Kr value

The value 40 is stored in the Kr.

The Cor value must be recalculated.

Store the calculated values in the EEPROM and the meter is

calibrated.

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

Corr = 495 x (1 + (39.61549 - 40) / 39.61549)

Corr = 495 x 0.990294

Corr = 490.1955

Corr = 490 (Convert to Integer)

Cor = Corr -1

Cor = 489

%Error =(Measured Energy - Real Energy)/Real Energy x 100

Krx = 641454 / Unom / Imax / M x 3600 x 1000 / 495 x (1 +

%Error / 100 )

Krx = 641454 / 230 / 80 / 6400 x 3600 x 1000 / 495 x 1.0283

Krx = 40.73661

Krx = 41 (Round up and make integer value)

Kr = Krx-1

Kr = 41-1

Kr=40

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

Corr = 495 x (1 + (40.7366 - 41) / 40.7366

Corr = 495 x 0.993534

Corr = 491.7995

Corr = 492 (Convert to Integer)

Cor = Corr-1

Cor = 491

The following example shows how to calibrate the meter

D14[2]

Metering direction select

0

1

Bi-directional energy measurement

Positive energy measurement

D14[3]

DC or AC measurement mode

0

1

AC measurement mode

DC measurement mode

D14[0]

Creep threshold

0

1

0.02% of rated current

0.01% of rated current

creep threshold. The creep threshold is implemented to

prevent the meter from accumulating energy when no load is

connected.

Cs is made up of bit 0 of byte D14.

Metering direction select (Ds)

The SA2002P may be configured to measure positive energy

or positive and negative energy.

Ds is made up of bit 2 of byte D14.

DC or AC measurement mode (Dc)

The SA2002P may be configured to measure AC energy or DC

energy. In case of AC measurement selection, the device will

track the mains frequency for offset cancellation purposes. In

DC measurement mode the device is locked to a fixed

frequency for offset cancellation. The FMO output is switched

to 28Hz in DC mode.

Dc is made up of bit 3 of byte D14.