SA2002P Datasheet, PDF (9/14 Pages) Sames – Programmable Single Phase Kilowatt-hour Energy IC for Mechanical Counter Application

SA2002P
sames
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.
D14[0] Creep threshold
0
0.02% of rated current
1
0.01% of rated current
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.
D14[2] Metering direction select
0
Bi-directional energy measurement
1
Positive energy measurement
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.
D14[3]
0
1
DC or AC measurement mode
AC measurement mode
DC measurement mode
Example of calculating Kr and Cor values
Metering specifications:
Unom
=
230V
Imax
=
80A
Meter constant =
6400 p/kWh
Calculate the Kr value:
Krx = 641454 / Unom / Imax / M x 3600x1000/495
Krx = 641454 / 230 / 80 / 6400 x 3600 x 1000 / 495
Krx = 39.61549
Krx = 40 (round Krx up to convert to integer)
Kr = Krx-1
Kr = 39
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
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).
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
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.
The following example shows how to calibrate the meter
Measure the %Error with a Watt hour standard
%Error =(Measured Energy - Real Energy)/Real Energy x 100
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
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
The value 40 is stored in the Kr.
The Cor value must be recalculated.
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
Store the calculated values in the EEPROM and the meter is
calibrated.
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