SA2002P
sames
PARAMETER DESCRIPTION
The initial value of Kr can be calculated from the above formula
using Cor's default value 495 as follows:
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.
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:
Pre-Divider (Cor), Rated Condition (Kr) and LED Pulse-
rate (Cled) registers
Kr
=
Round (Krx) - 1
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.
Where:
Krx is the real value and Kr is the integer value.
Once Kr has been established Cor can be calculated as
follows:
Corr
Cor
=
=
495 x (1 + (Krx - (Kr + 1) ) / Kr
Round (Corr) - 1
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.
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.
Counter Resolution (Cres)
A 13 bit divider divides the pulse rate from the rated conditions
divider down to the desired counter resolution.
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:
Cres can be calculated using the following formula:
LED pulses / kWh
Counter pulses / kWh
=
Cres
3600
641454
Cor x Kr
M =
Cled
X
Cres is made up of bits 0 to 6 o f byte D21 and byte D20.
X
((Unom x Imax)/1000)
D21[4:0] D20[7:0] Counter Resolution
Where:
M
=
=
=
=
Meter constant (pulses per kWh)
Meters nominal voltage
Counter Pulse-Width (Pw)
Unom
Imax
Cor
The pulse width for the mechanical counter driver output is
selectable to accommodate various step-motor and impulse-
counter requirements.
Meters maximum current rating
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.
Pw is made up of bits 7 and 6 of byte D22.
Cled depends on the two bits of byte D18:
D22[7]
D22[6] Counter Pulse-Width
D18[1]
D18[0] Cled dividing factor
1
0
0
-
284 ms
142 ms
71 ms
0
1
1
0
1
0
1
0
1
1
0
0.5
0.25
Creep Current Threshold (Cs)
This sets the LED pulse rate to fast mode
of 641454/ Cor pulses per second. Default
would be 641454/495 = 1296 pulses/sec.
The creep threshold is expressed relative to the rated current
of the meter. The SA2002P will not meter currents below the
8/14
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