SA9603B
ssaammeess
The delta value for the energy registers is between 0 and
8388607 for positive energy flow and between 0 and -8388607
for negative energy flow. For voltage the maximum usable
delta value is 17666215 as voltage is in a positive direction
only.
K
=
640 000
640 000 *2
p
for Active Energy
for Reactive Energy
Example:
V
= 230V
= 80A
I
When reading the registers care should be taken to check for a
wrap around condition.
Active Power
= 230V x 80A x (n/t) / 640 000
Reactive Power = 230V x 80A (n/t) / (640 000 x 2)/Pi)
N
= Difference in register values between
successive reads (delta value)
As an example lets assume that with a constant load
connected the delta value is 22260. Because of the constant
load, the delta value should always be 22260 every time the
register is read and the previous value subtracted (assuming
the same time period between reads). However this will not be
true when a wrap around occurs as the following example will
demonstrate:
T
= Time difference between successive
reads(inseconds)
To calculate the measured voltage, the following formula is
applied:
V
measured
=
V * n
940000*t
Previous register value
Present register value
Delta value
=
=
=
16744955
Where:
16767215
V
T
N
= RatedVoltage
16767215-16744955 = 22260
= Timedifferencebetweensuccessivereads
= Differenceinregistervaluesbetweensuccessivereads
After the next read the values are as follows:
Previous register value
Present register value
Delta value
=
=
=
16767215
12260
The Voltage calculated is the average voltage. The voltage
measurement will give an accuracy of better than 1% for a
voltage range of 50% to 115% of the rated mains voltage if the
voltageisapuresinewave.
12260 - 16767215 = -16754955
Computing this delta value will result in incorrect readings, in
other words a wrap around has occurred. A typical function to
check for wrap around condition would be as follows:
Themainsfrequencymaybecalculatedasfollows:
Function Check (delta_value);
Frequency
=
Crystalfrequency
RegisterValue*2
Begin
Temp_delta_value = abs(delta_value); {get rid of the minus
sign for example: abs(-151) = 151}
If (Temp_delta_value)> 8388607 then
Begin
CALIBRATION
For accurate results we would recommend the following
softwarecalibrationprocedure:
If (delta_value)> 0 then result: = (16777216-delta_value) *-1
else result : = (16777216+delta_value);
End;
Activeenergy
Establish a calibration factor for active energy (Ka) at pf close
to1.
End; {end function}
ActiveMeasured=Active_Register_ValuexKa
At rated conditions, the time for wrap around is as follows:
18.6 seconds for voltage
ReactiveEnergy
Withapfcloseto1establishthephaseerror:
PhaseError=arctan(VARMeasured/VARmeasured)
Foreachmeasurementcalculatethefollowing:
13 seconds for active and 21 seconds for reactive
The active and reactive energy measured per count, may be
calculated by applying the following formula:
2
2
VA
PHIcalibrated =
PHICorrected =
VARtrue
=
ActiveMeasured + VARmeasured
arctan (VARmeasured / ActiveMeasured
PHIcalibrated - PhaseError
Energy per Count
=
VI Watt seconds
K
=
VA * sin(PHICorrected)
Where:
V
=
Rated Voltage
I
=
Current (I )
MAX
7/12
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