SA9604A
period between reads). However this will not be true when a wrap around occurs as
the following example will demonstrate:
Previous register value
Present register value
Delta value
=
=
=
16744955
16767215
16767215 - 16744955 = 22260
After the next read the values are as follows:
Previous register value
Present register value
Delta value
=
=
=
16767215
12260
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:
Function Check (delta_value);
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
if (delta_value)>0 then result : = (16777216-delta_value) *-1
else result : = (16777216+delta_value);
end;
end; {end function}
At rated conditions, the time for wrap around is as follows:
18.6 seconds for voltage
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:
VI
Watt seconds
Energy per Count =
Where
K
V
I
=
=
=
Rated Voltage
Current (Imax
)
K
640 000
for Active Energy
2
640 000
*
for Reactive Energy
π
13/20
sa m e s
SAMES [ SAMES ]
