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SA9604APA

THREE PHASE BIDIRECTIONAL POWER/ENERGY METERING IC WITH SERIAL SPI INTERFACE

South African Micro Electronic Systems 

SA9604A

period between reads). However this will not be true when a wrap around occurs as

the following example will demonstrate:

Previous register value

=

16744955

Present register value

=

16767215

Delta value

=

16767215 - 16744955 = 22260

After the next read the values are as follows:

Previous register value

=

16767215

Present register value

=

12260

Delta value

=

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:

Energy per Count =

VI

K

Watt seconds

Where V

I

K

= Rated Voltage

= Current (I )

max

= 640 000 for Active Energy

640 000 * 2

π

for Reactive Energy

sames

13/20

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