SA9605A
The frequencies shown in the above table were chosen to allow a 4 - 3 - 2 scaling ratio
for rated conditions. This facility provides ease of interface with applications which use
the same post divider with mechanical counter or unchanged microcontroller software
for different current rated kWh meters.
For example, a meter manufacturer may wish to build meters for 3 system configurations
with rated current loading of 80ARMS, 60ARMS and 40ARMS. The rated line voltage is
230VRMS
.
FOUT1 Frequency
Consider the case where FOUT1 is the output of the energy counting block. For each
ofthethreeratedconditions, theinputcurrentsensingresistorsarechosentoensurethat
16µARMS flows into the current sensing pins.
Case 1 IL = 80ARMS
80 230
*
3
3
3
*
*
*
1 pulse on FOUT1 =
Case 2 IL = 60ARMS
1 pulse on FOUT1 =
Case 3 IL = 40ARMS
1 pulse on FOUT1 =
= 47.6Ws
= 35.7Ws
= 23.8Ws
1160
60 230
*
1160
40 230
*
1160
The amount of energy represented by one pulse for each of the three cases is different.
In addition to changing the current sensing resistor network, the energy counting block
must also be altered.
FOUT2 Frequency
Now consider the advantage of the user selectable frequency available on FOUT2.
Again the input current sensing resistors must be chosen to ensure that 16µARMS flows
into the current sensing pins.
Case 1 IL = 80ARMS
,
PGM1 = 0 PGM0 = 0
80 230
3
*
*
1 pulse on FOUT2 =
= 10.8kWs
5.11
Case 2 IL = 60ARMS
,
PGM1 = 0 PGM0 = 1
60 230
3
*
*
1 pulse on FOUT2 =
= 10.8kWs
3.83
Case 3 IL = 40ARMS,
1 pulse on FOUT2 =
sames
PGM1 = 1 PGM0 = 0
40 230
3
*
*
= 10.8kWs
2.55
8/14
SAMES [ SAMES ]
