SA9605A

sames

8/14

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 80A

The rated line voltage is

230V

FOUT1 Frequency

Consider the case where FOUT1 is the output of the energy counting block. For each

of the three rated conditions, the input current sensing resistors are chosen to ensure that

16µA

Case 1

I

1 pulse on FOUT1 =

80 * 230 * 3 = 47.6Ws

1160

Case 2

I

1 pulse on FOUT1 =

60 * 230 * 3 = 35.7Ws

1160

Case 3

I

1 pulse on FOUT1 =

40 * 230 * 3 = 23.8Ws

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 16µA

into the current sensing pins.

Case 1

I

PGM1 = 0

PGM0 = 0

1 pulse on FOUT2 =

80 * 230 * 3 = 10.8kWs

5.11

Case 2

I

PGM1 = 0

PGM0 = 1

1 pulse on FOUT2 =

60 * 230 * 3 = 10.8kWs

3.83

Case 3

I

PGM1 = 1

PGM0 = 0

1 pulse on FOUT2 =

40 * 230 * 3 = 10.8kWs

2.55