SA9605A
1.
Power Calculation
In the Application Circuit (Figure 1), the mains voltages from Line 1, Line 2 and Line
3, are converted to currents and applied to the voltage sense inputs IVN1, IVN2 and
IVN3.
The current levels on the voltage sense inputs are derived from the mains voltage
(3 x 230 VAC) being divided down through voltage dividers to 14V. The resulting
input currents into the A/D converters are 14µA through the resistors R
15
, R
16
and
R
17
.
For the current sense inputs the voltage drop across the current transformers
terminating resistors are converted to currents of 16µA for rated conditions, by
means of resistors R
8
, R
9
(Phase 1); R
10
, R
11
(Phase 2); and R
12
, R
13
(Phase 3).
The signals providing the current information are applied to the current sensor
inputs: IIN1, IIP1; IIN2, IIP2; and IIN3, IIP3.
In this configuration, with the mains voltage of 3 x 230 V and rated currents of 80A,
the output frequency of the SA9605A energy metering integrated circuit at FOUT1
is 1.16kHz. In this case 1 pulse will correspond to an energy consumption of 3 x 18.4
kW/1160Hz = 47.6 Ws.
The output frequency at FOUT1 and FOUT2 represents the absolute sum of the
energy measured on all three phases, regardless of the direction of energy flow
through the current sensors. This measurement method will assist meter
manufacturers to circumvent meter tampering by reversal of the phases.
2.
Analog Input Configuration
The current and voltage sensor inputs are illustrated below.
These inputs are protected against electrostatic discharge through clamping
diodes, in conjunction with the amplifiers input configuration.
The feedback loops from the outputs of the amplifiers A
I
and A
V
generate virtual
shorts on the signal inputs. Exact duplications of the input currents are generated
for the analog processing circuitry.
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