SA9604A

sames

15/20

7.2 Reactive Energy

With a pf close to 0 establish the phase error:

PhaseError = arctan (VARMeaured / ActiveMeasured)

For each measurement calculate the following:

VA

=

PHIcalibrated =

arctan (VARmeasured / ActiveMeasured)

PHICorrected =

PHIcalibrated - PhaseError

VARtrue

=

VA * sin(PHICorrected)

TYPICAL APPLICATION

In the Application Circuit (Figure 1), the components required for a three phase energy

metering application are shown.

Terminated current sensors (current transformers) are connected to the current sensor

inputs of the SA9604A through current setting resistors (R

The resistor values for standard operation are selected for an input current of 16

µA

RMS

into the SA9604A, at the rated line current.

The values of these resistors are calculated as follows:

Phase 1:

R

Phase 2:

R

Phase 3:

R

Where I

LX

=

Secondary CT current at rated conditions.

R

=

Current transformer termination resistors for the three phases.

R

R

P

3. The values should be selected so that the input currents into the voltage sense inputs

(virtual ground) are set to 14

µA

and C3 are for decoupling and phase compensation.

R

are set. R

will affect the output quadratically (i.e:

∆R = +5%, ∆P = +10%).

XTAL is a colour burst TV crystal (f = 3.5795 MHz) for the oscillator. The oscillator

frequency is divided down to 1.78975 MHz on-chip, to supply the digital circuitry and the

A/D converters.