CS5463 datasheet(15/44 Pages) CIRRUS

15 / 44 page

CS5463

DS678PP1

provides a pulse output that is proportional to the reac-

tive power or apparent power. Output E3 can also be set

to display the sign of the voltage applied to the voltage

channel or the PFMON comparator output.

The apparent power (S) is the combination of the active

power and reactive power, without reference to an im-

pedance phase angle, and is calculated by the CS5463

using the following formula:

Power Factor (PF) is the active power (PActive) divided

by the apparent power (S)

The sign of the power factor is determined by the active

power.

The CS5463 calculates the reactive power, QTrig utiliz-

ing trigonometric identities, giving the formula

Average reactive power, QAvg is generated by averag-

ing the voltage multiplied by the current with a 90o phase

shift difference between them. The 90o phase shift is re-

alized by applying an IIR digital filter in the voltage chan-

nel to obtain quadrature voltage (see Figure 3). This

filter will give exactly -90o phase shift across all frequen-

cies, and utilizes epsilon (

ε) to achieve unity gain at the

line frequency.

The instantaneous quadrature voltage (VQ) and current

(I) samples are multiplied to obtain the instantaneous

quadrature power (Q). The product is then averaged

over N conversions, utilizing the formula

Fundamental active (PF) and reactive (QF) power is cal-

culated by performing a discrete Fourier transform

(DFT) at the relevant frequency on the instantaneous

voltage (V) and current (I). Epsilon is used to set the fre-

quency of the internal sine (imaginary component) and

cosine (real component) waveform generator. The har-

monic active power (PH) is calculated by subtracting the

fundamental active power (PF) from the active power

(PActive).

The peak current (Ipeak) and peak voltage (Vpeak) are

the instantaneous current and voltage, respectively,

with the greatest magnitude detected during the last

computation cycle. Active, apparent, reactive and fun-

damental power are updated every computation cycle.

4.4 Linearity Performance

The linearity of the VRMS, IRMS, active, reactive and

power-factor power measurements (before calibration)

will be within ±0.1% of reading over the ranges speci-

fied, with respect to the input voltage levels required to

cause full-scale readings in the IRMS and VRMS regis-

ters. Refer to Accuracy Specifications on page 7.

Until the CS5463 is calibrated, the accuracy of the

CS5463 (with respect to a reference line-voltage and

line-current level on the power mains) is not guaranteed

to within ±0.1%. (See Section 7. System Calibration on

page 36.) The accuracy of the internal calculations can

often be improved by selecting a value for the Cycle

Count Register that will cause the time duration of one

computation cycle to be equal to (or very close to) a

whole number of power-line cycles (and N must be

greater than or equal to 4000).

V *

RMS

I *

Energy-to-pulse

+ Σ

ACoff*

√

ACTIVE

√

Poff*

PulseRate*

*DENOTES REGISTER NAME.

AVG

Inverse

PF*

√

TRIG*

Figure 4. Power Calculation Flow.

SVRMS IRMS

PActive

------------------

QTrig

S2 P

Active

–

QAvg

∑

-------------------------

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