CS5464 datasheet(16/46 Pages) CIRRUS

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CS5464

DS682PP1

The average reactive power calculation (QAvg, Q2Avg) is

generated by averaging the voltage then multiplying

that value by the current measurement with a 90° phase

difference between the two. The 90° phase shift is real-

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

nel to obtain quadrature voltage (see Figure 3 and 4).

This filter will give exactly -90° phase shift across all fre-

quencies, and utilizes epsilon (

ε) to achieve unity gain

at the line frequency.

The instantaneous quadrature voltage (VQ, V2Q) and

current (I, I2) samples are multiplied to obtain the in-

stantaneous quadrature power (Q, Q2). The product is

then averaged over N conversions, utilizing the formula

The peak current (Ipeak, I2peak) and peak voltage (Vpeak,

V2peak) are the instantaneous current and voltage, re-

spectively, with the greatest magnitude detected during

the previous computation cycle. Active, apparent, reac-

tive, and fundamental power are updated every compu-

tation cycle.

4.4 Tamper Detection

The third channel (inputs IIN2

±) can be used for tamper

detection when required by the application. Typically us-

ing a shunt resistor to save cost, the tamper input mon-

itors the current through the neutral connection. See

Figure 19 on page 43.

The CS5464 calculates active power, P and P2, using

current channel inputs, IIN

± and IIN2±, respectively.

The active powers are then compared, looking for devi-

ations greater then a programmable threshold, as an in-

dicator of a connection fault, potentially caused by

tampering. When tamper detect is enabled (by default)

the current channel that produces the larger active pow-

er will be registered in the pulse output accumulation

registers and pulse output pins.

4.5 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 CS5464 is calibrated, the accuracy of the

CS5464 (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 39.) 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 4000

or greater).

Avg

∑

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