CS5464 datasheet(16/46 Pages) CIRRUS

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CS5464

DS682F3

4.8 Power and Energy Results

The instantaneous voltage and current samples are

multiplied to obtain the instantaneous power (P1, P2)

(see Figure 3 and 4). The product is then averaged over

conversions to compute active power (P1AVG,

P2AVG).

Apparent power (S1, S2) is the product of RMS voltage

and current as shown:

Power factor (PF1, PF2) is active power divided by ap-

parent power as shown below. The sign of the power

factor is determined by the active power.

Wideband reactive power (Q1WB, Q2WB) is calculated

by doing a vector subtraction of active power from ap-

parent power.

Quadrature power (Q1, Q2) are sample rate results ob-

tained by multiplying instantaneous current (I1, I2) by in-

stantaneous quadrature voltage (V1Q, V2Q) which are

created by phase shifting instantaneous voltage (V1,

) 90 degrees using first-order integrators. (see Figure

3 and 4). The gain of these integrators is inversely relat-

ed to line frequency, so their gain is corrected by the Ep-

silon

Reactive power (Q1AVG, Q2AVG) is generated by inte-

grating the instantaneous quadrature power over N

samples.

4.9 Peak Voltage and Current

Peak current (I1PEAK, I2PEAK) and peak voltage

(V1PEAK, V2PEAK) are the largest current and voltage

samples detected in the previous low-rate interval.

4.10 Power Offset

The power offset registers, P1OFF (P2OFF) can be used

to offset erroneous power sources resident in the sys-

tem not originating from the power line. Residual power

offsets are usually caused by crosstalk into current

paths from voltage paths or from ripple on the meter or

chip’s power supply, or from inductance from a nearby

transformer.

These offsets can be either positive or negative, indicat-

ing crosstalk coupling either in phase or out of phase

with the applied voltage input. The power offset regis-

ters can compensate for either condition.

To use this feature, measure the average power at no

load using either Single or Continuous Conversion com-

mands. Take the measured result (from the P1AVG

(P2AVG) register), invert (negate) the value and write it

to the associated power offset register, P1OFF (P2OFF).

V1ACOFF

(V2ACOFF)

I1ACOFF

(I2ACOFF)

P1OFF (P2OFF)

Figure 5. Low-rate Calculations

RMS



ACTIVE

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

ACTIVE

–

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