ADE7763ARS datasheet(40/56 Pages) AD

40 / 56 page

ADE7763

Rev. A | Page 40 of 56

mpensates for phase error by inserting a small

time delay or advance on the voltage channel input. Phase leads

up to 1.84° and phase lags up to 0.72° at 50 Hz can be corrected.

The error is determined by measuring the active energy at IB and

two power factors, PF = 1 and PF = 0.5 inductive.

Some CTs may introduce large phase errors that are beyond the

range of the phase calibration register. In this case, coarse phase

compensation has to be done externally with an analog filter.

The phase error can be obtained from either CF or LAENERGY

measurements:

Error =

Phase Calibration

The PHCAL register is provided to remove small phase errors.

The ADE7763 co

)

(

)

(

expected

LAENERGY

−

(52)

If watt gain and offset calibration have been performed, there

should be 0% error in CF at unity power factor, and then

Error = %ERRORCF(IB,PF = 0.5)/100

(53)

The phase error is

Phase Error (°) = −Arcsin

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

Error

(54)

The relationship between phase error and the PHCAL phase

correction register is

PHCAL = INT

()

⎟

⎠

⎞

⎜

⎝

⎛

360

PERIOD

Error

Phase

0x0D

(55)

The expression for PHCAL can be simplified using the

assumption that at small x

Arcsin(x) ≈ x

d in the voltage channel by PHCAL is

AL − 0x0D) × 8/

s a time delay if

sit e, b

ts a time advance if this

he is

f PHCAL = 0x0D.

ction of the

)

The delay introduce

Delay = (PHC

CLKIN

(56)

The delay associated with the PHCAL register i

PHCAL − 0x0D is po iv

ut represen

quantity is negati . T re

no time delay i

The phase correction is in the opposite dire

phase error.

Phase Correction (°) = − (PHCAL − 0x0D

PER

Calibrating Phase Using a Reference Meter Example

A power factor of 0.5 inductive can be assumed if the

output rate of the reference meter is half of its PF

Then, the percent error between CF and the pulse output o

IOD

× 360

(57)

pulse

= 1 ate.

r ca

the reference mete

n be used to perform the preceding

calculations.

WRITE PHCAL VALUE TO THE PHCAL

MEASURE THE % ERROR BETWEEN

THE CF OUTPUT AND THE

REFERENCE METER OUTPUT

SET ITEST = Ib, VTEST = VNOM, PF = 0.5

CALCULATE PHCAL. SEE EQUATION 55.

Figure 75. Calibrating Phase Using a Reference Meter

For this example:

CF %ERROR at PF = 0.5 Inductive: %ERRORCF(IB,PF = 0.5) = 0.215%

PERIOD Register Reading:

PERIOD = 8959

Then PHCAL is 11 using Equations 57 through 59:

Error = 0.215%/100 = 0.00215

Phase Error (°) = −Arcsin

−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

00215

PHCAL = INT

⎟

⎠

⎞

⎜

⎝

⎛

−

360

8959

+0x0D = −2 + 13 = 11

PHCAL can be expressed as follows:

PHCAL =

INT

⎟⎟

⎞

⎜⎜

⎛

⎟⎟

⎞

⎜⎜

⎛

−

100

Arcsin

PERIOD

ERROR

(58)

⎠

⎝

⎠

⎝

0x0D

Note that PHCAL is a signed, twos complement register.

Setting the PHCAL register to 11 provides a phase correction

of 0.08° t

Phase Correction (°) = −

o correct the phase lead:

PERIOD

PHCAL

−

360

)

0x0D

(

Phase Corr

−

8960

360

)

0x0D

(

ection (°) = −

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