ADE7763ARS datasheet(41/56 Pages) AD

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ADE7763

Rev. A | Page 41 of 56

ith an Accurate Source Example

Calibrating Phase w

With an accurate source, line cycle accumulation is a good

method of calibrating phase error. The value of LAENERGY

must be obtained at two power factors, PF = 1 and PF = 0.5

inductive.

SET HALF LINE CYCLES FOR ACCUMULATION

IN LINECYC REGISTER ADDR. 0x1C

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

CALCULATE PHCAL. SEE EQUATION 55.

SET MODE FOR LINE CYCLE

ACCUMULATION ADDR. 0x09 = 0x0080

ENABLE LINE CYCLE ACCUMULATION

INTERRUPT ADDR. 0x0A = 0x04

READ LINE ACCUMULATION ENERGY

ADDR. 0x04

RESET THE INTERRUPT STATUS

READ REGISTER ADDR. 0x0C

INTERRUPT?

YES

RESET THE INTERRUPT STATUS

READ REGISTER ADDR. 0x0C

INTERRUPT?

WRITE PHCAL VALUE TO THE PHCAL

For this example:

Line Frequency:

f = 50 Hz

tor:

CFDEN = 489

Base Current:

Ib = 10 A

Half

LINECYCIB = 2000

PERI D Register:

PERIOD = 8959

Expected Line Accumulation at Unity Power Factor (from Watt

Gain ection):

LAENERGYIB(expected) = 19186

Acti

Energy Reading at PF = 0.5 inductive:

LAENERGYIB, PF = 0.5 = 9613

Figure 76. Calibrating Phase with an Accurate Source

Meter Constant:

MeterConstant(imp/Wh) = 3.2

Line Voltage:

Vnominal = 220 V

CF Numerator:

CFNUM = 0

CF Denomina

Line Cycles Used at Base Current:

The error using Equation 52 is

Error =

0021

19186

9613

−

Phase Er

−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

0021

ror (°) = −Arcsin

Using Equation 55, PHCAL is 11.

PHCAL = INT

0x0D

360

8959

−

⎟

⎠

⎞

⎜

⎝

⎛

−

Note that PHCAL is a signed, twos complement register.

The phase lead is corrected by 0.08 degrees when the PHCAL

n (°) = −

Phase Correctio

PERIOD

PHCAL

−

360

)

0x0D

(

Phase Correction (°) = −

−

8960

360

)

0x0D

(

VRMS and IRMS Calibration

VRMS and IRMS are calculated by squaring the input in a

digital multiplier.

)

cos(

)

sin(

)

sin(

)

(

−

(59)

The s

s value is extract

ass

filter

t of the output o

the rms value. An offset correction is provided to cancel noise

Ther

oise from the 2ω term because the low-pass

filter does not completely attenuate the signal. This noise can be

min

by synchronizing the rms register readi

zero crossing of the voltage signal. The IRQ

quare of the rm

ed from v (t) by a low-p

. The square roo

f this low-pass filter give

and offset contributions from the inpu

e is ripple n

imized

ngs with the

output can be

al.

ngs of the voltage input.

configured to indicate the zero crossing of the voltage sign

This flowchart demonstrates how VRMS and IRMS readings

are synchronized to the zero crossi

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