ADE7763ARSZ datasheet(39/56 Pages) AD

39 / 56 page

Data Sheet

ADE7763

Rev. C | Page 39 of 56

WGAIN = INT

480

17174

19186

























−

Note that WGAIN is a signed, twos complement register.

With WDIV and CFNUM set to 0, LAENERGY can be

expressed as

LAENERGYIB(expected) =

))

(

)

(

CFDEN

CLKIN

PERIOD

LINECYC

INT

expected

The calculated Wh/LSB ratio for the active energy register,

using Equation 35 is 6.378 × 10−4 is

378

imp/Wh

200

)

489

(

LSB

−

Watt Offset

Offset calibration allows outstanding performance over a wide

dynamic range, for example, 1000:1. To do this calibration two

measurements are needed at unity power factor, one at Ib and

the other at the lowest current to be corrected. Either calibra-

tion frequency or line cycle accumulation measurements can be

used to determine the energy offset. Gain calibration should be

performed prior to offset calibration.

Offset calibration is performed by determining the active energy

error rate. After determining the active energy error rate, calcu-

late the value to write to the APOS register to correct the offset.

APOS = −

CLKIN

Rate

Error

AENERGY

(45)

The AENERGY registers update at a rate of CLKIN/4. The twos

complement APOS register provides a fine adjustment to the

active power calculation. It represents a fixed amount of power

offset to be adjusted every CLKIN/4. The 8 LSBs of the APOS

1/256 of the least significant bit of the internal active energy

of the AENERGY[23:0] active energy register.

See the following sections for steps to determine the active

energy error rate for both line accumulation and reference

meter calibration options.

Calibrating Watt Offset Using a Reference Meter Example

Figure 73 shows the steps involved in calibrating watt offset

with a reference meter.

WRITE APOS VALUE TO THE APOS

MEASURE THE % ERROR BETWEEN THE

CF OUTPUT AND THE REFERENCE METER

OUTPUT, AND THE LOAD IN WATTS

SET ITEST = IMIN, VTEST = VNOM, PF = 1

CALCULATE APOS. SEE EQUATION 45.

Figure 73. Calibrating Watt Offset Using a Reference Meter

For this example:

Meter Constant:

MeterConstant(imp/Wh) = 3.2

Minimum Current:

IMIN = 40 mA

Load at Minimum Current:

WIMIN = 9.6 W

CF Error at Minimum Current: %ERRORCF(IMIN) = 1.3%

CF Numerator:

CFNUM = 0

CF Denominator:

CDEN = 489

Clock Frequency:

CKIN = 3.579545 MHz

Using Equation 45, APOS is −522 for this example.

CF Absolute Error = CFIMIN(nominal) − CFIMIN(expected)

(46)

CF Absolute Error =

(%ERRORCF(IMIN)) × WIMIN ×

3600

(imp/Wh)

ant

MeterConst

(47)

CF Absolute Error =

000110933

3600

200

100













Then,

AENERGY Error Rate (LSB/s) =

CF Absolute Error ×

CFNUM

CFDEN

(48)

AENERGY Error Rate (LSB/s) =

0.000110933 ×

05436

490 =

Using Equation 45, APOS is −522.

APOS = −

522

579545

05436

−

APOS can be represented as follows with CFNUM and WDIV

set at 0:

APOS =

−

CLKIN

CFDEN

ant

MeterConst

ERROR

IMIN

)

(

)

(

3600

(imp/Wh)

)

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ADE7763ARSZ 数据表(PDF) 39 Page - Analog Devices

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