ADE7753ARSRL datasheet(40/60 Pages) AD

40 / 60 page

ADE7753

Rev. C | Page 40 of 60

CFDEN =

)

(

)

(

−

⎟

⎠

⎞

⎜

⎝

⎛

expected

nominal

INT

(44)

CFDEN =

489

)

490

(

9556

958

−

⎟

⎠

⎞

⎜

⎝

⎛

INT

This value for CFDEN should be loaded into each meter before

calibration. The WGAIN and WDIV registers can then be used

to finely calibrate the CF output. The following sections explain

how to calibrate a meter based on ADE7753 when using a

reference meter or an accurate source.

Calibrating Watt Gain Using a Reference Meter Example

The CFDEN and CFNUM values for the design should be

written to their respective registers before beginning the

calibration steps shown in Figure 80. When using a reference

meter, the %ERROR in CF is measured by comparing the CF

output of the ADE7753 meter with the pulse output of the

reference meter with the same test conditions applied to both

meters. Equation 45 defines the percent error with respect to

the pulse outputs of both meters (using the base current, Ib):

%ERRORCF(IB) =

100

)

(

)

(

−

ref

(45)

CALCULATE CFDEN VALUE FOR DESIGN

WRITE CFDEN VALUE TO CFDEN REGISTER

ADDR. 0x15 = CFDEN

WRITE WGAIN VALUE TO THE WGAIN

MEASURE THE % ERROR BETWEEN

THE CF OUTPUT AND THE

REFERENCE METER OUTPUT

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

02875-A-006

CALCULATE WGAIN. SEE EQUATION 46.

Figure 80. Calibrating Watt Gain Using a Reference Meter

For this example:

Meter Constant:

MeterConstant(imp/Wh)

= 3.2

CF Numerator:

CFNUM = 0

CF Denominator:

CFDEN = 489

% Error measured at Base Current:

%ERRORCF(IB) = -3.07%

One LSB change in WGAIN changes the active energy registers

and CF by 0.0244%. WGAIN is a signed twos complement

−3.07% error, WGAIN is 126:

WGAIN = INT

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

0244

)

(IB

ERROR

(46)

WGAIN = INT

126

0244

⎟

⎠

⎞

⎜

⎝

⎛ −

−

When CF is calibrated, the AENERGY register has the same

Wh/LSB constant from meter to meter if the meter constant,

WDIV, and the CFNUM/CFDEN ratio remain the same. The

Wh/LSB ratio for this meter is 6.378 × 10−4 using Equation 39

with WDIV at the default value.

(imp/Wh)

)

(

)

(

LSB

ant

MeterConst

WDIV

CFDEN

CFNUM

378

490

imp/Wh

200

)

490

(

LSB

−

Calibrating Watt Gain Using an Accurate Source Example

The CFDEN value calculated using Equation 44 should be

written to the CFDEN register before beginning calibration and

zero should be written to the CFNUM register. First, the line

accumulation mode and the line accumulation interrupt should

be enabled. Next, the number of half line cycles for the energy

accumulation is written to the LINECYC register. This sets the

accumulation time. Reset the interrupt status register and wait

for the line cycle accumulation interrupt. The first line cycle

accumulation results may not have used the accumulation time

set by the LINECYC register and should be discarded. After

resetting the interrupt status register, the following line cycle

readings will be valid. When LINECYC half line cycles have

elapsed, the IRQ pin goes active low and the nominal LAENERGY

with the test current applied can be read. This LAENERGY

value is compared to the expected LAENERGY value to deter-

mine the WGAIN value. If apparent energy gain calibration is

performed at the same time, LVAENERGY can be read directly

after LAENERGY. Both registers should be read before the next

interrupt is issued on the IRQ pin. Refer to the

section for more details.

details the steps

that calibrate the watt gain using an accurate source.

Apparent Energy

Calculation

Figure 81

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