Datasheet

ADE7753
Rev. C | Page 41 of 60
WRITE WGAIN VALUE TO THE WGAIN
REGISTER: ADDR. 0x12
CALCULATE CFDEN VALUE FOR DESIGN
WRITE CFDEN VALUE TO CFDEN REGISTER
ADDR. 0x15 = CFDEN
SET HALF LINECYCLES FOR ACCUMULATION
IN LINECYC REGISTER ADDR. 0x1C
SET I
TEST
= I
b
, V
TEST
= V
NOM
, PF = 1
CALCULATE WGAIN. SEE EQUATION 47.
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?
NO
NO
YES
YES
02875-A-007
RESET THE INTERRUPT STATUS
READ REGISTER ADDR. 0x0C
INTERRUPT?
Figure 81. Calibrating Watt Gain Using an Accurate Source
Equation 47 describes the relationship between the expected
LAENERGY value and the LAENERGY measured in the test
condition:
WGAIN = INT
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
12
)(
)(
21
nominalIB
expectedIB
LAENERGY
LAENERGY
(47)
The nominal LAENERGY reading, LAENERGY
IB(nominal)
, is the
LAENERGY reading with the test current applied. The
expected LAENERGY reading is calculated from the following
equation:
LAENERGY
IB(expected)
=
INT
⎟
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎜
⎝
⎛
×
+
+
×
WDIV
CFDEN
CFNUM
TimeonAccumulatiCF
expectedIB
1
1
(s)
)(
(48)
where CF
IB(expected)
(Hz) is calculated from Equation 34, accumula-
tion time is calculated from Equation 37, and the line period is
determined from the PERIOD register according to Equation 38.
For this example:
Meter Constant: MeterConstant(imp/Wh)
= 3.2
Test Current: I
b
= 10 A
Line Voltage: V
nominal
= 220 V
Line Frequency: f
l
= 50 Hz
Half Line Cycles: LINECYC
IB
= 2000
CF Numerator: CFNUM = 0
CF Denominator: CFDEN = 489
Energy Reading at Base Current:
LAENERGY
IB (nominal)
= 17174
Period Register Reading: PERIOD = 8959
Clock Frequency: CLKIN = 3.579545 MHz
CF
expected
is calculated to be 1.9556 Hz according to Equation 34.
LAENERGY
expected
is calculated to be 19186 using Equation 48.
CF
IB(expected)
(Hz) =
)(cos(
s/h3600
A10V220imp/Wh200.3
ϕ×
×
×
= 1.9556 Hz
LAENERGY
IB(expected)
=
INT
⎟
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎜
⎝
⎛
×
+
+
×××
WDIV
CFDEN
CFNUM
CLKINPERIODLINECYCCF
IB
expectedIB
1
1
/82/
)(
LAENERGY
IB(expected)
=
INT
1
1489
1
)10579545.3/(889592/20009556.1
6
⎟
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎜
⎝
⎛
+
××××
=
19186)4.19186(
=
INT
WGAIN is calculated to be 480 using Equation 47.
WGAIN = INT 48021
17174
19186
12
=
⎟
⎠
⎞
⎜
⎝
⎛
×
⎟
⎠
⎞
⎜
⎝
⎛
−
Note that WGAIN is a signed twos complement register.
With
WDIV and CFNUM set to 0, LAENERGY can be
expressed as