ade7763 Analog Devices, Inc., ade7763 Datasheet - Page 39

• Manufacturer Part Number: ade7763
• Description: Single-phase Active And Apparent Energy Metering Ic
• Manufacturer: Analog Devices, Inc.

Calibrating Watt Offset with an Accurate Source Example
Figure 74 is the flowchart for watt offset calibration with an
accurate source.
For this example:
Meter Constant:
Line Voltage:
Line Frequency:
CF Numerator:
CF Denominator:
Base Current:
Half Line Cycles Used at Base Current:
Period Register Reading:
Clock Frequency:
Expected LAENERGY Register Value at Base Current
(from the Watt Gain section):
Minimum Current:
Figure 74. Calibrating Watt Offset with an Accurate Source
SET HALF LINE CYCLES FOR ACCUMULATION
ENABLE LINE CYCLE ACCUMULATION
ACCUMULATION ADDR. 0x09 = 0x0080
CALCULATE APOS. SEE EQUATION 45.
READ LINE ACCUMULATION ENERGY
SET I
IN LINECYC REGISTER ADDR. 0x1C
WRITE APOS VALUE TO THE APOS
RESET THE INTERRUPT STATUS
RESET THE INTERRUPT STATUS
INTERRUPT ADDR. 0x0A = 0x04
READ REGISTER ADDR. 0x0C
READ REGISTER ADDR. 0x0C
SET MODE FOR LINE CYCLE
TEST
REGISTER: ADDR. 0x11
= I
INTERRUPT?
INTERRUPT?
MIN
ADDR. 0x04
YES
YES
, V
MeterConstant(imp/Wh) = 3.2
V
f
CFNUM = 0
CFDEN = 489
I
LINECYC
PERIOD = 8959
CLKIN = 3.579545 MHz
LAENERGY
I
l
b
MIN
TEST
= 50 Hz
nominal
= 10 A
= 40 mA
= V
= 220 V
NOM
(IB)
NO
NO
, PF = 1
IB(expected)
= 2000
= 19186
Rev. A | Page 39 of 56
Number of Half Line Cycles used at Minimum Current:
Active Energy Reading at Minimum Current:
The LAENERGY
where:
LAENERGY
from the watt gain calibration.
LINECYC
accumulated over when measuring at I
More line cycles could be required at the minimum current to
minimize the effect of quantization error on the offset calibration.
For example, if a test current of 40 mA results in an active energy
accumulation of 113 after 2000 half line cycles, one LSB variation
in this reading represents a 0.8% error. This measurement does
not provide enough resolution to calibrate a <1% offset error.
However, if the active energy is accumulated over 37,500 half
line cycles, one LSB variation results in 0.05% error, reducing the
quantization error.
APOS is −672 using Equations 55 and 49.
LAENERGY
INT
LAENERGY
INT
LAENERGY Absolute Error =
LAENERGY
LAENERGY Absolute Error = 1395 − 1370 = 25
AENERGY Error Rate (LSB/s) =
AENERGY Error Rate (LSB/s) =
APOS = −
APOS = −
35700
LAENERGY
25
IMIN
I
. 0
2 /
10
IB(expected)
MIN
I
04
LINECYC
B
is the number of half line cycles that energy is
. 0
AENERGY
IMIN(expected)
IMIN(expected)
IMIN(nominal)
. 3
expected
069948771
. 3
19186
LAENERGY
Absolute
579545
579545
is the expected LAENERGY reading at I
8
at I
2 /
8959
CLKIN
MIN
=
=
35700
− LAENERGY
2000
Error
10
Error
10
LINECYC
LAENERGY
is 1255 using Equation 49.
2
6
6
IB
35
(
expected
Rate
. 0
8
069948771
INT
672
(IMIN)
)
MIN
CLKIN
PERIOD
2
IMIN(nominal)
(
IMIN(expected)
1369
.
35
LINECYCI
= 35700
LINECYC
.
80
)
= 1395
ADE7763
1370
MIN
IB
b
(49)
(50)
(51)