ADE7753 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7753' PDF : 60 Pages View PDF
ADE7753
Calibrating Watt Offset with an Accurate Source Example
Figure 83 is the flowchart for watt offset calibration with an
accurate source.
SET ITEST = IMIN, VTEST = VNOM, PF = 1
SET HALF LINE CYCLES FOR ACCUMULATION
IN LINECYC REGISTER ADDR. 0x1C
SET MODE FOR LINE CYCLE
ACCUMULATION ADDR. 0x09 = 0x0080
ENABLE LINE CYCLE ACCUMULATION
INTERRUPT ADDR. 0x0A = 0x04
RESET THE INTERRUPT STATUS
READ REGISTER ADDR. 0x0C
NO
INTERRUPT?
YES
RESET THE INTERRUPT STATUS
READ REGISTER ADDR. 0x0C
NO
INTERRUPT?
YES
READ LINE ACCUMULATION ENERGY
ADDR. 0x04
CALCULATE APOS. SEE EQUATION 49.
WRITE APOS VALUE TO THE APOS
REGISTER: ADDR. 0x11
02875-A-009
Figure 83. Calibrating Watt Offset with an Accurate Source
For this example:
Meter Constant:
MeterConstant(imp/Wh)
= 3.2
Line Voltage:
Vnominal = 220 V
Line Frequency:
fl = 50 Hz
CF Numerator:
CFNUM = 0
CF Denominator:
CFDEN = 489
Base Current:
Ib = 10 A
Half Line Cycles Used at Base Current:
LAENERGYIMIN(nominal) = 1395
The LAENERGYexpected at IMIN is 1370 using Equation 53.
LAENERGYIMIN(expected) =
INT
⎜⎜⎝⎛
I
MIN
IB
×
LAENERGYIB(expected
)
×
LINECYCI MIN
LINECYC IB
⎟⎟⎠⎞
(53)
LAENERGYIMIN(expected) =
INT
⎜⎝⎛
0.04
10
×19186 ×
35700
2000
⎟⎠⎞
=
INT (1369.80)
= 1370
where:
LAENERGYIB(expected) is the expected LAENERGY reading at Ib
from the watt gain calibration.
LINECYCIMIN is the number of half line cycles that energy is
accumulated over when measuring at IMIN.
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 an 0.8% error. This measurement
does not provide enough resolution to calibrate out 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 Absolute Error =
LAENERGYIMIN(nominal) − LAENERGYIMIN(expected)
LAENERGY Absolute Error = 1395 − 1370 = 25
(54)
AENERGY Error Rate (LSB/s) =
LAENERGY Absolute Error
×
CLKIN
(55)
LINECYC / 2
8 × PERIOD
AENERGY Error Rate (LSB/s) =
25 × 3.579545 ×106 = 0.069948771
35700 / 2 8 × 8959
AENERGY Error Rate × 235
APOS = −
CLKIN
APOS = −
0.069948771× 235
3.579545 ×106
= −672
LINECYC(IB) = 2000
Period Register Reading: PERIOD = 8959
Clock Frequency:
CLKIN = 3.579545 MHz
Expected LAENERGY Register Value at Base Current
(from the Watt Gain section):LAENERGYIB(expected) = 19186
Minimum Current:
IMIN = 40 mA
Number of Half Line Cycles used at Minimum Current:
LINECYC(IMIN) =
35700
Active energy Reading at Minimum Current:
Rev. C | Page 43 of 60
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