EVAL-ADE7753ZEB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-ADE7753ZEB' PDF : 60 Pages View PDF
ADE7753
CFDEN =
INT
⎜⎛
⎜⎝
CFIB(nominal)
CFIB(expected )
⎟⎞
⎟⎠
−1
(44)
CFDEN =
INT ⎜⎝⎛
958
1.9556
⎟⎠⎞
−
1
=
(490
− 1)
=
489
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) = CFIB − CFref (IB) × 100
CFref (IB)
(45)
CALCULATE CFDEN VALUE FOR DESIGN
WRITE CFDEN VALUE TO CFDEN REGISTER
ADDR. 0x15 = CFDEN
SET ITEST = Ib, VTEST = VNOM, PF = 1
MEASURE THE % ERROR BETWEEN
THE CF OUTPUT AND THE
REFERENCE METER OUTPUT
CALCULATE WGAIN. SEE EQUATION 46.
WRITE WGAIN VALUE TO THE WGAIN
REGISTER: ADDR. 0x12
02875-A-006
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
register and can correct for up to a 50% error. Assuming a
−3.07% error, WGAIN is 126:
WGAIN
=
INT
⎜⎜⎝⎛ −
% ERRORCF ( IB )
0.0244%
⎟⎟⎠⎞
(46)
WGAIN
=
INT
⎜⎝⎛ −
−3.07%
0.0244%
⎟⎠⎞
= 126
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.
(CFNUM + 1) ×WDIV
Wh
LSB
=
(CFDEN + 1)
MeterConstant(imp/Wh)
1
Wh
LSB
=
(490 +1)
3.200 imp/Wh
=
1
490 × 3.2
=
6.378 ×10 −4
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 Apparent Energy
Calculation section for more details. Figure 81 details the steps
that calibrate the watt gain using an accurate source.
Rev. C | Page 40 of 60
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