ADE7753 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7753' PDF : 60 Pages View PDF
ADE7753
Voltage rms compensation is done after the LPF3 filter (see
Figure 56).
VRMS = VRMS0 + VRMSOS
(64)
where:
VRMS0 is the rms measurement without offset correction.
VRMS is linear from full-scale to full-scale/20.
To calibrate the offset, two VRMS measurements are required,
for example, at Vnominal and Vnominal/10. Vnominal is set at half of the
full-scale analog input range so the smallest linear VRMS
reading is at Vnominal/10.
VRMSOS = V1 ×VRMS2 −V2 ×VRMS1
(65)
V2 − V1
where VRMS1 and VRMS2 are rms register values without offset
correction for input V1 and V2, respectively.
If the range of the 12-bit, twos complement VRMSOS register is
not enough, the voltage channel offset register, CH2OS, can be
used to correct the VRMS offset.
Current rms compensation is performed before the square root:
IRMS2 = IRMS02 + 32768 × IRMSOS
(66)
where IRMS0 is the rms measurement without offset correction.
The current rms calculation is linear from full-scale to full-
scale/100.
To calibrate this offset, two IRMS measurements are required,
for example, at Ib and IMAX/50. IMAX is set at half of the full-scale
analog input range so the smallest linear IRMS reading is at
IMAX/50.
IRMSOS =
1 × I12 × IRMS2 2 − I 2 2 × IRMS12
32768
I22 − I12
(67)
where IRMS1 and IRMS2 are rms register values without offset
correction for input I1 and I2, respectively.
Apparent Energy
Apparent energy gain calibration is provided for both meter-to-
meter gain adjustment and for setting the VAh/LSB constant.
VAENERGY =
VAENERGYinitial
×
1
VADIV
× ⎜⎝⎛1 +
VAGAIN
212
⎟⎠⎞
(68)
VADIV is similar to the CFDEN for the watt hour calibration. It
should be the same across all meters and determines the VAh/LSB
constant. VAGAIN is used to calibrate individual meters.
Apparent energy gain calibration should be performed before
rms offset correction to make most efficient use of the current
test points. Apparent energy gain and watt gain compensation
require testing at Ib while rms and watt offset correction require
a lower test current. Apparent energy gain calibration can be
done at the same time as the watt-hour gain calibration using
line cycle accumulation. In this case, LAENERGY and
LVAENERGY, the line cycle accumulation apparent energy
register, are both read following the line cycle accumulation
interrupt. Figure 87 shows a flowchart for calibrating active and
apparent energy simultaneously.
VAGAIN
=
INT
⎜⎛
⎜
⎝
⎜⎛
⎜⎝
LVAENERGYIB(expected)
LVAENERGYIB(nominal)
−
1⎟⎟⎠⎞
×
212
⎟⎞
⎟
⎠
(69)
LVAENERGYIB(expected) =
INT
⎜⎛
⎜
⎜
⎜⎝
VAh
LSB
Vnominal × I B
constant × 3600
s/h
×
Accumulation
⎟⎞
time(s)⎟
⎟
⎟⎠
(70)
The accumulation time is determined from Equation 37 and the
line period can be determined from the PERIOD register accord-
ing to Equation 38. The VAh represented by the VAENERGY
register is
VAh = VAENERGY × VAh/LSB constant
(71)
The VAh/LSB constant can be verified using this equation:
VAh
LSB
constant
=
VA
×
Accumulation time(s)
3600
LVAENERGY
(72)
Rev. C | Page 46 of 60
Share Link: 
