ADE7753 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7753' PDF : 60 Pages View PDF
ADE7753
Calibrating Phase with an Accurate Source Example
With an accurate source, line cycle accumulation is a good
method of calibrating phase error. The value of LAENERGY
must be obtained at two power factors, PF = 1 and PF = 0.5
inductive.
SET ITEST = Ib, VTEST = VNOM, PF = 0.5
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 PHCAL. SEE EQUATION 59.
WRITE PHCAL VALUE TO THE PHCAL
REGISTER: ADDR. 0x10
02875-A-011
Figure 85. Calibrating Phase 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:
LINECYCIB = 2000
PERIOD Register:
PERIOD = 8959
Expected Line Accumulation at Unity Power Factor (from Watt
Gain Section:
LAENERGYIB(expected) =
19186
Active Energy Reading at PF = .5 inductive:
= .5 = 9613
The error using Equation 56 is
Error =
9613 −19186 2
19186 2
= 0.0021
LAENERGYIB, PF
Phase
Error
(°)
=
−Arcsin
⎜⎜⎝⎛
0.0021
3
⎟⎟⎠⎞
=
−0.07°
Using Equation 59, PHCAL is calculated to be 11.
PHCAL
=
INT
⎜⎝⎛
−
0.07°
×
8959
360°
⎟⎠⎞
+
0x0D
=
−2
+
13
=
11
Note that PHCAL is a signed twos complement register.
The phase lead is corrected by 0.08° when the PHCAL register
is set to 11:
Phase Correction (°) = − (PHCAL − 0x0D)× 360°
PERIOD
Phase Correction (°) = − (11 − 0x0D)× 360° = 0.08°
8960
VRMS and IRMS Calibration
VRMS and IRMS are calculated by squaring the input in a
digital multiplier.
v2(t) = 2 Vsin(ωt)× 2 V sin(ωt) = V 2 −V 2 × cos(2ωt) (63)
The square of the rms value is extracted from v2(t) by a low-pass
filter. The square root of the output of this low-pass filter gives
the rms value. An offset correction is provided to cancel noise
and offset contributions from the input.
There is ripple noise from the 2ω term because the low-pass
filter does not completely attenuate the signal. This noise can be
minimized by synchronizing the rms register readings with the
zero crossing of the voltage signal. The IRQ output can be
configured to indicate the zero crossing of the voltage signal.
This flowchart demonstrates how VRMS and IRMS readings
are synchronized to the zero crossings of the voltage input.
SET INTERRUPT ENABLE FOR ZERO
CROSSING ADDR. 0x0A = 0x0010
RESET THE INTERRUPT STATUS
READ REGISTER ADDR. 0x0C
INTERRUPT?
NO
YES
READ VRMS OR IRMS
ADDR. 0x17; 0x16
RESET THE INTERRUPT STATUS
READ REGISTER ADDR. 0x0C
02875-A-003
Figure 86. Synchronizing VRMS and IRMS Readings with Zero Crossings
Rev. C | Page 45 of 60
Share Link: 
