Datasheet

ADE7758 Data Sheet
Rev. E | Page 52 of 72
If it is not known, the line period is available in the ADE7758
frequency register, FREQ (0x10). To configure line period
measurement, select the phase for period measurement in the
MMODE[1:0] and set LCYCMODE[7]. Equation 72 shows how
to determine the value that needs to be written to xPHCAL
using the period register measurement.
°
××
=
360
]0:11[
__
s6.9
FREQ
WeightLSBPHCAL
ErrorPhase
xPHCAL
(72)
Example: Phase Calibration Using Line Accumulation
This example shows only Phase A phase calibration. All three
PHCAL registers can be calibrated simultaneously using the
same method.
For this example, I
TEST
= 10 A, V
NOM
= 220 V, power factor = 0.5
inductive, and frequency = 50 Hz. Also, LINECYC = 0x800.
With I
TEST
, V
NOM
, and 0.5 inductive power factor, the example
ADE7758 meter shows 7318d in the AWATTHR (0x01) register.
14804d in the AWATTHR register. This is equivalent to
−1.132% error.
%132.101132.0
2
14804
2
14804
–7318
−=−==Error
The Phase Error in degrees using Equation 66 is 0.374°.
()
°=
⎟
⎠
⎞⎛
− 01132.0
⎜
⎝
=° 374.0
3
sin–ArcErrorPhase
Using Equation 72, the value written to APHCAL (0x3F), if at
50 Hz, the FREQ (0x10) register = 2085d, is 17d. Note that a
PHCAL_LSB_Weight of 1.2 µs is used because the %Error is
negative.
11x017
360
2085
2.1
6.9
374.0 ==××°=APHCAL
For unity power factor (after gain calibration), the meter shows
STEP 1
SET MMODE,
LCYCMODE,
LINECYC AND
MASK REGISTERS
STEP 2
SET UP SYSTEM
FOR I
MIN
,V
NOM
@PF=1
STEP 3
RESET STATUS
REGISTER
STEP 4
READ ALL
xWATTHR
REGISTERS AFTER
LENERGY
INTERRUPT
END
FOR STEP 8
READ ALL xVARHR
AFTER LENERGY
INTERRUPT
FOR STEP 8, CALCULATE
xVAROS FOR ALL PHASES
STEP 5
CALCULATE
xWATTOS FOR ALL
PHASES
FOR STEP 8, WRITE TO
ALL xVAROS REGISTERS
STEP 6
WRITE TO ALL
xWATTOS
REGISTERS
STEP 7
SET UP SYSTEM
FOR I
TEST
,V
NOM
@
PF = 0, INDUCTIVE
STEP 8
REPEAT STEP 3 TO
STEP 8 FOR
xVARHR, xVAROS
CALIBRATION
04443-083
Figure 84. Power Offset Calibration Using Line Accumulation