71M6515H
A Maxim Integrated Products Brand
Energy Meter IC
DATA SHEET
JULY 2011
We calculate PHADJ from φS, the desired phase lag:
tan(φS )
[
1+ (1− 2−9 )2 − 2(1− 2−9 )cos(2πf0T)
]
PHADJ = 220
(1− 2−9 )sin(2πf0T) − tan(φS )
1− (1− 2−9 )cos(2πf0T)
Finally, we calculate the new calibration current gain coefficient, including compensation for a slight gain increase in the phase
calibration circuit.
CAL _ I
1
CAL _ INEW
=
2−20 PHADJ(2 + 2−20 PHADJ − 2(1− 2−9 )cos(2πf0T))
AXI
1+
1− 2(1− 2−9 )cos(2πf0T) + (1− 2−9 )2
Calibration with Five Measurements
The five measurement method provides more orthogonality between the gain and phase error derivations. This method
involves measuring EV, E0, E180, E60, and E300. Again, set all calibration factors to nominal, i.e. CAL_IA = 16384, CAL_VA =
16384, PHADJ_A = 0..
First, calculate AXV from EV:
1. AXV = EV +1
Calculate AXI from E0 and E180
:
IV AXV AXI cos(0 −φS )
IV cos(0)
2.
3.
E0 =
−1 = AXV AXI cos(φS ) −1
IV AXV AXI cos(180 −φS )
IV cos(180)
E180
=
−1 = AXV AXI cos(φS ) −1
4.
5.
E0 + E180 = 2AXV AXI cos(φS ) − 2
E0 + E180 + 2
AXV AXI
=
2cos(φS )
(E0 + E180 ) 2 +1
6.
AXI
=
AXV cos(φS
)
Use above results along with E60 and E300 to calculate φS.
IV AXV AXI cos(60 −φS )
7.
E60
=
−1
IV cos(60)
= AXV AXI cos(φS ) + AXV AXI tan(60)sin(φS ) −1
IV AXV AXI cos(−60 −φS )
8.
E300
=
−1
IV cos(−60)
= AXV AXI cos(φS ) − AXV AXI tan(60)sin(φS ) −1
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