71M6515H Datasheet, PDF (25/57 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
We calculate PHADJ from φ_S, the desired phase lag:
[ _[ ] _{] PHADJ}
=
2
20
⎡
⎢
⎣
(1
−
tan(φ_S ) 1 + (1 − 2^−9 )² − 2(1 − 2^−9 ) cos(2πf₀T )
2^−9 ) sin(2πf₀T ) − tan(φ_S ) 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 _NEW
=
CAL _ I
A_XI
1
1
+
2 ^−20
PHADJ (2 + 2^−20 PHADJ − 2(1 − 2^−9 ) cos(2πf₀T
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 E_V, 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 A_XV from E_V:
1.Î A_XV = E_V + 1
Calculate A_XI from E₀ and E₁₈₀:
2.
E₀
=
IV
A_XV A_XI cos(0 − φ_S )
IV cos(0)
−1 =
A_XV
A_XI
cos(φ_S ) − 1
3.
E₁₈₀
=
IV
A_XV A_XI cos(180 − φ_S )
IV cos(180)
−1 =
A_XV
A_XI
cos(φ_S ) −1
4. E₀ + E₁₈₀ = 2 A_XV A_XI cos(φ_S ) − 2
5.
A_XV A_XI
=
E₀ + E₁₈₀ + 2
2 cos(φ_S )
6.Î
A_XI
=
(E₀ + E₁₈₀ ) 2 + 1
A_XV cos(φ_S )
Use above results along with E₆₀ and E₃₀₀ to calculate φ_S.
7.
E₆₀
=
IV
A_XV A_XI cos(60 − φ_S )
IV cos(60)
−1
= A_XV A_XI cos(φ_S ) + A_XV A_XI tan(60) sin(φ_S ) − 1
8.
E₃₀₀
=
IV
A_XV A_XI cos(−60 − φ_S )
IV cos(−60)
−1
= A_XV A_XI cos(φ_S ) − A_XV A_XI tan(60) sin(φ_S ) − 1
Page: 25 of 57
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