Datasheet

71M6515H
Energy Meter IC
DATA SHEET
JULY 2011
Page: 27 of 60 © 2005−2011 Teridian Semiconductor Corporation 1.6
A Maxim Integrated Products Brand
We calculate PHADJ from φ
S
, the desired phase lag:
[ ]
[ ]






−−−−
−−−+
=
−−
−−
)2cos()21(1)tan()2sin()21(
)2cos()21(2)21(1)tan(
2
0
9
0
9
0
929
20
TfTf
Tf
PHADJ
S
S
πφπ
πφ
Finally, we calculate the new calibration current gain coefficient, including compensation for a slight gain increase in the phase
calibration circuit.
29
0
9
0
92020
)21()2cos()21(21
))2cos()21(222(2
1
1_
_
−−
−−−
−+−−
−−+
+
=
Tf
TfPHADJPHADJ
A
ICAL
ICAL
XI
NEW
π
π
Calibration with Five Measurements
The five measurement method provides more orthogonality between the gain and phase error derivations. This method
involves measuring E
V
, E
0
, E
180
, E
60
, and E
300
. 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.
1+=
VXV
EA
Calculate A
XI
from E
0
and E
180
:
2.
1)cos(1
)0cos(
)0cos(
0
−=−
−
=
SXIXV
SXIXV
AA
IV
AAIV
E
φ
φ
3.
1)cos(1
)180cos(
)180cos(
180
−=−
−
=
SXIXV
SXIXV
AA
IV
AAIV
E
φ
φ
4.
2)cos(2
1800
−=+
SXIXV
AAEE φ
5.
)cos(2
2
1800
S
XIXV
EE
AA
φ
++
=
6.
)cos(
12)(
1800
SXV
XI
A
EE
A
φ
++
=
Use above results along with E
60
and E
300
to calculate φ
S
.
7.
1
)60cos(
)60cos(
60
−
−
=
IV
AAIV
E
SXIXV
φ
1)sin()60tan()cos( −+=
SXIXVSXIXV
AAAA φφ
8.
1
)60cos(
)60cos(
300
−
−
−−
=
IV
AAIV
E
SXIXV
φ
1)sin()60tan()cos( −−=
SXIXVSXIXV
AAAA φφ