71M6534H Demo Board User’s Manual
Page: 44 of 86
© 2005-2007 TERIDIAN Semiconductor Corporation
V2-0
12.
Î
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+
+
−
=
−
)
2
)(
60
tan(
)
(
tan
180
0
300
60
1
E
E
E
E
S
φ
Now that we know the A
XV
, A
XI
, and
φ
S
errors, we calculate the new calibration voltage gain coefficient from the
previous ones:
XV
NEW
A
V
CAL
V
CAL
_
_
=
We calculate PHADJ from
φ
S
, the desired phase lag:
[
]
[
]
⎥
⎦
⎤
⎢
⎣
⎡
−
−
−
−
−
−
−
+
=
−
−
−
−
)
2
cos(
)
2
1
(
1
)
tan(
)
2
sin(
)
2
1
(
)
2
cos(
)
2
1
(
2
)
2
1
(
1
)
tan(
2
0
9
0
9
0
9
2
9
20
T
f
T
f
T
f
PHADJ
S
S
π
φ
π
π
φ
And we calculate the new calibration current gain coefficient, including compensation for a slight gain increase
in the phase calibration circuit.
2
9
0
9
0
9
20
20
)
2
1
(
)
2
cos(
)
2
1
(
2
1
))
2
cos(
)
2
1
(
2
2
2
(
2
1
1
_
_
−
−
−
−
−
−
+
−
−
−
−
+
+
=
T
f
T
f
PHADJ
PHADJ
A
I
CAL
I
CAL
XI
NEW
π
π
2.1.3 FAST CALIBRATION
The calibration methods described so far require that the calibration system sequentially applies currents at
various phase angles. A simpler approach is based on the calibration system applying a constant voltage and
current at exactly zero degrees phase angle. This approach also requires much simpler mathematical
operations.
Before starting the calibration process, the voltage and current calibration factors are set to unity (16384) and
the phase compensation factors are set to zero.
During the calibration process, the meter measures for a given constant time, usually 30 seconds, and is then
examined for its accumulated Wh and VARh energy values. Access to the internal accumulation registers is
necessary for this method of calibration. The phase angle introduced by the voltage and/or current sensors is
then simply determined by:
Wh
VARh
a
tan
=
ϕ
CAL_VA
is determined by comparing the applied voltage to the measured voltage, or:
measured
applied
V
V
VA
CAL
⋅
=
16384
_
CAL_IA
is determined by comparing applied real energy with the measured apparent energy (and
compensating for the change applied to
CAL_VA
):
⋅
⋅
⋅
=
VA
CAL
VAh
Wh
IA
CAL
measured
applied
_
16384
_
The derivation of these formulae is shown in the Appendix.
Содержание 71M6534H
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