Datasheet

71M6515H
Energy Meter IC
DATA SHEET
JULY 2011
Page: 26 of 60 © 2005−2011 Teridian Semiconductor Corporation 1.6
A Maxim Integrated Products Brand
Calibration with Three Measurements
The simplest calibration method is to make three measurements. Typically, a voltage measurement and two Watt-hour (Wh)
measurements are made.
If the voltage measurement has the error E
V
and the two Wh measurements have errors E
0
and E
60
, where E
0
is measured
with φ
L
= 0 and E
60
is measured with φ
L
= 60. These values should be simple ratios—not percentage values. They should be
zero when the meter is accurate and negative when the meter runs slow. The fundamental frequency is f
0
. T is equal to 1/f
S
,
where f
S
is the sample frequency (2520.62Hz). Set all calibration factors to nominal: CAL_IA = 16384, CAL_VA = 16384,
PHADJ_A = 0.
From the voltage measurement, we determine that
1.
1+=
VXV
EA
We use the other two measurements to determine φ
S
and A
XI
.
2.
1)cos(1
)0cos(
)0cos(
0
−=−
−
=
SXIXV
SXIXV
AA
IV
AAIV
E
φ
φ
2a.
)cos(
1
0
S
XIXV
E
AA
φ
+
=
3.
1
)60cos(
)60cos(
1
)60cos(
)60cos(
60
−
−
=−
−
=
S
XIXV
SXIXV
AA
IV
AAIV
E
φφ
3a.
[ ]
1
)60cos(
)sin()60sin()cos()60cos(
60
−
+
=
SSXIXV
AA
E
φφ
1)sin()60tan()cos( −+
=
SXIXVSXIXV
AAAA
φφ
Combining 2a and 3a:
4.
)tan()60tan()1(
0060 S
EEE φ ++=
5.
)60tan()1(
)tan(
0
060
+
−
=
E
EE
S
φ
6.








+
−
=
−
)60tan()1(
tan
0
060
1
E
EE
S
φ
and from 2a:
7.
)cos(
1
0
SXV
XI
A
E
A
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
VCAL
VCAL
_
_ =