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| 71M6515H Datasheet, PDF (24/57 Pages) Teridian Semiconductor Corporation – Energy Meter IC | |||
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71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
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 EV and the two Wh measurements have errors E0 and E60, where E0 is measured
with ÏL = 0 and E60 is measured with ÏL = 60. These values should be simple ratiosânot percentage values. They should be
zero when the meter is accurate and negative when the meter runs slow. The fundamental frequency is f0. T is equal to 1/fS,
where fS 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.Ã AXV = EV + 1
We use the other two measurements to determine ÏS and AXI.
2.
E0
=
IV
AXV AXI cos(0 â ÏS )
IV cos(0)
â1 =
AXV
AXI
cos(ÏS ) â 1
2a.
AXV AXI
=
E0 +1
cos(ÏS )
3.
E60
=
IV
AXV AXI cos(60 â ÏS )
IV cos(60)
â1 =
AXV
AXI
cos(60 â ÏS )
cos(60)
â1
3a.
E60
=
AXV
AXI [cos(60) cos(ÏS ) + sin(60) sin(ÏS )] â 1
cos(60)
= AXV AXI cos(ÏS ) + AXV AXI tan(60) sin(ÏS ) â 1
Combining 2a and 3a:
4. E60 = E0 + (E0 + 1) tan(60) tan(ÏS )
5.
tan(Ï S
)
=
E60 â E0
(E0 + 1) tan(60)
6.Ã
ÏS
=
tan
â1
ââââ
(
E0
E60 â E0
+1) tan(60)
âââ â
and from 2a:
7.Ã
AXI
=
E0 +1
AXV cos(ÏS )
Now that we know the AXV, AXI, and ÏS errors, we calculate the new calibration voltage gain coefficient from the previous ones:
CAL _ VNEW
=
CAL _V
AXV
Page: 24 of 57
© 2005-2008 TERIDIAN Semiconductor Corporation
V1.4
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