Teridian 71M6534H, Руководство пользователя

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71M6534H Demo Board User’s Manual
Page: 52 of 86
© 2005-2007 TERIDIAN Semiconductor Corporation
V2-0
2.2.6 COMPENSATING FOR NON-LINEARITIES
Nonlinearity is most noticeable at low currents, as shown in Figure 2-6, and can result from input noise and
truncation. Nonlinearities can be eliminated individually for each channel by using the
QUANT_n
variables
(
QUANT_A, QUANT_B, QUANT_C
).
0
2
4
6
8
10
12
0.1 1 10 100
I [A]
e
rro
r [
%
]
error
Figure 2-6: Non-Linearity Caused by Quantification Noise
The error can be seen as the presence of a virtual constant noise current. Assuming a noise current of 10mA,
this current hardly contributes any error at currents of 10A and above, whereas the same noise current be-
comes dominant at small measurement currents.
The value that should to be used for
QUANT_n
can be determined by the following formula:
LSB IMAX VMAX
I V
error
n QUANT
⋅ ⋅
⋅
− =
100
_
Where error = observed error at a given voltage (V) and current (I),
VMAX = voltage scaling factor, as described in section 1.8.3,
IMAX = current scaling factor, as described in section 1.8.3,
LSB =
QUANT_n
LSB value = 1.04173*10
-9
W
Example
: Assuming an observed error in channel A as in Figure 2-6, we determine the error at 1A to be +1%. If
VMAX is 600V and IMAX = 208A, and if the measurement was taken at 240V, we determine
QUANT_A
as
follows:
042 , 846 , 1
10 04173 . 1 208 600
1 240
100
1
_
9
− =
⋅ ⋅ ⋅
⋅
− =
−
A QUANT
QUANT_A
is to be written to the CE location 0x26 (see the Data Sheet). It does not matter which current value
is chosen as long as the corresponding error value is significant (5% error at 0.2A used in the above equation
will produce the same result for
QUANT_A
).
Input noise and truncation can cause similar errors in the VAR calculation that can be eliminated using the
QUANT_VARn
variables.
QUANT_VARn
is determined using the same formula as
QUANT_n
.