C+D Accuracy
The basic impedance accuracy depicted in Figure 2-1 applies to capacitance measurements when
the impedance is interpreted to be 1/2π f C, where f is the test frequency in Hz and C is the
capacitance in Farads. For convenience, Figure 2-1 is redrawn in Figure 2-3 with lines of constant
capacitance superimposed. Also, Table 2-3 is recreated for capacitive impedances as Table 2-5.
Note from Table 2-5 that the range error factor K
l
is negligible for capacitances below 1590/f µF and
K
h
is negligible for capacitances above 159/f µF.
The accuracy of the capacitance measurement is calculated from equation (1) above, with the
additional stipulation that if the measured D has a value less than 0.1, then the basic capacitance
accuracy factor should be multiplied by the factor (1 + D). Let the basic capacitance accuracy factor
be denoted A
c
.
A
c (measured)
% = ± [ Ac
× K
i
× K
v
+ 100 × (K
h
+ K
l
)] (4a)
Then the accuracy of the D calculation is given by
Accuracy of D = ± [A
c
/100] (4b)
Note that the accuracy of D is specified as a magnitude, not as a percentage.
0.55% 0.35% 0.55%
0.35% 0.25% 0.35%
0.20%
Figure 2-3 Basic Impedance Accuracy for Capacitances
1
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