ACCURACY
3-7
C + R ACCURACY
Accuracy of C = ± [A x K
i
x K
v
+ (K
h
+ K
l
) x 100] %
A = Basic Capacitance Accuracy
Factor from graph on page 4-6.
If the unit is in the constant voltage
(CV) mode, or under internal or
external bias, double the basic
accuracy factor.
K
i
= Integration Time Factor (see K
i
Table below)
K
v
= Voltage Error Factor (see K
v
table
below).
K
h
, K
l
= Extreme Range Error Term (see
K
h
, K
l
table below).
Accuracy of R = ± [A
c
x (1+1/|D|)] %
A
c
= the accuracy of the capacitance
measurement (above)
and D = R2πfC
Note that for small values of D it is possible to
have negative resistance values because the
resistance accuracy depends on the magnitude of
C, not of R.
For D > 0.1, the impedance accuracy must first be
calculated. To do this, first calculate the
impedance of the DUT by adding the resistive and
capacitive elements, either in series or in parallel,
as is appropriate. Use the impedance accuracy
graph and equation on page 4-2 to obtain an
impedance accuracy. The accuracy of C and R are
calculated from the impedance accuracy as
follows:
Accuracy of C = ± [Z
ac
x (1 + |D|)] %
Accuracy of R = ± [Z
ac
x (1 + 1/|D|)] %
where Z
ac
is the impedance accuracy.
If the unit is in the constant voltage (CV) mode or
under internal or external bias, double the basic
accuracy for Z.
K
i
Table
Meas Rate Frequency
Z
m
K
i
slow, med all 1
fast 100 Hz-1 kHz 6.25 Ω<Z
m
<400 kΩ 3
fast all other 2
Z
m
= 1/2πfC = impedance of device
K
v
Table
V
out
(V rms) K
v
1.0 - 0.55 1 / V
out
0.5 - 0.3 0.5 / V
out
0.25 - 0.15 0.25 / V
out
0.10 0.11/V
out
Note that K
v
equals one for the primary drive
voltages (1.0, 0.5 and 0.25 Vrms).
K
h
& K
l
Table
Frequency K
l
K
h
100,120 Hz (2 pF / C
m
)(C
m
/ 2000 mF)
1 KHz (0.1 pF / C
m
)(C
m
/ 200 mF)
10 KHz (0.01 pF / C
m
)(C
m
/ 10 mF)
100 KHz (0.01 pF / C
m
)(C
m
/ 100 µF)
C
m
= the capacitance of the device being
measured.
Note that K
l
is negligible for capacitances less than
1590/f µF and K
h
is negligible for capacitances
above 159/f µF, where f is the output frequency.
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