ACCURACY
3-7
C + R ACCURACY
Accuracy of C = ± [A x Ki x Kv + (Kh + Kl) 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.
Ki = Integration Time Factor (see Ki
Table below)
Kv
=
Voltage Error Factor (see Kv table
below).
Kh, Kl
=
Extreme Range Error Term (see
Kh, Kl table below).
Accuracy of R = ± [Ac x (1+1/|D|)] %
Ac
=
the accuracy of the capacitance
measurement (above)
and D = R2
π
fC
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 = ± [Zac x (1 + |D|)] %
Accuracy of R = ± [Zac x (1 + 1/|D|)] %
where Zac 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.
Ki Table
Meas Rate Frequency Zm
Ki
slow, med all
1
fast
100 Hz-1 kHz 6.25
Ω
<Zm<400 k
Ω
3
fast
all other
2
Zm = 1/2
π
fC = impedance of device
Kv Table
Vout (V rms)
Kv
1.0 - 0.55
1 / Vout
0.5 - 0.3
0.5 / Vout
0.25 - 0.15
0.25 / Vout
0.10
0.11/Vout
Note that Kv equals one for the primary drive
voltages (1.0, 0.5 and 0.25 Vrms).
Kh & Kl Table
Frequency
Kl
Kh
100,120 Hz
(2 pF / Cm)
(Cm / 2000 mF)
1 KHz
(0.1 pF / Cm)
(Cm / 200 mF)
10 KHz
(0.01 pF / Cm) (Cm / 10 mF)
100 KHz
(0.01 pF / Cm) (Cm / 100
µ
F)
Cm = the capacitance of the device being
measured.
Note that Kl is negligible for capacitances less than
1590/f
µ
F and Kh is negligible for capacitances
above 159/f
µ
F, where f is the output frequency.
