Agilent Technologies 4263B - Selecting Circuit Model for Capacitance Measurement; Small Capacitance Values; Large Capacitance Values; Capacitance Circuit Model Selection

4263B
Selecting
Circuit
Model
for
Capacitance
Measurement
The
following
description
gives
some
practical
guide
lines
for
selecting
the appropriate
capacitance
measurement
circuit
model.
Small
Capacitance
V
alues
Small
capacitance
yields
a
large
reactance
,
which
implies
that
the eect
of the
large value
parallel
resistance
(Rp)
has
relatively
more
signicance than
that of
the low
value series
resistance
(Rs).
So
the
parallel
circuit
model (Cp-D
, Cp-Q,
or Cp-G)
is the
one
to
use
.
(Refer
to
Figure
7-2
(a).)
Large
Capacitance
V
alues
When
the
measurement
involves
a large
value of
capacitance (low
reactance),
Rs
has
relatively
more
signicance
than
Rp
,so
the series
circuit model
(Cs-D
,
Cs-Q,
or
Cs-Rs)
is
the
one
to
use
.
(Refer
to
Figure
7-2
(b).)
Figure
7-2.
Capacitance
Circuit
Model
Selection
The
following
are
rules
of
thumb
for
selecting
the
circuit
model according
to the
reactance
of
the
capacitor
.

Above
approx.
10
k
:
Use
parallel
circuit model

Below
approx. 10
:
Use series
circuit
model

Between
above values
: F
ollow the
manufacturer's
recommendation
F
or
example,
to measure
a20
nF capacitor
at
100
Hz
(reactance
is
approximately
80
k),
the
parallel circuit
model is
suitable.
7-4 Impedance Measurement Basics