Agilent Technologies 4284A, Operation Manual

Page: 173 / 460

P arallel/Series
Circuit Mode
T o measure L, C, or R, there are t w o equiv alen t circuit mo dels, the
parallel and series mo des as sho wn in T able 6-1, and the 4284A can
select the mo de b y setting the FUNC (C
p
, C
s
, L
p
or L
s
) on the
MEAS SETUP page. T o determine whic h mo de is b est, consider the
relativ e imp edance magnitude of the reactance and R
s
and R
p
.
T able 6-1. P arallel/Series Circuit Mode
Circuit Mo de Measuremen t
F unction
Denition of D, Q and G
C
p
mo de C
p
-D
C
p
-Q
C
p
-G
C
p
-R
p
D =
1
2 fC
p
R
p
=
1
Q
G =
1
R
p
C
s
mo de C
s
-D
C
s
-Q
C
s
-R
s
D = 2 fC
s
R
s
=
1
Q
L
p
mo de L
p
-D
L
p
-Q
L
p
-G
L
p
-R
p
Q =
R
p
2 fL
p
=
1
D
G =
1
R
p
L
s
mo de L
s
-D
L
s
-Q
L
s
-R
s
Q =
2 fL
s
R
s
=
1
D
Selecting Circuit Mode
of Capacitance
The following description gives some practical guide lines for selecting
the capacitance measuremen t circuit mo de.
Small Capacitance (modeled b y (a) in Figure 6-3)
Small capacitance yields large reactance, whic h implies that the eect
of the parallel resistance (R
p
) has relativ ely more signicance than
that of series resistance (R
s
). The low v alue of resistance represen ted
b y R
s
has negligible signicance compared with the capacitive
reactance, so the parallel circuit mo de (C
p
-D or C
p
-G) should b e
used.
Large Capacitance (modeled b y (b) in Figure 6-3)
When the con v erse is true and the measuremen t in v olv es a large
v alue of capacitance (lo w imp edance), R
s
has relativ ely more
signicance than R
p
, so the series circuit mo de (C
s
-D or C
s
-Q)
should b e used.
Measurement Procedure and Examples 6-5