Agilent Technologies 4339B - Page 116

Theory
of
Operation
4339B
Theory of
Operation
This
section
provides
the
4339B's
theory of
operation.
In
\Overall
Measurement
Theory"
and \Overall
Block Diagram
", we
will discuss
the
measurement
theory
with
the
ungrounded DUT
measurement conguration.
These descriptions
can
also
be
applied
to
the
measurement
of
a grounded
DUT,
considering the
test
signal
ow
shown
in
Figure
3-10
(b).
Overall
Measurement Theory
The
4339B measures
the
Device
Under
T
est
(DUT)
resistance
in
the
following
manner
.
Figure
3-8.
Simplied
Model
of
Impedance
Measurement
Figure
3-8
shows
a
simplied
model
of
the
4339B
measuring
a
DUT.
In the
Figure 3-8
,the
DUT
is
connected
in
series
with
a
test
voltage
source
,
V
,and
an ammeter
,A.
Rs is
the
4339B
's
source
resistance
(
R
s
=
1
k
)
and
Ri
is
the
input
resistance (
Ri
=1
k
).
In
the
resistance
measurement
mode
(the
measurement
parameter
is
R),
the
4339B
displays
the
\derived"
DUT
resistance
,
Rx
.
In
other
words
,
if
the
ammeter measures
Ix when
the
source
voltage
is
V ,
the 4339B
displays the
DUT resistance
Rx ,
calculated using
the following
equation:
Rx
=
V
Ix
0 ( Rs
+ Ri
)
In the current measurement mode (the measurement parameter is I), the
4339B measures
the actual current value
, Ix , which ows through the DUT
, and displays the value for the
measurement result. F
or example
,if
R
x
is 100 k, and
V is 1 V, the measurement result will be
9.8  A(
1 V
100 k +2 k
). If you measure a DUT whose resistance value is lower
, the 4339B 's source
resistance, Rs , and input resistance
, Ri , aect the measurement current
value, Ix , more.
3-26 Function Reference