Theory
of
Operation
This
section
describes
the
general
overall
operation
of
the
4338B
and
the
operation
of
each
assembly
.
Overall
Measurement
Theory
The
4338B
measures
the
resistance
of
the
Device
Under
T
est
(DUT)
by
measuring
vector
voltage
to
current
ratio
.
A
vector
is
a
value
which
consists
of
a
magnitude
and
a
phase
.
The
DUT
resistance
is
the
real
part
of
vector
impedance
which
is
determined
by
the
vector
ratio
between
the
voltage
across
the
DUT
and
the
current
owing
through
the
DUT
.
Figure
4-1.
V
oltage
Current
Ratio
Measurement
Principle
In
Figure
4-1,
a
DUT
is
connected
in
series
with
a
signal
source
,
voltmeter
V
,
and
ammeter
A.
If
the
ammeter
measures
i
amperes
when
the
source
voltage
is
v
volts
,
the
DUT's
impedance
Zx
is
expressed
by:
Z
x
=
v
i
The
DUT
resistance
,
R,
is
the
real
part
of
Zx
expressed
in
the
complex
real-imaginary
number
format:
Z
x
=
R
+
j
X
where
,
j
is
the
imaginary
unit
and
X
is
the
reactance
.
Note
F
or
accurate
and
stable
low-resistance-measurement,
the
4338B
employs
an
ac
voltage
source
,
rather
than
a
dc
voltage
source
.
The
4338B
essentially
consists
of
a
signal
source
,
a
vector
voltmeter
,
and
a
vector
current
meter
.
T
roubleshooting
4-3
