Advertisement
Model 4277A
SECTION III
Note
When
turned
on,
the
4277A
automatically performs a Check Sum
Test as part of its turn-on Self Test.
The
Check
Sum
Test
cheeks
the
contents of memory. If incorrect, E68
will be displayed on DISPLAY A and
memory
will
be
cleared.
The
instrument will be set to the initial
control settings (refer
to
paragraph
3-38).
3-42. OPEN and SHORT Zero Offset values
(refer to paragraph 3-51) and reference values
for deviation measurements (refer to paragraph
3-60) are also memorized by the continuous
memory function. On instruments equipped with
the
Comparator/Handler
Interface
option
(Option 002), all high and low limits and all
16064A
control
settings
(except
RUN)
are
memorized.
DC
bias
voltage
(Option
001)
settings, however, are not memorized.
3-43.
RESETTING CONTINUOUS MEMORY
3-44.
To reset, or clear, continuous memory,
proceed as follows:
(1)
Turn off the 4277A.
(2)
Press and hold both FREQ/DC BIAS Step
Control Keys ( @ d]).
(3)
Turn on the 4277A,
3-45.
UNKNOWN TERMINALS
3-46.
Generally, the mutual inductance between
test leads, noise from nearby equipment,and the
residuals and strays of conventional connection
methods significantly affect the accuracy of
impedance
measurements
made
at
high
frequencies.
To minimize these error sources
and
thereby
ensure
optimum
measurement
accuracy, the 4277A employs a four-terminal
pair
connection
method.
The
UNKNOWN
terminals
consist
of
four
BNC
female
connectors t
H
cur
(high
current),
H
pot
(high
potential),
L pot
(low potential), and
Lcur
(low
current).
The current terminals
(Hcur
and
Lcur)
provide the test signal current, and the potential
terminals
(Hpot
and
Lpot)
detect the voltage
across the DUT (device under test). To connect
a sample, the four-terminal pair configuration
must
be
converted
to
a
two-terminal
configuration.
This is done by connecting the
outer conductors of the terminals to each other
and then
Hcur
to
Hpoi
and
Lcur
to
Lpot,
as shown in
Figure 3-8.
The principle of the four-terminal
pair measurement is illustrated in Figure 3-9.
At first glance, the arrangement appears to be
an expanded four terminal method with a built-in
guard
structure.
This
is
true.
Thus,
the
four-terminal
pair
method
combines
the
advantages of the four terminal method in low
impedance measurements while providing the
shielding
required
for
high
impedance
measurements.
The distinctive feature of the
four-terminal pair configuration is that the outer
shield works as the return path for the test
signal current. The same current flows through
both the center conductors and the outer shield
conductors
(in
opposite
directions),
yet
no
external magnetic fields are generated around
the conductors (the magnetic fields produced by
the
currents
through
the
inner
and
outer
conductors
completely
cancel
each
other).
Because the measurement signal current does
not develop an inductive magnetic field, the test
leads do not contribute additional measurement
errors due to mutual-inductance between the
individual leads.
Hence, the four-terminal pair
method provides
best
measurement accuracy
while
minimizing
the
effects
of
stray
capacitance and residual inductance inherent in
the test leads or test fixture.
Note
Because
test
leads
have
residual
inductance,
the
resultant
additional
measurement
error
increases
in
capacitance
measurements
in
proportion to the square of the test
frequency.
Figure 3-8. Four Terminal Pair DUT Connections.
Advertisement
