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Model 4277A
SECTION IIT
Capacitance:
Up to 20pF
1
OPEN
Conductance:
Up to 2^8
J
Inductance:
Up to 2UH
\
SHORT
Resistance:
Up to 2Q
J
Note
During Zero Offset Adjustment, OF or
CF
may appear
on
DISPLAY
A or
DISPLAY B.
Zero Offset Adjustment,
however, is performed correctly unless
error code "ElO" is displayed.
Note
After Zero Offset Adjustments, CF and
0000 may be alternately displayed on
DISPLAY A if the measurement mode
is
other
than
C-G
and
nothing
is
connected to the test fixture.
This is
normal; it is not a malfunction.
Note
OPEN
and
SHORT
Zero
Offset
Adjustments
cannot
be
performed
without a test fixture.
Figure 3-13.
Parasitic Impedances Incident to
DUT Connections.
However, the four-terminal pair measurement
system must be converted to a two terminal
configuration
at
the
sample
because
most
components have only two terminals. Moreover,
additional stray capacitance is introduced when
the sample is connected to the test fixture.
Figure 3-13 illustrates lead impedance and the
stray
capacitances
between
the
component's
leads.
3-53. ACTUAL MEASUREMENT EQUIVALENT
CIRCUIT
3-54. The test fixture or test leads used to
connect
a
sample
to
the
instrument's
UNKNOWN
terminals
becomes
part
of
the
sample which the instrument
measures.
The
four-terminal pair configuration employed in the
4277A
minimizes residual impedance
circuit.
The residual impedance, inherent in the test
fixture or test leads, can be eliminated by the
4277 A's
ZERO
offset
function
(refer
to
paragraph 3-51).
3-55.
Diverse
parasitic
elements
present
between
the
sample
and
the
UNKNOWN
terminals
will
affect
measurement
results.
These parasitic elements are series resistive and
reactive elements and parallel conductive and
susceptive
elements.
Figure 3-14 shows
the
equivalent
circuit
of
the
samples
parasitic
elements (R + jX is the sample's impedance). In
Figure
3-14,
Lo
represents
the
residual
inductance of the component's leads, and Ro is
lead resistance. G o is the conductance between
the leads, and Co
is the sum of all stray
capacitances shown in Figure 3-13.
Reactive
factors in the residual impedance and susceptive
factors in the stray admittance have a greater
effect
on
measurements
made
at
higher
frequencies.
Figure 3-14. Equivalent Circuit Including Residual Impedance.
3-41
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