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SECTION III
Model 4277A
Note
3-32. CIRCUIT MODE
When a C-D measurement is made with
the instrument controls set as follows,
the number of display counts depends
on frequency, as shown in Figure 3-6.
CIRCUIT MODE.AUTO (
)
LC I Z i
RANGE
MANUAL
Test Frequency.15.9kHz - 20.0kHz
or 159kHz - 200kHz
As
an
example,
suppose
you're
measuring a ISOpF capacitor on the
lOOpF
range
at
17kHz,
and
the
measured value is 175.62pF. If the test
frequency is increased to 19kHz, OF
will
be
displayed
on
DISPLAY
A
because the maximum number of counts
at this higher frequency is only 17000,
as shown in Figure 3-6.
C Counts
fV
1
- - 19000
1
rs"- -
18000
i 1 i^V-
-17000
1
'
'
'
1
!
1
1
-
15900
1 1
'
i
D Value
•
I
i
-1-8000
-1-6000
1
^
i
l\'
-1.4000
-
1.2000
I'll
1
1
1
f
'
1
1
1
1
1
15.9K I7K
I8K
19K
20K
I59K I70K i80K I90K 200K
Test Frequency
(Hz)
Figure 3-6. Number of Counts vs Frequency.
3-33. An impedance can be represented by a
simple
series or
parallel equivalent circuit
consisting of resistive and reactive elements.
This is possible because both equivalent circuits
have identical impedances at a
given
test
frequency by properly establishing the values of
the equivalent circuit elements. The equivalent
circuit measurement mode is selected by setting
the CIRCUIT MODE control. When the CIRCUIT
MODE
is
set
to
AUTO,
the
4277A
will
automatically select the circuit
mode most
appropriate for the range and function settings.
Equivalent series circuit mode is automatically
selected when the measurement range is lOOflor
below.
Equivalent
parallel circuit
mode
is
automatically selected when the measurement
range is Ikfi or above.
By setting CIRCUIT
MODE manually, either circuit mode can be
selected, regardless all measurement ranges.
3-34. Capacitance
and
inductance
measurements
can
be
performed
in
either
equivalent series circuit mode or equivalent
parallel
circuit
mode.
However,
measured
values obtained in each mode are different. The
difference in measured values is related to the
loss factor of the sample being measured. The
impedance of a sample measured in both series
and parallel circuit mode is the same at a
particular frequency. Therefore, the following
equations are satisfied:
jX
R
jB
<KZHWro
=
G
Z = R + jX
Y
= G . jB
G + jB =
1
R + jX
R
X
R2" V
^ R2 + X2
3-34
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