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Section
III
Paragraphs
3-45 and 3-46
Measurements
Requiring
Corrections
Model 4342A
3-45.
Measuring
Distributed
Capacitance
(Preferred
Method).
3-46.
The impedance
of a coil
at its
self-
resonant
frequency
is resistive
and usually
high.
This
characteristic
may be utilized
for
measuring
distributed
capacitance.
Proceed
as follows:
1.25
(fo=SELF-RESONANT
FREQUENCY OF COIL)
Figure
3-9.
Typical
Variation
of Effective
Q
and Inductance
with
Frequency.
TUNING CAPACITANCE
IN pF
Figure
3-10.
Correction
Chart
for
Distributed
Capacitance.
a.
b.
C.
d.
e.
f.
g.
h.
1.
j.
k.
Connect
inductor
sample to be tested
to the 4342A measurement
COIL (HI and
LO) terminals.
Set L/C dial
control
to approximately
400pF and AC dial
control
to OpF.
Note C dial
reading
as Cl.
Depress
a trial
FREQUENCY RANGE button
and rotate
FREQUENCY dial
to search
for
the frequency
at which panel
Q
meter
shows a maximum deflection.
If
no peak deflection
can be observed,
change FREQUENCY RANGE setting
and
repeat
the procedure.
Adjust
FREQUENCY dial
control
for
max-
imum Q meter
deflection.
Note the
dial
frequency
reading
as fl.
Set measurement
frequency
to approxi-
mately
ten times
the frequency
fl
noted
in step
d.
Replace
the inductor
sample with
a
stable
coil
(16470
series
supplemental
inductor)
capable
of resonating
in the
measuring
circuit
at this
higher
fre-
quency.
Adjust
the L/C dial
control
for
maxi-
mum Q meter
deflection.
Connect
the test
inductor
to the
meas-
urement
CAPACITOR (HI and GND) termi-
nals.
Adjust
the L/C dial
control
for
again
obtaining
maximum Q meter
deflection.
If
the
L/C dial
control
has to be
rotated
in the direction
of higher
capacitance,
increase
the measurement
frequency.
If
it
has to be rotated
towards
a lower
capacitance,
decrease
the frequency.
Alternately
connect
and disconnect
the
test
inductor
to/from
the
CAPACITOR
terminals
and adjust
the FREQUENCY
dial
control
(if
necessary,
change
FREQUENCY RANGE setting)
until
the
in-
fluence
of the test
inductor
to tuning
conditions
is non-existent
(indicated
Q value
may change).
Note dial
fre-
quency reading
as fo.
This
frequency
is identical
with
the self
resonant
frequency
of the
inductor.
Distributed
capacitance
of the induc-
tor
sample is given
by the following
equation.
Substitute
measured
values
of Cl,
fo,
and f~ in the equation:
3-14
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