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Model
4342A
Section
III
Paragraphs
3-47 to 3-50
Measurements
Requiring
Corrections
Cd =*
D..oO.o..O.
(eq.
3-7)
Where, Cd:
distributed
capacitance
in
farads.
Cl :
C dial
reading
(farads)
noted
in step b.
fo:
measurement
frequency
(hertz)
noted
in step
j.
f1:
measurement
frequency
(hertz)
noted
in step
d.
Note
If
fo>fl,
the eq.
3-7 is simplified
as follows:
Cd =
2
Cl
. . . . . . . . . . . (eq.
3-7)
3-47.
Measuring
Distributed
Capacitance
(Approximate
Method,
CdllOpF).
3-48.
A distributed
capacitance
more than
approximately
1OpF may be measured
with
the
simplified
procedure
described
below
(this
procedure
is useful
for
obtaining
approximate
values
of distributed
capacitance
with
an
accuracy
which
serves
practical
purposes):
a.
Connect
inductor
sample
to the meas-
urement
COIL (HI and LO) terminals.
b.
Set L/C dial
control
to approximately
50pF and AC dial
control
to OpF.
Note
the C dial
reading
as Cr.
C.
Depress
a trial
FREQUENCY RANGE button
and rotate
FREQUENCY dial
control
to
search
for
the frequency
at which
panel
Q meter
shows a maximum deflec-
tion.
If
no peak deflection
can be
observed,
change FREQUENCY RANGE set-
ting
and repeat
the procedure.
d.
Adjust
FREQUENCY dial
control
for
max-
imum panel
Q meter
deflection.
Note
this
frequency
as fr.
e.
Change FREQUENCY dial
setting
to f2
equal
to fl/n
(n should
be a selected
integer,
e.g.
2 or 3).
f.
Adjust
L/C dial
and AC dial
controls
for
again
obtaining
maximum meter
deflection.
Note the sum of C dial
and AC dial
readings
as Cz.
g-
Distributed
capacitance
is given
by
the
following
equation.
Substitute
measured
values
of Cl,
Cp, fl
and f2
in the equation:
Cd = w
. . . . . .
. . (eq.
3-9)
fl
n
=-
f2
Where,
Cd:
Cl :
c2 :
f1:
f2:
distributed
capacitance
in
farads.
C dial
reading
(farads)
noted
in step
b.
C dial
reading
(farads)
noted
in step
f.
measurement
frequency
(hertz)
noted
in step d.
measurement
frequency
(hertz)
given
in step
e.
Note
If
fz is exactly
one half
of fl,
then
Cd
=
'2
-
4c1
3
. . . . . . . . . . .
(eq.
3-10)
An average
of several
measurements
using
different
values
of Cl will
im-
prove
the results
of this
measurement.
The best
accuracy
to be expected
with
this
method,
however,
is in the range
of +2pF.
3-49.
CORRECTION FOR Q.
3-50.
To use the
indicated
Q for
the purpose
of calculating
L and Rs (in determining
the
actual
equivalent
circuit),
it
must be cor-
rected
for
the effects
of the distributed
capacitance.
The corrected
Q and the Q value
measured
by the Q meter
can be obtained
from
the
following
equation:
Qt = Qi
' +CCd . . . . . . . . . . . (eq.
3-11)
Then,
Correction
factor
=
C + Cd
C
. . . . . . . . . . . (eq.
3-12)
Where, Qt:
corrected
Q value.
Qi:
indicated
Q value.
c:
sum of C and AC dial
readings.
Cd:
distributed
capacitance
of
sample.
3-15
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