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Model 4342A
Parallel
Connection
Measurements
Section
III
Paragraphs
3-67 and 3-68
e.
Connect
unknown
inductor
to measure-
ment CAPACITOR (HI and GND) terminals.
f.
Restore
resonance
by adjusting
the L/C
and AC dial
controls.
Note sum of the
C dial
and AC dial
readings
as C2 and
panel
meter
AQ reading.
If
meter
pointer
scales
out
at the
left
end of
the scale
(AQ full
scale),
reset
the
function
for
normal
Q measurement.
The difference
in Q is calculated
from
the two Q values
as AQ = Q1 - Q2.
EC. Inductance
of the unknown inductor
is:
L=
1
w21c2
-
Cl)
(H) . . . . . (eq.
3-17)
3-67.
Low Capacitance
Measurement
(<45OpF)
3-68.
When the measuring
circuit
is reso-
nated
using
a reference
inductor,
a capacitor
placed
in parallel
with
the
tuning
capacitor
will
lower
the tuning
frequency.
To restore
resonance
at the measurement
frequency,
the
tuning
capacitance
must be reduced
as much as
the capacitance
of the sample.
Hence,
the
sample value
can be determined
by noting
the
difference
between
the tuning
capacitor
dial
readings.
After
the sample
is connected,
quality
factor
and equivalent
parallel
re-
sistance
can be calculated
from a reduction
of panel
Q meter
indication.
To measure
a capacitance
sample,
proceed
as
follows:
Where, W= 2~r times
the measurement
frequency.
Q value
of the unknown
is:
Q
=
4142
CC2
-
Cl)
AQCl
-'--**'-
(eq.
3-18)
Where,
AQ
=
QI
- 42
Equivalent
parallel
resistance
is:
Rp = -QLQ-
(52) . . . . . . . . . . (eq.
3-19)
wC1 AQ
h.
The capacitance
required
to tune
the
coil
at the measuring
frequency
is
simply,
c = c2 - Cl . . . . . . . . . . . . . . . (eq.
3-20)
Note
If
the measurement
frequency
is
higher
than
the self-resonant
fre-
quency of the unknown inductor,
the
unknown will
not
appear
inductive
but
capacitive,
and Cp will
be less
than
Cl.
Apparent
capacitance
of
the unknown in such frequency
region
is:
Ca = Cl - CZ . . . . . . . . . . .
(es.
3-21)
and equivalent
parallel
conductance
is
a.
b.
C.
d.
e.
f.
Select
a reference
inductor
which
can
resonate
at the desired
measurement
frequency
and connect
it
to measure-
ment COIL (HI and LO) terminals.
Set L/C dial
control
to desired
tuning
capacitance
and AC dial
to zero.
Note
the tuning
capacitance
Cl.
Note
If
the approximate
value
of the
capacitor
sample is known,
select
a value
for
Cl such that
the dif-
ference
between
Cl and the
sample
value
is 30 to 100pF.
Depress
appropriate
FREQUENCY RANGE
button
and adjust
FREQUENCY dial
con-
trol
for
a maximum Q meter
deflection.
Note frequency
fl
and panel
Q meter
reading
Q1.
Depress
AQ button
and adjust
AQ ZERO
(COARSE and FINE) controls
so that
meter
pointer
indicates
zero
(full
scale)
on AQ scale.
Note
Press AQ button
to release
AQ func-
tion
and recheck
for
correct
reso-
nance.
Again depress
the AQ button
and recheck
for
AQ zero indication.
Connect
the unknown capacitor
to meas-
urement
CAPACITOR (HI and GND) termi-
nals.
Restore
resonance
by adjusting
the
L/C
and AC dial
controls.
Note sum of the
L/C dial
and AC dial
readings
as C2
and panel
meter
AQ reading.
If
meter
3-19
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