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Model 4342A
Direct
Connection
Measurements
Section
III
Paragraphs
3-30 to 3-34
3-30.
BASIC Q METER MEASUREMENTS.
3-31.
QUALITY FACTOR AND INDUCTANCE
MEASLREMENT~ (DIRECT C~NNK-U~N).
3-32.
This
paragraph
and those
which
follow
describe
the
fundamental
operating
procedures
for
quality
factor
and inductance
measure-
ments which
are
typical
applications
of the
Q Meter.
An inductor
usually
has some
distributed
capacitance
(Cd).
The self-
resonant
frequency
(fo)
of the
inductor
is
determined
by its
self-inductance
and the
Cd.
The 4342A measuring
circuit
consideration
of
distributed
capacitance
is shown in Figure
3-7.
If
the
Q meter
indication
is Qt when Cd
is
zero,
then
the presence
of Cd will
influ-
ence the voltage
across
the
resonating
induc-
tor
such that
the Q meter
will
actually
indi-
cate
a Q value
lower
than
Qt.
The indicated
Q value
(Qi)
and the Qt can be correlated
by
a correction
factor
(which
is a function
of
Cd and the
tuning
capacitance)
each with
the
other.
A similar
correction
factor
also
applies
to difference
of inductance
readings
resulting
from
the presence
of Cd.
A de-
tailed
discussion
of correction
factors
is
given
in paragraph
3-50.
When the
Cd is less
than
l/20
of the
tuning
capacitance,
the
difference
between
Qi and Qt (Li
and Lt are
similar
in meaning)
is within
5%.
r-
I
I
Cd +
I
I
L,
0
GND
Figure
3-7.
Distributed
Capacitance
in
Direct
Connection.
3-33.
Q Measurement.
3-34.
To read
the
quality
factor
of an in-
ductance
sample
directly
from
the
Q meter
indication,
proceed
as follows:
a.
Connect
unknown
to measurement
COIL
(HI and LO) terminals.
b.
Depress
an appropriate
FREQUENCY RANGE
button
and set FREQUENCY dial
control
to the
desired
frequency.
C.
d.
e.
f.
g*
Adjust
L/C dial
control
for
maximum
panel
Q meter
deflection
on the
instrument.
Note
Alternatively,
the
resonance
may be
taken
by setting
the
L/C dial
to a
desired
position
and adjusting
the
FREQUENCY dial
for
maximum Q meter
deflection.
Depress
Q RANGE button
as appropriate
for
obtaining
a Q meter
deflection
more than
one-third
of
full
scale
and
less
than
full
scale.
Re-adjust
L/C dial
(or
FREQUENCY dial)
control
for
maximum deflection.
If
panel
meter
deflection
exceeds
full
scale,
up-range
the
Q RANGE and con-
tinue
the
adjustment.
For easily
ob-
taining
a precise
resonance,
use the
AC dial
control.
Note
The AC dial
control
facilitates
accurate
adjustment
for
establish-
ing
resonance
especially
in high
Q
measurements.
Read panel
Q meter
indication
on the
meter
scale
designated
by the
appro-
priate
scale
lamp indicator
lit.
Note
The measured
Q value
corresponds
to
the
"indicated
Q" of the
sample.
To derive
series
equivalent
resistance
of the
sample,
substitute
the
Q meter
FREQUENCY, C dial,
AC dial,
and Q
readings
in the
following
equation:
Rs = l/wCQWO.l59/fCQ
. . . . . (eq.
3-2)
Where,
Rs:
equivalent
series
resist-
ance in ohms.
f:
frequency
dial
reading
in
hertz.
0:
2~r times
the
frequncy
(2wf).
c:
sum of C and AC dial
read-
ings
in farads.
Q:
panel
Q meter
reading.
3-11
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