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Section
III
Paragraphs
3-18 to 3-23
Model 4342A
at these
particular
L frequencies.
The induc-
tance
at a measurement
frequency
other
than
the "L"
frequency
can be determined
by substi-
tuting
frequency
and L/C dial
(C scale)
read-
ings
in equation
3-l.
3-18.
Expansion
of measurement
ranges.
3-19.
For higher
or lower
value
inductances
(above or below
the shaded area in Figure
3-4),
a parallel
or series
connection
of the
unknown to the measuring
circuit
enables
the
measurement
to be made.
To obtain
the value
of the desired
parameter,
these
methods
em-
ploy
a comparison
of the Q meter
indications.
The Q meter
measuring
circuit
is first
re-
sonated
with
a reference
inductor.
Then the
sample is connected
in parallel
or in series
with
the measuring
circuit
and the circuit
again
resonated.
The sample value
is calcu-
lated
from the difference
in Q meter
indica-
tion
measurements
made before
and after
con-
necting
the
sample.
In the equation
from
which
the sample values
are obtained,
the
values
inherent
in the reference
inductor
are
subtracted
from the measurement
quantities.
Consequently,
the characteristics
of the ref-
erence
inductor
do not
(theoretically)
affect
measurement
results.
In addition
to their
expanded
measurement
ranges,
the parallel
and series
methods
have
some measurement
capability
advantages
which
do not
appear
when using
direct
methods.
A detailed
description
of these
advantages
is
given
in the
discussion
in paragraph
3-58.
3-20.
Capacitance
Measurement.
3-21.
For capacitor
samples,
either
a paral-
lel
or series
connection
method may be used
when measuring
either
the capacitance
or the
Q value.
The criteria
for
selecting
the ap-
propriate
connection
method
concerns
only
the
sample value
and is irrespective
of the meas-
urement
frequency.
Capacitances
higher
than
approximately
450pF (up to approximately
0.2uF)
are normally
measured
by the series
method
and
lower
capacitances
are easily
measured
by the parallel
method.
Generally,
capacitors
can be measured
at the desired
frequency
by using
an appropriate
inductor
as
a measurement
aid.
3-22.
Resistance
Measurement.
3-23.
Resistance
values
are fundamentally
calculated
from measured
Q values.
Thus,
the
connection
method
selected
depends
upon the
sample value
and the measurement
frequency.
Figure
3-5 shows approximate
limits
for
both
parallel
and series
measurements.
The upper
shaded area
indicates
the
combinations
of fre-
quency and measurable
resistance
values
for
parallel
measurements.
Similarly,
the lower
shaded area
indicates
the values
for
series
measurements.
For sample values
between
the
upper
and lower
shaded areas,
it
is difficult
I
I
I
III
I
I
III
I
I
III
I
I
III
IOK
lOOK
IM
IOM
l3OM
FREQUENCY
(Hz)
Figure
3-4.
Inductance
Measurement
Ranges
vs. Frequency
(direct
method).
3-6
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