Model 4342P
3-55. PARALLEL AND SERIES CONNECTION
MEASUREMENT METHODS.
3-56. GENERAL.
3-57. In practical applications of the Q
meter,
the expanded measurement capabilities
of parallel and series connection measure-
ments yield various advantages. For example,
the parallel method permits measuring induc-
tor samples at frequencies about its self-
resonant frequency (fo). In addition, in-
ductance just below resonance, impedance at
resonance, and apparent capacitance above fo
can be measured.
This is especially useful
for measurement of inductors which are de-
signed to resonate with tuning capacitors
less than 20pF at their respective nominal
working frequencies. A great number of coils
known as "peaking coils" fall into this
category. If there is no requirement for
particular measurement conditions, the coil
can be measured using the direct connection
method. Here, the measurement parameter
values may be read directly from Q meter
indications. However, if the sample re-
quires measurement with a tuning capacitance
of less than 20pF, a direct measurement is
impossible (due to the minimum capacitance of
the tuning capacitor). A parallel measure-
ment will provide the desired data eliminat-
ing the limitations of the direct connection
method.
3-58. Sometimes parallel or series connec-
tion measurements offer improved measurement
accuracies. At first glance, these measure-
ment configurations appear to be incompatible
with the stray capacitance, residual induct-
ance and other unwanted additional factors
incident in the use of supplemental equipment
Section III
Paragraphs 3-55 to 3-61
such as reference inductors and the test
terminal adapter. Actually,
these residual
factors do not contribute additional errors
in the measurement results.
In quality
factor measurements,
the "indicated Q" va.lues
obtained by parallel or series methods are
usually a better approximation of "effective
Q" than those obtained by direct methods. As
the differences between the measured values
and the effective values decrease further to
small orders of magnitude, parallel and
series methods are sometimes also used for
samples which can he measured by direct
methods.
3-59.
Measured values in parallel and series
methods are theoretically given only by the
variable quantities which yield to differences
in tuning conditions before and after connect-
ing the sample. The constant quantities in
the measuring circuit, which do not vary for
the duration of measurement, are not factors
in the results of the calculations for the
individual measurement parameters.
Since re-
sidual impedances in measuring circuit as
well as inherent values of reference inductors
are almost constant, these values are mathe-
matically eliminated and also do not influ-
ence the measurement results.
So, what
additional measurement errors are contributed
by the parallel and series methods?
Let's discuss them in detail.
3-60. Additional Error Discussion.
3-61. Certain residual impedance elements
change with the method of connection of the
sample; in addition, the residual impedance
also depends upon the mutual distances be-
tween the sample and the individual compo-
nents of the measurement apparatus. Typical
circuit models showing such residual factors
are illustrated in Figure 3-11.
CI, and C5 in
Stray Capacitances about
Measurement Terminals
Rotor plates
Stator plates
Distributed Inductances
In Tuning Capacitor
(B)
3-17
(A)
Figure 3-11. Residual Parameters.
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