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1693 RLC Digibridge
Notice that the appearance of a device can be mis-
leading. (For example, an inductor is capacitive if test
frequency is above resonance; or a component part
can be mislabeled or unlabeled.)
For more information about both a negative RLC and
negative QDR, see paragraph 3.3.3.
3.3.2 Equivalent Circuits - Series,
Parallel
The results of R, L, or C measurements of many com-
ponents depend on which of two equivalent circuits
is chosen to represent it - series or parallel.
The more nearly "pure" the resistance or reactance,
the more nearly identical are the "series" and "paral-
lel" values of the principal parameter. However, if D
is high or Q low, Cs differs substantially from Cp and
Ls differs substantially from Lp; and these values are
frequency dependent. Usually several measurements
at frequencies near the desired evaluation will reveal
that either series measurements are less frequency de-
pendent than parallel, or the converse. The equivalent
circuit that is less frequency dependent is the better
model of the actual device.
We first give general rules for selection of measure-
ment parameters, then some of the theory.
Making the Selection. The power-up selection is
"series", confirmed by the SERIES indicator being
lit, on the keyboard. To change the selection, press
the [EQUIVALENT CIRCUIT] key.
Specifications. The manufacturer or principal user
of the DUT probably specifies how to measure it.
(Usually "series" is specified.) Refer also to the ap-
plicable: MlL or EIA specifications, Select "parallel"
or "series" and the test frequency according to the
applicable specifications. If there are none known,
be sure to specify with your results whether they
are "parallel" or "series" and what the measurement
frequency was.
34
3.3.2.1 Suggested Test
Conditions:
• Capacitors less than 10 pF: Parallel, 10 kHz.
• Capacitors from 10 to 400 pF: Series or
Parallel, 10 kHz.
• Capacitors from 400 pF to 1 µF: Series, 1 kHz.
• Capacitors greater than 1 µF: Series, 0.1 or
0.12 kHz.
Unless otherwise specified or for special reasons,
always select "series" for capacitors and inductors.
This has traditionally been standard practice. For
very small capacitance, select a higher measurement
frequency for best accuracy. (Refer to paragraph 3.6.)
Conversely, for very large capacitance, select a lower
measurement frequency for best accuracy.
• Inductors less than 10 µH: Series, 100 kHz.
• Inductors from 10 µH to 1 mH. Series, 10 kHz.
• Inductors from 1 mH to 1 H: Series, 1 kHz.
• Inductors greater than 1 H: Series, 0.1 kHz.
Select "series" as explained above. For very small
inductance, select a higher measurement frequency
for best accuracy. Conversely, for very large induc-
tance, select a lower measurement frequency for best
accuracy.
• Resistors, below about 1 kΩ Series, 1 kHz.
Usually the specifications call for dc resistance, so
select a low test frequency to minimize ac effects.
Select "series" because the reactive component most
likely to be present in a low resistance resistor is series
inductance, which has no effect on the measurement of
series R.
• Between 1 kΩ and 10 MΩ: Parallel, 0.250 kHz.
• Resistors greater than 10 MΩ: Parallel,
0.030 kHz.
As explained above, select a low test frequency. Select
"parallel" because the reactive component most likely
to be present in a high-resistance resistor is shunt ca-
pacitance, which has no effect on the measurement of
parallel R. If the Q is less than 0.1, the measured Rp
is probably very close to the d DC resistance.
Operation
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