a 5cm length of 1mm diameter wire has an inductance of 50nH
a 5cm length of 2mm diameter wire has an inductance of 40nH
The known inductance of the wire used for the S/C trim should be subtracted from the
measured DUT inductance.
A similar, stable fixture arrangement should be used for four-terminal measurements of surface-
mount or leadless components: contact the Microtest Applications Department if this kind of
fixture is required.
The Q is always low, but self-capacitance is not normally a problem at the meter’s measurement
frequencies. Where possible, make the measurements at the same AC level as the level used
during trimming.
When an inductor is measured at a frequency much lower than that for which it is designed (e.g.
an HF choke tested at AF) it will tend to behave as an inductive resistor. In these circumstances,
the inductance measurement accuracy is widened by the factor (1 + 1/Q).
Air-cored coils are particularly susceptible to noise pick up and should be kept well clear of any
test equipment that may contain power transformers or display scan circuitry. Also avoid
proximity to metal objects which may modify inductor characteristics.
5.4 Measurement of Iron-Cored and Ferrite Inductors
The effective value of iron-cored and ferrite inductors can vary widely with the magnetization,
and therefore the level, of the test signal. Ideally, they should be measured at the AC level and
frequency of use. When core materials can be damaged by excessive magnetization (for example,
some tape heads and microphone transformers), check before connection that the test signal
level is acceptable.
The meter is not designed to pass DC through inductors: if this facility is required please
contact the Microtest Applications Department; the Microtest Precision Magnetics meter
PMA3260A is designed specifically for this type of measurement, and when used with one or
more 3265A 25A Bias Units, up to 125A DC is available.
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