Atlas LCR45 User Guide January 2019 – Rev 4
Page 5
Introductory notes about impedance
All passive components (inductors, capacitors and resistors) have an
impedance. Impedance typically has the units of Ohms. It is a combination of
the component’s resistive and reactive characteristics.
For resistors, the impedance is usually dominated by its DC resistance and this
will largely stay constant over a fairly wide range of frequencies.
Inductors and capacitors however, will exhibit an impedance (still measured in
Ohms) that is highly dependent on frequency.
Additionally, inductive and capacitive elements further complicate matters by
exhibiting a voltage across them that is not in phase with the current through
them.
All of these effects can be described by measuring the “Complex Impedance”
of a component. Despite the word “Complex”, it is neat way of combining the
impedance (in Ohms) of a component with the current/voltage phase that the
component exhibits into a single “complex number”.
For example, a 220µH inductor may have an impedance of:
Z = 11.6 + j276.5 Ohms at 200kHz
The first number (11.6) is the Real part of the complex number and represents
the resistive element of the component at the current test frequency. That
could be DC winding resistance, ferrite core losses and other “lossy”
parasitics.
The second number, (276.5) prefixed with j, is the Imaginary part of the
complex number and represents the reactance of the component (often given
the symbol of X).
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