A LISN (line impedance stabilization network) is used to provide an impedance to the power input of the EUT (equipment under test). This is an essential tool for when operators need to stabilize power lines so they can perform conducted emissions measurements. There are three main functions of LISNs, as a way to divert unwanted signals from a power source, an RF noise measurement port, and resistance of an electric circuit or component to an alternating current (impedance).
During a test setup, a LISN is connected to a power source that is conducted to the EUT. For the consistency of conducted emissions testing, the standard of line impedance is set to 50 µH. The LISN also serves as a filter for RF noise to preserve the quality of EMC measurements. An EMI receiver or spectrum analyzer is able to measure these RF emissions. To provide known impedance and an RF measurement port, a LISN is placed between an AC or DC power source and the EUT.
It is important to understand the frequency, current type, and voltage the test standard requires when choosing the right LISN. For DC power you will need a single-phase DC LISN and for AC power sources you will need a three-phase AC LISN.
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