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What is a LISN used for

What is a LISN used for

What measurement do we need?

A LISN is a Line Impedance Stabilisation Network. It outputs the noise signals from the DUT over a 50 Ohm load, to be measured by a spectrum analyzer.
LISN: What is it used for | ELab Tools

How is it used

The spectrum analyzer sweeps from 150kHz to 30Mhz and makes a graph of the noise levels. Depending on the device’s category limit lines apply.
Both the L and N line are measured and both must be below the limit line.

Line noise

To prevent interfering noise comming from the mains wall socket to be measured, a pre-filter is provided.
The design of the LISN circuit is compliant to CISPR 16-1-2 (an international standard used for testing).

Chasing noise

If the limit is crossed, the engineer must locate the root cause of the noise and take measures to reduce it. Now having a Common-mode and Differential-mode measurement becomes very important.
If the differential-mode noise is high (as would be expected from an inverter or switched mode power supply), more or better decoupling of the L to N may be the solution. If the common-mode noise remains high, decoupling to the PE (earth) may be useful.

Interested? Ask our distributors

What can you measure

  • noise on L and N over 50 Ohm
  • Common mode noise
  • Differential mode noise
⇛   LISN, Line impadance stabilisation