A line impedance stabilization network (LISN) is a device used in conducted and radiated radio-frequency emission and susceptibility tests, as specified in various

electromagnetic compatibility Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy whic ...

(EMC)/EMI test standards (e.g., by

CISPR The ''Comité International Spécial des Perturbations Radioélectriques'' (CISPR; en, International Special Committee on Radio Interference) was founded in 1934 to set standards for controlling electromagnetic interference in electrical and elec ...

International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and ...

CENELEC CENELEC (french: Comité Européen de Normalisation Électrotechnique; en, European Committee for Electrotechnical Standardization) is responsible for European standardization in the area of electrical engineering. Together with ETSI (telecommun ...

, U.S. Federal Communications Commission, MIL-STD,

DO-160 DO-160, Environmental Conditions and Test Procedures for Airborne Equipment is a standard for the environmental testing of avionics hardware. It is published by the Radio Technical Commission for Aeronautics (RTCA) and supersedes DO-138. Outline ...

Sections 20-21-22). A LISN is a

low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filt ...

typically placed between an AC or DC power source and the EUT (equipment under test) to create a known impedance and to provide a

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the up ...

(RF) noise measurement port. It also isolates the unwanted RF signals from the power source. In addition, LISNs can be used to predict conducted emission for diagnostic and pre-compliance testing.

Functions of an LISN

Stable line impedance

The main function of a LISN is to provide a precise impedance to the power input of the EUT, in order to get repeatable measurements of the EUT noise present at the LISN measurement port. This is important because the impedance of the power source and the impedance of the EUT effectively operate as a voltage divider. The impedance of the power source varies, depending on the geometry of the supply wiring behind it. The anticipated inductance of the power line for the intended installation of the EUT also plays a role in identifying the correct type of LISN needed for testing. For example, a connection in a building will often use 50 μH inductor, whereas in automobile measurement standards a 5 μH inductor is used to emulate a shorter typical wire length.

Isolation of the power source noise

Another important function of a LISN is to prevent the high-frequency noise of the power source from coupling in the system. A LISN functions as a

, which provides high impedance to the outside RF noise while allowing the low-frequency power to flow through to the EUT.

Safe connection of the measuring equipment

Typically, a spectrum analyzer or an EMI receiver is used to take the measurements during an EMC test. The input port of such an equipment is very sensitive and prone to damage if overloaded. A LISN provides a measurement port with, usually, 50 Ω output impedance. The stabilized impedance, the built-in low-pass filter function, and the DC rejection properties of the LISN measurement port makes it easy to couple the high frequency noise signal to the input of the measuring equipment.

LISN types

Under a particular EMC test standard, a specific LISN type is required for evaluating and characterizing the operation of the EUT. Different types of LISNs are available for analyzing DC,

single-phase In electrical engineering, single-phase electric power (abbreviated 1φ) is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loa ...

or 3-phase AC power connections. The main parameters for selecting the proper type of LISN are impedance, insertion loss, voltage rating, current rating, number of power conductors and connector types. The upper frequency limit of the LISN also plays an important role when conducted emissions measurements are used for predicting radiated emissions problems. A 100 MHz LISN is used in those cases.

Notes

2. Staggs, David. "Using a LISN as an Electronic System EMC Diagnostic Tool" (PDF). The Electro Mechanics Company. http://www.unitest.com/pdf/LisnElec.pdf Retrieved 24 March 2020.

References

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Sources

* MIL-STD 461E, ''REQUIREMENTS FOR THE CONTROL OF ELECTROMAGNETIC INTERFERENCE CHARACTERISTICS OF SUBSYSTEMS AND EQUIPMENT'', 1999 Laboratory equipment Electronic test equipment