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INSTRUCTION MANUAL FOR LI-3100
LINE IMPEDANCE STABILIZATION NETWORK (LISN)
7.0 LISN Theory
7.1
Overview
Line Impedance Stabilization Networks used supply standardized line impedance to the EUT
during conducted emissions testing which is independent of the external power line impedance.
The standardized impedance enables consistent readings for RF noise measurements on the
power line. The model LI-3100 consists of two separate LISN networks housed in separate
enclosure for testing EUTs with single phase power requirements.
In addition to providing standardized impedance, the LISN also acts as a low pass filter for the
power to equipment under test. The LISN blocks RF noise from the power line from reaching the
equipment under test, however, the power to the equipment passes through the LISN with
minimal effect. This filter comprises of single stage low pass LC filter. Therefore, it has capacitor
and an inductor for the filter. The inductor used in the LI-3100 is air core type to eliminate the
possibility of saturation and to provide stability.
The LISN also provides a low impedance path for the RF noise from the EUT to the measuring
equipment, thereby facilitating the measurement of the RF noise. The insertion loss of the
measured noise may be significant especially at low frequencies. Therefore, at frequencies
below 400 kHz, the insertion loss correction factor must be compensated for highest accuracy
noise measurement.
The figure below is a typical schematic of a 5 µH LISN as specified in the CISPR-16-1-2, MIL-Std
461 standard. The LISN does not incorporate any internal 10 µF capacitor, so the requirement
specified in DO-160 for the 10 µF capacitor is to be fulfilled externally.
Figure 1 –
Example of an equivalent LISN circuit
Distributed by: Reliant EMC LLC, +1 408 916
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5750, [email protected], www.reliantemc.com
