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INSTRUCTION MANUAL
LI-550C
LINE IMPEDANCE STABILIZATION NETWORK
19121 El T oro R d ● S il vera d o, Ca lifo rnia 926 76 ● (94 9) 459 - 9600 ● com - p ower.com
REV021317
6.0
LISN
T
HEORY
Line Impedance Stabilization Networks provide 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-550C consists of two separate LISN
networks housed in separate enclosures 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 attenuation. This filter is comprised of a single stage low
pass LC filter. The inductors (L) used in the LI-550C are 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 EUT RF noise. The
insertion loss factors provided with every LISN network. It may be significant at low
frequencies; especially below 400 kHz. Therefore, the insertion loss correction factors
should always be considered for the highest measurement accuracy.
Example schematic of the LISN as well as the respective impedance requirements are
specified in the CISPR 25 and CISPR-16-1-2 standards. A typical circuit diagram of an LISN
is given in figure below.
Figure 5: Example of equivalent LISN circuit
