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Figure 3:
Conducted emissions test set-up
Figure 4:
Radiated emissions test set-up
pre-compliance testing themselves
the tests can be performed in a
room with a minimal amount of test
equipment. The equipment required
for conducted emissions testing is an
LISN (Line Impedance Stabilization
Network) and a spectrum analyzer.
The LISN is a passive network used
to minimize the noise conducted
from commercial power lines
and also provides a controlled
impedance test port to monitor
the conducted emissions from
the EUT (Equipment Under Test).
The spectrum analyzer used for
conducted emissions testing can
be a basic model with the ability to
perform measurements from 150
kHz through 30 MHz. Many vendors
of spectrum analyzers include
the ability to perform quasi-peak
measurements and incorporate
conformance parameter limits in the
display to simplify EMC compliance
testing.
Preliminary testing for radiated
emissions can be accomplished
with a spectrum analyzer and an
appropriate antenna. The spectrum
analyzer should have the capability
to make measurements from 30
MHz through at least 900 MHz. The
ability of the spectrum analyzer to
perform quasi-peak measurements
and display conformance parameter
limits in the display will make the
preliminary testing tasks easier
to perform. The antenna used for
preliminary radiated emissions
testing should have a bandwidth
similar to the spectrum analyzer
and the gain versus frequency
characteristics needing to be
known. It is preferable to be able
to perform the radiated emissions
testing in an electrically quiet room
with at least three meters (10 feet)
between the radiated emissions
EMC antenna and the EUT. An initial
measurement in the room with
the EUT powered off will provide
information regarding the ambient
RF noise present during the testing.
Most management teams appreciate
projects
completed
under
budget and ahead of schedule.
Unfortunately, EMC compliance
issues can be a common source of
last minute budget and schedule
increases for projects. Performing
pre-compliance EMC testing during
the system assembly phases of a
project can help to eliminate those
last minute changes to a design that
impact budgets and schedules. Pre-
compliance EMC testing also helps
to ensure no issues arise during
final compliance testing. Full service
power supply vendors, such as CUI,
have the equipment and experience
to assist in power supply design and
selection, including pre-compliance
and final EMC testing.
New-Tech Magazine Europe l 65