Automotive EMC Questions
3. What does an EMC Expert System look for in
an automotive design?
The potential EMC problems that an
automotive EMC expert system looks for can be
divided into four categories; intra-harness
coupling, inter-harness coupling, field coupling
and EM emissions. EMC design rule checking is also
performed.
Intra-harness Coupling
Intra-harness coupling algorithms evaluate the
crosstalk between systems with wires that share the
same wiring harness. Common impedance coupling,
electric field coupling and magnetic field coupling
are all evaluated independently. The levels of
crosstalk in the final vehicle design will depend
on many factors (e.g. the exact positioning of
wires in a harness, exact impedance of connections,
etc.) that are not available in the computer
database. Therefore, a worse-case analysis is
performed that is intended to alert the user of a
potential problem even though a specific
implementation may not exhibit that problem.
Inter-harness Coupling
Inter-harness coupling algorithms evaluate the
crosstalk between two wiring harnesses due to
common impedance coupling, electric field coupling
or magnetic field coupling. They employ information
regarding the relative placement of harnesses and
harness connectors in the vehicle. Like the
intra-harness algorithms, they perform a worse-case
coupling analysis.
Field Coupling
Field coupling algorithms evaluate the noise
coupled to wire harnesses and receiving antennas
due to electric and magnetic fields generated
within or external to the vehicle. These algorithms
employ various methods to estimate this coupling
depending on the nature of the exciting field.
External field strengths and frequencies are
derived from component or vehicle EMC test
specifications. Internal field information is
obtained from the EM emissions algorithms.
EM Emissions
The electromagnetic emissions algorithms quantify
the worse-case field emissions from the various
electronic systems on a vehicle. Both intentional
and unintentional emission sources are
evaluated.
Rule Checking
Rule checking algorithms look for design features
that violate basic EMC design rules. In this case
no attempt is made to quantify the effect of the
violation.
References
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