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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.