EMC Expert Systems for Evaluating Automotive Designs

Todd H. HubingMichelin Professor of Vehicular ElectronicsClemson University

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There are more computers in the typical new automobile than in a typical campus

computer learning center.

Automobiles are Complex Electronic Systems

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Engine ignition (spark, timing) Entertainment systems

Fuel injection Braking (anti-lock brakes)

Emissions controls Steering (steering assist, 4-wheel steering)

Collision avoidance systems Seat & pedal positions

Heating/air conditioning Communication systems

Navigation systems Safety systems

Suspension systems Noise cancellation

Transmission controls Security systems

Lights, horn, wipers, defrosters …

Functions typically controlled electronically include:

Automobiles are Complex Electronic Systems

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Automobiles are Complex Electronic Systems

Many current automobile designs have nearly 100 microprocessors

Number of processors expected to double in 5 years.

A typical automobile contains about 5 miles of wiring.

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Electromagnetic Compatibility is a Growing Concern

RF susceptibility

ESD susceptibility

EMI affecting wireless communications

Conducted Intra-system interference

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SPICE or EM Models Don’t Locate EMC Problems

(Although, they can be used to evaluate a suspected problem.)

C11

Cm

L11

L22

M

RNEVS

RS

C22

RFE

I1

I2RL+

+

--V2

V1

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What is an EMC Expert System?

Reviews existing automobile specifications in a database.

Looks for possible EMC problems

Evaluates potential problems (likely worst case)

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EMC Expert System Objectives

Develop an EMC expert system to detect andeliminate potential EMC problems early in the designprocess

System (vehicle) levelUse design maxims and simple formulae Work with incomplete informationRun repeatedly throughout design cycleComplement – not replace – human expert and more sophisticated numerical modeling toolsGuide non-expert

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EMC Expert System Structure (TOP)

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EMC Expert SystemStructure (The Rest)

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Estimation of Intra-Harness Coupling

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Procedure for Developing Algorithm

Start with multi-conductor transmission line equationsSimplify equations by assuming:

Transmission line geometry is uniform along lengthCoupling media is airTransmission lines are losslessThe definition of the maximum coupling is:

2

1

MAX

MAX

VXV

=

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Simplified Formulas

22

mMAX

m

CXC C

=+

When two circuits are next to each other (in the same harness bundle, strong coupling)

When two circuits are in different harness bundles (weak coupling) and the aggressor and victim circuits are both shorted or both open at far end

22

mMAX

m

CXC C

=+

Other cases have similar equations

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Experimental Setup

Wire length: 87 cm Wire radii: 0.8 mm, 20#Height : 1.5 to 4.5 cm Distance: 2 mm to 9 cmGround plane: 40” × 24” Termination: short, open, 300 ohm

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Measurement Setup

Culprit and Victim circuits

Signal Generator

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Example Result

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Estimation of Field-to-Harness Coupling

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Expert System Estimate

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Measurement Set-Up

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Comparison to Simulation Results

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Conclusions

Number and complexity of automotive electronic systems is rising rapidly

Many design decisions are made before first prototype is built

Expert system software will enable designers to detect possible EMC problems early in the design process.