IEEE UK EMC Society Meeting: Automotive EMC
June 2003, MIRA Nuneaton
The UK EMC Society of the IEEE hold regular events around the UK (mainly in the South East) that are free to members. I was fortunate enough to be able to attend this Automotive EMC event despite not being a member and was one of approximately 30 attendees who made the trip to MIRAsí impressive facility at Nuneaton. MIRA itself provided 3 of the four speakers, the fourth was from Ford and the speaker was no doubt a regular visitor and customer of MIRA.
Automotive EMC Environment and Requirements
This paper outlined the differences in the automotive OEM test specifications and compared them to the minimum regulatory standards that they all exceed. The presentation started by defining the automotive as a mobile EMC environment and illustrating some of the immunity issues this entails. Some recent product recall issues were presented and an indication of the costs of these compared to EMC testing was provided. Other non-recall customer complaints were also presented to illustrate that not all EMC problems are serious enough for recall, but customer complaints are still a cause of concern. The EMC specifications of Ford, PSA, VAG, BMW and Renault were compared; illustrating differences in limit levels, frequency ranges and in some cases test methods.
Testing of Specialist Systems, Airbag Robustness, ABS System Test
The presentation gave some interesting dilemmas in testing of complex automotive systems such as airbags, ABS systems, adaptive cruise control (ACC) and other complex systems. The ABS system was covered in detail and the system used at MIRA that links the dynamometer with the test system and applies a braking event at each frequency point during the test sequence was used to illustrate the complexity (the test set-up was visited at the end of the day, see below). The ACC system had a moving target for the ACC radar that similarly had to be controlled to generate ACC events at each frequency step. An alternative method of measuring airbag deployment device immunity using measured heating effect under radiated fields was presented that allows a lower cost test for the device without the expense of a full deployment system. The result provides a demonstrable degree of margin for the immunity level applied. Other systems discussed in lesser detail were remote keyless entry (RKE), parking aids, alarms and the increasing use of in-vehicle networks.
The requirements for vehicle EMC e-mark certification were covered and some of the implications for vehicle OEMs with respect to safety. The vehicle development life span was used to illustrate the most likely sign-off points for e-marking, suggesting up to 42 months before product launch for some items. The selection of worse case examples for final vehicle testing was highlighted, requiring sample vehicles fully loaded with electronics and in a variety of body/engine/trim specifications. Ensuring adequate coverage of product range within reasonable cost constraints is an issue for OEMís and test services alike.
The implication that a user (owner) or fitter and supplier of services and aftermarket products could essentially be committing an offence in installing non e-marked devices within Europe did not raise the discussion one might have expected. The talk concluded with the future of the European directive, which includes frequency extension to 2GHz and transient immunity test (as per ISO 7637) to be included. This sparked a lively debate after the presentation on the lack of ESD testing in the standard and the potential safety hazard this could imply. The speakers' opinion being that the testing is only a final check and that the OEM would have designed in the appropriate safe guards, however, anecdotal evidence discussed on the day suggests this is not always the case or can be defeated by assembly errors.
Developments in Electromagnetics Research
The title should have been "Developments in Simulation and Modeling" as this was the prime focus of this presentation. Recent simulation studies of electric powered vehicles, both hybrid and fuel cell powered, illustrated reasonable correlation between simulation and available measured results. The facilities available at MIRA for simulation of test chamber studies and vehicle body configurations was presented. A major reason for use of simulation was that test cycle times often exceed the battery capacity of the device under test. Another reason for use is to extend theoretical studies beyond the limits of affordable measurement facilities with projections of high field immunity simulations up to 10GHz being possible in simulation without melting the vehicle under test!
The day concluded with a
tour of one of MIRAsí semi-anechoic chambers in which a Ford Focus was
undergoing radiated immunity testing of its ABS system, a test Peter Philips had
discussed earlier. The chamber was
impressively dimensioned at 21m x 10m x 11m and featured a dynamometer with
variable wheel geometry up to 6m and one of the largest log-periodic antenna
this writer has seen, measuring approximately 5m across its longest elements.
The RF power delivery system to this dimension of antennae and chamber
was similarly impressive, if somewhat noisy due to the forced air cooling, and
capable of delivering over 100V/m to a vehicle under test from 10kHz up to 1GHz.
Despite the obvious MIRA bias to the event it was still an informative half-day session. The short tour of the chamber featuring a Ford Focus undergoing ABS testing was instructive, although to some extent failed to convey the extensive time this type of testing takes. A worthwhile event, well attended by IEEE members and well organised by MIRA.
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