EMC Awareness
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Radiocommunications Agency EMC Awareness |
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Automotive
Interference to Antilock Braking Systems (ABS)
Concerns about use of mobile transmitters in cars
Vehicles interfere with satellite TV and satellite communications
| Interference to Antilock Braking Systems (ABS) |  |
Description
Early ABS systems on both aircraft and automobiles were susceptible to EMI. Accidents occurred when the brakes functioned improperly because EMI disrupted the ABS control system. For aircraft, the initial solution was to provide a manual switch to lock out the ABS function when it was inoperable due to EMI and to use the normal braking system. Later, the solution was to qualify the ABS system prior to flight, based in the expected electromagnetic environment they would be exposed to.
For automobile systems, the solution was to ensure, if EMI occurs, that the ABS system degrade gracefully to normal braking – essentially an automatic version of the aircraft manual switch. Eventually, automobile ABS was qualified by EMI testing before procurement.
During the early years of ABS, a particular make of automobile equipped with ABS had severe braking problems along a certain stretch of the German Autobahn. The brakes were affected by a nearby radio transmitter as drivers applied them on a curved section of highway. The near-term solution was to erect a mesh screen along the highway to attenuate the EMI.
Mobile phones and passing taxi radios have been known to interfere with Anti-skid Braking Systems (ABS) and airbags, causing drivers to lose control of the car.
Commentary
ABS is a safety-critical system now used on millions of motor cars and a lesser number of aircraft. Since ABS depends upon the correct operation of electronics (and the software that runs on the electronics), since all electronics devices, circuits and systems are susceptible to electromagnetic interference (EMI), and since the electromagnetic environments for cars and planes can be quite severe, this makes the EMC of ABS a very important issue for safety reasons.
References and links
Items 2.3.1.16 and 2.3.1.17 on NASA Reference Publication 1374 (RP-1374), “Electronic Systems Failures and Anomalies Attributed to Electromagnetic Interference”, which can be downloaded from: http://trs.nis.nasa.gov/archive/00000296.
“Study to predict the electromagnetic interference for a typical house in 2010” by Anita Woogara, Bristol University, & Smith Group, 17 September 1999, available via http://www.radio.gov.uk/topics/research/topics.htm#emc.
Links to Mitigation Techniques
| Installation | Design & Development | Resources | |
| Unintentional RF demodulation |  |
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| Software design to improve immunity (e.g. Motor Industry Software reliability Association, and IEC 61508) |
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| PCB layout for EMC | |
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| Filtering with CM cable-mounted chokes |  |
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| Filtering | |
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| Shielding of areas and volumes | |
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| Shielding of cables | |
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| Concerns about use of mobile transmitters in cars | |
Description
Millions of motorists are risking their lives every time they use mobile phones while driving. New research has revealed (that) signals sent from mobiles can disrupt sophisticated electronic control units fitted in most modern cars. And it is feared that in some instances this could scupper vehicles’ braking and engine systems. One major manufacturer has also warned that the transmissions from mobiles could trigger air bags fitted to the car.
The alert over making calls in the car was given by the AA following research into the problem. The motoring organisation is now urging drivers to ensure they stop their cars before making any calls. Last night an AA spokesman said: “It is the same as aircraft operators asking people to switch off their mobiles while on a plane. The mobile is transmitting all the time and there is the possibility of interference with electronics in the car. You might get a misfire or your braking system might not operate. The answer is to only use the phone when you are stationary or to install an outside aerial.”
Mobile radios have been known to cause police cars’ central locking system to operate (note: these were not cellphones, police handsets are more powerful and operate on different frequencies).
One car manufacturer found that if a CB was operated in proximity to their car, the central locking engaged, locking the passengers within the vehicle. Another prestige car manufacturer found that whenever the vehicle passed by an operating ambulance or fire station, the airbags activated.
Test carried out by Volvo in Sweden showed that phones operating independently of car electrics can trigger airbags and interfere momentarily with control systems.
A liquid crystal type of dashboard display suffered interference from a nearby taxicab radio. And radio transmitters fitted to official vehicles have caused the following problems, when transmitting…
Some cruise controls and engine management systems have been analysed and found to be susceptible to electromagnetic interference (EMI). Cruise control systems can accelerate a car beyond the driver's ability to control the vehicle, due to EMI. This event is often called a "Sudden Acceleration Incident" in the US. EMI could cause the engine of a vehicle to operate at Wide-Open Throttle without the driver depressing the accelerator pedal.
Commentary
Modern engine management systems, ABS, airbags and many other systems on a modern motor car depend upon the correct operation of electronics, and of the software that runs on the electronics.
Unfortunately, all electronics (and software, because it employs electronics) can be made to malfunction by electromagnetic interference (EMI), and the motor car’s electromagnetic environment (both internal to the car and the outside ambient) can be very arduous. Major automotive manufacturers recognise this by subjecting the electronic devices used in their vehicles to very demanding tests for both emissions and immunity.
Since all electronics devices, circuits, software and systems are susceptible to electromagnetic interference (EMI), and since the road and roadside electromagnetic environment can be very severe, this makes the EMC of motor cars a very important issue, not least for safety reasons.
It isn’t hard to see how the use of a hand-held cellphone in a car (which is a commonplace activity despite being specifically prohibited by most car owner manuals) or a vehicle mobile transmitter installation that has not been done correctly or has suffered damage or corrosion, could expose certain vehicle electronic sub-assemblies to RF fields at frequencies and/or levels to which they were never tested.
For example, holding certain types of cellphone close to the steering wheel exposes the circuit which ignites the explosives that deploy the air bag to RF fields at about 1.8GHz and well over 100V/m, when according to the Automotive EMC testing is only necessary up to 1GHz and 24V/m – though to be fair, most vehicle manufacturers test their models to well in excess of this, as they don’t want to be subject to litigation if problems occur.
There is also the problem of ‘after-market modifications’, where owners or others who are unskilled in automotive EMC fit additional equipment or modify existing equipment, or repair the car after an accident. This can add new EMC problems or defeat existing interference-control measures put in place by the original manufacturer.
References and links
Bill Caven, writing in the Daily Record (Scotland, U.K.) 10th Jan 2000, page 23.
Ian Fletcher, writing in the Sunday Mirror, 9th Jan 2000, page 9.
“Study to predict the electromagnetic interference for a typical house in 2010” by Anita Woogara, Bristol University, & Smith Group, 17 September 1999, available via http://www.radio.gov.uk/topics/research/topics.htm#emc.
“Safety implications of EMC: how things can go wrong” by Graham Hicks, ERA Technologies Ltd, presented at the session on “EMC – The Practical Realities”, June 21-22 1994, part of the Electrotech Conference at the National Exhibition Centre, Birmingham U.K., http://www.era.co.uk.
“Critical nature of EMC” by Schaffner EMC Ltd, published in ‘Components in Electronics’ magazine, May 2002, page 22.
“Mobile threat to drivers” by Mark Ward, Computer Weekly, August 12th 1993 page 1.
“Dial D for danger?”, by John Langley, Weekend Telegraph (Motoring Section), December 4th 1993, page 14.
“EMC for automotive digital control systems”, Dr Ian Noble of Rover Group, at the IEE colloquium “EMC in high integrity digital systems”, 17 May 1991, IEE Digest No. 1991/104 available from http://www.iee.org.uk/Library.
Go to: http://www.mizenengineering.com/cur.htm#1, select “Cruise controls” and/ or “Electronic engine controls”.
“Cruise controls, computers, and electromagnetic interference”, Douglas B. Abrams of Abrams & Abrams, P.A., Attorneys at Law, USA, http://www.abramslawfirm.com/Sudden_acceleration.html.
“A Note on Automobile Cruise Control Faults and Sudden Acceleration” Dr Antony Anderson, http://www.antony-anderson.com/Cruise/1-intro.htm
“Road Transport”, Annex G to the IEE’s guide on “EMC and Functional Safety”, 2000, lists numerous electronic systems employed on modern cars, some of which are more obviously safety-critical than others. Download the guide and its annexes from: http://www.iee.org/Policy/Areas/Emc/index.cfm.
“Study on the Application of Directive 95/54/EEC in respect of the EMC of Road Vehicles”, a report for the European Commission DG III by York EMC Services Ltd, downloadable from: http://www.yorkemc.co.uk/Research/Automotive/Summary.htm.
The Motor Industry Research Association (MIRA) has a survey of the ‘external electromagnetic environment’ of the U.K., from the point of view of a motor car. Its findings tally well with similar ‘road’ surveys from Japan and the U.S.A: http://www.mira.co.uk.
“Can you trust your car?” by Ivan Berger, Contributing Editor, IEEE Spectrum, April 2002, pp41-45, reporting a discussion with David Ladd, communications manager at Siemens VDO Automotive (Auburn Hills, Mich., USA).
Links to Mitigation Techniques
| Installation | Design & Development | Resources | |
| Circuit design to reduce demodulation | |
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| PCB layout for EMC | |
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| Filtering with CM cable-mounted chokes | |
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| Filtering | |
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| Shielding of areas and volumes | |
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| Shielding of cables | |
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| Vehicles interfere with satellite TV and satellite communications | |
Description
Radar detectors that warn drivers they are approaching a police speed trap can emit signals that cause interference to SKY digital television (and numerous other microwave communications systems).
Although it is suspected that this type of interference is widespread, only a small number of cases have been reported. This is because most people would attribute the freezing or break-up of their digital TV picture to a glitch in their equipment, or SKY’s transmission, rather than interference. Relatively few people notice if this type of interference always occurs when a particular vehicle (fitted with a radar detector) passes their property.
The European Commission’s Directorate on General Enterprise have been made aware that equipment approved to their Automotive EMC Directive 95/54/EC has been found to interfere with radio systems operating in the 10-20GHz frequency range. It used to be considered that products that came under the 95/54/EC and were ‘e’ marked were excluded from being covered by the EMC Directive 89/336/EEC and so did not require CE marking.
However, it is now the Directorate’s opinion that 89/336/EEC applies to all of the EMC aspects that are not covered by 95/54/EC. Since 95/54/EC only covers emissions up to 1GHz, 89/336/EEC covers emissions from automotive equipment from 1GHz to 400GHz. Sadly, most of the applicable test standards under 89/336/EEC only test emissions to 1GHz, but at least the Protection Requirements of 89/336/EEC require that no interference is caused regardless of the frequency.
In the USA, where satellite TV is not very common, significant interference has occurred to satellite terminals used to link retail establishments with remote computers for verifying credit card transactions. Accordingly, the Federal Communications Commission (FCC) has announced that from August 2002 all radar detectors manufactured or imported in the USA must meet the Part 15 emissions limits in the 11.7-12.2GHz band.
Commentary
Automotive EMC directives and most of the commercial/industrial emissions standards required for regulatory compliance in Europe do not measure emissions at frequencies above 1GHz. Yet SKY Television and other providers of satellite-based services, including the GPS used by vehicles for navigation, all operate at over 1GHz.
Radar speed trap detectors use swept-frequency oscillators operating in the microwave frequency bands. Clearly, it is important to ensure that these (and other products) do not interfere with satellite and other services that use the microwave bands.
The fact that there are few commercial/industrial test standards in Europe that cover emissions at frequencies above 1GHz does not mean that emissions at such high frequencies are not regulated. It is up to all manufacturers to ensure that their products do not interfere with services (such as satellite TV) that operate above 1GHz.
EN 55011 and FCC “Part 15” emissions test standards cover up to at least 18GHz, as do military emissions standards, so these tests can be employed by manufacturers wishing to test their products using a standardised and repeatable test method.
References and links
Personal communication from John Mellish of the Radiocommunication Agency’s Radio Investigation Service, June 2003.
“Proposed changes in the Guidance to the Automotive EMC Directive 95/54/EC and the EMC Directive 89/336/EEC to jointly impose both “e Marking” and “CE Marking” on vehicles and vehicle equipment”, ERA Technology Ltd, Safety and EMC Newsletter, Number 68, April 2003, page 7, http://www.era.co.uk/accessera/iee/semcnews.htm.
“FCC stiffens rules for radar detectors”, Conformity, September 2002, page 8, via http://www.conformity.com
“Guidelines on the application of Directive 89/336/EEC. Chapter 15 – Application of the Directive to some specific cases. Section 15.3 – Application to Motor vehicles”, http://europa.eu.int/comm/enterprise/electr_equipment/emc/guides/chapfift.htm.
“All radar detectors marketed must be FCC approved effective October 27, 2002”, DA 02-2852 October 28 2002, http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-02-2852A1.pdf?date=021028.
Links to Mitigation Techniques
| Installation | Design & Development | Resources | |
| Circuit design for RF stability | |
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| Transmitter frequency control | |
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