17EMC & Compliance Journal September 2003

IntroductionThe electronics content of vehicles has been increasingdramatically, particularly over the last 15 years or so and ispredicted to continue into the next decade, some estimatessuggest the value of electronics in a medium sized vehicle willrepresent 30% of the total vehicle cost by 2010. The increasein vehicle electronic components and modules has occurrednot only in electronic control units (ECU) for the vehicle itself,but also more recently in mobile communications, information,security and entertainment systems in the vehicle.

In light of this growth it is important that the multiple ECU’sin a vehicle are compatible electromagnetically and will notinterfere with off-board systems (especially roadsideequipment). The EMC of vehicles, especially spark ignitionengines, has been a consideration globally for much longerthan most commercial EMC standards have existed. In Europethe first directive for the suppression of spark-ignition noisewas published in 1972 (72/245/EEC). In North America theSociety of Automotive Engineers (SAE) have had standardsavailable on EMC since the early 1990’s and the InternationalStandards Organisation (ISO) and CISPR have providedautomotive specific EMC standards since 1990.

In the European Union (EU) there is a specific directive forautomotive EMC (EU directive 95/54/EC which amends 72/245/EEC) that covers the majority of automotive assembliesas well as the vehicles themselves and is embodied in legislation(several non EU member countries in Europe also adopt thisdirective under regulation ECE 10.02). There is no similarlegislative equivalent in North America (USA and Canada) orthe Rest of the World (RoW), hence automotive OEM’s havedeveloped their own internal standards that allow them to meetthe requirements of all the geographic markets into which theysell. Consequently the field of automotive EMC testing mayappear complicated having many different standards, somespecific to OEM’s, some international (CISPR/ISO), somegeographic (SAE in North America) and some legislativerequirements (95/54/EC).

Components or Electronic Sub-AssembliesThe term “electronic sub-assembly” (ESA) refers to almostany electrical or electronic device fitted to a vehicle. Thedefinition includes the more obvious sub-systems such asengine management unit (EMU), body control modules (BCM)and heating, ventilation and air-conditioning (HVAC) systems.The term ESA also includes what might be otherwiseconsidered as components such as manifold absolute pressure(MAP) sensor, solid-state relays (SSR) and motors. Theinternational automotive EMC standards usually refer to bothcomponents and modules as electronic sub-assemblies and hereno difference will be made between them, although most ofthe discussion will be based on modules rather than singlecomponents.

There are two categories of electrical/electronic equipmentfitted to vehicles; those fitted by the vehicle manufacturer(OEM fit) and after-market equipment (user fitted orprofessionally installed). In many cases the same companiesare supplying the OEM and after-market product and thesewill be tested to the same EMC standards. Equipment intendedas after-market fit only may not be as well regulated withrespect to EMC as OEM fitted and will generally only meetthe minimum requirements for the market.

Radiated Emissions StandardsThe two radiated emissions standards in common use;95/54/EC and CISPR-25, share many common features in theirchamber (Absorber Lined Screened Enclosure; ALSE,figure 1) test set-up and the results of each are almostcomparable. The “almost” is due to minor and often annoyingdiscrepancies, for example CISPR-25 tests for radiatedemissions specifies the ground plane at 0.9m from the chamberfloor, 95/54/EC specifies 1m. It is also possible to do the testson an Open Area Test Site (OATS) instead of a chamber, butthe calibration for OATS is significantly more time consumingand consequently more expensive via a test service, hence thepreference for ALSE facilities for these tests.

Figure 1: Radiated Emissions measurements from an automotiveESA (satellite navigation display) and harness (photo courtesy of

Trafficmaster/3C Test Ltd)

EMC Test Standards for Automotive Electronic Components

By Martin O'Hara, Senior Design Consultant, Telematica Systems Ltd

Table 1: International Automotive Standards for Component Testing

18EMC & Compliance Journal September 2003

The 95/54/EC standard covers the frequency range 30MHz to1GHz with fixed test levels for broadband and narrowbandemissions (figure 2). The levels are contiguous across thefrequency range and are simple pass/fail limits, although aswith most EMC test the “absolute” limits are complicated bythe standard insetting by 2dB on the quoted reference levels.Most people test to the quoted limits directly, it is only whenan emission is close to the reference limit that the 2dB insetlevel is used, and if submitting for type approval the final wordis provided by the approval body (the VCA in the case of UKtested products). It is not necessary to test at all the frequenciesin the range 30MHz to 1GHz, the directive allows for theselection of 13 test frequencies across this range (within 13defined frequency bands), however, as these test frequenciesare selected from the largest excursions during a pre-scan, it isusual to sweep the whole frequency range rather than selecttest points.

Figure 2: PSA and Ford limit lines extending the test frequencyto 2GHz

CISPR-25 covers a wider frequency range (150kHz to960MHz) and has broadband and narrowband limits(broadband includes peak and quasi-peak detector limits). Thetest levels are not continuous across this frequency range,instead being applied only to utilised radio frequency bands(figure 3). In CISPR-25 there are five classes of limit that canbe applied, often the customer will specify these, if no specificcustomer requirements (i.e. for the after-market) then themanufacturer often performs the tests and applies whateverlimit the ESA passes.

Figure 3: CISPR 25 Broadband peak and 95/54/EC limit lines

CISPR-25 includes provision for testing radiated emissions ina TEM cell. The test can be performed up to 175MHz onlyand includes seven classes of limit lines. The levels are equalacross all the measurement bands in the TEM cell test for eachclass limit. This type of testing is typically performed in-houserather than at a test service, as the wider frequency range andability to test to 95/54/EC at the same time makes the chamber

a more appealing test solution for test service providers as wellas manufacturers.

OEM specifications are based around the CISPR-25 chamberset-up (some also allow the TEM test for the lower frequencyrange). Most fill in the missing measurement bands, however,there is no consistency between OEM on how this is performed.For example PSA fill in the intermediate measurement bandsbelow 30MHz with the lower limit level from the previousband (i.e. if class 4 is applied from 150kHz to 300kHz, class 3limit from this band is applied from 300kHz to 530kHz), above30MHz the 95/54/EC limits plus 10dB is used in the gaps.Ford applies their own (non-CISPR-25) limit level and onlyutilise the test set-up of the standard. Most OEM specificationsextend the upper frequency range, going to 2GHz to coverGSM frequencies at 1.8GHz and 1.9GHz, a few extend furtherto 2.5GHz and 3GHz to encompass Bluetooth technologies.

Radiated Immunity StandardsThere are two radiated immunity standards in common use;95/54/EC for European legislative purposes and ISO 11452for most OEM standards. There are common tests betweenthe two standards and both allow a variety of methods to beemployed in the testing. One common test component is theuse of amplitude modulation (AM) at 1kHz to a depth of 80%that is used for both test standards discussed here.

Figure 4: Automotive ESA (EMU) radiated immunity testing in a150mm stripline (photo courtesy of Motorola)

The EU directive 95/54/EC permits testing using both 150mmand 800mm striplines, TEM cell (up to 200MHz), bulk currentinjection (BCI) and free-field (ALSE). Each test method hasdifferent limits and the directive specifies that tests should beat 25% above the defined limit (table 2). Testing across thecomplete frequency range required by 95/54/EC (20MHz to1GHz) is complicated if any method other than free field isused, as most of the other test methods are difficult to calibrateabove 400MHz. As with the radiated emissions testing, it ispermissible to test at specific test points (14 test points required,frequency bands not explicitly defined).

Table 2: Immunity Limit Levels as defined in 95/54/EC

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ISO 11452 comes in 7 parts the first of which is the generaldefinitions, the other 6 are different test methods and limitscomprising of free field (ALSE), TEM, BCI, 150mm stripline,parallel plate antenna and direct RF injection (table 3). Aswith most international standards there are multiple classes oflimit levels that the manufacturer or customer can specify;typically there are 4 defined classes within each test methodand a “user defined” class without limits. Although limit levelsdo vary by test method, the classes encompass the range 25V/m to 200V/m for direct field measurement methods, 25mA to100mA for BCI and 0.1W to 0.5W for direct injection.

Table 3: ISO 11452 Test Methods and Frequency Range

Figure 5: BCI testing over ground plane(photo courtesy of Trafficmaster/3C Test Ltd)

The OEM standards primarily utilise the methods and limitsof ISO 11452. It is not uncommon for multiple immunity teststo be specified with BCI often used for the lower frequency (1to 400MHz) and free field for tests from 20MHz to the upperdefined frequency limit. There are many OEM specificationsthat extend beyond the 1GHz limit of 95/54/EC, however, fewrequire testing to the upper frequency limit of 18GHz as definedin ISO 11452-2 (General Motors extend to 10GHz) and mosthave upper limits concurrent with their radiated emissionsspecification (i.e. typically in the 2GHz to 3GHz range). TheOEM tests also use continuous wave (CW) tests as well asAM, and many include pulsed modulation (PM), in place ofAM, at higher frequencies (above 1GHz).

Conducted EmissionsCISPR-25 is the primary automotive standard for conductedemissions, containing tests and limit levels for both power andsignal line conducted noise. Automotive radiated emissionstesting is to ensure the ESA, and hence completed vehicle,does not interfere with equipment external to the vehicle aswell as on-board receivers, automotive conducted emissionstests are purely to ensure the ESA does not interfere with otheron-board equipment. The wired supply and signalling systemfor a vehicle is a self contained system and does not directlyinterface with off-board equipment while in use.

There are two test methods for conducted emissions in CISPR-25; measurements via a LISN (50Ω/5µH) for power lineemissions (figure 6) and measurements from a current probefor signal/control line emissions. There are again 5 classes oflimit lines (as per radiated emissions in CISPR-25) and againbroadband and narrowband limits, with peak and quasi-peakdetector limits for the broadband measurement. The conductedemissions test covers the frequency range 150kHz to 108MHz,with five specific radio frequency bands.

Figure 6: Testing the conducted emissions of ESA power lines via50Ω/5Ω/5Ω/5Ω/5Ω/5µH LISN (photo courtesy of Trafficemaster/3C Test Ltd)

As with radiated emissions, OEM specifications utilise the testset-up of CISPR-25 for power line emissions and apply theirown limits, most filling in the omitted test bands. A few of theOEM specifications extend the test frequency range (e.g. BMWcover 30kHz to 120MHz, figure 7). Signal/control line testingis not as universally well specified, many OEM specificationsuse methods not covered by the CISPR-25 standard and someomit testing noise on these lines other than at audio frequencies.

Figure 7: General Motors (GM) and BMW conducted emissionslimits for power lines

EMC & Compliance Journal September 2003

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Conducted ImmunityConducted immunity to transients standard (ISO 7637) containssome of the most fundamental test methods to ensure that anESA can function within an automotive electrical environment.Although this standard has no current statutory requirement, itis one of the most basic “good practice” tests that should beapplied to any ESA.

The ISO 7637 standard is currently under review, at the presenttime it comes in 3 parts, the first for 12V systems, second for24V systems and third for signal/control line immunity. TheISO review has already re-issued the first part as a generaldefinitions paper and will combine the 12V and 24V testinginto the second part with the signal/control testing probablyretained in part 3. There are different transient pulses that willbe retained and/or dropped in the review and consequently thediscussion here is more general that in previous sections as thefinalised test standards are not yet published.

The transient immunity standard encompasses noise that islikely to be observed on the power and signal lines of anautomotive wiring network. These include inductive noisefrom motors, supply dropout during cranking and load dump;where the battery is disconnected while the alternator is stillrunning. There are four classes of limits applicable within thestandard, as well as the usual “customer specified” level. Powerline transients (figures 8 to 10) are applied directly onto thepower supply, the signal/control line transients are coupledcapacitively via a coupling clamp (figure 11).

Figure 8: Inductive transient noise applied to 12V power supply lines

Figure 9: Transient during cranking on 12V power supply

Figure 10: Load dump transient on 12V supply line

Figure 11: Signal/control line transients test set-up using couplingclamp (photo courtesy of Trafficmaster/3C Test Ltd)

There are a series of functional classifications that are commonto many ISO automotive standards (see text box). Thefunctional categories allow a product to either operatecontinuously during a transient event or to simply survive atransient while not functioning during the event. Thefunctional classification is obviously determined by theapplication an ESA is intended for, a powertrain ESA wouldbe expected to operate during transients (class A), whereas atelematic unit can cease functioning during the transient andrecover after the event (class C).

OEM specifications use the pulses and set-up of ISO 7637 withtheir own set of applied levels and functional classifications.The OEM specifications modify some of the pulse shapes tobe specific to the power network, motors and alternatorstypically used in their vehicles, hence are similar to ISO 7637with minor nuances in the voltage levels and pulse shapes (risetimes and dwell times are usually different between OEMspecifications).

Immunity to Electrostatic Discharge (ESD)The vehicle is an isolated product in that it does not share acurrent return common with the “earth” reference. The currentreference to ground on a vehicle is usually to the negativeterminal of the battery, hence is not the standard groundreference of most commercial tests or products. Consequentlya different body model and test standard has been developedfor automotive ESD testing; ISO 10604.

Figure 12: ESD testing ESA at connector while powered (photocourtesy of Trafficmaster/3C Test Ltd)

The body model uses a 2kΩ series resistor and 150pF capacitorfor discharge while outside a vehicle and 330pF capacitor fordischarge inside a vehicle. There are the usual air and directcontact discharge tests to both the ESA body and to the

EMC & Compliance Journal September 2003

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standards community (and before Chrysler were merged withDaimler-Benz). The majority of SAE standards are nowencompassed in international standards and although still oftenquoted for North American products, they are mainlysuperseded by their ISO and CISPR equivalents.

Table 4: SAE Standards for Component Testing and theirInternational Equivalent

There are some SAE component standards that have not beenadopted by the international standard bodies. Some of theunadopted SAE standards are encompassed in a few of theOEM specifications, however, many of these are being droppedin favour of alternative tests that are encompassed by existinginternational standards and consequently are not included here.

The SAE standards were developed to allow North Americansuppliers to produce compliant products for their home OEMmarket. With most of the SAE standards now covered byinternational equivalents it is debatable whether there is a needfor the SAE standards to be separately maintained and updated.

Choice of Test StandardsAssuming that an OEM standard has not been provided (i.e. aproduct is not designed for OEM line fit), then the choice ofapplicable standards is open to interpretation, with theexception of products for sale in Europe.

In Europe the choice of standard for radiated emissions andimmunity is determined by legal requirements. It is requiredto show proof of meeting the standards and to “e” mark anESA via the type approval process of 95/54/EC. This is theminimum requirement for sale of a product intended forautomotive use in the EU, however, it would be sensible for amanufacturer to also test for transient immunity, ESD andconducted emissions to ensure that the ESA will not causeproblems for the customer and consequently give them a “badname”.

The following are recommended test standards to use for threegeographic regions where no OEM specification is available.Due to the legal nature of the European standards, if an ESA isto be sold in multiple regions it should tested to the Europeanstandard 95/54/EC as a minimum, others can be added at therequest of regional authorities.

EMC & Compliance Journal September 2003

connectors and/or any metal fixings. The standard also includestesting for air and contact discharge at the electrical terminalsof the ESA while unpowered (i.e. no ground return) to simulatehandling during assembly, this requires any accumulatedcharge to be bled from the ESA between applied discharges.

The discharge levels cover ±2kV up to ±25kV, the higher levelsprimarily reserved for equipment classed as pyrotechnic, thisincludes airbag deployment devices and in some OEMspecifications fuel systems. The minimum number ofdischarges is specified as 3 per polarity with at least 5s betweenapplied test pulses. The standard includes the usual ISOfunctional classifications (see text box).

ISO Functional Status ClassificationDirectly taken from ISO 10605:2001.

All classifications given below are for the total device/systemfunctional status.

NOTE: The word “function” as used here concerns onlythe function performed by the electronic system.

Class A: all functions of a device or system perform asdesigned during and after exposure to interference.

Class B: all functions of a device/system perform asdesigned during exposure; however, one or more of themmay go beyond the specified tolerance. All functions returnautomatically to within normal limits after exposure isremoved. Memory functions shall remain class A.

Class C: one or more functions of a device or system donot perform as designed during exposure but returnautomatically to normal operation after exposure is removed.

Class D: one or more functions of a device or system donot perform as designed during exposure and do not returnto normal operation until exposure is removed and the deviceor system is reset by a simple “operator/use” action.

Class E: one or more functions of a device or system donot perform as designed during and after exposure andcannot be returned to proper operation without repairing orreplacing the device or system.

The automotive ESD standard is almost universally adoptedwithin OEM specifications. A few OEM specifications usethe commercial body model definition of IEC 61000-4-2 (330Ωseries resistor), it is difficult to know whether this is an errorby the OEM or a deliberate effort to apply a higher stress to anESA? Not all OEM specifications currently include the un-powered test as this is a relatively new addition to the standard(updated in December 2001).

Society of Automotive Engineers (SAE)StandardsThe SAE have been the leading influence in producingstandardisation for the North American automotive market.Their standards reflect what the “big 3” US OEMs (GeneralMotors, Ford and Chrysler) were doing in the last decade,before some of the standards were adopted by the international

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Table 7: Worldwide EMC Standards

Products tested to these standards would be acceptable in theNorth American market as the SAE standards are equivalent.

Martin O'Hara is Senior Design Consultant, TelematicaSystems Limited and can be contacted on tel: +44 (0)1234759232, or email: martin@tmsl.com.

EN9

Automotive EMC TestingIf you are used to only testing commercial products, it willsound strange to hear that automotive tests for emissionsand immunity are conducted mainly on the connectingharness rather than the ESA itself, that the ESA is keptstationary (it is not rotated on a turntable) and measurementsare made with the antenna at only 1m from the test set-up.The ESA and harness are placed on a metal grounded planerather than an isolated table (the plane is usually placed onthe test table); this is representative of the metal body of avehicle, although the ground is connected to the chambermains earth as well as the battery supply negative terminal.The harness and ESA is supported by an insulating mediumat 50mm from the ground plane, hence is not laid directlyon the ground plane.

These differences, along with the LISN (5µH rather than50µH) and specific harness requirements, make automotiveEMC testing significantly different to the majority ofcommercial EMC tests and consequently many commercialEMC test services are unable to perform automotive EMCtesting. Automotive EMC testing is a specialised field withinthe EMC test services sector with its own test accreditation(Automotive EMC Laboratory Recognition Program,AEMCLRP) and a list of test houses with automotive EMCcapability is available on the Automotive EMC network(www.AutoEMC.net).

ESA Test Standards by Geographic Market

Table 5: European EMC Test Standards

The above are not all legal requirements, only 95/54/EC islegally required and for an ESA that does not effect theoperation of the vehicle the radiated emissions test is the onlylegal requirement.

Table 6: North American EMC Standards

The above standards are not compulsory but again indicatesound engineering practice has been considered in the designof products intended for this market.

In the US automotive products are explicitly exempt from FCCPart 15 rules under section 15.103 Exempt Devices; “a) Adigital device utilized exclusively in any transportation vehicleincluding motor vehicles and aircraft.”

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