EMC Test Standards for Automotive Electronic Components
By Martin O'Hara, Senior Design Consultant, Telematica Systems Ltd
Introduction
Components or Electronic Sub-Assemblies
The electronics content of vehicles has been increasing
dramatically, particularly over the last 15 years or so and is
predicted to continue into the next decade, some estimates
suggest the value of electronics in a medium sized vehicle will
represent 30% of the total vehicle cost by 2010. The increase
in vehicle electronic components and modules has occurred
not 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.
The term “electronic sub-assembly” (ESA) refers to almost
any electrical or electronic device fitted to a vehicle. The
definition includes the more obvious sub-systems such as
engine management unit (EMU), body control modules (BCM)
and heating, ventilation and air-conditioning (HVAC) systems.
The term ESA also includes what might be otherwise
considered as components such as manifold absolute pressure
(MAP) sensor, solid-state relays (SSR) and motors. The
international automotive EMC standards usually refer to both
components and modules as electronic sub-assemblies and here
no difference will be made between them, although most of
the discussion will be based on modules rather than single
components.
In light of this growth it is important that the multiple ECU’s
in a vehicle are compatible electromagnetically and will not
interfere with off-board systems (especially roadside
equipment). The EMC of vehicles, especially spark ignition
engines, has been a consideration globally for much longer
than most commercial EMC standards have existed. In Europe
the first directive for the suppression of spark-ignition noise
was published in 1972 (72/245/EEC). In North America the
Society of Automotive Engineers (SAE) have had standards
available on EMC since the early 1990’s and the International
Standards Organisation (ISO) and CISPR have provided
automotive specific EMC standards since 1990.
There are two categories of electrical/electronic equipment
fitted to vehicles; those fitted by the vehicle manufacturer
(OEM fit) and after-market equipment (user fitted or
professionally installed). In many cases the same companies
are supplying the OEM and after-market product and these
will be tested to the same EMC standards. Equipment intended
as after-market fit only may not be as well regulated with
respect to EMC as OEM fitted and will generally only meet
the minimum requirements for the market.
Radiated Emissions Standards
In the European Union (EU) there is a specific directive for
automotive EMC (EU directive 95/54/EC which amends 72/
245/EEC) that covers the majority of automotive assemblies
as well as the vehicles themselves and is embodied in legislation
(several non EU member countries in Europe also adopt this
directive under regulation ECE 10.02). There is no similar
legislative equivalent in North America (USA and Canada) or
the Rest of the World (RoW), hence automotive OEM’s have
developed their own internal standards that allow them to meet
the requirements of all the geographic markets into which they
sell. Consequently the field of automotive EMC testing may
appear complicated having many different standards, some
specific to OEM’s, some international (CISPR/ISO), some
geographic (SAE in North America) and some legislative
requirements (95/54/EC).
The two radiated emissions standards in common use;
95/54/EC and CISPR-25, share many common features in their
chamber (Absorber Lined Screened Enclosure; ALSE,
figure 1) test set-up and the results of each are almost
comparable. The “almost” is due to minor and often annoying
discrepancies, for example CISPR-25 tests for radiated
emissions specifies the ground plane at 0.9m from the chamber
floor, 95/54/EC specifies 1m. It is also possible to do the tests
on an Open Area Test Site (OATS) instead of a chamber, but
the calibration for OATS is significantly more time consuming
and consequently more expensive via a test service, hence the
preference for ALSE facilities for these tests.
Figure 1: Radiated Emissions measurements from an automotive
ESA (satellite navigation display) and harness (photo courtesy of
Trafficmaster/3C Test Ltd)
Table 1: International Automotive Standards for Component Testing
EMC & Compliance Journal September 2003
17
The 95/54/EC standard covers the frequency range 30MHz to
1GHz with fixed test levels for broadband and narrowband
emissions (figure 2). The levels are contiguous across the
frequency range and are simple pass/fail limits, although as
with most EMC test the “absolute” limits are complicated by
the standard insetting by 2dB on the quoted reference levels.
Most people test to the quoted limits directly, it is only when
an emission is close to the reference limit that the 2dB inset
level is used, and if submitting for type approval the final word
is provided by the approval body (the VCA in the case of UK
tested products). It is not necessary to test at all the frequencies
in the range 30MHz to 1GHz, the directive allows for the
selection of 13 test frequencies across this range (within 13
defined frequency bands), however, as these test frequencies
are selected from the largest excursions during a pre-scan, it is
usual to sweep the whole frequency range rather than select
test points.
a more appealing test solution for test service providers as well
as manufacturers.
OEM specifications are based around the CISPR-25 chamber
set-up (some also allow the TEM test for the lower frequency
range). 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 bands
below 30MHz with the lower limit level from the previous
band (i.e. if class 4 is applied from 150kHz to 300kHz, class 3
limit from this band is applied from 300kHz to 530kHz), above
30MHz the 95/54/EC limits plus 10dB is used in the gaps.
Ford applies their own (non-CISPR-25) limit level and only
utilise the test set-up of the standard. Most OEM specifications
extend the upper frequency range, going to 2GHz to cover
GSM frequencies at 1.8GHz and 1.9GHz, a few extend further
to 2.5GHz and 3GHz to encompass Bluetooth technologies.
Radiated Immunity Standards
There are two radiated immunity standards in common use;
95/54/EC for European legislative purposes and ISO 11452
for most OEM standards. There are common tests between
the two standards and both allow a variety of methods to be
employed in the testing. One common test component is the
use of amplitude modulation (AM) at 1kHz to a depth of 80%
that is used for both test standards discussed here.
Figure 2: PSA and Ford limit lines extending the test frequency
to 2GHz
CISPR-25 covers a wider frequency range (150kHz to
960MHz) and has broadband and narrowband limits
(broadband includes peak and quasi-peak detector limits). The
test 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 can
be applied, often the customer will specify these, if no specific
customer requirements (i.e. for the after-market) then the
manufacturer often performs the tests and applies whatever
limit the ESA passes.
Figure 4: Automotive ESA (EMU) radiated immunity testing in a
150mm stripline (photo courtesy of Motorola)
The EU directive 95/54/EC permits testing using both 150mm
and 800mm striplines, TEM cell (up to 200MHz), bulk current
injection (BCI) and free-field (ALSE). Each test method has
different limits and the directive specifies that tests should be
at 25% above the defined limit (table 2). Testing across the
complete frequency range required by 95/54/EC (20MHz to
1GHz) is complicated if any method other than free field is
used, as most of the other test methods are difficult to calibrate
above 400MHz. As with the radiated emissions testing, it is
permissible to test at specific test points (14 test points required,
frequency bands not explicitly defined).
Figure 3: CISPR 25 Broadband peak and 95/54/EC limit lines
CISPR-25 includes provision for testing radiated emissions in
a TEM cell. The test can be performed up to 175MHz only
and includes seven classes of limit lines. The levels are equal
across all the measurement bands in the TEM cell test for each
class limit. This type of testing is typically performed in-house
rather than at a test service, as the wider frequency range and
ability to test to 95/54/EC at the same time makes the chamber
Table 2: Immunity Limit Levels as defined in 95/54/EC
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EMC & Compliance Journal September 2003
ISO 11452 comes in 7 parts the first of which is the general
definitions, the other 6 are different test methods and limits
comprising of free field (ALSE), TEM, BCI, 150mm stripline,
parallel plate antenna and direct RF injection (table 3). As
with most international standards there are multiple classes of
limit levels that the manufacturer or customer can specify;
typically there are 4 defined classes within each test method
and a “user defined” class without limits. Although limit levels
do vary by test method, the classes encompass the range 25V/
m to 200V/m for direct field measurement methods, 25mA to
100mA for BCI and 0.1W to 0.5W for direct injection.
Conducted Emissions
CISPR-25 is the primary automotive standard for conducted
emissions, containing tests and limit levels for both power and
signal line conducted noise. Automotive radiated emissions
testing is to ensure the ESA, and hence completed vehicle,
does not interfere with equipment external to the vehicle as
well as on-board receivers, automotive conducted emissions
tests are purely to ensure the ESA does not interfere with other
on-board equipment. The wired supply and signalling system
for a vehicle is a self contained system and does not directly
interface with off-board equipment while in use.
There are two test methods for conducted emissions in CISPR25; measurements via a LISN (50Ω/5µH) for power line
emissions (figure 6) and measurements from a current probe
for signal/control line emissions. There are again 5 classes of
limit lines (as per radiated emissions in CISPR-25) and again
broadband and narrowband limits, with peak and quasi-peak
detector limits for the broadband measurement. The conducted
emissions test covers the frequency range 150kHz to 108MHz,
with five specific radio frequency bands.
Table 3: ISO 11452 Test Methods and Frequency Range
Figure 6: Testing the conducted emissions of ESA power lines via
50Ω/5µH LISN (photo courtesy of Trafficemaster/3C Test Ltd)
As with radiated emissions, OEM specifications utilise the test
set-up of CISPR-25 for power line emissions and apply their
own limits, most filling in the omitted test bands. A few of the
OEM specifications extend the test frequency range (e.g. BMW
cover 30kHz to 120MHz, figure 7). Signal/control line testing
is not as universally well specified, many OEM specifications
use methods not covered by the CISPR-25 standard and some
omit testing noise on these lines other than at audio frequencies.
Figure 5: BCI testing over ground plane
(photo courtesy of Trafficmaster/3C Test Ltd)
The OEM standards primarily utilise the methods and limits
of ISO 11452. It is not uncommon for multiple immunity tests
to be specified with BCI often used for the lower frequency (1
to 400MHz) and free field for tests from 20MHz to the upper
defined frequency limit. There are many OEM specifications
that extend beyond the 1GHz limit of 95/54/EC, however, few
require testing to the upper frequency limit of 18GHz as defined
in ISO 11452-2 (General Motors extend to 10GHz) and most
have upper limits concurrent with their radiated emissions
specification (i.e. typically in the 2GHz to 3GHz range). The
OEM tests also use continuous wave (CW) tests as well as
AM, and many include pulsed modulation (PM), in place of
AM, at higher frequencies (above 1GHz).
EMC & Compliance Journal September 2003
Figure 7: General Motors (GM) and BMW conducted emissions
limits for power lines
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Conducted Immunity
Conducted immunity to transients standard (ISO 7637) contains
some of the most fundamental test methods to ensure that an
ESA can function within an automotive electrical environment.
Although this standard has no current statutory requirement, it
is one of the most basic “good practice” tests that should be
applied to any ESA.
The ISO 7637 standard is currently under review, at the present
time it comes in 3 parts, the first for 12V systems, second for
24V systems and third for signal/control line immunity. The
ISO review has already re-issued the first part as a general
definitions paper and will combine the 12V and 24V testing
into the second part with the signal/control testing probably
retained in part 3. There are different transient pulses that will
be retained and/or dropped in the review and consequently the
discussion here is more general that in previous sections as the
finalised test standards are not yet published.
Figure 11: Signal/control line transients test set-up using coupling
clamp (photo courtesy of Trafficmaster/3C Test Ltd)
There are a series of functional classifications that are common
to many ISO automotive standards (see text box). The
functional categories allow a product to either operate
continuously during a transient event or to simply survive a
transient while not functioning during the event. The
functional classification is obviously determined by the
application an ESA is intended for, a powertrain ESA would
be expected to operate during transients (class A), whereas a
telematic unit can cease functioning during the transient and
recover after the event (class C).
The transient immunity standard encompasses noise that is
likely to be observed on the power and signal lines of an
automotive wiring network. These include inductive noise
from motors, supply dropout during cranking and load dump;
where the battery is disconnected while the alternator is still
running. There are four classes of limits applicable within the
standard, as well as the usual “customer specified” level. Power
line transients (figures 8 to 10) are applied directly onto the
power supply, the signal/control line transients are coupled
capacitively via a coupling clamp (figure 11).
OEM specifications use the pulses and set-up of ISO 7637 with
their own set of applied levels and functional classifications.
The OEM specifications modify some of the pulse shapes to
be specific to the power network, motors and alternators
typically used in their vehicles, hence are similar to ISO 7637
with minor nuances in the voltage levels and pulse shapes (rise
times and dwell times are usually different between OEM
specifications).
Immunity to Electrostatic Discharge (ESD)
The vehicle is an isolated product in that it does not share a
current return common with the “earth” reference. The current
reference to ground on a vehicle is usually to the negative
terminal of the battery, hence is not the standard ground
reference of most commercial tests or products. Consequently
a different body model and test standard has been developed
for automotive ESD testing; ISO 10604.
Figure 8: Inductive transient noise applied to 12V power supply lines
Figure 9: Transient during cranking on 12V power supply
Figure 12: ESD testing ESA at connector while powered (photo
courtesy of Trafficmaster/3C Test Ltd)
The body model uses a 2kΩ series resistor and 150pF capacitor
for discharge while outside a vehicle and 330pF capacitor for
discharge inside a vehicle. There are the usual air and direct
contact discharge tests to both the ESA body and to the
Figure 10: Load dump transient on 12V supply line
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EMC & Compliance Journal September 2003
connectors and/or any metal fixings. The standard also includes
testing for air and contact discharge at the electrical terminals
of the ESA while unpowered (i.e. no ground return) to simulate
handling during assembly, this requires any accumulated
charge to be bled from the ESA between applied discharges.
standards community (and before Chrysler were merged with
Daimler-Benz). The majority of SAE standards are now
encompassed in international standards and although still often
quoted for North American products, they are mainly
superseded by their ISO and CISPR equivalents.
The discharge levels cover ±2kV up to ±25kV, the higher levels
primarily reserved for equipment classed as pyrotechnic, this
includes airbag deployment devices and in some OEM
specifications fuel systems. The minimum number of
discharges is specified as 3 per polarity with at least 5s between
applied test pulses. The standard includes the usual ISO
functional classifications (see text box).
ISO Functional Status Classification
Directly taken from ISO 10605:2001.
All classifications given below are for the total device/system
functional status.
NOTE: The word “function” as used here concerns only
the function performed by the electronic system.
Table 4: SAE Standards for Component Testing and their
International Equivalent
Class A: all functions of a device or system perform as
designed during and after exposure to interference.
There are some SAE component standards that have not been
adopted by the international standard bodies. Some of the
unadopted SAE standards are encompassed in a few of the
OEM specifications, however, many of these are being dropped
in favour of alternative tests that are encompassed by existing
international standards and consequently are not included here.
Class B: all functions of a device/system perform as
designed during exposure; however, one or more of them
may go beyond the specified tolerance. All functions return
automatically to within normal limits after exposure is
removed. Memory functions shall remain class A.
Class C: one or more functions of a device or system do
not perform as designed during exposure but return
automatically to normal operation after exposure is removed.
The SAE standards were developed to allow North American
suppliers to produce compliant products for their home OEM
market. With most of the SAE standards now covered by
international equivalents it is debatable whether there is a need
for the SAE standards to be separately maintained and updated.
Class D: one or more functions of a device or system do
not perform as designed during exposure and do not return
to normal operation until exposure is removed and the device
or system is reset by a simple “operator/use” action.
Choice of Test Standards
Assuming that an OEM standard has not been provided (i.e. a
product is not designed for OEM line fit), then the choice of
applicable standards is open to interpretation, with the
exception of products for sale in Europe.
Class E: one or more functions of a device or system do
not perform as designed during and after exposure and
cannot be returned to proper operation without repairing or
replacing the device or system.
In Europe the choice of standard for radiated emissions and
immunity is determined by legal requirements. It is required
to show proof of meeting the standards and to “e” mark an
ESA via the type approval process of 95/54/EC. This is the
minimum requirement for sale of a product intended for
automotive use in the EU, however, it would be sensible for a
manufacturer to also test for transient immunity, ESD and
conducted emissions to ensure that the ESA will not cause
problems for the customer and consequently give them a “bad
name”.
The automotive ESD standard is almost universally adopted
within OEM specifications. A few OEM specifications use
the commercial body model definition of IEC 61000-4-2 (330Ω
series resistor), it is difficult to know whether this is an error
by the OEM or a deliberate effort to apply a higher stress to an
ESA? Not all OEM specifications currently include the unpowered test as this is a relatively new addition to the standard
(updated in December 2001).
Society of Automotive Engineers (SAE)
Standards
The following are recommended test standards to use for three
geographic regions where no OEM specification is available.
Due to the legal nature of the European standards, if an ESA is
to be sold in multiple regions it should tested to the European
standard 95/54/EC as a minimum, others can be added at the
request of regional authorities.
The SAE have been the leading influence in producing
standardisation for the North American automotive market.
Their standards reflect what the “big 3” US OEMs (General
Motors, Ford and Chrysler) were doing in the last decade,
before some of the standards were adopted by the international
EMC & Compliance Journal September 2003
21
Automotive EMC Testing
If you are used to only testing commercial products, it will
sound strange to hear that automotive tests for emissions
and immunity are conducted mainly on the connecting
harness rather than the ESA itself, that the ESA is kept
stationary (it is not rotated on a turntable) and measurements
are made with the antenna at only 1m from the test set-up.
The ESA and harness are placed on a metal grounded plane
rather than an isolated table (the plane is usually placed on
the test table); this is representative of the metal body of a
vehicle, although the ground is connected to the chamber
mains earth as well as the battery supply negative terminal.
The harness and ESA is supported by an insulating medium
at 50mm from the ground plane, hence is not laid directly
on the ground plane.
Table 7: Worldwide EMC Standards
Products tested to these standards would be acceptable in the
North American market as the SAE standards are equivalent.
Martin O'Hara is Senior Design Consultant, Telematica
Systems Limited and can be contacted on tel: +44 (0)1234
759232, or email: martin@tmsl.com.
Free
These differences, along with the LISN (5µH rather than
50µH) and specific harness requirements, make automotive
EMC testing significantly different to the majority of
commercial EMC tests and consequently many commercial
EMC test services are unable to perform automotive EMC
testing. Automotive EMC testing is a specialised field within
the EMC test services sector with its own test accreditation
(Automotive EMC Laboratory Recognition Program,
AEMCLRP) and a list of test houses with automotive EMC
capability is available on the Automotive EMC network
(www.AutoEMC.net).
The latest edition, just published, of the EMC &
Compliance Test Laboratories Directory includes for the
first time a separate section on EMC Test Equipment.
The Test Laboratories section has a foreword written by
Dave Imeson, Chairman of the EMC Competent Bodies
& Secretary of EMCTLA, and includes 30 Test Labs.
The new Test Equipment section has comprehensive details
on 14 companies.
ESA Test Standards by Geographic Market
To obtain your copy Enter Enquiry No. 20 or email:
test@nutwood.eu.com.
Table 5: European EMC Test Standards
The above are not all legal requirements, only 95/54/EC is
legally required and for an ESA that does not effect the
operation of the vehicle the radiated emissions test is the only
legal requirement.
Table 6: North American EMC Standards
The above standards are not compulsory but again indicate
sound engineering practice has been considered in the design
of products intended for this market.
In the US automotive products are explicitly exempt from FCC
Part 15 rules under section 15.103 Exempt Devices; “a) A
digital device utilized exclusively in any transportation vehicle
including motor vehicles and aircraft.”
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