Updated: Mar 11
This article is a quick introduction to Electromagnetic Compatibility (EMC) emission testing in the automotive sector. The automotive industry is one of the biggest industries in the world and it is moving fast due to the shift from traditional combustion engine vehicles to hybrid and electrical ones. Here you will learn about the different applicable standards and how EMC emission tests are executed.
1. Emission standards
In the automotive sector, different standards are defining radiated emission tests. The following list shows some of them, defined by the International Special Committee on Radio Interference (CISPR), the Society of Automotive Engineers (SAE), the International Organization for Standardization (ISO), or the United Nations Economic Commission for Europe (UNECE). Nonetheless, there are some standards defined by vehicle manufacturers. Each of them uses to define their own standards, for the vehicles they manufacture and for the subassemblies installed in them.
1.1 International standards
UNECE R10 is a regulation of the Economic Commission for Europe of the United Nations (UNECE). It gathers EMC requirements for components and vehicles to be type-approved.
CISPR 12  is applicable to vehicles and boats propelled by an internal combustion engine, electrical means, or both and it specifies the limits and methods of radiated emission measurements to protect off-board receivers from 30 MHz to 1000 MHz. SAE J551-2 is equivalent to CISPR 12.
CISPR 25  is applicable to vehicles, boats, and internal combustion engines with a speed of more than 6 km/h. This standard is intended to protect receivers from disturbances produced by conducted and radiated emissions arising in a vehicle in the frequency range from 150 kHz to 5925 MHz. It is frequently used as a base standard for other ones. The limits are intended to provide protection for on-board receivers installed (per the manufacturer’s guidelines) in a vehicle from disturbances produced by components/modules in the same vehicle. SAE J551-4 and SAE J1113-41 are equivalent to CISPR 25.
CISPR 36  defines limits and methods of measurement to provide protection for off-board receivers from emissions by electric and hybrid electric vehicles propelled by an internal traction battery when operated on the road and over the frequency range from 150 kHz to 30 MHz. The following vehicles are excluded:
Electric vehicles to which CISPR-14-1 applies.
Vehicles where the electric motor is only used to start up the internal combustion engine (micro hybrids).
Vehicles where the electric motor is used for additional propulsion only during acceleration (mild hybrid vehicles).
Vehicles with a traction battery voltage < 100 V or > 1000 V.
Electric and hybrid road vehicles with a sustainable speed ≤ 6 km/h
1.2 Manufacturer based standards (OEM)
GMW3091 and GMW3097 are General Motors EMC specifications for vehicles, components, and subsystems, respectively.
FMC1278 is a Ford EMC specification for electrical and electronical components and subsystems.
1.3 On-board radiators vs. off-board radiators
Standards such as CISPR 25  define tests to ensure that any component to be installed in a vehicle will not interfere with other systems already installed within it (on-board radio-emitters). At the same time, standards such as the CISPR 12  or CISPR 36  are to protect off-board receivers (e.g., receivers in the vicinity of a car) from emissions generated by the vehicle.
2. Emission tests
2.1 Sources of emission
Within a car, there are many sources of electric and electromagnetic emissions. The most classical one is the motor. In normal use, a motor can generate noise with a broadband spectrum. On top of that, there are many electronic devices such as audio or infotainment systems that can lead to interference with other systems.
2.2 Wiring harnesses
Wires are critical elements in any electronic system. They play a key role in EMC. Their construction and length shall be carefully defined. For the execution of EMC tests, all wires need to have identical lengths, which they will have in the real application. Furthermore, wires need to be properly defined in the EMC test plan.
2.3 Radiated emissions
Depending upon the standard, each test method might have some subtle variations. Due to its wide use, the tests described here are based on the CISPR 25 standard .
Frequency range: 0.15 MHz to 960 MHz.
An EMI receiver with Peak (PK), Quasi-peak (QP), or average (AV) detector, as defined in the CISPR 16-1-1 standard.
A Line Impedance Stabilization Network (LISN), also known as Artificial Mains Network (AMN), Artificial Network (AN), or V-Network.
Different types of antennas: a monopole rod antenna, a biconical one, or a double-ridge guide horn.
An Absorber-Line Shielded Environment (ALSE).
The wiring harness shall be supported 50 mm above the ground plane by a non-conductive material and arranged in a straight line.
The EUT shall operate under typical loading such as the maximum emission state occurs. These conditions must be defined in the test plan to guarantee test repeatability.
The EUT shall be wired as it will be in the vehicle.
If the EUT has a power return line remotely grounded, one LISN is installed for the positive supply line and one for the power return line.
If the EUT has a power return line locally grounded, only one LISN is required, for the positive supply line.
The distance between the center of the wiring harness and the antenna must be 1000 mm ± 10 mm.
2.4 Conducted Emissions
The goal of the conducted emissions test is to verify that the noise introduced through the wires, both power, and communications, do not exceed the limits. Conducted phenomena usually happen in long wavelengths, so the frequency bands where tests are performed are the lowest ones. However, since radiated and conducted phenomena can happen simultaneously, sometimes the frequency range is increased. Depending upon the standard, each test method might have some subtle variations. Due to its wide use, the tests described here are based on the CISPR 25 standard .
Frequency range: from 105 kHz to 108 MHz, to be sure that commercial radio frequencies are not disturbed by the system.
Shielded enclosure: it is not compulsory to execute conducted emissions tests within a shielded chamber, but it is required that the ambient electromagnetic noise levels are, at least, 6 dB below the limits specified in the planned test.
Receiver: a measurement instrument capable of doing Quasi-Peak (QP) and Average (AV) measurements.
Current probe: to transform the measured current into a voltage signal to be read by the receiver.
The wiring harness must be placed 50 mm above the ground plane. All the wires shall be placed parallel and adjacent.
The EUT and all parts of the test set-up shall be a minimum of 100 mm from the edge of the ground plane.
Emissions on power leads must be measured with the voltage method, using an Artificial Network (AN) or a Line Impedance Stabilization Network (LISN), while emissions on signal leads must be measured through the current method, hence using a current probe.
Methods: emissions on power leads shall be measured using an artificial mains network as an isolator. Emissions on control/signal leads shall be measured using a current probe.
Voltage measurement: the emissions are measured at the measurement port of the Artificial Network (AN or LISN).
Current method: the current circulating through a wire is measured using a current probe, which is installed around the wire. The current probe shall be placed in the following positions and measure the emissions at each of them:
500 mm from the EUT connector.
1000 mm from the EUT connector.
50 mm from the LISN port.
Globally, the following automotive EMC emission standards are widely adopted:
CISPR 12. For the protection of off-board receivers from 30 MHz to 1000 MHz of combustion engines, hybrid and electrical vehicles; in a residential environment.
CISPR 25. For the protection of on-board receivers from 150 kHz to 5925 MHz of vehicles, boats, internal combustion engines, trailers, devices, and any electronic/electrical component intended for use in vehicles, boats, trailers, and devices.
CISPR 36. For the protection of off-board receivers from 150 kHz to 30 MHz of electric and hybrid vehicles; in residential a environment.
 INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE. CISPR 12. Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of off-board receivers https://webstore.iec.ch/preview/info_cispr12%7Bed6.0%7Db.pdf [11.Feb.2022]
 INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE. CISPR 25. Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of on-board receivers.
 INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE. CISPR 36. Electric and hybrid-electric road vehicles – Radio disturbance characteristics – Limits and methods of measurement for the protection of off-board receivers below 30 MHz. https://webstore.iec.ch/preview/info_cispr36%7Bed1.0%7Db.pdf [11.Feb.2022]
 Current probe TBCP3-1000. https://www.tekbox.com/product/TBCP3_1000_Manual.pdf [11.Feb.2022]