Electromagnetic Compatibility (EMC) standards are crucial for the automotive industry, ensuring that vehicles and their components operate reliably without causing electromagnetic interference. Developed primarily by organizations like CISPR, ISO, and SAE, these standards dictate the testing, severity, and sensitivity levels that automotive components, or Emc Car Parts, must meet. This article delves into the key EMC standards and chamber testing requirements for automotive components, providing an in-depth look at CISPR and ISO regulations.
Automotive EMC standards are predominantly established and maintained by three major international bodies: CISPR (International Special Committee on Radio Interference), ISO (International Organization for Standardization), and SAE (Society of Automotive Engineers). CISPR and ISO focus on developing global standards, while SAE primarily caters to North American requirements, though its standards often influence international regulations. Historically, SAE played a significant role in creating EMC standards, many of which were later adopted and refined by CISPR and ISO for international application. As SAE standards transition into international norms, the original SAE versions are often withdrawn as standalone standards, serving instead to document any deviations from the globally accepted versions.
Beyond these overarching industry standards, individual vehicle manufacturers also implement their own internal corporate standards. These manufacturer-specific guidelines specify the EMC testing protocols, stringency levels, and susceptibility thresholds that both individual components and complete vehicles must adhere to. While historically, US-based manufacturers referenced SAE standards, the increasingly global nature of the automotive market has led most manufacturers worldwide to adopt CISPR and ISO standards as the backbone of their internal EMC requirements.
Understanding CISPR and ISO Automotive EMC Standards
CISPR Subcommittee D is the primary body responsible for crafting and maintaining standards related to emission measurements from vehicles and their components. Conversely, ISO Technical Committee 22/Subcommittee 32/Working Group 3 (ISO/TC22/SC32/WG3) focuses on developing and updating standards for immunity testing of automotive vehicles and components. ISO standards within the automotive sector are broadly categorized into vehicle-level standards (ISO 11451-xx) and component-level standards (ISO 11452-xx, ISO 7637-xx).
Table 1 provides a detailed overview of key CISPR and ISO EMC standards relevant to the automotive industry. These standards define various test types, including Radiated Immunity (RI), Conducted Immunity (CI), Radiated Emissions (RE), Conducted Emissions (CE), and Electrostatic Discharge (ESD), along with the corresponding test setups and chamber requirements.
| Document No. | Title | Type | Equivalent | Test Setup | Chamber Requirement |
|---|---|---|---|---|---|
| ISO‑11451‑1 | Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated electromagnetic energy — Part 1: General principles and terminology | N/A | SAE J551/1 | Definitions | N/A |
| ISO‑11451‑2 | Part 2: Off Vehicle Radiation Sources | RI | SAE J551‑11 (Note 1) | Vehicle Radiated Immunity test in an anechoic chamber | Vehicle Absorber lined chamber |
| ISO‑11451‑3 | Part 3: On‑board transmitter simulation | RI | SAE J551‑12 (Note 2) | Vehicle Absorber Lined Shielded Enclosure (ALSE) is required | Vehicle Absorber lined chamber |
| ISO‑11451‑4 | Part 4: Bulk Current Injection (BCI) | RI | SAE J551/13 (Note 3) | Test was designed for machines and vehicles too large to fit in a standard vehicle EMC | Outdoor Test Site (OTS) or Vehicle Absorber lined chamber |
| ISO‑11451‑5 | Part 5: Reverberation chamber | RI | None | Vehicle Radiated Immunity test in a reverberation chamber | Reverberation chamber |
| ISO‑11452‑1 | Road vehicles — Component test methods for electrical disturbances from narrowband radiated electromagnetic energy — Part 1: General principles and terminology | N/A | SAE J1113/1 | Definitions | N/A |
| ISO‑11452‑2 | Part 2: Absorber lined chamber | RI | SAE J1113/21 (Note 4) | An absorber lined chamber is required. Antennas and field generator to cover the range are required. No need to scan | Absorber lined chamber |
| ISO‑11452‑3 | Part 3: Transverse electromagnetic (TEM) cell | RI | SAE J1113/24 (Note 5) | TEM cell | N/A |
| ISO‑11452‑4 | Part 4: Bulk current injection | RI | SAE J1113/4 | Radiated immunity using the BCI method | Shielded room |
| ISO‑11452‑5 | Part 5: Stripline | RI | SAE J1113/23 (Note 6) | Radiated immunity using a stripline | Shielded room |
| ISO‑11452‑7 | Part 7: Direct radio frequency (RF) power injection | RI | SAE J1113/3 (Note 7) | Conducted immunity test 250 kHz to 500 MHz | Bench or Shielded room |
| ISO‑11452‑8 | Part 8: Immunity to magnetic fields | RI | SAE J1113/22 (Note 8) | Helmholtz coils are used | Bench test: no shielded room required |
| ISO‑11452‑9 | Part 9: Portable transmitters | RI | None | Small antennas are used in conjunction with amplifiers and signal sources to simulate portable transmitters | Absorber lined chamber |
| ISO‑11452‑10 | Part 10: Immunity to conducted disturbances in the extended audio frequency range | CI | SAE J1113/2 (Note 9) | Conducted immunity test 15 Hz to 500 MHz | Bench test: no shielded room required |
| ISO‑11452‑11 | Part 11: Reverberation Chamber | RI | SAE J1113/28 (Note 10) | Reverberation chamber – Mode Tuned | Reverberation chamber |
| ISO 7637‑1 | Road vehicles — Electrical disturbances from conduction and coupling — Part 1: Definitions and general considerations | N/A | SAE J1113/1 | Definitions | N/A |
| ISO‑7637‑2 | Part 2: Electrical transient conduction along supply lines only | CI | SAE J1113/11 | Conducted immunity to transients as they are applied directly to the power leads of the test item. | Bench test: no shielded room required |
| ISO‑7637‑3 | Part 3: Electrical transient transmission by capacitive and inductive coupling via lines other than supply lines | CI | SAE J1113/12 | Conducted immunity to transients as they are applied directly to the I/O lines of the test item. | Bench test: no shielded room required |
| ISO‑10605 | Road vehicles — Test methods for electrical disturbances from electrostatic discharge | ESD | SAE J1113/13 J551/15 | ESD testing performed on a module on a bench or a vehicle in a temperature and humidity‑controlled environment | Bench test: no shielded room required |
| CISPR 12 | Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of off‑board receivers | RE | SAE J551/2 (Note 11) | Vehicle Radiated Emissions | OTS or Vehicle Absorber lined chamber |
| CISPR 25 | Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of on‑board receivers | RE | SAE J551/4 (Note 12) | Clause 5: Vehicle portion of the standard. This is to measure the amount of noise generated by the vehicle will be induced into the on‑board receiver antenna port. | Vehicle Absorber lined chamber |
| CISPR 25 | Vehicles, boats, and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of on‑board receivers | CE & RE | SAE J1113/41 (Note 13) | Clause 6: Component (module) test section where conducted and radiated emissions are measured. | Absorber lined chamber |
| CISPR 36 | Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of off‑board receivers | RE | SAE J551/5 (Note 14) | Vehicle Radiated Emissions | OTS or Vehicle Absorber lined chamber |
Note 1 SAE J551‑11 Withdrawn as a complete standard and reserved for use to document differences from ISO 11451‑2. At the present time J551‑11 is not used.
Note 2 SAE J551‑12 Withdrawn as a complete standard and reserved for use to document differences from ISO 11451‑3. At the present time J551‑12 is not used.
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Note 3 SAE J551‑13 Withdrawn as a complete standard and reserved for use to document differences from ISO 11451‑4. At the present time J551‑13 is not used.
Note 4 SAE J1113‑21 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑2. At the present time J1113‑21 is not used.
Note 5 SAE J1113‑24 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑3. At the present time J1113‑24 is not used.
Note 6 SAE J1113‑23 This standard has been withdrawn. Note 7 SAE J1113‑3 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑7. At the present time J1113‑3 is not used.
Note 8 SAE J1113‑22 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑8. At the present time J1113‑22 is not used.
Note 9 SAE J1113‑2 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑10. At the present time J1113‑2 is not used.
Note 10 SAE J1113‑28 Withdrawn as a complete standard and reserved for use to document differences from ISO 11452‑11. At the present time J1113‑28 is not used.
Note 11 SAE J551‑2 Withdrawn as a complete standard and reserved for use to document differences from CISPR 12. At the present time J551‑2 is not used.
Note 12 SAE J551‑4 Withdrawn as a complete standard and reserved for use to document differences from CISPR 25. At the present time J551‑4 is not used.
Note 13 SAE J1113‑41 Withdrawn as a complete standard and reserved for use to document differences from CISPR 25. At the present time J1113‑41 is not used.
Note 14 SAE J551‑5 Withdrawn as a complete standard and reserved for use to document differences from CISPR 36. At the present time J551‑5 is not used.
Table 1: Key CISPR and ISO EMC Standards for the Automotive Industry
Similar to ISO EMC standards, SAE EMC standards are also categorized into vehicle (SAE J551-xx) and component (SAE J1113-xx) standards. As indicated in the notes of Table 1, many SAE standards are no longer active as complete standards, having been replaced by international ISO and CISPR equivalents. Table 2 provides an overview of the currently active SAE EMC standards for automotive components and vehicles, highlighting their equivalence to ISO or CISPR documents. It’s important to note that these tables are not exhaustive but serve to illustrate the complexity and breadth of EMC standards in the automotive sector.
| SAE Doc No. | Title | Type | Equivalent | Test Setup | Chamber Requirement |
|---|---|---|---|---|---|
| SAE J551/1 | Performance Levels and Methods of Measurement of Electromagnetic Compatibility of Vehicles, Boats (up to 15 m), and Machines (16.6 Hz to 18 GHz) | SAE J551/1 | |||
| SAE J551/5 | Performance Levels and Methods of Measurement of Magnetic and Electric Field Strength from Electric Vehicles, 150 kHz to 30 MHz | RE | CISPR 36 Vehicles | Vehicle ALSE may be used | OTS or Vehicle Absorber lined chamber |
| SAE J551/15 | Vehicle Electromagnetic Immunity – Electrostatic Discharge (ESD) | ESD | ISO-10605 Clause 10 | ESD test at the vehicle level would not need a shielded enclosure. | No shielded room required |
| SAE J551/16 | Electromagnetic Immunity – Off-Vehicle Source (Reverberation Chamber Method) – Part 16 – Immunity to Radiated Electromagnetic Fields | RI | None | Vehicle Sized Reverberation Chamber is needed for this test. Method allows for the reverberation test along with a “hybrid test which utilizes direct illumination and reverberation. | Vehicle Sized Reverberation Chamber |
| SAE J551/17 | Vehicle Electromagnetic Immunity – Power Line Magnetic Fields | RI | None | Magnetic Field RI testing at the vehicle level would not need a shielded enclosure. | No shielded room required |
| SAE J1113/1 | Electromagnetic Compatibility measurement procedures and limits for vehicle components (except aircraft), 60 Hz-18 GHz | N/A | ISO-11452-1 | Definitions | N/A |
| SAE J1113/4 | Immunity to radiated electromagnetic fields- bulk current injection (BCI) method | RI | ISO-11452-4 | Radiated immunity using the BCI method | Shielded room |
| SAE J1113/11 | Immunity to conducted transients on power leads | CI | ISO-7637-2 | Conducted immunity to transients | Bench test: no shielded room required |
| SAE J1113/12 | Electrical interference by conduction and coupling – coupling clamp | CI | ISO-7637-3 | Conducted immunity to different coupling mechanisms | Bench test: no shielded room required |
| SAE J1113/13 | Electromagnetic compatibility procedure for vehicle components-immunity to electrostatic discharge | ESD | ISO-10605 | ESD testing performed on a bench in a temperature and humidity-controlled environment | Bench test: no shielded room required |
| SAE J1113/27 | Immunity to radiated electromagnetic fields reverberation method | RI | None | Reverberation chamber – Continuous Stirred | Reverberation chamber |
Table 2: Additional Active SAE Automotive EMC Standards
Government regulations and directives often reference CISPR and ISO standards for EMC compliance. For instance, European Directive 2004/104/EC, succeeding 95/54 EC, mandates EMC requirements for vehicles in Europe. Specifically, its sections concerning automotive components align with the guidelines outlined in CISPR 25.
CISPR 12, CISPR 25, and CISPR 36: Emissions Standards in Detail
CISPR 12 and CISPR 36 focus on limiting “radio disturbance characteristics for the protection of off-board receivers,” ensuring vehicles don’t interfere with public radio and TV reception. CISPR 25, on the other hand, addresses “radio disturbance characteristics for the protection of receivers used on-board vehicles,” aiming to minimize interference within the vehicle itself.
It’s important to distinguish that CISPR 12 and CISPR 36 are frequently employed for regulatory compliance, ensuring vehicles with internal combustion engines or electric powertrains do not disrupt off-board radio and television reception, even when stationary or charging. CISPR 25, however, is primarily utilized by vehicle manufacturers to guarantee the reliable performance of on-board receivers, thus enhancing consumer satisfaction and product quality. Poor on-board receiver performance due to electromagnetic interference can negatively impact user experience and brand reputation.
Figure 1 illustrates the types of equipment covered under CISPR 12 and CISPR 25, encompassing road vehicles, boats, and various devices powered by internal combustion engines or electric propulsion systems. CISPR 12’s scope is broad, covering devices that could potentially affect off-board receivers. CISPR 36 is more specific, applying only to electric road vehicles. Notably, CISPR 25 is relevant only to devices equipped with on-board receivers. For example, a chainsaw (with no receiver) would fall under CISPR 12 but not CISPR 25.
[Figure 1: EUTs within the scope of CISPR 12 and CISPR 25]
CISPR 12 radiated emissions testing is conducted at distances of 3 or 10 meters, although limits are set to protect off-board receivers at distances of 10 meters or more. Tests are typically performed at Open Test Sites (OTS) or in Absorber-Lined Shielded Enclosures (ALSE) that are correlated to OTS performance. For boats, measurements can also be taken on water. The correlation of ALSE to OTS is an ongoing area of discussion within CISPR, with efforts underway to develop a standardized validation method for ALSE, OATS, and OTS for vehicle measurements, planned for inclusion in the upcoming 7th Edition of CISPR 12.
CISPR 36 radiated emissions measurements are taken at a 3-meter distance using a loop antenna, focusing on magnetic field emissions. These tests are also typically performed on OTS, OATS, or ALSE. Site validation for CISPR 36 is currently under consideration for future editions.
CISPR 25 is divided into two key sections: one for full vehicle testing to assess noise levels received by vehicle antennas, and another for component/module level testing, focusing on both conducted and radiated emissions. This article primarily focuses on the module radiated emissions testing section of CISPR 25, with a brief overview of adaptations for electric vehicles. Specifically, the discussion will center on the chamber requirements mandated by the standard.
CISPR 25 mandates that the electromagnetic noise floor in the test area must be at least 6 dB lower than the lowest emission level being measured. With some radiated emission limits as low as 18 dB(µV/m), the ambient noise must be no more than 12 dB(µV/m) for a compliant test environment. Therefore, RF-shielded rooms are essential to block external RF signals and ensure the Equipment Under Test (EUT), or EMC car part, is the dominant source of measured emissions.
[Figure 2: A shielded room blocks the noise from outdoor sources of EM interference]
While shielded rooms may be too small for resonant modes at lower frequencies, resonance increases with frequency. These modes can introduce significant measurement errors. To mitigate this, lining the shielded room with RF absorber material on the ceiling and walls significantly reduces internal reflections, ensuring a direct coupling path between the EUT and the measurement antenna. Such a room becomes an Absorber-Lined Shielded Enclosure (ALSE). Current CISPR 25 standards (Ed 5:2021) cover frequencies from 150 kHz to 5.95 GHz. Absorber technology faces challenges in achieving substantial absorption below 70 MHz. However, the electrically small chamber sizes at lower frequencies and the 1-meter measurement distance minimize resonant behavior, allowing the standard to prioritize absorber performance at 70 MHz and above. The standard requires absorbers to have at least -6 dB absorption at normal incidence.
Various absorber technologies are available, including polystyrene-based hybrid absorbers. These combine ferrite tiles with polystyrene EMC absorbers, offering efficient and cost-effective performance. A typical hybrid absorber might have a 60cm x 60cm base and 60cm height, utilizing expanded polystyrene (EPS) loaded with lossy materials and fire retardants. Uniform loading during manufacturing ensures superior RF performance and consistent absorption. The closed-cell EPS structure makes these absorbers suitable for humid environments, contributing to a controlled and predictable test environment. Figure 3 illustrates the performance of a polystyrene hybrid absorber.
[Figure 3: Typical performance of polystyrene absorber]
Polyurethane absorbers, typically 36 inches (1m) deep, like EHP 36, offer improved high-frequency performance due to their material depth. However, lacking the ferrite component of hybrid absorbers, they exhibit reduced low-frequency absorption. Figure 4 shows the performance of polyurethane absorbers and their compliance with CISPR 25 limits.
[Figure 4: Typical performance of 36” polyurethane absorber material]
CISPR 25 guidelines dictate the layout and dimensions of a typical ALSE, starting with the EUT size, which determines the test bench dimensions. Figure 5 shows a standard test bench used for CISPR 25 and ISO 11452-2 testing.
[Figure 5: A typical conductive test bench]
As shown, the bench must accommodate the largest EUT and associated cabling. Cables are organized in a harness along the bench’s front edge, forming a significant part of the EUT and the primary focus of antenna illumination, especially at lower frequencies where cable coupling dominates. Similar procedures are found in MIL-STD 461 and ISO 11452. A Line Impedance Stabilization Network (LISN) provides a defined impedance for the power supply to the device.
Figure 6 illustrates bench sizing. The ground plane bench must extend to the shield and is often grounded to the shielded room wall. Grounding to the ALSE wall, particularly with hybrid absorbers, can reduce resonant conditions in the 10-70 MHz range. However, grounding to the floor is also permitted.
[Figure 6: Sizing the bench]
CISPR 25 specifies a minimum reference ground plane (bench) width of 1000 mm and a minimum length of 2000 mm, or the length needed to support the EUT plus 200 mm, whichever is greater.
Minimum chamber dimensions depend on these bench dimensions and absorber characteristics. Using 0.6m hybrid absorbers, chamber width and length are determined by the absorber length plus a 1-meter clearance between the bench/DUT and absorber tips, as shown in Figure 7. For testing electric motors, the motor, if separate, still connects to the ground plane and extends it, subject to minimum distance rules (Figure 8).
[Figure 7: Width and length of the CISPR 25 chamber (multiple antenna types shown for reference)]
[Figure 8: Increased width of CISPR 25 chamber for e-motor dyno (multiple antennas shown for reference)]
Chamber height and length are further defined by separation distances. Crucially, emissions must be measured at least 1 meter from the cable harness to the antenna. Additionally, no antenna part can be closer than 1 meter to the absorber tips. These rules, combined with antenna dimensions, dictate minimum chamber length and height. The 1-meter cable harness distance is measured from the axis of monopole rod and biconical antenna elements, from the LPDA tip, and from the horn antenna’s front face. LPDAs, typically around 1m long for 200 MHz to 1 GHz, are often the longest antennas. Adding the 1m test distance and 1m antenna length, plus 1m clearance behind the antenna, defines chamber length (Figure 8).
Chamber height is determined by the longest vertical antenna, usually the active rod monopole, which is about 80 cm long and positioned with its ground plane at bench height (nominally 90 cm). The 1-meter separation rule between antenna and absorber tip again determines minimum chamber height, as shown in Figure 9.
[Figure 9: Height of the CISPR 25 chamber with multiple antennas shown for reference.]
Based on these considerations, a chamber lined with 0.6m hybrid absorber, sized 5.2 meters wide, 6.2 meters long, and 3.6 meters high, meets minimum CISPR 25 test requirements and also accommodates ISO 11452-2. Being a shielded environment, it can also handle most tests requiring a shielded room.
CISPR 25 refers to CISPR 16-1-4 for antenna and receiver specifications. Recommended antennas include active rod monopoles for low frequencies, biconical antennas (30-200 MHz), LPDAs (200 MHz-1 GHz), and dual ridge horn (DRH) antennas (1-5.95 GHz). Bi-log antennas are not permitted and have been removed from CISPR 25 5th Edition.
CISPR 25 5th Edition includes Annex I, detailing ALSE validation methods for component-level radiated emission tests. While Annex J in the 4th Edition offered both reference measurement and modeling methods, the 5th Edition focuses solely on modeling-based validation for the 150 kHz to 1 GHz range. Validation methods above 1 GHz are under discussion for future editions.
CISPR 25 also covers vehicle antenna emission measurements and, in its 5th Edition, includes specific setups and limits for testing electric vehicles (EVs), hybrid electric vehicles (HEVs), and their components like inverters and batteries. These vehicles and components require specialized testing due to high currents and voltages during operation and charging. New test conditions are added for vehicles connected to mains or charging stations, aligning with European directive ECE Regulation 10, which references CISPR 25 and CISPR 12 for test setups and techniques.
ISO 11452-2: Component Immunity Testing
ISO 11452-2 is a key vehicle component immunity standard for the 200 MHz to 18 GHz range. It, like many automotive and aerospace standards, mandates relatively high field strengths for immunity testing. Table 3 outlines the severity levels, ranging from 25 V/m to 100 V/m and above. Below 200 MHz, antenna efficiency decreases and size increases, leading ISO 11452-2 to recommend bulk current injection, TEM cell, and stripline methods (ISO 11452 parts 4, 3, and 5) for more efficient low-frequency immunity testing.
| Severity Level | Field |
|---|---|
| I | 25 V/m |
| II | 50 V/m |
| III | 75 V/m |
| IV | 100 V/m |
| V | (open to the users of the standard) |
Table 3: ISO 11452-2 Severity Levels
ISO 11452-2 also requires ALSE testing. Shielded rooms are essential to contain the RF fields used for immunity testing, protecting external equipment from unintended disruption or damage. Regulations in the US and globally restrict unlicensed radiation at frequencies that could interfere with licensed broadcasts, further emphasizing the need for shielded environments.
Testing frequencies above 200 MHz increase the likelihood of resonant modes within shielded rooms, necessitating absorbers to minimize measurement errors. ISO 11452-2 requires chamber reflectivity of -10 dB in the EUT area. Materials shown in Figures 3 and 4 exceed this -10 dB reflectivity from 200 MHz to 18 GHz, meaning the same absorbers used for CISPR 25 chambers can be used for ISO 11452-2, with appropriate separation distances. Antenna selection for ISO 11452-2 prioritizes efficient field generation, considering amplifier costs. Dual ridge horn antennas are recommended for 200 MHz to 2 GHz, with octave and standard gain horns preferred above 2 GHz.
Conclusion
This article provides a foundational understanding of key EMC standards for automotive vehicles and components, focusing on CISPR and ISO standards. It has outlined the revision status of these standards and related documents. Part 2 of this series will delve into designing EMC chambers that meet CISPR 25 requirements and are also suitable for ISO 11452-2 testing, offering practical guidance for EMC test facilities.
References
Part 2 of this article
