Craig Fanning Explains CISPR 12/25 Radiated Emissions Testing

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March 28, 2022

It’s no secret that every generation of motor vehicles is more reliant on electronics for safe and economical operation. Collision avoidance and automatic parallel parking are examples of the high-tech heights our cars have reached.  Electric vehicles (EVs) raise the technological bar even higher with highly integrated electronics governing every system from transmissions to touch screens.

As electronics become more complex, the need to assure their reliability becomes more critical. Electromagnetic compatibility (EMC) is in the first rank of concerns for vehicle original equipment manufacturers (OEMs) along with mechanical stability, moisture resistance, heat tolerance, and the other parameters that have bearing on a vehicle’s safe operation.

OEMs have had automotive EMC standards in place for many years. They share the same objectives as those issued by CISPR, the European standards body, and the Society of Automotive Engineers (SAE). The radiofrequency (RF) phenomena haven’t changed, but the vehicles have, and that means more scrutiny on EMC testing.

Elite’s Craig Fanning is one of the industry leaders in automotive EMC. He serves as vice-chair and working-group convener for CISPR/D, focusing on vehicle electronics. Craig leads Elite’s automotive-testing effort and shares some background on that work. 

The Standards

CISPR, ISO, and SAE are the organizations that draft and maintain international automotive EMC standards. SAE’s focus is on North American applications. Standards bodies tend to follow each other’s work and share information, and SAE standards have in some cases been incorporated into international standards. When the global standard is published, the equivalent SAE standard is withdrawn and becomes a reference that documents any differences from the newer global standard.

Beyond that, the vehicle OEMs have their own requirements they apply to themselves and to their suppliers. Because North American OEMs sell their products around the world, international standards are a substantial part of their internal requirements. Elite is recognized by domestic and international OEMs to perform tests to their specific company requirements, in addition to the broader CISPR, ISO, and SAE standards.

CISPR 12 as it Applies to Components

There are two broad categories of automotive EMC standards: those applying to the whole vehicle, and those applying to components within the vehicle. ISO, for example, publishes ISO 11451-xx for whole vehicles, and ISO 11452-xx and ISO 7637-xx for components (“xx” are the sub-documents specific to a category and test type).

CISPR 12 spells out vehicle-level radiated emissions. CISPR 25 focuses on component-level emissions and system immunity. A basic distinction is that CISPR 12 is intended to protect devices outside the vehicle off-board receivers from harmful RF emissions, while CISPR 25 is used to protect receivers and devices mounted on the vehicle on-board receivers.

Craig has written about this and offered an example to illustrate the difference: “A chainsaw with an internal combustion engine (but with no on-board receivers) would need to meet the requirements of CISPR 12, but CISPR 25 would not apply to this chainsaw since it does not utilize any on-board receivers.”

CISPR 12 radiated emission tests can be done at a 3m or 10m distance, which works neatly with the typical size of a semi-anechoic chamber. Elite’s experience in all forms of automotive EMC testing and a variety of test chambers is well-equipped to perform the mandated tests.

CISPR 25 for Whole-Vehicle and Component Tests

CISPR 25 is intended to protect the vehicle’s onboard receivers and is written in two parts. One applies to full-vehicle tests, employing antennas mounted on the vehicle to detect emissions from the vehicle’s own systems.  The intent is to measure how much noise finds its way into the radio from its antenna. Vehicles are unique is size, shape, and type of service.  Craig recommends starting with Elite’s blog series, “Prepare for Vehicle EMC Testing in 10 Steps,”, or for more detail Elite’s e-book, “10 Steps to Successful Automotive EMC Testing,” can be downloaded for reference.

The second part applies to conducted and radiated emission from the components within the vehicle. Those components typically are a manageable size and can be tested in a 3m chamber.  Elite has a number of chambers that are well-suited to those measurements, and Elite works with customers to match the product with the appropriate test environment.

CISPR 25 ranges from 150 kHz to 5.95 GHz, a range that can be a challenge in absorber-lined test chambers. The standard gives guidance on test-chamber sizing and layout. Because each product and its applications are different, Craig encourages those needing a test to contact Elite to determine which chamber and what configuration is applicable to a specific product. A test plan can then be developed to assure meaningful results.

Strategies for a Successful Test

For any specific test or application, different portions of these standards will apply. If your automotive product needs EMC tests and verification to CISPR, ISO, SAE, or OEM requirements, contact Elite. Craig and Elite’s team of experts can work with you to find the right standard, the right test facility, and help you devise a test plan that assures a trusted result.

Contact Elite’s automotive-testing group for the information you need.

Read more in Craig Fanning’s previous article with InCompliance magazine.

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