CISPR 25 Testing for Automotive Electronics: What Engineers Need to Know

What Is CISPR 25 and Why Is It Important?

CISPR 25 is the international standard for measuring radio-frequency disturbances from vehicles, boats, and internal combustion engines. It specifies limits and test methods for conducted and radiated emissions from automotive components and full vehicles to ensure electromagnetic compatibility (EMC). Compliance with CISPR 25 is crucial for automotive electronics engineers designing ECUs, infotainment systems, power converters, and EV modules. Non-compliance can lead to regulatory rejection, warranty claims, and safety risks, particularly in safety-critical systems like ADAS and braking.

How Does CISPR 25 Define Its Scope and Key Requirements?

CISPR 25 applies to component-level and vehicle-level testing, covering frequencies from 150 kHz to 1 GHz, extendable to 2.5 GHz for radiated emissions. The standard mandates using quasi-peak and average detectors to prevent emissions from interfering with radio services. Unique to CISPR 25 is its focus on radiated emission measurements closer to the equipment under test (EUT) than standards like CISPR 16. Ambient noise in the test area must be at least 6 dB below the lowest limit, often necessitating an RF-shielded semi-anechoic chamber.

Real-World Example: Infotainment System Compliance

In a case study involving in-vehicle infotainment displays, engineers faced emissions exceeding CISPR 25 limits by 2.51 dB in the 555-960 MHz range. By implementing conductive foam gaskets on PCBAs, they achieved an 8 dB reduction, bringing emissions within compliance.

What Are the Key Test Types and Procedures?

Conducted Emissions

Conducted emissions are measured using Artificial Networks (ANs) or Line Impedance Stabilization Networks (LISNs) for voltage or current probes at multiple cable locations. This ensures emissions compliance of power line and signal line emissions without vehicle integration.

Radiated Emissions

Radiated emissions testing is performed in semi-anechoic chambers to simulate real-world conditions. Engineers must document load conditions, voltage levels, and EUT orientation meticulously. The testing covers frequency bands up to 2.5 GHz, using various antennas such as rod, biconical, log-periodic, and horn types, depending on the frequency range.

Immunity Testing References

CISPR 25 also references ISO 11452 methods for immunity testing, specifying severity levels up to 100 V/m. These tests ensure that automotive electronics can withstand electromagnetic interference in real-world scenarios.

What Are the Common Pitfalls in CISPR 25 Testing?

Overlooking Ambient Noise Levels

One frequent issue is failing to maintain ambient noise levels below the required 6 dB margin. Engineers must ensure that the test environment, such as an anechoic chamber, meets these stringent requirements to avoid erroneous results.

Inadequate Pre-Compliance Testing

Skipping thorough pre-compliance testing can lead to costly failures during certified tests. It's essential to perform in-house testing with spectrum analyzers and antennas to identify and address emission peaks early.

Neglecting Component-Level Testing

Focusing solely on vehicle-level tests without addressing component-level sources can result in non-compliance. Engineers should target PCBAs as primary sources and implement shielding solutions like POCONS shield cans and spring contacts to address potential emission issues.

What Are the Best Practices for CISPR 25 Compliance?

Comprehensive Documentation

Maintaining detailed documentation of test setups, procedures, and results is crucial for troubleshooting and verifying compliance. This includes recording the EUT orientation, load conditions, and test environment specifics.

Use of Shielding Solutions

Incorporating effective shielding solutions, such as those offered by POCONS, can significantly reduce emissions. These solutions help in meeting stringent class limits, particularly for sensitive systems.

Regular Calibration and Maintenance

Regular calibration of test equipment and maintenance of anechoic chambers ensures accurate and reliable results. This proactive approach minimizes the risk of non-compliance due to equipment errors.

FAQs

What Is the Frequency Range Covered by CISPR 25?

CISPR 25 covers frequencies from 150 kHz to 1 GHz, extendable to 2.5 GHz for radiated emissions testing.

How Does CISPR 25 Differ from CISPR 16?

CISPR 25 focuses on radiated emissions measurements closer to the EUT, while CISPR 16 provides general methods for EMC testing.

What Types of Antennas Are Used in Radiated Emissions Testing?

Radiated emissions testing uses various antennas, such as rod, biconical, log-periodic, and horn antennas, depending on the frequency range.

Why Is Pre-Compliance Testing Important?

Pre-compliance testing helps identify and mitigate emission peaks early, reducing the risk of costly failures during certified tests.

How Can Shielding Solutions Aid in Compliance?

Shielding solutions, like POCONS shield cans, can help reduce emissions, making it easier to meet stringent class limits required by CISPR 25.