EMC testing

What is EMC testing?

EMC is the capability of an electrical device or system to operate in an electromagnetic environment without disturbing it or being disturbed by it. EMC testing is a critical step in the development and certification of electronic products. It is fundamental to creating reliable, interoperable and legally-compliant electronic products. In most countries, EMC testing is mandatory for product certification and market access.

Why is EMC testing important?

Modern electronics are rapidly growing in complexity. This is true for all markets - be it consumer, medical, automotive, industrial, aerospace or military. This means that the interference-free coexistence of electrical and radio products cannot be taken for granted. Only targeted measures for EMC testing and suppression can ensure safe and reliable connectivity.

There are many real-world phenomena that can cause EMC anomalies within an electrical or electronic device. These can be caused by:

• External events, such as radio frequency (RF) or electrical disturbances that are located near the equipment under test (EUT)
• Internal events, such as emissions from internal components or disturbances
• Disturbances caused by human interaction with the device, e.g., electrostatic discharge (ESD)

What are the consequences if such anomalies are not addressed before the product reaches the end user?

• An EMC-related anomaly in a medical device, such as a cardiovascular pacemaker, can endanger a person’s life.
• Emissions from a mobile device can interfere with safety-critical sensor functions in a vehicle or airplane or industrial robot.
• Disturbances caused by electronic devices within a home can affect household appliances.

Designing and testing for EMC can help avoid such failures and malfunctions. Another important reason for EMC testing is compliance with relevant regulations, such as directives, harmonized standards, manufacturer requirements and internal company requirements. We’ll take a deeper look at this in the next section.

EMC standards and testing in different industries

EMC testing is all about standards. All electronic products must meet the requirements set by standardization organizations such as IEC, CISPR, ISO, IEEE, CENELEC, ETSI, FCC, ANSI, RTCA or the MIL-STD committee. These organizations define acceptable emission and immunity levels, and compliance to their requirements is often a legal requirement for market access. There are hundreds of different EMC-related standards, which typically differ based on geographic location and expected use environment.

Navigating the EMC standardization landscape can be daunting. In its most simplified form, the hierarchy of EMC standards can be divided into five categories:

• Basic standards define test methods, such as the radiated immunity test according to EN/IEC 61000-4-3.
• Generic standards define test levels, limits, frequency range, modulation and general test conditions.
• Product standards outline test conditions and criteria for specific product types.
• Manufacturer-driven standards contain special test levels and test conditions.
• Internal company requirements define special margins and tolerances.

Different electronic equipment require compliance to different standards. For example:

• Applicable standards for commercial equipment, such as industrial, scientific, medical (ISM), consumer electronics, IT/multimedia, household appliances and lighting equipment include CISPR 11 to 35, IEC/EN 61000-X-X series and any product specific standards.
• For medical applications, such as hearing aids, medical implants and diagnostic machines, IEC 60601-1-2 and ISO 14708-X can also apply.
• Relevant standards for automotive applications, such as infotainment or communication modules, components or the full vehicle, include CISPR 12, CISPR 25, ISO 11451, ISO 11452, and country specific or OEM specific standards.
• Military and aerospace applications require compliance to MIL STD 461, MIL STD 464 or RTCA DO 160, and many others.

To learn more about EMC standards, visit our dedicated webpage on EMC testing standards.

EMC testing process

Today, products have more demanding requirements in terms of safety, reliability, connectivity and time to market than ever before. This naturally leads to more complex test scenarios - it's no surprise that over 50% of all products fail during first pass EMC testing. Setbacks at this stage can be costly and cause delays in bringing the product to market. The good news is that precompliance testing can mitigate this failure rate and improve the chances of first-pass success.

Precompliance testing is recommended to discover potential issues early in the design cycle and increase the probability of passing formal compliance tests. Precompliance testing can be stopped at any time, and the causes of failure can be thoroughly analyzed, tested and debugged. You can learn more about this on our webpages for easy benchtop EMI debugging and precompliance testing.

Compliance tests are typically performed by a certified third-party lab or test house. In some cases, they are also done by the manufacturers themselves. Compliance testing must follow the strict and precise procedures defined by EMC standards. It requires specialized equipment, special facilities (e.g., anechoic chambers) and trained personnel - all of which can make compliance testing more expensive.

As shown in the figure above, precompliance testing and debugging should be incorporated into the design process itself. This makes it easier to find interference issues.

EMF and wireless coexistence testing

The increasing use of wireless and multi-technology products within crowded RF environments creates additional challenges, beyond the conventional scope of evaluating devices for unwanted emissions and susceptibility to external emissions.

Wireless coexistence testing in line with the ANSI C63.27-2021 standard assesses the ability of the EUT to properly function in the electromagnetic environments in which it will be used. Human exposure to radio frequency electromagnetic fields (EMF) from LTE or 5G mobile networks (as well as other sources) is regulated by national and international standards. EMF testing involves measuring the field strength of these emissions and detecting the signal source.

EMC testing methods

Electromagnetic interference (EMI) or emissions testing ensures that electronic devices do not emit excessive electromagnetic radiation that could interfere with other devices or systems. Electromagnetic susceptibility (EMS) or immunity testing, on the other hand, assesses a device’s ability to operate without disruptions in the presence of electromagnetic interference from external sources.

In this guide, we’ll focus on four EMC test methods:

• Conducted emissions
• Conducted immunity
• Radiated emissions
• Radiated immunity

Additional test types like flicker, harmonics, ESD, surge, magnetic field immunity and electrical fast transient (EFT)/burst testing are not covered in the scope of this guide.

First, let’s discuss some basics. For conducted testing, the measured signals are the ones introduced by the EUT onto the AC power or “mains” network, most often through the EUT’s power cord. These signals are usually in the frequency range of 9 kHz to 30 MHz. The EUT is plugged into a line impedance stabilization network (LISN), which is then connected to the measurement instrument. The LISN filters and isolates high frequency noise from mains network so ideally only the noise from the EUT can be measured.

A typical setup for conducted emissions testing includes:

• EMI test receiver
• Test automation software
• Transducers, such as LISNs or artificial mains network (AMN)

A conducted immunity test setup for commercial testing in the frequency range of 150 kHz to 80 MHz usually includes:

• Shielded room (recommended)
• Coupling/decoupling network (CDN) or electromagnetic clamp as the transducer
• Bulk current injection (BCI) probe for automotive or MIL testing
• Signal generator
• RF power amplifiers
• Power sensors
• Transducers
• EMC test software to automate, control and deliver the right power level and modulation to the EUT according to relevant standards.

For radiated testing, the signals radiated by the EUT are measured. It is usually performed in the frequency range of 30 MHz to 1 GHz, but some standards require testing at much higher frequencies. These tests need antennas and often also a shielded absorber chamber or suitable open-air test site. Many industries, such as automotive, military and aerospace, also use the reverb test method (i.e., testing in a reverberation chamber).

Let’s take a detailed look at the setup for a radiated emission test system. The example shown below uses a semi-anechoic chamber (SAC) for an equipment under test. It is equipped with:

• Turntable and antenna mast with height scan capability
• EMI test receiver that ensures correct frequency scanning and level detection according to relevant EMC standards
• EMC test software that collects data points from different positions and maps EMI radiation in an automated setup
• Selection of antennas with different specified frequency ranges from 30 MHz to 6 GHz (log periodic antenna) or extended frequencies (horn antennas)

The figure below shows a radiated immunity test setup where the distance between the tip of antenna and the EUT is 3 m. It includes:

• Shielded absorber chamber
• Pre-calibrated field probes to verify field uniformity
• Signal generator
• RF power amplifiers
• Power sensors
• Transducers
• EMC test software to automate, control and deliver the right power level and modulation to the EUT according to relevant standards

EMC test challenges and solutions

Now that you understand the fundamentals of EMC testing, we can go over some challenges and how to address them with EMC test solutions.

Key challenges in EMC testing include shorter standardization cycles and limited testing resources.

This drives the need for faster test times and higher automation. Fast Fourier transform (FFT) or time domain scan testing has become the default test method for prototype precompliance testing as well as final compliance testing. Time domain-measuring test receivers, such as the R&S®ESW , can significantly increase test speed and reliability.

Higher automation can be achieved by using a software solution like R&S®ELEKTRA, which offers many benefits during:

• Test planning: setup, templates
• Test execution: instrument control, automation
• Analysis and reporting: customized charts, adding multiple tests to report

If you are planning on setting up your own in-house EMC test facility, it is important to balance your ambitions with available budget. Consider:

• Current and future testing needs
• Location requirements (like power line filters, electricity, fire protection, etc.)
• EUT weight and sizes, which determine chamber dimensions
• Availability of trained personnel
• Cost of calibration, service and maintenance
• Scalability and possibility of future upgrades or expansions

As an EMC test leader for over 50 years, Rohde & Schwarz has a long history of providing test and measurement expertise to EMC standard organizations - and we use our insider knowledge to develop test equipment that support EMC standards across all industries. We supply test equipment, systems, software, upgrades, turnkey solutions (including chambers), trainings, calibration and service. We are a trusted EMC test solution and service partner, guiding you through the process of creating solutions that fit your needs today and meet the demands of tomorrow.

For more information please contact us.