Steps to Ensure Success in EMI and EMC Testing

Electromagnetic compatibility (EMC) refers to a device’s ability to function correctly in the presence of other electrical devices or EMI sources without disturbing them. A product is considered EMC-compliant if it can operate as intended without creating electromagnetic conditions that negatively impact other systems or devices.

To meet both national and international regulations, products often undergo EMI and EMC testing at specialised facilities. Because these tests are costly—even in the event of a failure—many organisations choose to run EMC pre-compliance testing internally first. Companies with advanced labs may also perform full compliance testing on-site.

EMI pre-compliance testing involves running a series of checks on devices to evaluate their electromagnetic emissions before official certification testing. The goal is to catch and fix potential EMI issues early in development, ensuring the product will meet EMC standards and regulatory requirements when submitted for compliance.

EMC testing generally falls into two categories: immunity testing and emissions testing.

• Immunity Testing: RF energy is applied to a device under test (DUT), also called equipment under test (EUT), to confirm it continues to function properly in that environment.

• Emissions Testing: Measures the RF emissions—both radiated and conducted—of a DUT/EUT to verify they remain within the limits set by the relevant standards.

• Radiated Emissions: The intentional or unintentional release of electromagnetic energy from a device. Testing ensures emissions from the DUT/EUT meet required limits. 
• 
• Conducted Emissions: The transfer of electromagnetic energy from a device into its power lines. Like radiated emissions, conducted emissions are regulated, and testing checks that levels remain within the approved thresholds.

EMC compliance tests are often performed off-site before product production begins. Open-air test sites (OATS) are reference environments used by many standards and are particularly useful for emissions testing of large systems. More commonly, prototypes are tested indoors in controlled environments such as anechoic chambers, reverberation chambers, or gigahertz transverse electromagnetic (GTEM) cells.

Without pre-compliance, only about half of products pass EMC testing on the first attempt. Improving the odds of success means understanding both the process and the standards applied:

• Identify Standards: EMC regulations vary depending on the country and type of product. The first step is to determine which standards apply and learn the associated procedures and limits.

• Run Pre-Compliance Testing: Full EMC compliance testing can take up to two weeks and cost as much as $20,000 per submission. Failing the first attempt often means redesigns and repeat visits to the test house, multiplying both time and cost.

• Select a Testing Lab: After passing pre-compliance testing, devices must be formally certified by an EMC lab. Accredited labs are recommended for reliable results, though not always required. In some cases—such as devices covered by FCC certification procedures—an accredited FCC lab is mandatory.

To replicate compliance test conditions affordably, an EMC pre-compliance setup typically includes:

• Spectrum analyser with quasi-peak detector

• Optional preamplifier

• Antenna with non-metallic stand for radiated emissions testing

• Line impedance stabilisation network (LISN) for conducted emissions

• Power limiter for conducted emissions testing

• EMC near-field probes for diagnostics (optional)

• Oscilloscope with time and frequency correlation for debugging (optional)

• EMC testing software

Choosing a location is important—rural areas, basements, or conference rooms help minimise external signals that could mask device emissions. Accuracy can also be improved by ensuring a solid ground plane and reducing reflective surfaces in the test area.

Pre-compliance testing offers an affordable way to increase the likelihood of passing EMC compliance first time. Early in the design phase, applying EMC-focused design techniques reduces susceptibility to interference. Later, pre-compliance tests catch problems before certification.

Key benefits include:

• Detecting errors early and addressing them quickly

• Lower testing and design costs

• Improved project flexibility

• Reduced risk of compliance failure

• Avoiding both over-design and under-design

Full EMI Compliance Chamber vs Tektronix Spectrum Analyser

A full EMI compliance chamber is the benchmark for certification, but a Tektronix Spectrum Analyser provides a cost-effective alternative for pre-compliance testing. It helps detect issues early and increases the likelihood of first-time success at the compliance lab.

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