What Is EMC Testing?

EMC testing is the measurement of a product’s electromagnetic compatibility (EMC): its ability to work as intended in its electromagnetic environment without disturbing anything else in that environment. Every electronic product gives off some electrical noise and is exposed to noise from others, so EMC testing checks both sides.

Emissions testing measures how much interference the product produces, along its cables and through the air, and compares it with legal limits. Immunity testing, also called susceptibility testing, exposes the product to the disturbances it will meet in service and checks that it keeps working. A product that passes both is unlikely to interfere with radios and other equipment, or to crash when someone switches on a motor next to it.

Emissions are measured in the two ways interference travels. The limits depend on the product standard and on whether the product is Class A, for commercial and industrial sites, or Class B, for homes and the stricter limits that go with them.

Immunity tests use the IEC 61000-4 series of basic standards. Each one recreates a real-world disturbance, and the product standard sets which tests apply and at what level.

Results are judged against performance criteria. Criterion A means normal operation throughout the test. Criterion B allows a temporary loss of function that recovers by itself. Criterion C allows a loss of function that needs the operator to intervene, such as a restart. The product standard says which criterion each test must meet.

Most products go through the same stages, whether they are tested by the manufacturer’s own lab or by an independent one:

In Great Britain, EMC is a legal requirement under the Electromagnetic Compatibility Regulations 2016, shown by a UKCA mark, and the government has said the CE mark will continue to be accepted for most products. In the EU and Northern Ireland, the EMC Directive 2014/30/EU applies and the product carries a CE mark. Both cover emissions and immunity, and using harmonised standards gives a presumption of conformity.

In the US, the FCC regulates emissions only. Most computers are unintentional radiators under FCC Part 15 Subpart B, authorised through a supplier’s declaration of conformity, with Class A or Class B limits. Immunity is not required by the FCC, so it is driven by industry standards and customer specifications. Canada uses ICES-003 for the same purpose.

EMC is separate from product safety. A computer also needs a safety standard such as IEC 62368-1, and marks such as UL or ETL refer to safety, not EMC.

An industrial computer is tested in one configuration, and EMC can change when that configuration does. Adding a wireless modem, a capture card, unshielded cables or a different power supply all affect emissions and immunity. Vehicle computers face extra tests for supply transients, covered in our guide to E-Mark certification for automotive computers. Defence programmes usually specify MIL-STD-461 instead of the civil standards.

When comparing industrial PCs, look for the actual standards and class on the datasheet, not just a CE or FCC logo, and check that the immunity standard matches the site: IEC 61000-6-2 for heavy industry, EN 50121-3-2 for trains.

We integrate industrial computers with the modules, cabling and power supplies each installation needs as standard, keep builds close to the manufacturer’s tested configuration, and can obtain the EMC declarations behind a datasheet’s marks.