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EMC/EMI testing is a critical step in the design and manufacturing processes of electronic devices. Various regulatory bodies, including the FDA, FCC, and ISO, have set specific limits on the emissions that can be released from an electronic device. These EMC (electromagnetic compatibility) regulations provide improved reliability and safety for anyone using electrical and electronic equipment because they assure the device does not interfere with the operation of other equipment or fail to operate as intended due to interference from others emissions. Failing to pass EMC compliance testing can result in fines and product recalls.

So purchasing instruments that can spot potential EMC/EMI issues prior to EMC testing is worth the investment.

Though EMI and EMC are very similar, there are a few differences between the two.

What is EMI?

Sometimes called radio frequency interference (RFI), electromagnetic interference (EMI) occurs when electromagnetic energy disrupts the operation of an electronic device. The source of EMI can be man-made, such as other electrical devices like switch-mode power supplies, personal computers, or naturally occurring, such as electrical storms, solar radiation, or even cosmic noises.

What is EMI

What is EMC?

Electromagnetic compatibility (EMC) is the ability of a device to operate as intended in an environment with other electrical devices or sources of EMI without affecting those other devices. A device is said to be EMC-compliant when it does not influence the electromagnetic environment to the extent that other devices and systems are negatively affected.

What is EMC

What is EMC/EMI compliance testing?

To ensure compliance with EMI and EMC national and international regulations, many companies employ the services of a specialized testing facility. Since these tests are expensive—even if the product fails—several companies perform EMC pre-compliance testing in-house. If they have a sophisticated enough lab, companies may also perform EMC compliance testing in-house.

EMC/EMI testing setup

EMC/EMI testing is typically divided into two categories: immunity testing and emissions testing.

Immunity testing

Immunity testing is the process of transmitting RF energy onto a device under test (DUT) (also referred to as equipment under test or EUT) to determine if the DUT/EUT operates correctly when in such an environment.

Emissions testing

Emissions testing is the process of measuring the RF emissions – both radiated and conducted – of a DUT/EUT to determine if its emissions levels do not exceed the limits defined by the appropriate standard. Emissions testing includes both radiated and conducted emissions tests.

Radiated emissions

Radiated emissions are the intentional and unintentional release of electromagnetic energy from an electronic device. A radiated test is performed to ensure emissions emanating from the DUT or EUT comply with the applicable limits.

EMC/EMI testing for radiated emissions

Conducted emissions

Conducted emissions are the coupling of electromagnetic energy from a device to its power cord. Like radiated emissions, the allowable conducted emissions from electronic devices are controlled by different regulatory agencies and testing is performed to ensure emission levels are below the applicable limits.

EMC/EMI testing for conducted emissions

EMI/EMC Testing Applications

EMI/EMC testing is part of the product development process and testing is mandatory in most markets. Though all electronic devices are subject to EMC testing, the following are some of the most common applications for EMC testing.

MARKET SEGMENTS Equipment Type
ISM MEDICAL Industrial, scientific and medical equipment
Medical electrical apparatus
AUTOMOTIVE Vehicles, boats and internal combustion engines
Components and modules on board vehicles
MULTIMEDIA Sound and TV broadcast receivers
Information technology and telecommunications equipment (ITE)
Professional audio/video/multimedia equipment
APPLIANCES Electrical devices, household appliances and tools
LUMINAIRES Fluorescent lamps and luminaires
MILITARY Military equipment and systems

How to test for EMI and EMC-compliance

EMC-compliance tests are commonly done off-site prior to the production of a device. Open-air test sites, or OATS, are the reference sites used for most standards. They are especially useful for emissions testing of large equipment systems. However, RF testing of a physical prototype is more often carried out indoors, in a specialized EMC test chamber. Types of chambers include anechoic, reverberation, and the gigahertz transverse electromagnetic cell (GTEM cell).

EMC compliance testing can take up to two weeks to complete—not including the time it takes to get your product into the test queue—and can cost up to $20,000 per submission. A failure in EMC compliance can result in expensive redesigns and product launch delays. And since nearly 50 percent of products fail their first EMC compliance test when pre-compliance isn’t considered, it’s likely that you’ll need to repeat your visit to the test house, multiplying costs over time.

Save time and money with pre-compliance EMC testing

As a fast and affordable alternative to using a fully accredited compliance lab, many companies invest in an on-site pre-compliance test solution to evaluate product designs. In the early development stages, design-for-EMC techniques are combined with diagnostics to build products with low susceptibility to both external and internal interference. Later in the development cycle, pre-compliance testing is used to catch compliance problems and improve the probability of a successful first pass of full EMC-compliance testing.

Additional benefits of pre-compliance EMC testing, include:

  1. Detects errors early, fixing potential issues
  2. Lowers testing and design costs
  3. Projects become more agile
  4. Lowers risk of failure and leads to assured compliance
  5. Addresses both over and under design and engineering
  6. Reduces future warranty issues

Pre-compliance EMC/EMI testing process

Learn more about the financial benefits of EMI/EMC pre-compliance testing.

Setting up a pre-compliance EMC testing site

When selecting a test site, rural areas, conference rooms, and basements are good options because they minimize external signals that might mask the DUT emission levels you are trying to measure. Other considerations for improving accuracy include having a good ground plane and reducing the number of reflective objects around the test area.

EMC/EMI testing products

EMI and EMC testing products

The goal of EMC pre-compliance testing is to mimic the compliance test set up within an acceptable margin to uncover potential problems and reduce risk of failure prior to the expensive compliance test. EMC pre-compliance testing typically involves:

  • Spectrum analyzer with quasi-peak detector
  • Preamplifier (optional)
  • Antenna with non-metallic stand for radiated emissions
  • Line impedance stabilization network (LISN) for conducted test
  • Power limiter for conducted test
  • Near field probes for diagnostics (optional)
  • Oscilloscope with frequency and time correlation capabilities to assist in debugging (optional)