Electromagnetic compatibility (EMC) is the branch of electronics that concerns the unintentional generation, propagation, and reception of electromagnetic energy. The formal process of compliance testing ensures that unwanted effects like electromagnetic interference (EMI) or physical damage in operational electronic equipment is not present, making sure that devices will safely work in a reliable manner. The goal of EMC is to correct operation of different equipment in a common electromagnetic environment.
In the last blog, we talked about the difference between Pre-Compliance and Compliance testing – where Pre-Compliance is an informal, cost-effective, and low risk method to ensure your Compliance testing will pass.
Today we will talk about the formal Compliance regulatory standards and the general process for final compliance testing.
EMC Compliance Testing deals with 4 main tests:
Emission issues involve the deliberate or accidental generation of electromagnetic energy.
Susceptibility involves the tendency of electrical equipment to malfunction or break down in the presence of unwanted emissions or radio frequency inference (RFI).
Immunity is the opposite of susceptibility; it is the ability of the equipment to function correctly in the presence of RFI.
Coupling is the mechanism by which emitted interference reaches the DUT. There are several types of coupling:
- Conductive: When coupling path between source and the receptor is formed by direct electrical contact with a conductive surface (i.e: transmission line, wire, cable, etc.)
- Inductive: When a source and receiver are separated by a short distance
- Capacitive: When a varying electrical field exists between two adjacent conductors, inducing a change in voltage on the receiving conductor
- Magnetic: Type of inductive coupling, when a varying magnetic field exists between two parallel conductors, including a change in voltage along the receiving conductor
- Radiative: Occurs when a source and DUT are separated by a large distance. The source and DUT act as radio antennas, the source radiates an electromagnetic wave
Figure 1: The use of an anechoic chamber is a crucial component for final compliance testing.
The EMC testing process involves open-air test sites that are the reference point in most CISPR standards. This Is especially useful for emissions testing of large equipment systems. RF testing of a physical prototype is most often carried out indoors in an EMC test chamber, like an anechoic chamber, which is a room designed to completely absorb reflections of either sound or electromagnetic waves. This room is isolated from external waves from entering its surroundings.
EMC tests are regulated for standard compliance. These standards help regulate and make uniform product EMC performance. An example of one of the standards is CISPR, as mentioned in the previous blog. CISPR’s work involves the equipment and methods for measuring interference, and establishes limits and immunity requirements for electronic devices. Different countries have different organizations that enforce these requirements. In America, the Federal Communications Commission (FCC) is the group that enforces these compliance testing and certifications. This means, in America, the FCC enforces specific CISPR requirements for electronics that are sold, while another country may enforce another group of CISPR requirements. The FCC requirements only relate to radiated and conducted emissions. The difference between America and Europe is that there are no immunity limits, this is associated with European EMC certification. Generally compliance with national or international standards are usually laid down by laws passed by individual nations, so it will vary from place to place.
CISPR is divided into various subcommittees depending on the specific type of electronics. The different subcommittees are:
- CIS/A - covers radio interference measurements and statistical methods
- CIS/B - covers interference pertaining to industrial, medical, and scientific RF equipment
- CIS/D - deals with electromagnetic disturbances that are related to electronic equipment on vehicles, and other devices that are power ed by internal-combustion engines
- CIS/F - deals with interference relating to household appliances and lighting
- CIS/H - sets the limits for the protection of radio services
- CIS/I/ - deals with EMC of information technology, multimedia equipment, and receivers
Figure 2: CISPR regulations guide you to what standards your device needs to pass.
Compliance testing is a very formal process that is heavily regulated from place to place, so it is best to ensure your devices are likely to pass this compliance testing with the use of pre-compliance testing, which is a low risk, cost effective method to ensure you meet the final compliance requirements, depending on what country your product will be sold.
For more information on pre-compliance testing, check out the Making Conducted and Radiated Emissions Measurements application note for more information. Please like, comment, or share!