The number of electrical/electronic devices are growing continuously in every home / industrial environment. Electromagnetic disturbances emanating from one device may cause interference/malfunction to another electronic device in the same environment. These disturbances are commonly known as Electro- Magnetic Interference (EMI).
EMI can cause service interruption, data loss, permanent damage to equipment and failure when left uncontrolled. The stakes are even higher with medical and defence equipment.
There are two main types of emissions — conducted EMI and radiated EMI. Conducted EMI passes through conductors such as wires or power lines. Radiated EMI travels through the air and does not require a conductor. However, both are equally damaging.
To meet legislation such as the EU Directive on EMC, in addition to other international regulations such as FCC, EMI filtering is now an essential element of equipment design.
The first and most effective option is to eliminate or minimise interference at the source itself. So that no external solutions need to be deployed. Reduce emission levels to acceptable limits. Alter the path of the emission from the identified source towards your equipment.
However, external solutions such as filters, shields, grounding are often deployed to minimise the impact of EMI on sensitive equipment.
RFI refers to noise that falls in the Radio Frequency range within the entire electromagnetic frequency spectrum. Whereas EMI can refer to any frequency of electromagnetic noise. RFI is a subset of EMI and includes only electromagnetic currents with a frequency between 3 KHz and 300 GHz. RFI can also be conducted or radiated and can cause a variety of problems with electronic devices, just like any other EMI. Conducted RFI is most often found in the low frequency range of 3 kHz to 30MHz and radiated RFI in higher frequency ranges.
EMC is a term used to describe how a device performs in an environment of electromagnetic noise. EMC includes two factors — a device's tolerance to emissions (noise immunity) and how much emission it produces. The goal is to limit the unintentional generation, propagation and reception of electromagnetic energy. EMC is characterised by several aspects.
Annoying Effects – Momentary disturbance in Radio/TV transmission when the mixer or microwave is switched on
Disturbing Effects – Unwanted reset in computers / digital equipment, Changes in status / settings, Excessive energy consumption
Catastrophic Effects – Loss of data, Burnout of electronic components, Change of threshold settings, Improper / Unwarranted operations, Biological hazards
A number of different EMC standards, each with their own requirements related to test set-up, power levels, frequencies, and many other details, have been developed over time. Different standards have been adopted by different nations, with some standards designed for harsh military requirements, while others are intended for a benign suburban environment.
Governing bodies in the European Union with respect to EMC include the IEC, CISPR, and the European Committee for Electro-technical Standardization (CENELEC). The IEC coordinates international standardization and related matters, while CENELEC and CISPR are largely responsible for approving detailed EMC standards to demonstrate compliance with the EMC Directive. Products sold in the European Union must be in compliance with EMC Directive, 89/392/EEC. Products that meet the EMC directive carry the "CE" mark that signifies the manufacturer's assertion of compliance.
MIL-STD (latest being MIL-STD-461F issued in December 2008) defined by the Department of Defence, USA is a system-level standard that specifies EMC requirements and limits. It consists of EMC requirements, EMC test set-up and methodology and EMC definitions and acronyms.
It is based on the operational platform for deployment (surface, ships, aircraft, etc.) and location on that platform (internal or external). The overall requirement is comprised of eighteen sub-tests that cover diverse system characteristics ranging from emissions conducted via power leads to spurious and harmonic radiated emissions.
This testing is not inexpensive and is quite elaborate. The five core tests (RS103, RE102, CS101, CS114 and CS116) will require roughly two days of lab time; the entire standard, seven to ten days.