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Electromagnetic interference (or EMI, also called radio frequency interference or RFI) is a disturbance that affects an electrical circuit due to either electromagnetic conduction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit or the Sun.

Have you ever wondered why the interference that you receive on the radio communications bands can sometimes disrupt the intended signals?  Interference probability is based on the potential power transfer densities involved due to the proximity of equipment and antenna systems; the various transfer mechanisms, and equipment performance.

The electromagnetic transfer mechanisms may vary depending on modes of operation, propagation conditions, and other variables.  The propagation paths that exist for signal transfer from the transmitters to a receiver within the RF environment of a radio communications band can be numerous. 

Antenna-to-antenna coupling parameters may vary depending on antenna gain, directivity, beam width, side lobes, polarization, separation, propagation conditions of the path (path loss), etc.    The receiver characteristics which influence performance include noise, dynamic range, sensitivity, selectivity (RF, IF), desensitization, adjacent signal susceptibility, intermodulation, cross modulation and spurious response susceptibility. 

The terms EMI and RFI are often used interchangeably. EMI is actually any frequency of electrical noise, whereas RFI is a specific subset of electrical noise on the EMI spectrum. There are two types of EMI. 

Conducted EMI is unwanted high frequencies that ride on the AC wave form. 

Radiated EMI is similar to an unwanted radio broadcast being emitted from the power lines. There are many pieces of equipment that can generate EMI, variable frequency drives included. In the case of variable frequency drives, the electrical noise produced is primarily contained in the switching edges of the PWM controller. As the technology of drives evolves, switching frequencies increase. These increases also increase the effective edge frequencies produced, thereby increasing the amount of electrical noise. 

Schaffner have released an information booklet called “Basics in EMC & Power Quality”. You can download it from the ‘catalogue’ section of the this website.

If you are occasionally experiencing interference with your telephone system, flickering computer monitors, reliability issues with computer networks, instrumentation errors, or misbehaving electronics you are most likely experiencing RFI in your electrical environment. RFI can wreak havoc with your electronics, computers and telephones, making your workplace difficult to work in. Since most machines have control electronic circuits, they may become difficult to control or unreliable. RFI The disturbance may interrupt, obstruct, degrade or limit the effective performance of the circuit.

EMC (Electromagnetic Compatibility) means nothing more than “an electronic or electrical product shall work as intended in its environment. The electronic or electrical product shall not generate electromagnetic disturbances, which may influence other products”. In other words, EMC deals with problems of noise emission as well as noise immunity of electronic and electrical products and systems. Electromagnetic disturbances occur as conducted interference as well as radiated emissions and immunity problems.

Depending on your application, there are many ways to reduce the effects of RFI. For conducted RFI, you can choose from a large range of RFI filters, chokes & pulse transformers. For radiated RFI, you can choose from a large range of shielding products.

RFI filters are available as feed-through components, or as PCB filters, IEC inlet filters and power entry modules, 3-phase filters, 3-phase and neutral line filters, output filters, EMC/EMI chokes and pulse transformers.

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