Electromagnetic interference (EMI) is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.
Conducted EMI is caused by the physical contact of the conductors as opposed to radiated EMI which is caused by induction (without physical contact of the conductors). For lower frequencies, EMI is caused by conduction; for higher frequencies, it is caused by radiation.
EMI can cause malfunctions in electronic devices. Specifically, EMI causes suppression of signals generated internally in a device, external ambient interference with equipment operation, or emissions generated internally that will interfere with equipment operation.
This may certainly include access control equipment. When installing an access control system, the information included here should be taken into consideration in order to eliminate or at least reduce the occurrence and possibility of EMI noise in an electrical system.
Electromagnetic Interference can arise in many ways and from a number of sources. The different types of EMI can be categorized in a number of ways. One way of categorizing the type of EMI is by the way it was created:
- Man-made EMI: This type of EMI generally arises from other electronics circuits, although some EMI can arise from switching of large currents.
- Naturally occurring EMI: This type of EMI can arise from sources such as cosmic noise, as well as lightning and other atmospheric types of noise.
A method of categorizing another type of EMI is by its duration:
- Continuous interference: This type of EMI generally arises from a circuit that is emitting a continuous signal. However, background noise, which is continuous, may be either man-made or naturally occurring.
- Impulse noise: This type of EMI may be man-made or naturally occurring. Lightning, electrostatic discharge, and switching systems all contribute to impulse noise.
It is also possible to categorize the different types of EMI by their bandwidth.
Narrowband: Typically this form of EMI is likely to be a single carrier source, possibly generated by an oscillator of some form. Another form of narrowband EMI is the spurious signals caused by intermodulation and other forms of distortion in a transmitter such as a mobile phone or a Wi-Fi router. These spurious signals will appear at different points in the spectrum and may cause interference to a user of the radio spectrum. As such, these spurious signals must be kept within tight limits.
Broadband: There are many forms of broadband noise that can arise from a great variety of sources. Man-made broadband interference can arise from such sources as arc welders where a spark is continuously generated. Naturally occurring broadband noise can come from the Sun. It can cause sun-outs for satellite television systems when the Sun appears behind the satellite and noise can mask the wanted satellite signal. Fortunately, these kinds of episodes only last for a few minutes.
You may also refer to the following Power Management video for additional overview information about power.