All electrical, electronic and electromechanical devices emit an amount of electromagnetic energy to the environment while they are operating. The effect of this emitted or existing energy to the devices or systems is known as “Electromagnetic Interference” (EMI). Electromagnetic Interference can be cauesd by spatial radiation of the energy from the devices as well emissions from the conductors of the device by conducted emission.
“Source, coupling path and the affected system (victim)” are the three basic elements of an electromagnetic interference problem. For radiated emissions air is the coupling path and for conducted emissions the conductors or cables between the source and the victim are the coupling paths in general.
“Electromagnetic Compatibility” (EMC) is to continue to work in an electromagnetic environment without causing interference and without being effected from interference. In other words it can be defined as working without affecting other devices and without being affected by other devices.
If we explain the electromagnetic interference problem in an example specifically; a mobile phone affecting the navigation system of an aircraft in the same environment, while doing its function as voice or data communication; or looking from other side, for an aircraft’s navigation system being affected by a mobile phone can be stated as electromagnetic interference problem.
In this problem, the source is the mobile phone, coupling path is air and the affected system is the aircraft’s navigation systems. The operation of a drill that is connected to the same power grid line with a television can be given as an example to the conducted interference. In this interference problem the drill as the source of interference, using the power grid line, the cables as a coupling path creates noise or system distortion on the screen of the TV, which is the in the role of victim. Electromagnetic compatibility may be mentioned just only for the situation where non of the systems have been affected in these two interference problems.
Electromagnetic interference can bring a variety of results. It can be simple ailments just as the interference seen on a TV screen or distortion heard from the speaker phones of a music system because of a mobile phone. But also it may result major affects as causing an aircraft to fall down by disrupting its systems or triggering the ignition system of an explosive causing wrong commands thus being responsible for serious life threats.
Nowadays EMC has became a more critical subject. From military to space technology fields, medicine to industrial applications or the automotive industry has to comply with the EMC requirements of each segment. There are manynaional or international civilian and military standards to provide EMC. These standards basically define the limits of electromagnetic energy which is allowed to be emitted to the environment or the limit of the energy level from the environment allowed for susceptibility or immunity of the specific devices. Thus, EMC test are appiled according to the methods and test set ups given in the standards. EMC tests are done due to two different problems totally given under four subjects.
In the susceptibility (immunity) tests applied to monitor the amonut of exposure, the required test signals generated by signal generators are applied to the device itself or to the conductors of the device, directly in contact or by using a probe. This type of test is known as “Conducted Immunity (susceptibility) Test”. Performing the same test by coupling the electromagnetic signals via air is known as “Radiated Immunity (susceptibility) Test”. At the end of the test the deterioration and the amount of exposure of the device is monitored, and then evaluated according to the standards.
The control of the device, whether it has emission within the limits of the standards or not is done by measuring and monitoring the electromagnetic energy emitted during operation by using antennas directly from device or probes from conductors. These tests are named as “Radiated Emission” and “Conducted Emission” tests consequently. EMC tests can also cover the effects of natural phenomena as electrostatic discharge (ESD) or lightning.
If considered at the design stage of the device or system, the solution of the EMC problem that may occur can be maintained with minimum cost and time. Measures to be taken against EMI problems widely varies, but requires serious and an experienced engineering work.
The fundamental solution for radiated interference problems can be summarized as leaving the required distances between the conductors and systems and also shielding the emitting or victim section. Solutions for the conducted interference problems can be stated as effective grounding, filtering where required and proper bonding.
In Turkey, public institutions and private institutions have individual studies on EMC. Especially in universities and TUBITAK carry out activities for EMC, design, consultancy, testing.
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