The letters EMC stand for electro-magnetic compatibility and likewise EMI stands for electro-magnetic interference. There are standards that are used to determine whether or not a test article is susceptible to, or emits, an unacceptable level of interference. It can be either radiated or conducted in form. The standards are defined by regulatory agencies worldwide and are specific to particular scenarios. There are literally hundreds of different standards that various types of equipment must meet depending on their application and country of origin.
Electronic devices cannot be sold unless they pass the standards specified for the type of device it is, and the location or environment it is being used in. This is a safety and compatibility requirement. This makes testing mandatory.
Some of the more universal regulatory bodies that define these standards are:
As you can see there is broad geographic coverage to ensure that systems developed in one region are not affected, nor affect, systems in another region. The testing of these standards requires highly specialized test equipment, such as antennas, EMI couplers, EMI receivers, and anechoic chambers as well as more universally known pieces of equipment such as signal generators, spectrum analyzers, oscilloscopes and amplifiers.
EMI can be either continuous or transient. Some examples include CW, or continuous wave, interference ranging from audio to tens of GHz or higher. Transient EMI can be anything from an electrical motor and/or inductive load switching to power line noise and harmonics to lightning strikes. Remember that this is not a comprehensive listing.
There are four ways EMI can couple either into a piece of equipment, called susceptibility, or emanate from equipment, called emission. Each mode requires different test equipment and a different test set up. Depending on what is being tested, the set up and test equipment needed will be defined by the respective standard.
These are illustrated in the image above.
With this type of test the coupled EMI is generated by imposing the interference onto the article under test’s physical connections such as power line, input or output, and controller interface. This requires highly specialized equipment. An example of this type of equipment is a Teseq NSG4070 Conducted RF Immunity Test System. This will allow a controlled level of EMI to be coupled into the device under test to ensure it will meet its particular standard.
This type of EMI coupling uses a conductive plate to capacitively induce EMI into the test article. An example of this type of equipment is a Haefely IP4A Capacitive Coupling Clamp, in addition with a typical Immunity Test System such as a Haefely AXOS5 or emtest NX5.
By using a Haefely MAG100 you can generate magnetic fields to induce EMI into the test article. This can simulate interference that is generated by high current cabling such as DC welding equipment, or any high current DC application. Another example would be automotive battery testing which involves large currents.
This is perhaps the largest area of EMI testing, likely because this EMI can occur at great distances. It also has the widest range of applicable and useful test equipment. Radiated EMI is almost always done in an anechoic chamber. Otherwise you have to travel to a remote location far from any airports, broadcast transmitters and structures. This is called “open field” testing and is not addressed in this article. Anechoic chambers are used in conjunction with transmit and receive antennas, often the same antenna since antennas are bidirectional, also known as being reciprocal. There are occasions when testing is done using two anechoic chambers with the unit under test in one chamber and the equipment being used to test it in a second chamber. This provides maximum isolation when testing to extremely low levels of interference. When testing susceptance the antenna will be driven with a signal generator or a specialized signal source as specified by the standard being tested to. An example of a specialized source could be a wireless base station emulator or just an arbitrary noise source. When testing for emissions the same antenna can be used but connected to a spectrum analyzer or EMI receiver like a Rhode & Schwarz ESU40 for example. Speaking of antennas, they can be of several types including dipole, bi-conical, yagi, exponential horn, ridged waveguide and/or whip. Again, the type of antenna used for testing will be specified in the standard being applied.
Since 2005, Axiom Test Equipment has been providing a variety of EMI/EMC test equipment for rent or sale. Additionally, we repair most brands and types of EMI/EMC test equipment. Major manufacturers we carry include, Rhode & Schwarz, Keysight (formerly Agilent), Amplifier Research, Solar, emtest, ETS-Lindgren, Teseq, Haefely, AE Techron, and more. Axiom Test Equipment offers a complete range of EMI/EMC test equipment for your specific requirements. View these online at, http://www.axiomtest.com/Compliance-Testing-_-EMC,-ESD,-EMI,-RFI/.