On a flight, during takeoff captain observe interference on Navigation System. They found a passenger was using a Laptop. Even, you are requested to switch off your mobile phones or change to Airplane mode while travelling by plane. Why?
This is because Cell phones, as well as other personal electronic devices such as laptops; tabs etc emit signals from High Frequency clock oscillators. The resulting Electromagnetic Interference (EMI) can affect aircraft navigation, communication and control systems.
After Electrical, Electronics and Photometry, ITC India Pvt Ltd has spread its wings in EMC testing.
So, what is EMC (Electro Magnetic Compatibility)?
EMC: EMC is defined as the ability of electronic and communication equipment to be able to operate satisfactorily in the presence of interference and not be a source of interference to nearby equipment.
EMC = EME + EMI
EME: Electromagnetic Emission (Interference), EMI: Electromagnetic Immunity.
EMC Testing is required to confirm that a particular product follows the required standards. It divides into
Open-air test sites, or OATS, are the reference sites in most standards. They are especially useful for emissions testing of large equipment systems.
However RF testing is most performed indoors, in a exclusive EMC test chamber. Types of chamber include anechoic, reverberation and the gigahertz transverse electromagnetic cell.
Emission Testing : Emissions are generally measured for radiated field strength and where appropriate for conducted emissions along cables and wiring. Inductive (magnetic) and capacitive (electric) field strengths are near-field effects, and are only important if the device under test is designed for location close to other electrical equipment.
For conducted emissions, typical transducers include the LISN (line impedance stabilisation network) or AMN (artificial mains network) and the RF current clamp.
For radiated emission measurement, antennas are used as transducers. Typical antennas specified include dipole, biconical, log-periodic, double ridged guide and conical log-spiral designs. Radiated emissions must be measured in all directions around the DUT.
Typically a spectrum analyzer is used to evaluate the emission levels of the DUT across a wide band of frequencies (frequency domain). Particular spectrum analyzers for EMC testing are available called EMI test receivers or analyzers. EMI receivers along with specified transducers can often be used for both conducted and radiated emissions. Pre-selector filters may also be used to reduce the effect of strong out-of-band signals on the front-end of the receiver.
Some pulse emissions are more usefully characterized using an oscilloscope to capture the pulse waveform in the time domain.
Radiated field susceptibility testing generally involves a high-powered source of RF or EM energy and a radiating antenna to direct the energy at device under test.
Conducted voltage and current susceptibility testing generally requires a high-powered signal generator, and a current clamp or other type of transformer to inject the test signal.
Transient signals are used to test the immunity of the DUT against powerline disturbances including surges, lightning strikes and switching noise.In motor vehicles, similar tests are performed on battery and signal lines.
Electrostatic discharge testing is typically performed with a piezo spark generator called an “ESD pistol“. Higher energy pulses, such as lightning or nuclear EMP simulations, can require a large current clamp or a large antenna which completely surrounds the DUT. Some antennas are so large that they are located outdoors, and care must be taken not to cause an EMP hazard to the surrounding environment.