Electromagnetic Compatibility of Electronic Devices - Assignment Example

The quality of a device is more significant in any case; often it is the main factor of preferences. Same is the situation of the electronic devices as well which are at times getting influenced by the radiations and exhibits varied behaviours of input and output. Thus, different standard measures of quality should be employed, to get assurance on the matter of vulnerability and immunity of the devices to various influential factors; so, Electromagnetic Compatibility (EMC) tests come to meet this requirement. “EMC stands for Electro Magnetic Compatibility, a term for the behaviour of an apparatus in terms of Electro magnetic interference it generates and the immunity to impeached Electro magnetic field on its enclosure and cables.” (EMC directive 2004/108/EC, 2009). It guarantees that only a limited amount of RF interference is created by any electronic or electric appliance. The devices which are proved to be of good quality through the EMC test will be less prone to effects due to various RF radiations along with immunity to all the instabilities and erroneous input output signals. This helps in the correct operation of other devices since they are not affected. It also guarantees that positive amount of electromagnetic fields is resisted by the devices. The electronic power amplifier usually produces radio frequency energy and hence EMC directive can be applied for almost every electronic and electrical device which is more prone to electromagnetic interference can be used to analyse the case of electronic power amplifiers as well. There are three disciplines for EMC which are the conducted path, the radiated path and the combination of the two. Basically, there are three types of standards - the generic standards, the basic standards and the product and product family standards. The tests of EMC are carried out to check whether the devices are up to the standards predetermined and expected. EMC “Directive allows for self-certification to harmonized standards. Clearly this route is dependent on the availability of suitable standards and CENELEC has been mandated to produce such. The most important standards that have so far been harmonized are the "generic" standards.” (Williams, 1996). The European Standardization bodies develop the harmonized standards. Testing of the electronic power amplifier is needed for ensuring that the device meets the standards. The methods of testing may not be similar to those in the standards because the environment of testing can vary. The EMC standards clearly define the procedures for testing that includes the susceptibility test as well as the immunity test. The factors to which the device is more prone to and more immune to get affected are identified by the EMC tests. It often does the measurement at low power levels. The test procedures should be observed and adequate care should be given to it. The tests are carried out on the subsystems to calculate the applications of EMC performances. A number of varied tests are conducted independently, each describing the quality of the power amplifier in terms of various aspects of perfection in the electronic applications. Electromagnetic susceptibility is the measure of resistance to electrical disturbance and electromagnetic interference is the measure of electrical noise conducted by the device. Selection of radio frequency probe is very important in EMC testing. The EMC tests are very difficult and it requires good skill and knowledge. A small variation in any setup like the arrangement of wires etc will produce variation in the output of the test. The basic requirements for the tests are electrostatic discharges, electromagnetic RF fields, oscillatory waves, fast transient waves. These things are used in EMC testing of almost all electronic devices. “RF immunity testing to IEC1000-4-3 and -4-6 is now an established requirement for an EMC test facility.” (What to look for in an EMC amplifier, n.d., p.1). This test uses a circuit with power amplifier integrated so that the RF field strengths and quality levels are determined to define the performance of the system of components under test. The EMC susceptibility test frequency range is large. The EMC test engineers should understand the limitations in the design and performance of the amplifier. They do tests after understanding the limitations of the electronic power amplifier, so that steps can be taken accordingly. To design and understand the proper working of power amplifier, it is necessary to conduct an EMC test which is done under different electrical environment. Power amplifiers are finding their applications in a wide range of electronic devices owing to their advantages. (300W bridged-paralleled power amplifier, 2008). The above diagram shows a power amplifier used to generate a balanced output with an unbalanced feed at the input at about 300w power rating. The manufacturing of amplifiers can result in various qualities of amplifiers; thus to dig out the best, normal or poor quality ones, various tests are employed on them. By doing the EMC test the manufacturers get knowledge about the electromagnetic energies which are accidentally developed and how the developed energy affects its performance. By performing EMC test we can get an idea about how the product fulfils the important EMC regulations and directives. This will help them to identify the reliability of power amplifier, cost of service etc. It can also help understand the problems within the product and correct that problem before manufacturing. EMC directives are used to those products that have faced the problem by EMI (Electromagnetic Interference).Therefore, it is very important to analyse whether the product complies with the EMC directive or not. The main advantage of compliance with the EMC directive is that, it mainly focuses the protection of the manufactured products. The basic EMC directives regarding protection of manufactured products include “The electromagnetic disturbance generated by the apparatus does not exceed a level specified in harmonized EMC Standards. This level is that above which radio and telecommunications equipment or other equipment may not be able to operate as intended. It has a level of immunity to the electromagnetic disturbance to be expected in its intended use, which allows it to operate without unacceptable degradation of its specified performance.” (Electromagnetic compatibility (EMC) directive, 2009). When we use an EMC test for power amplifier, it should be in compliance with the EMC Directives. Power amplifiers are used in an electronic circuit, where high switching current is needed to amplify the input signals. The electronic power amplifiers used in various devices are the important components as they control the power derivatives and power factor of the device. There are several phenomena like transient, and continuous radio frequency may happen in an electromagnetic environment. This will create several problems in the performance of the product. The problems that may happen due to these phenomena can be understood by means of EMC testing. Due to improper usage of electronic circuit and the fault circuit connections, ESD (electronic discharges), switching transients etc act as the natural causes for transient phenomenon. This may happen in very few seconds and a high amplitude fluctuation will completely destroy the whole circuit and the components in the power amplifier circuit. Therefore, ‘Transient Immunity Testing ‘is the appropriate EMC test for the power amplifier circuit. Transient immunity test is used to test the system on the transient response aspects exhibited by it. ESD, EFT, lightning surge test are some of the Transient Immunity Testing. The electrical fast transient (EFT) happens when the circuit is off. At that time the current through the circuit is suddenly stopped and this leads to the breaking of air gap and causes a small amount of current flow through the circuit and it affects the voltage spikes in the circuit and leads to circuit breakage. To reduce the fast electrical transient effect in the power amplifier circuit, it is necessary to follow the below statement. “a) Internal circuit design is bandwidth limited wherever possible, and the PCB layout prevents large interference voltages from appearing within the circuit; b) Interfaces must be filtered or screened to a structural low impedance earth so that common mode pulses are prevented from entering the circuit.” (Electrical fast transient testing-standard and methodology, 2009). The EFT testing is done by using IEC61000-4-4 slandered. The IEC61000-4-4 standard of EFT is helpful for conducting and analyzing the EFT test. By means of suitable coupling methods, appropriate waveform is given to the main connection. For the coupling of AC or DC main, a capacitor of value 33nF is generally used. These coupling and decoupling capacitors are there in the EFT simulator. The decoupling capacitor is designed in such a way that it will block the returning of EFT burst to the power mains. The methods of EMC testing with power amplifiers can be done either with TEM or GTEM cells. “TEM cell is a transmission line with characteristic impedance of which is realized by gradually expanding the size of a coaxial transmission line.” (Heinrich, et al., 2008, p.267). This is the abbreviation for Transverse Electro Magnetic and is widely used in EMC testing. The parameter of plate separation is used to execute EMC test with the usage of TEM cell. The efficiency of the cell is good and is installed for the EMC test due to the advantages offered. Similar device is GTEM cell, which as well is used in EMC testing procedure. “The ETS-Lindgren Gigahertz Transverse Electromagnetic (GTEM!™) Cell is a precision electromagnetic compatibility (EMC) test instrument primarily intended for use as an EMC radiated immunity and radiated emissions test facility.” (Model 5400 series, 2008, p.11). GTEM helps in analyzing the immunity of the devices from various radiations. The power amplifier should be given this test as well as a part of the EMC test procedure. Even this equipment works on the principle of plate separation and the immunity of the amplifier to the radiations can be checked by GTEM Cell. The test apparatus include the testing instrument i.e. GTEM Cell and the device under test which is the electronic power amplifier. The theory of reciprocity indicates that the testing of radiations should be within the check amount. The applications of GTEM Cells are especially due to the capacity of the highly speedy approach of pulses to the system. (Heinrich, et al., 2008, p.267). The discussions on “the issue of gain compression in RF power amplifiers, especially how a manufacturer specifies the output power of an amplifier and the corresponding pitfalls that may be faced when interpreting a specification sheet for an amplifier” is of great significance in the performance analysis. (Mullineaux, 2004). Gain compression is a phenomenon of the amplifying devices measured which determines the drop in the gain of the amplifier with respect to the non linearity of the input output proportionality of the system. The gain due to discrepancy defines the stability offered by the amplifying circuit and nonlinearity refers to poor performance of the amplifier. EMC test is widely used for the testing of various electronic devices to check their compatibility, efficiency and immunity at different environments posing challenges. The investigation on the EMC testing of electronic power amplifiers is of considerable significance because of the wide installation of those in various devices and the performance of all those devices are dependent on the performance of the amplifiers. The EMC test result approving good quality is preferred while selecting the electronic power amplifier used in different applications. Thus the finale of the discussion identifies the significance of EMC in the electronics field of the contemporary technological flourish. EMC provides the guaranteed result expected from the device which assures the error free output. The EMC tests for power amplifiers can be viewed as more important than any devices because of the wide applications they find in the electronic appliances and circuits. The surety about the amplifiers’ performance will be of considerable importance in such circuits; indicating the worth of the EMC test in the entire technological sector. Reference List Electrical fast transient testing-standard and methodology, 2009. Electronics Project Design. [Online] Available at: http://www.electronics-project-design.com/ElectricalFastTransient.html [Accessed 10 December 2009]. Electromagnetic compatibility (EMC) directive: EMC directive in brief, 2009. Technology International Group. [Online] Available at: http://www.techintl.com/emc.cfm [Accessed 10 December 2009]. EMC directive 2004/108/EC: what is the EMC directive?, 2009. [Online] Available at: http://www.cetest.nl/emc-directive.htm [Accessed 10 December 2009]. Heinrich, R. et al., 2008. Application of GTEM cells for IC EMC testing. [Online] Available at: http://www.teseq.com/com/en/service_support/technical_papers/07_P129.pdf [Accessed 11 December 2009]. Model 5400 series: Gigahertz transverse electromagnetic (GTEM !) cell: operation manual, 2008. ETS. Lindgren: An ESCO Technologies Company. [Online] Available at: http://www.ets-lindgren.com/manuals/5407.pdf [Accessed 10 December 2009]. Mullineaux, T., 2004. Article: rating power amplifiers for RF immunity testing (EMC test equipment). High Beam Research. [Online] Available at: http://www.highbeam.com/doc/1G1-113311115.html [Accessed 10 December 2009]. What to look for in an EMC amplifier, n.d. [Online] Available at: http://www.elmac.co.uk/pdfs/wtlf-amp.pdf [Accessed 10 December 2009]. Williams, T., 1996. A critique of the EMC directive. Elmac Services. [Online] Available at: http://www.elmac.co.uk/critemcd.htm [Accessed 10 December 2009]. 300W bridged-paralleled power amplifier, 2008. Cool Circuit. [Online] Available at: http://www.coolcircuit.com/gadgets/2008/02/20/300w-bridged-paralleled-power-amplifier/ [Accessed 11 December 2009]. Read More