Techniques Used in the Design of Parts of a Complex Electronic Product - Report Example

Designing for EMC Introduction EMC plays an increasingly important part in the design of electronic products and systems. In this case study, the researcher would discuss the techniques used and best practices incorporated in the design of various parts of a complex electronic product (system) to increase the chances of final system becoming compliant to the EMC directive (IEE Guide 2000). The researcher would create this design to be integrated in a computer room of a bank headquarter that has a computer suite of 12 workstations and other peripheral equipments. The researcher would also ensure that the system was designed and installed in such a manner that it is electromagnetic compatible. This study would also analyse the various sub systems used in the bank and discuss means to eliminate electromagnetic waves emitting from these systems. The paper would also identify the gap areas in the system that may not fulfil the required EMC standards and provide recommendations to address the issues. It is imperative to design a system taking extra precautions for the banking environment as any malfunctioning in the system would not only mean serious implications on the safety aspects but may also translate into financial risk for the bank. Such risks would arise from filing of liability suits, withdrawing of accounts and losing the confidence of the customer on the bank (Armstrong 2001). This is a huge problem as modern offices, especially banks, use various sophisticated electronics and computer-based technology such as printers, data farms, server equipment and UPS system. The paper, therefore, would explore ways to create a system that would integrate these systems seamlessly, while complying with the EMC directives. The paper would describe the various EMC directives and introduce an engineering design that would comply with these directives and provide a cost-effective solution to manage the equipments, systems and other installations in the bank. Understanding EMC directives It has been found that most of the safety regulations in the bank are focused on providing safety from physical injuries such as fire, electric shock etc. However, in the paper, the researcher is concentrating on the functional safety that is handling risks arising from misuse of electronic devices, systems and equipments. EMC directives cover some basic functional safety norms to handle complex electronic equipments and programs in a systematic manner. As electronic technology has become widespread in today’s world, it is important to implement an electronic technology that is not only accurate but also reliable to the system. However, due to EMI, most of the electronic technologies may suffer from possibility of damage and inaccurate data reporting (Armstrong 2002). As the electromagnetic (EM) environment of a system also includes the electromagnetic disturbance in the operational area, it has been seen that this disturbance has increased manifold due to the use of data communication devices, wireless and power conversion equipments. Therefore, it is believed that the modern day equipments are likely to suffer more failures. It has been found that the EM disturbances is damaging and interfering with the transistors and integrated circuits (ICs) that are being used to develop electronic systems and products. This has also been complicated due to the decrease in the size of the features, increase in the operational speed and failure of the operating voltages. Such issues further make the electronic signals weak resulting into damaging the internal structure. Also, as software uses ICs and electronic signals, it is possible that the system might suffer from malfunctions or errors, which in turn would cause system failure (Mardiguian 2000). Many believe that most of the electronic hazards are covered through safety standards and therefore, extra attention towards EMC is not required. However, inadequate EMC may cause safety hazards as well and make the existing safety provisions look incomplete. Application of EMC design One of the major EMC problems that any electronic product or system faces is the emission of high frequencies generated internally which often interfere with the reception of a radio or other such equipments. This causes interfering with the external environment and thereby, producing lower quality analogue signals or corrupting the digital system. Therefore, EMC standards are used to specify the amount of input current, which should be in harmony with the surrounding environment (Brown & Radasky 2004). However, if these directives were used as an integral part while creating the product design, most of these requirements would be met easily. However, it has been seen that as these requirements are not considered to be of viable importance for the product, they are not incorporated in the design until the production stage. Integrating EMC principles at the later stage could be expensive as well as time consuming (Brown & Radasky 2004). Therefore, for this particular design, the researched has incorporated EMC principles at the designing stage itself. Cable coupling The cables are used as the major coupling connectors to join the product or the system with the environment. These cables are also well-organized transducers joined to the outside world through low frequency conduction and radiation. These radiations are especially found near the resonant frequencies. The cable often carries high frequency signals like video or data; however, common-mode noise inside the cable is much more a forceful interference. In case of digital circuits, this noise could develop in the 0V due to the functioning of other circuits such as a video clock (Mardiguian 2000). Therefore, one of the most important aspects of the EMC design is to create harmony between the cables and the unit through the method of filtering. However, in case the noise is found in the 0V circuit also, then the filtering would not be effective. Therefore, the noise in the circuit itself has to be controlled. Direct coupling Together with controlling the noise in the circuit, it is also imperative to control the internal circuits of the product’s interaction with the external system. Therefore, the internal structures such as the wiring, the various metal parts and even the chassis should be designed in such a manner that it does not catch any noise (Parker et al 2002). In order to control noise in the subsystem 1 of the computer room, especially the air conditioning and the thermal management system, the researcher used different engineering strategies. The researcher conducted the thermal analysis of the system and found that the major area of concern in the thermal management system is the heatsink. The researcher further analyzed how the heatsink contributes towards raising emission. Therefore, at the designing stage itself the researcher made a few adjustments keeping in mind the effect of the changes on EMC. For this EMC design, the researcher has taken special care of the heatsinks, because they create various EMC related problems on PCBs. The researcher attempted to find the effect of heatsink on digital device emissions like microprocessors. The figure below provides a view of the circuit complete with a heatsink, processor and 0V plane. Source: Williams 2010 In this model, the RF noise is created by the processor; while the voltages are in conjure to the 0V plane. Further the capacitively joined directly to the heatsink metal. The thermal contact between the heatsink and chip needs to be good, which can be seen at the production of C1 or increased coupling capacitance. The heatsink has increased capacitance towards its environment, especially the enclosure. This in turn would energise the enclosure with the current generated from the frequency of the clock. However, any fault in the enclosure would mean that the frequencies might radiate outside and create noise. Thus, for controlling this noise, the heatsink should be prevented from carrying increased levels of noise from the clock (Williams 2010). In order to create low frequency resonances according to the heatsink capacitance, the 0V connection inductance should be lower than 1nH. This means to make the system effective, several 0V contacts on the outside of the heatsink should be given. The model also emphasises the fact that the heatsink should not be connected with the enclosure, which would enable to lower the emission. Further, the system also took care of the air conditioning installed in the computer room. The air conditioning system, along with the thermal management system carefully monitors and maintains a correct working temperature for the IT equipment, and any sudden rise initiates a shut down after all data and current operations are completed, to avoid any loss. Therefore, it was also imperative to understand that the system needs to be electro-magnetically compatible which will provide it with an ability to resist electro-magnetic influence that too without losing any functional abilities. However, it was also taken care of that the electro-magnetic emissions did not cross the approved limit (Williams 2010). Research has found that air-conditioning of EMC-sealed enclosed spaces is important. It has been seen that enclosures often cause weakening in the integration of overall EMC. In order to solve this issue, the researcher used a protective screen with special dimensions that helped in installing an exhaust filter, and therefore, the electro-magnetic emissions were controlled in a proper manner. Grounding and PCB layout The sub system 2 consists of a suite of ICT equipments that is being powered through the same single-phase mains. These equipments are placed in close proximity and are connected through high quality screened cables. Most ICT equipments are possible emitters of electromagnetic wave. Further, the influence of air pressure, temperature and humidity also contributes towards EM emissions from ICT equipments. One of the major factors that give rise to emissions from ICT equipments is the pressure, temperature and humidity content near the earth’s surface. In case these equipments are placed near the ground, the amount of emission would also be more (Beck & Sroka 1999). Therefore, the researcher designed the system in such a manner that emissions from ICT equipments placed at the ground level could be managed easily. Ground is defined as a point or a plane that is used as a reference in a circuit or a system. However, in case of ground current flow, the currents would be very less because of electric fields or environmental magnetic fields. Therefore, it is important to place the ground connections carefully in order to reduce the noise voltages, which may get created in the ground impedances. However, in case of non-important circuits, it is not essential to remove the ground currents completely (Beck & Sroka 1999). In order to create this design, care was taken not to create any breaks in the plane beneath the critical tracks. This would help in decreasing the diversion of the return current flow as well the effective loop area. Further, these tracks should not put at the edge of the plane, as should below. Source: Williams 2010 Therefore, even before starting the design, it is important to find out the critical tracks by ranking them in terms of bandwidth, frequency and impedance. Further, these identified critical tracks need to be routed closely to the ground plane. This layer spacing needs to be thin to provide better ground plane (Williams 2010). Another approach that was used for this design was to use a single 0V plane for the entire circuit. This helps in avoiding the difficult method to decide the place where the circuit should get split. That apart, it is imperative to put the reference of interface ground as a part of the design, even when it is not shown on the functional circuit diagram. Filtering The researcher took special care for filtering in the design as it had direct correlation with the sub systems 3 and 4 of the computer room. These systems includes a UPS system and a software monitoring system which provide sufficient power to ensure all essential operations can be maintained whilst the system closes down safely if necessary or goes to standby. This UPS system must be monitored in order to enable it to react accordingly in response to a fault or power failure. The UPS works by converting DC into AC with the use of an inverter. However, during this process, the inverter produces electro-magnetic emissions and may create interferences with other devices (Sekh & Chawla 2002). The researcher used filters to suppress the amplitude of the voltage or current flow. These filters would help in preventing a frequency to enter into a circuit. Further, filters such as electronic filters can also filter current and voltage and eliminate unnecessary or excess flow of voltage into the circuit. It is also important to decouple unshielded I/O lines with the ground reference. The point where this decoupling needs to take place at the point where the lines leave or enter the enclosure. This would help in bypassing the currents and prevent in-flowing in the circuits from the cables (Parker et al 2002). In such cases chokes as well as RF filter capacitors are essential. These capacitors need to be placed at the ground level for minimising the inductance. Further, the chokes also need to be wound carefully and mounted for decreasing capacitance. Further, the filter should have good frequency performance and must be installed properly (Parker et al 2002). Use a conductive enclosure The unit should be put inside a screened box, especially for very noisy circuits or circuits that are susceptible to noise. However, this approach might not be effective in case other principals are not followed carefully. As interfaces are a kind of breach, it is essential to filter or screen it. A breach can also be formed in the ventilation or viewing openings or other discontinued spaces, which does not have any electrical contact like doors or seams. These breaches should be treated properly, and should only be given certain levy in case of low frequency screening (Brown & Radasky 2004). Further, the enclosure material does not have much importance and even plastics coated conductively may provide significant performance. In order to meet the EMC requirements without an enclosure screen, an appropriate interface control and PCB layout practice should be used. Challenges and recommendations Although, most of the above given design ideas would help in taking care of the EMC directives, there might be some gap areas which might endanger the security aspects of the system. However with the help of a few modifications in the engineering methods, these challenges can be taken care of easily. Ground impedance: It has been seen that ground impedance is generally being controlled by inductance at frequencies that are higher than kHz. Further, this inductance is majorly dependent on the length of the PCB wire or track (Beck & Sroka 1999). In order to circumvent this issue, one can use parallel ground tracks that would create the ground layout in the form of a grid structure. This would help in increasing the amount of paths the ground return current may take. Further, this would also reduce the ground inductance for the single route as well. Ground plane: A ground plane occurs when various parallel paths are given and also has continuous ground conductor. In case of PCB level, such planes are easily recognisable and provide low ground path inductance (Williams 2010). However, such a situation occurs only when the plane is not broken up by any other tracks. Therefore, it is important to understand that ground plane is used to provide low ground impedance of high-frequency and not to be used as a shield. Reducing ground inductance: The ground inductance needs to be reduced so that the self-generated ground noise can be minimised as well. Further, this will help in minimising the differential ground voltages that is being generated through the incoming interference (Williams 2010). However, one should also understand that ground inductance cannot be removed entirely. Thus, the interface grounds should be set in such a way that the interference currents would be redirected without any trouble away from the circuit through the cables. References: Armstrong, Keith 2001, ‘New Guidance on EMC-Related Functional Safety’, IEEE EMC International Symposium, Montreal, 13-17 August 2001 Proceedings, pp. 774-779. Armstrong, Keith 2002, ‘New Guidance on EMC and Safety for Machinery’, IEEE International EMC Symposium, Minneapolis, 19 - 23August 2002 Conference Proceedings, pp. 680-685. Beck, F and Sroka, J 1999, ‘EMC Performance of Drive Application Under Real Load Condition’, Schaffner EMV AG application note, 11th March 1999. Brown, Simon J and Radasky, Bill 2004, ‘Functional Safety and EMC’, presented at the IEC Advisory Committee on Safety (ACOS) Workshop VII, Frankfurt am Main, Germany, March 9-10 2004. IEE Guide to EMC and Functional Safety’, 2000, IEE, viewed on April 6, 2010, . Mardiguian, Michel 2000, ‘Combined Effects of Several, Simultaneous, EMI Couplings’, IEEE International Symposium on EMC, Washington D.C., 21-25 August 2000, pp. 181-184. Parker, W H, Tustin W and Masone, T 2002, ‘The Case for Combining EMC and Environmental Testing’, ITEM 2002, pp 54-60. Sekh, C. and K. Chawla 2002. ‘EMC evaluation & analysis of UPS, Proc. INCEMIC 2001-2002, pp: 37-42. Williams, Tim 2010, ‘Designing for EMC,’ Elmac Services. Read More