Feature System design
Taking a modular approach to system design
Depending on the area of application, embedded systems are subject to highly varied requirements in terms of mechanical stability such as shock and vibration resistance, IP and EMC protection and cooling. Christian Ganninger and David Martin of Pentair – Schroff, explore how, by using a modular approach to system design, new possibilities for fulfilling these different requirements can be identified
n such applications as rail and traffic systems, defence systems or use near rotating machines, embed- ded systems will need to withstand relatively high levels of shock and vibration resistance. However, the selection of a suitable Schroff system platform, plus off-the-shelf compo- nents, will enable standard systems to be created with shock and vibration resistance levels from two to 40g. Individual configuration of the mechanical system is also possible using Schroff 19in subracks, with side panels of various thicknesses (screw- fixed or tox-cold welded), 19in brackets and corner profiles and various versions of horizontal rails. Selecting from either a lightweight horizontal rail with single- point fixing, a heavy rail with two-point fixing or a version with three-point fixing, enables the system design to meet a wide range of shock resistance requirements, from relatively low up to 25g. This discrete solution is usually sufficient for mobile applications, some low impact defence systems and other similar environments.
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A modular enclosure platform Where higher levels of robustness are called for, the Titan system platform is used. This comprises aluminum components (base, top cover, side, front and rear elements) bolted together. A hole grid in the side com- ponents, top cover and base allows other optional parts such as mounting brackets to be attached. The front and rear elements are symmetrically designed and have identical hole posi- tions and bolt-on dimensions, where various cut-outs can be integrated for sockets or switches, for example. The guides for the PCBs are milled into the base and top cover of the case. The Titan modular enclosure platform is designed for shock and vibration levels of up to 40g, although it
is not suitable for non-military applica- tions. Designed specifically for defence systems, Pentair offers the Titan ATR system, which also achieves shock and vibration resistance values of 40g. These system platforms can also be equipped with high IP and EMC protec- tion. The cooling of the components is achieved with conduction cooling. There is also a mechanical system that combines these two platforms: 19in subracks with high IP and EMC protection plus conduction cooling. Such a system, which is constructed using off-the-shelf components, can be used in the laboratory for testing conduction-cooled boards. Once the technology or application is tested in the lab, the same components can then be built into a Titan ATR system.
IP and EMC protection
By their very nature, standard subracks do not offer high levels of IP or EMC protection since they are very open. Protection of the installed system components is generally achieved by fitting the subrack into a cabinet with appropriate EMC gaskets at the front. If the system itself has to achieve a high level of EMC protection, it must be completely encased. The Titan and Titan ATR system both meet this EMC requirement and can be specified with either a pure IP gasket or a com- bined IP and EMC gasket.
Cooling requirements In most cases the cooling requirement and the type of cooling are selected on the basis of two criteria: the level of dissipation loss and the location of the installation. If the boundary conditions are met, air cooling by convection or forced air cooling is the preferred choice and, in terms of cost, offers the best value.
Enclosure & Safety Solutions SUMMER 2013 Above:
Individually configured subrack-based system
Completely closed Titan ATR system: high shock and vibration
resistance, high IP and EMC protection and high heat dissipation capacity
Should such cooling methods be insufficient, conduction cooling and water cooling come into play at either cabinet or system level. This may be the case, for example, in a laboratory, if the system is to achieve a very high level of IP or EMC protection, which precludes effective air cooling. In this type of system, the plug-in boards are conduc- tion cooled in one area and the heat then extracted by fans on the side of the system, while the standard system boards are cooled by the fans only. The Titan ATR system, however, offers a more effective method using a combination of conduction and air cooling. Heat is drawn from the PCBs via a simple board frame or a closed frame (clamshell) to the surface of the case, fitted with cooling fins. A sheet metal cover is placed over the heat sinks and a fan with suction chamber is fitted at the rear of the case – the pres- ence of the cover creates an air channel. The internal fan blows the air through the heatsinks and out of the system. When high level IP protection is not required but protection against direct contact is necessary at board level, a fur- ther cooling solution is available. Here the boards are enclosed, in a clamshell for example, that has suitable air open- ings at the top and bottom. Air is then forced through these air channels and the heat drawn away from the boards. Another option is to use liquid cooling of hotspots on the boards combined with forced air cooling.
Bus technologies and PSUs
For a complete system, easily modifiable standard back- planes are available for various bus technologies, including VME, VPX, VXS, CompactPCI, CompactPCI Plus
IO and
CompactPCI Serial, as well as a range of standard power supply units (PSUs). As a holistic solution, Pentair can configure the complete system to meet the demands set by the appli- cation environment.
Schroff UK
www.schroff.co.uk
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