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RAIL INDUSTRY FOCUS


of supply following a unit failure? Beyond this, how will the system receive and send data and, in turn, is the same means available for response and control? Is there an ‘industry standard’ cabling structure involved? Can wireless or infrared be used for a remote connection to whatever is being controlled, or are fibre-optic links present? Copper connections will require


GETTING ENCLOSURE SPECIFICATION ON TRACK


When specifying enclosures for rail industry applications, there are many points to consider – ranging from the nature of the application, environmental factors and IP ratings, to power requirements and accessibility, as Rittal explains


The nature of the application will naturally have an effect on the enclosure selection and relevance, as will the environment in which it is to be used


T


here are a wide choice of enclosures available for rail engineers and IT


managers. As instrumentation comes in a plethora of forms, it therefore follows that the enclosures used to house them need to be just as varied. As a result, the enclosures range


from weatherproof outdoor cabinets with various internal fittings to suit the


“Placing critical electronics next to a busy railway line requires particular care. Not only may they be more prone to external damage, vandalism or graffiti, but there will be changes in external temperature”


equipment and application, through custom and proprietary desktop and portable cases, to relatively simple plastic and metal boxes, frequently customised to fit the application.


THINK ABOUT THE APPLICATION The nature of the application will naturally have an effect on the product selection and relevance, as will the environment in which it is to be used. Whether static or mobile, the enclosure may need to withstand shock, vibration, moisture and/or dust ingress. Placing critical electronics next to a busy


railway line or road requires particular care. Not only may they be more prone to external damage, vandalism or graffiti,


but there will be changes in external temperature, as well as environmental conditions such as wind, rain, ice and snow to face. The enclosure may also need to be ergonomically designed for easy user access, and EMC will almost certainly be an issue.


OUTDOOR ENCLOSURES VS IP RATINGS There is, however, one major misconception which we want to address here – the interpretation of IP ratings in these situations. IP ratings provide an indication of the performance of an enclosure in preventing dust and water from entering, under varying conditions and over a limited time period. We therefore recommend using an


enclosure specifically designed for outdoor use rather than just ‘the highest IP rating’. This is because the seals, which will withstand limited exposure to a hose, may not be designed to withstand freezing in winter, or days of non-stop rain. Furthermore, the solar gain effect can


be greatly reduced by using a double- skinned design, lowering cooling bills in the long term.


POWER REQUIREMENTS There is also a need to consider the power requirements. How will the power be supplied and distributed? Does the PSU need to be plug-in for easy exchange? Or even N+1 redundant to ensure continuity





different space and handling, both up to and inside the enclosure, while wireless/infrared options may need additional circuitry (with accompanying space), as well as suitable sites for antennae or target windows. Cooling creates more potential


enclosure problems. If there is a need to keep dirt, moisture and EMC out, how can cooling air get both in and out of the enclosure? As processing power and system power increases, so does the need to remove the heat generated.


ACCESSIBILITY AND SERVICE Accessibility and service or exchange are important issues over the lifetime of the instrumentation because even a simple box becomes problematic when it takes a disproportionate amount of time to access a compartment. In a 482.6mm (19”) environment,


the cabinet may include a lockable door while, inside, the subracks have easily exchanged ‘Hot-Swap’ circuit boards, power supplies and fan systems. These are partly enabled by utilising the subrack rear for Input/Output cabling, to leave the front clear for service exchange.


HIGH RELIABILITY SYSTEMS Reliability depends not only on the quality of the components and the design, but also whether the equipment is maintained within its design parameters, particularly temperature. Correctly cooled systems generally increase the MTBF (Mean Time Between Failures) of critical components. Conversely, we know that inadequate dust filters can become congested quickly, preventing proper airflow from cooling the system. Proper consideration of the


environment the electronics will normally operate under will ensure mechanical, EMC, dust and liquid protection is provided, reducing the risk of external factors damaging the electronics inside. Future upgrades and how they will be


achieved may also need to be considered at the outset of the project, both from an accessibility and space perspective. Is the system designed to be modular and will a simple replacement, or addition of one part, facilitate expected future expansion?


Rittal www.rittal.co.uk


DESIGN SOLUTIONS | OCTOBER 2018 25


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