Enclosures
Outdoor railway trackside cabinets for electronic systems
By Alan Vincent, sales director, Foremost Electronics F
or railway systems, absolute safety and reliability are of utmost importance as failure in sensitive equipment can have catastrophic consequences. This level of safety must also be provided by electronic cabinets installed outdoors trackside, at train stations, signal boxes, or at level crossings. These cabinets protect electronic systems for trackside and signalling applications, radio-based train control systems, and the measurement and evaluation electronics of safety systems on high-speed railway lines, such as axle counters or temperature detection on the train wheels. Today, more and more electronics can also be found on the platform including passenger information systems and comprehensive video surveillance providing information and security. This article explains the most important features required by outdoor cabinets for rail applications, whether trackside, at stations, or in signal boxes.
Requirements and challenges Trains traveling at speeds of up to 300 km/h can cause high wind speeds and vibrations. In addition, outdoor cabinets are exposed to a wide variety of environmental influences such as heat, cold, humidity, dust, and vandalism. Compliance to international standards regarding mechanical stability, special railway standards and certifications must also be observed such as shock, vibration, and EMC protection. Relevant certifications and standards to be met include: n EN 50125-3 For protection against shock and vibration (1-3 m distance from the track) and wind resistance up to 180 km/h. Specially designed for railway applications and describes the environmental requirements for signalling and telecommunications equipment. These conditions include pressure, temperature, wind, rain, hail, and vibrations and shock events.
n IEC 61969-3 (EN 1627 and EN 1630) RC2 (old WK2) for protection against vandalism which defines various resistance classes (RC) in terms of burglary resistance. The individual
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resistance classes indicate how long a product can withstand the break-in attempt of a perpetrator. A higher class means stronger intrusion protection. EN 1630 describes the corresponding test procedures.
n EN 50121 For electromagnetic compatibility, it specifies limit values and measurement procedures for the interference emission and immunity of electrical and electronic equipment intended for use in railway applications. The specifications are defined for the frequency range of 0 to 400 GHz.
A modular design of outdoor cabinet offers a flexible solution that ensures smooth and reliable operation of sensitive electronics in outdoor locations. While offering a convenient way to supply a bespoke solution it also provides the ability to be reconfigured if system requirements change. Specially designed, tested, and certified to meet the various requirements for trackside outdoor railway applications, the characteristics and properties of an outdoor cabinet also have a significant impact on the total cost
Components in Electronics
of ownership. These not only include the acquisition costs, but also the long-term energy, repair, and maintenance costs. The better the cabinet protects the application, the lower the TCO can be kept over the entire life cycle of the application. The main focus here is primarily on ensuring a specified operating temperature range so that the electronics remain functional and reliable over a long period of time, allowing maintenance and repair costs to be reduced.
Outdoor modular cabinets add value by significantly reducing total cost of ownership, operational costs, improving safety, and increasing reliability and service life.
Optimal thermal performance The issue of cooling is of prime importance when installed outdoors. Not only must the power loss of the installed components be dissipated, but daily or seasonal outside temperatures must also be considered. The thermal output of the cabinet must ensure an operating temperature appropriate to the electronics from -40°C to +60°C in an ambient temperature of -40°C to +80°C.
Not only does the specified operating temperature of the electronics and the heating caused by solar radiation play a role here, but so does the heat generated by the internal electronics. Ensuring an operating temperature specified by the manufacturer for the internal electronics ensures reliable operation, and extends the service life and operating life of the application. Depending on the framework conditions, the exact cooling requirement needs to be determined. Natural or free convection as a heat dissipation solution meets its limits when handling large amounts of heat. This is because the amount of dissipated heat (energy) has a linear relationship with the temperature difference between the inside and outside. Q = k • A • (TInside – TEnvironment) Increasing the heat transfer coefficient k can help here, but this requires switching over to the forced type of convection cooling. Depending on the requirements, additional cooling components such as air-filtered fans or an air-conditioning cooling unit are now installed to achieve the optimal operating temperature. To ensure an optimal operating
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