EETimes India - November 16, 2008 - (Page 4)

In Focus | Data acquisition Embedded system eases rail maintenance By Anders Norlin Frederiksen Worldwide Industrial Marketing Manager Analog Devices, Inc. Marco Schmid Senior Engineer Schmid Elektronik Engineering AG The increase in the number of passengers taking public transport by rail calls for higher train speeds and shorter stop intervals, subjecting the railways to extreme mechanical stress. Defects, which are not only annoying but also dangerous, unavoidably start appearing. A new and systematic maintenance solution aims to address these defects, and support the monitoring and maintenance of rail- and tramways. Analog Devices’ Blackfin processors and National Instruments LabVIEW software are used to secure all measurement and field data and store it for immediate action. Under the hood When new rail- and tramways are laid out, high quality assurance verifies correct track positions prior to concreting. Once in operation, though, several defects start to appear in the rail parameters (figure 1). This is due to the mechanical contact between the wheels and the rails in relation with a highly complex dynamic springmass model ranging from the train chassis to the railway underground. The defects, their critical parameters and tolerance windows are classified by railway engineering standards: Rail track geometry—The track gauge is the distance between two rails and responsible for the so-called “sinusoidal ride” of the train. This keeps the spot where the wheel and rail meet, constantly moving to minimise wear-out. Variances in the track inclination can make passing trains shake and shudder. Mostly caused by the giving way of the railway underground, inclination defects can also be kicked off by surface irregularities such as corrugations and holes. Systematic inclination profiles are however necessary to minimise accelerating forces to the passengers when a train is riding in and out of a curve. A correct track-to-track distance prevents any chance of collision when trains are crossing at high speed. Longitudinal surface profiles— Cracks and breakouts are among the most feared since they can lead to catastrophes such as derailing. Corrugations on the other hand are wavy irregularities with a characteristic wavelength between 20 to 100 mm and are annoyingly noisy when their amplitudes exceed 0.05 mm. From 0.3 mm peaks, however, the vibration can leave irreversible damage to the railway bed. It is also in their nature to move along the rails, and scientists still debate where they originate. Single holes are mostly generated by turning or jumping wheels and follow the mathematical equation of a polynomial. They are responsible for the sudden bumps on a tramway ride. Regular bumps that are often experienced on older railways are due to the welding interfaces of the 18-m railway sections. Cross sections—The head geometry of a newly installed rail follows an exactly calculated contact geometry, which optimises the critical wheel-to-rail interface. The shape consists of tangential lines and specific radii allowing the wheel to roll off efficiently and smoothly with a safe horizontal guide. Figure 1: Rail parameters are divided into track geometry, longitudinal profiles and cross-sections. Figure 2: GPS data is used to pinpoint measurements in Geographic Information Systems (GIS). Rail measurement The key requirement for systematic and target-oriented rail maintenance is a comprehensive knowledge of the current state of the rail- or tramway network’s geometry. This is achieved using a smart measurement strategy that combines odometer results (distance measuring), track geometry, longitudinal profiles, and cross sections with exact GPS locations. All these parameters are acquired by mobile metering devices or complete measuring vehicles. Initiated and pre-processed by embedded processors, the measurement data is transferred into high-level analysis software that allows post-analysis of the measurements and identification of defects on a digital map (figure 2). Track geometry—The rail gauge is measured using no contact inductive sensor principles with accuracies in the 0.01 mm range. Software-based FIR low-pass filters suppress high-frequency noise while subsequent moving average filters ensure that no “pseudo-peaks” are occurring in a result that is expected to be continuous. A similar approach is applied to the inclination sensor that operates like an electronic waterlevel with an angular range of ±10° and an accuracy of < 0.025°. Due to the physical principle, results are only valid in a certain frequency range, typically below 1Hz. Measuring the track-to-track distance requires a set of complex and computational demanding floating-point algorithms to finally deliver the relatively simple result of the absolute horizontal and vertical distance. A highprecision laser beam which is continued on page 4 EE Times-India | November 16-30, 2008 | www.eetindia.com http://www.embeddeddesignindia.co.in/SEARCH/SUMMARY/technical-articles/embedded processor.HTM?ClickFromNewsletter_081116 http://www.eetindia.com/STATIC/REDIRECT/Newsletter_081116_EETI02.htm?ClickFromNewsletter_081116

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EETimes India - November 16, 2008 Contents Farnell Embedded System Eases Rail Maintenance National Semiconductor Working With IT for Networked DAQ Digital Telemetry Advances Torque Measurement Events

EETimes India - November 16, 2008

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