Analog Dialogue 42-09, September \2008\ Maintaining Public Railways with Lower Cost and Improved Saf

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Specifications	Analog Dialogue 42-09, September \2008\ Maintaining Public Railways with Lower Cost and Improved Safety Analog Dialogue 42-09, September \2008\ Analog Devices, Inc.
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Analog Dialogue 42-09, September (2008) 1 Maintaining Public Railways with Lower Cost and Improved Safety By Anders Norlin Fr

Specifications	Analog Dialogue 42-09, September \2008\ Maintaining Public Railways with Lower Cost and Improved Safety Analog Dialogue 42-09, September \2008\ Analog Devices, Inc.
Outline	Maintaining Public Railways with Lower Cost and Improved Safety Railway Tracks-a View “Under the Hood” Rail Track Geometry Longitudinal Surface Profiles Cross Sections Measure the Rails Track Geometry Longitudinal Profiles Cross Profiles Older Technology-Metering Devices Blackfin Processor as the Heart of the System Measuring Machines Locate the Defects Smart, Powerful LabVIEW Filters Find Defects Pinpointing Defects on a Digital Map Distribute Results to Other Applications Solving the Problem
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Content	Analog Dialogue 42-09, September (2008) 1 Maintaining Public Railways with Lower Cost and Improved Safety By Anders Norlin Frederiksen and Marco Schmid A new, systematic maintenance approach now makes it possible to measure, locate, and fix rail- and tramway defects when they appear. Mature railway-engineering know-how and cutting edge technologies— including Blackfin® processors and graphical system design techniques— combine to improve and optimize public transportation. Over the last decade, public transport by rail or tram has become a popular means of transportation. The number of passengers seeking a comfortable and safe ride is constantly rising. The increased loads call for higher train speeds and shorter stop intervals, thus exposing rails and tramways to increased mechanical stress. This, in turn, causes unavoidable early wear and annoying or dangerous defects (Figure 1).1 Dealing with the results of these stresses on rails and tramways requires increased emphasis on monitoring and maintenance. Analog Devices Blackfin2 processors and National Instruments graphically programmable LabVIEW™3 technology can play a central role in rail inspection systems, acquiring accurate measurements of field data, and storing it for further action. This can result in longer operation lifetimes for rails, improving economy and reliability in the public transport service. LASER-BASEDRAIL PROFILEMEASUREMENT NETWORKEDRAIL ANALYSIS LOCATING DEFECTS CORRECTING DEFECTS Figure 1. A systematic rail maintenance concept includes measuring, locating, and fixing rail defects. Rail Tracks—a View “Under the Hood” When new rail- and tramways are laid out properly, quality assurance verifies correct track positions prior to concreting. Inevitably, as time passes after installation, defects may start to creep in during daily operation. These defects are caused by the stresses of mechanical contact between the wheels and the rails as part of a highly complex spring-mass model, with dynamics ranging from the train’s chassis and loading to the railway foundations. In Europe, the critical parameters and tolerance windows of the defects are classified according to railway engineering standards.4–16 The goal of rail maintenance programs is to discover and measure the irregularities—and keep them at acceptable levels. www.analog.com/analogdialogue Figure 2. Rail parameters are divided into track geometry, longitudinal profiles, and cross sections. Rail Track Geometry The track gauge, or distance between two rails, affects the side-to-side motion of the train. This motion keeps the spot where the wheel and rail meet constantly moving to minimize wear-out. Variation in the track inclination can make passing trains shake and shudder. Typically caused by yielding of the railway foundations, inclination defects can also be caused by surface irregularities such as corrugations and holes. Some systematic inclination profiles, such as banking, are necessary, however, to minimize passenger discomfort caused by acceleration forces when a train is riding into and out of a curve. The correct track-to-track spacing prevents any chance of collision when trains are passing one another at high speed. Longitudinal Surface Profiles Cracks and breakouts are among the most feared defects, since they can lead to catastrophes such as derailing. Corrugations— wavy irregularities with a characteristic wavelength from 20 mm to 100 mm—are annoyingly noisy when their amplitudes exceed 0.05 mm. With 0.3-mm peaks, on the other hand, the vibration can cause irreversible damage to the railway bed. Corrugations move along the rails, and science is still not clear on where they originate. Single holes are mostly generated by turning or jumping wheels and can be described mathematically with polynomials. They’re 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-meter railway sections. Cross Sections The head geometry of a newly installed rail follows an exactly calculated contact geometry, which optimizes the critical wheel-to-rail interface. The shape is described by tangential lines and specific radii, providing horizontal guidance to allow the wheel to roll off economically, smoothly, and safely (Figure 2).
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Analog Dialogue 42-09, September \2008\ Maintaining Public Railways with Lower Cost and Improved Safety Analog Dialogue 42-09, September \2008\ Analog Devices, Inc.

Analog Dialogue 42-09, September \2008\ Maintaining Public Railways with Lower Cost and Improved Safety Analog Dialogue 42-09, September \2008\ Analog Devices, Inc.