Rail transport

In automated train operation (ATO), sensor systems must be installed in the vehicles themselves. Depending on the degree of automation, the operation of trains is either supported or take over completely by the train controller. Due to the inertia of trains, intelligent sensor solutions for optimizing the braking curve and speed regulation are the basis for reliable automated train operation.

Rail vehicles (high-speed trains, regional trains, trams, metros and urban railways) are tested for bogie stability according to EN 13749. This standard defines the procedure to be applied for the design of bogie frames. Rail transport components such as the bogie, axles, brakes and wheel bearings are subjected to extreme loads and must therefore be very robust.

ASC sensors feature protection class IP67 and IP68, which makes them ideal for testing bogie stability in different environmental conditions: cold, heat, humidity and dust. The models of the ASC OS series feature a hermetically sealed stainless steel housing so they can withstand the harshest ambient conditions. They are available in uniaxial, biaxial and triaxial versions, and in two technology variants: Low Noise (LN) and Medium Frequency (MF).

The exact localization of trains is extremely important for safety in rail transport. It is used for example for the release and occupation of track sections. In general, the location of trains is determined by means of the global navigation satellite system (GNSS), the special railway mobile communications system GSM-R and the train controls installed in the railway network. However, nearby UMTS/LTE signals can cause interference in the GSM-R network, and GNSS is not available everywhere – for example in tunnels – and therefore has to be bridged temporarily.

The gyroscopes ASC 281 (uniaxial) and ASC 283 (triaxial) are ideal for this application, because they feature high bias stability of <0.1 °/h and low angular random walk of <0.01 °/√h. In addition, inertial measurement units (IMUs) from ASC continuously detect the position and motion of trains with high precision. The ASC IMU 8 is the ideal solution for high-precision position measurement. ASC IMUs allow maximum freedom in the processing of data and a modular concept for optimal application-specific configuration.

Digitization of the railway enables entirely new fields of application in infrastructure monitoring on the basis of intelligent sensor solutions. Building information modelling (BIM), for example, will make digital twins of buildings, railway networks and other peripherals available. This will make it possible to provide immediate information about the current condition of the infrastructure and to derive insights for early identification of the future need for action and planning of maintenance tasks.

Characterization of the track geometry according to EN 13848 is part of the continuous track monitoring (CTM) process. Errors in the longitudinal height of the superstructure are detected by measuring the vertical acceleration in trains. This is a task for the IEPE accelerometer ASC P401A15 which has a wide frequency response range from 0.5 Hz to 15 kHz and a measurement range of ±50 g, ±100 g or ±500 g. Its excellent impact resistance of up to 5,000 g is mandatory for the high impact loads in rail transport.

Continuous condition monitoring also includes measurement of the track geometry in curves. Ideal for this task is the compact uniaxial gyroscope ASC 271, which features excellent bias stability and low g-sensitivity. Sensors from ASC play a key role in reducing speed restrictions and train delays.

Digitization in rail vehicles requires ever smarter and more compact sensor solutions. Smart sensors from ASC provide the answer to these challenges: They not only use A/D converters and filters to pre-process the measurement data, but can also analyze the pre-processed data using the integrated computer technology. The wireless transmission of signals by smart sensors also eliminates costly and time-consuming wiring. Especially in the case of complex monitoring applications with numerous degrees of freedom and parallel measurements, this significantly reduces the necessary peripheral devices.

In addition, the sensors can easily be integrated in networks or clouds. This means that continuous track monitoring not only identifies the actual condition of vehicles and infrastructure. Self-learning algorithms, for example, make it possible to predict the further progress of deviations in the track geometry. This serves as the basis for defining threshold values at which maintenance becomes necessary.

The success of predictive maintenance mainly depends on the sensor systems that are used. Their quality is decisive for the cost effectiveness and operational quality of the particular application.

The EN 12299 standard defines methods for analyzing the effects of train motions on passenger ride comfort. Human perception of mechanical vibrations varies greatly depending on their direction, frequency and amplitude. Inconveniences to passengers, however, occur primarily below 10 Hz, so that precise measurement of minimal linear motions and low-frequency vibrations and impacts is essential for analyzing ride comfort.

The uniaxial capacitive accelerometers ASC 4311LN and ASC 4411LN with low frequency and measurement ranges and a high signal-to-noise ratio are ideal for ride comfort measurements. They are very important for creating a pleasant train travel experience.

To test the operational stability of vehicle components, trains travel thousands of kilometers under harsh conditions, in which it is not uncommon for wheel sets and the bogie to be subjected to impacts of up to 400 g. Since high mechanical forces are also exerted on the sensors, they must be extremely robust and reliable, and designed for long-term stability.

Capacitive accelerometers from ASC are therefore ideal for operational stability tests of rail vehicles. The triaxial sensor ASC 5525MF in the version with a stainless steel housing features a wide frequency response range from 0 Hz to 7 kHz and outstanding impact resistance up to 6,000 g.

The piezoelectric accelerometers ASC P311A15 (side-connector) and ASC P311A25 (top-connector) are likewise ideal for operational stability tests in rail transport. They are based on the compression principle, which makes them ideal for applications with ongoing loads, such as high-amplitude vibrations or impacts. Operational stability tests enable early identification of potential weak points in trains and are crucial for the safety and reliability of rail vehicles.

The capacitive accelerometers ASC 5525MF and ASC 4425MF are often used in running dynamics tests according to EN 14363. The goal of these tests is quantification of the vehicle behavior under representative operating and infrastructure conditions. Precise measurements of low- to medium-frequency dynamic accelerations and analysis of vehicle behavior in curves are the basis for calculating derailment prevention.

More complex systems based for example on an inertial measurement unit (IMU) will play a key role in monitoring the vehicle dynamics of trains in the future. This requires reliable and compact sensors such as the ASC IMU 7. It features maximum freedom in the processing of data and a modular concept that allows application-specific configuration.

Optimization of the route capacities and increasing rail traffic volumes in the future will necessitate measures for fast response in the event of faults in trains. Analysis of vehicle dynamics, however, is not only used for assessing the actual condition of vehicles: intelligent sensor solutions also allow the early detection of future material weaknesses. They make it possible to initiate corrective actions before costly damage occurs. Information on vehicle dynamics is transmitted in real time and is available in the digital twin at all times. Such systems are based on high-performance sensor solutions from ASC and self-learning intelligent algorithms for post-processing of the motion data.

Analog inertial measurement units (IMUs) from ASC continuously detect the position and motion of objects with high precision.  The analog ASC IMU 8 features outstanding bias stability and angular random walk leading to tactical grade performance. The low noise and excellent long-term stability ensure reliable measurement of position changes in all 6 degrees of freedom.

Conventional continuous track monitoring (CTM) consists of performing test runs, analyzing the results at regular intervals and initiating maintenance tasks. Intelligent sensor solutions from ASC are used in the ongoing development of these CTM systems. They allow analysis of track geometry data in the sensor system itself, making data available at all times in a decentralized system. CTM is an essential part of smart maintenance, since it allows early identification of the need for action, therefore reducing maintenance costs.

The success of smart maintenance mainly depends on the sensor systems that are used. Their quality is decisive for the cost effectiveness and operational quality of the particular application.