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Kurzfassung Zur Durchführung einer zustandsabhängigen Instandhaltungsstrategie an Straßenbahnen sind Informationen zum momentanen technischen Zustand von Antriebskomponenten essentiell. Im Rahmen eines aktuell laufenden Kooperationsprojektes wird gezeigt, wie die messtechnische Erfassung von schwingungsdiagnostischen Signalen mithilfe von Sensornetzwerken erfolgen kann. Auf Basis einer komplexen Vorgehensweise für eine automatisierte Entscheidungsfindung werden geeignete Parameter bestimmt und mit scharfen und unscharfen Methoden ausgewertet.

Although condition monitoring is very important for a reliable operation of tram powertrain components, conventional wired sensor systems do not manage to find wide acceptance because of installation and security costs. To address those issues, we propose a novel condition monitoring system based on a wireless and energy self-sufficient sensor network, where the individual sensor nodes harvest energy from vibrations, occurring while the tram is in motion. First, we performed an experimental investigation to identify the most important boundary conditions for the system design. Second, we designed individual sensor nodes using parameters derived from the previous investigation. Finally, the sensor network was deployed and tested on the tram gearboxes. The obtained measurement data were recorded at a sufficient sampling rate of 4.56 kHz and were successfully transferred from the tram gearbox to the network base station within a radius of 10 m inside the tram despite factors such as reflections, fading and electromagnetic compatibility. A piezoelectric vibration harvester is the power supply for the sensor nodes and it delivers up to 21.22 mW for relevant vibration frequency range between 10 Hz and 30 Hz, thus enabling deployment of autonomous sensor nodes.Designs 2018, 2, 50 2 of 13 tram monitoring are presented in [3][4][5][6]. The power supply and data transmission within the sensor network must be wireless. In contrast, multiple cable bundles can be torn easily because of moving components caused by spring and damper strokes. Multiple cable bundles also lead to considerably increased maintenance and motor supply cables can induce parasitic influences in the measurement cabling. Long measurement cables reduce the transferable frequency range for an analogue signal, which limits the ability to analyse high frequency vibration signals. Another obvious advantage of the wireless diagnostic technology is the "drag and drop" of many individual sensors reducing installation and maintenance costs.As wireless sensor nodes power supply, Vibration Energy Harvesting (VEH) appears to be a promising solution [7]. Unlike batteries, VEH can provide a continuous energy supply, while the batteries are temperature-dependent, which leads to non-deterministic battery end-of-life and premature replacement. As expected, the logistical effort to change batteries results in increased maintenance costs. The advantage of using VEH with respect to other types of harvesting (e.g., thermal [8] or solar [9] harvesting) is the permanent availability of unused tram vibration energy. An example of the use of thermal harvesting is given in [10]. This harvesting technology is unsuitable for use in summer because the temperature difference between heat source and environment is smaller than in the winter. It is also observed that the gearboxes are operated far below their design parameters and it is unrealistic to expect radiation of large amounts of heat. Another alternative application scenario is presented in [11]. In this setup, a single wheel s...

Trams are the most durable and resource efficient forms of public transportation. However, because of the varying wear in dependence on their operation mode and load levels, there is a need for condition monitoring and early maintenance. Vibration sensors provide interesting possibilities to monitor the relevant tram drive components. In this contribution we investigate their use under real conditions. On the basis of cable bound vibration measurements, the influence of the crossed track section, the tram speed and the tram condition is shown. Based on the investigation results, a concept is proposed in which a meshed and wireless sensor network, event-triggered, can acquire vibration measurement data, which are suitable for the diagnosis of tram drive components. The proposed concept has the potential to operate the sensor nodes in an energy efficient way through decentralized data evaluation taking place on the sensor node.

Usage of commercially available electrochemical gas sensors is currently limited by both the working range of the sensor with respect to temperature and humidity and the spikes in sensor response caused by sudden changes in temperature or humidity. Using a thermostatically controlled chamber, the sensor response of ammonia and hydrogen sulfide sensors was studied under extreme, rapidly changing levels of humidity with the aim of analyzing nebulized water samples. To protect the sensors from damage, the gas stream was alternated between a saturated gas stream from a Flow Blurring® nebulizer and a dry air stream. When switching between high and low humidity gas streams, the expected current spike was observed and mathematically described. Using this mathematical model, the signal response due to the change in humidity could be subtracted from the measured signal and the sensor response to the target molecule recorded. As the sensor response is determined by the model while the sensor is acclimatizing to the new humid conditions, a result is calculated faster than that by systems that rely on stable humidity. The use of the proposed mathematical model thus widens the scope of electrochemical gas sensors to include saturated gas streams, for example, from nebulized water samples, and gas streams with variable humidity.

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Wireless sensors enable fast and easy recording of measurement data -also known as plug and play. Currently a very big challenge is providing of a stable long range power supply. The use of energy harvesting provides an opportunity to supply wireless sensors and to improve the stability of the sensor networks. To estimate the lifetime of sensors (in a network) a simulation tool based on MATLAB/Simulink was developed. IndexTermsEnergy Harvesting, simulation, MATLAB/Simulink, Energy self-sufficient measurement, vibrations diagnostic I. WIRELESS SENSORS FOR VIBRATION DIAGNOSTIC IN TRAMSThe right time for replacement a bearing of a tram in the "Leipziger Verkehrsbetriebe LVB" (Leipzig Public Transportation Service) can be found out only after costly inspections. This can result in an outage of the rail car lasting over several days.In the research project "TRAINCON" the University of Applied Sciences Leipzig (HTWK Leipzig), in cooperation with other project partners, developed methodology for wear detection using wireless and energy self-sufficient sensors. This methodology is based on several wireless, temporary affixed sensor nodes in a sensor network to measure for material wear. The measured data will be automatically recorded and if necessary preprocessed and finally sent over a base station where the master display is located. In a later stage an analysis of the measurement data will be performed and the system state will be automatically computed by using different types of evaluation methods. That way we will make it possible to infer a suggestion for a maintenance task.The use of energy self-sufficient sensors enables the use of the environmental energy to satisfy as much as possible, their energy requirements. The appropriate number of measurements depends on the type and distance of the data transfer as well as the available quantity of useable and storable environmental energy. A. Sensor Systems in TramsTo enable wear detection over acoustic emissions (structure-borne sound) as characteristics it is necessary to use acceleration sensors with a sample rate of more than 10 kHz. Depending on the sampling time interval, it might result in a high number of measurements to be sent or to be preprocessed before sending (to be compressed). harvester transceiver energy management storage sensor acoustic emission μ-controller wireless sensornode environmental energy Fig. 1 Sensor systems on Trams (picture reference LVB)The sensors' requirements for deployment in a tram are as follows: -be wireless -highly reliable -high energy lifetime -small size B. Energy Self-sufficient MeasurementThe use of energy harvesting, with other word to harvest the unused one as minor product accrued energy, provides 613