Time-synchronous sampling in wireless sensor networks

Peer Reviewe

Synchrone Datenerfassung mit drahtlosen Sensornetzwerken

Published in print by Universitätsverlag der TU Berlin, ISBN 978-3-7983-2980-5 (ISSN 2509-8950)Wireless sensor networks (WSN) are predicted to play a key role in future technological developments like the internet of things. Already they are beginning to be used in many applications not only in the scientific and industrial domains. One of the biggest challenges, when using WSN, is to fuse and evaluate data from different sensor nodes. Synchronizing the data acquisition of the nodes is a key enabling factor for this. So far research has been focused on synchronizing the clocks of the nodes, largely neglecting the implications for the actual measurement results. This thesis investigates the relation between synchronization accuracy and quality of measurement results. Two different classes of time synchronous data acquisition are investigated: event detection and waveform sampling. A model is developed that describes a WSN as a generic multi-channel data acquisition system, thus enabling direct comparison to other existing systems. With the help of this model it is shown, that synchronization accuracy should best be expressed as uncertainty of the acquired timing information. This way, not only the contribution of the synchronization to the overall measurement uncertainty can be assessed, but also the synchronization accuracy required for an application can be estimated. The insights from the uncertainty analysis are used to develop two distinct approaches to synchronous data acquisition: a proactive and a reactive one. It is shown that the reactive approach can also be used to efficiently implement synchronous angular sampling, i.e. data acquisition synchronous to the rotation of a machine's shaft. Furthermore, testing methods are suggested, that evaluate the synchronized data acquisition of an existing WSN as a whole. These methods can be applied to other data acquisition systems without changes, thus enabling direct comparisons. The practical realization of a WSN is described, on which the developed data acquisition methods have been implemented. All implementations were thoroughly tested in experiments, using the suggested testing methods. This way it was revealed, that a system's interrupt handling procedures may have a strong influence on the data acquisition. Furthermore, it was shown that the effective use of fixed-point arithmetic enables synchronous angular sampling in real-time during a streaming measurement. Finally, two application examples are used to illustrate the utility of the implemented data acquisition: the acoustic localization of two sensor nodes on a straight line and a simple order tracking at an induction motor test bench.Diese Dissertation untersucht die Zusammenhänge zwischen Synchronisationsgenauigkeit und Qualität der Messergebnisse. Zwei Klassen von zeitsynchroner Datenerfassung werden dabei betrachtet: die Detektion von Ereignissen und die Aufnahme von Kurvenformen. Es wird ein Modell entwickelt, welches ein WSN als ein allgemeines mehrkanaliges Datenerfassungssystem beschreibt. Dies ermöglicht den direkten Vergleich zwischen WSN und anderen Messsystemen. Weiter wird mit Hilfe des Modells gezeigt, dass die Synchronisationsgenauigkeit vorzugsweise als Unsicherheit der Zeitinformation angegeben werden sollte. Hierdurch kann nicht nur der Beitrag der Synchronisation zur gesamten Messunsicherheit bestimmt sondern auch die von einer Anwendung tatsächlich benötigte Synchronisationsgenauigkeit abgeschätzt werden. Ausgehend von den durch die Unsicherheitsbetrachtung gewonnenen Erkenntnissen werden ein proaktiver und ein reaktiver Ansatz zur synchronen Datenaufnahme entwickelt. Mit dem reaktiven Ansatz können Messdaten auch effizient drehwinkelsynchron, d. h. synchron zur Drehbewegung einer Maschinenwelle, aufgenommen werden. Es werden Testverfahren vorgeschlagen, mit denen sich die Synchronizität der Datenerfassung für ein WSN als Ganzes überprüfen lässt. Diese Verfahren lassen sich unverändert auf andere Messsysteme anwenden und ermöglichen somit direkte Vergleiche. Es wird die praktische Umsetzung eines WSN beschrieben, auf dem die entwickelten Methoden zur Datenerfassung implementiert wurden. Alle Implementierungen wurden mit den vorgeschlagenen Testverfahren untersucht. Hierdurch konnte gezeigt werden, dass die Interrupt-Bearbeitung der Sensorknoten entscheidenden Einfluss auf die Messdatenerfassung hat. Weiter konnte durch den Einsatz von Fixed-Punkt-Arithmetik die drehwinkelsynchrone Datenerfassung in Echtzeit realisiert werden. Schließlich wird die Nützlichkeit der implementierten Datenerfassung an zwei Anwendungen gezeigt: der akustischen Ortung zweier Sensorknoten sowie einer einfachen Ordnungsanalyse

Time-synchronous sampling in wireless sensor networks

Peer Reviewe

Time-synchronous sampling in wireless sensor networks

Peer Reviewe

Landscapes of Remembrance: Home and Memory in the Nineteenth-Century Bürgertum

This article examines the ways in which the nineteenth-century German middle class turned their homes into sites of family memory as part of a vibrant vernacular memory. The highly segmented organization of middle-class homes contributed to and grew out of this memory culture. The divisions of domestic space ascribed heightened meaning to particular zones, especially festive spaces like the “Christmas room.” Families filled domestic spaces with memory, putting family portraits and heirlooms on prominent display in the home. Middle-class Germans also filled the pages of personal memoirs with recollections of their childhood homes that almost always portrayed an idyllic environment. Ultimately, this article argues that family memory offers a window into the emotional universe of the nineteenth-century bourgeoisie and that the sanitizing narratives of family memory were used to impart a sense of stability and control

An open-source advanced maskless synthesizer for light-directed chemical synthesis of large nucleic acid libraries and microarrays

Large- to ultra-large-scale synthesis of nucleic acids is becoming an increasingly important tool for understanding and manipulating biological systems, as well as for developing new technologies based on engineered biological materials, including DNA-based nanofabrication, aptamers and writing digital data at the molecular level. Several technologies for large-scale synthesis have been developed over the years, but all of them remain inaccessible to most researchers due to their complexity and/or use of proprietary technologies. Here, we present a fully open source, benchtop device for ultra-large scale nucleic acid synthesis that is also highly flexible and adaptable, able to accommodate a wide range of monomers and chemistries, while providing unrestricted access to synthesis parameter space