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Smart Wireless Sensor Networks

Principle System Layout

Wire-based measurement systems for SHM consist of several sensors applied to the structure at relevant location. Sensors are available for a plethora of physical quantities, and have to be chosen according to the application demands. The sensor readings are analogue-digital converted in a central unit, where the digital data is also stored. Many systems allow online-retrieval of recorded data (compare Figure 1, left side).

In contrast to these aforementioned systems, wireless systems have no central data acquisition unit but one or several sensors are connected to a (usually) small data acquisition unit, which is called a measurement node. The complete measurement system consists of several independent nodes, linked to each other by a radio communication link, hence building a wireless sensor network. Additional elements of the system are the gateway, which relays the measurement data to a long-distance network for remote access, and a database for save data storage for later retrieval and optional post-processing. The WSN is operated remotely from an operation and maintenance terminal (O&M). See Figure 1, right side, for a general layout of a WSN.

Figure 2 gives a more detailed view on the general system layout. The autonomous wireless sensor nodes are depicted deployed on a building, sending their information via Smartswitches, if necessary, to a mandatory base station, called Smartgate. The Smartgate includes a wide area mobile connection, used for controlling the system and for sending data to central database and web server (Smartserver) within the operator's premises. The customer can access the information via a web access.

Figure 1: Wired SHM schematic with central measurement unit where individual sensors are connected to, versus the proposed wireless SHM with autonomous sensor nodes relaying measured data via a short-range transmission and (optionally) long-range mobile networks

Figure 2: General system layout

Principal structure of the SHM system software

To operate the WSN, a complex but flexible architecture of software components has been coded, which interact to form the WSN. To each of the hardware components, as described in chapter 6, belongs a software component that operates this component. A block diagram of the software system is shown in Figure 3. The measurement nodes ("Smartmotes") are the core of the system. The Smartmotes run two components: the sensor node boot loader ("wboot") and the sensor node application software, called "miranda". The Smartswitch is an optional system unit, which is not necessary for small-scaled deployments. The software component "uranus", running on the Smartswitch, is therefore postponed.

The Smartgate is the central node in the WSN and offers base station functionality. It is composed of the "starcatcher" application, which receives the radio messages from all the Smartmotes and forwards them to the "jupiter" application. "starcatcher" can be seen as the radio interface component of the "jupiter" application. "jupiter" itself, is a component that manages the WSN. Command messages can be injected into the network and also data can be displayed. The "callisto" application is optional and is used for on-site-interaction with the object.

Figure 3: Principle sketch of the SHM system software components including name conventions.

The Smartserver is a hardware unit which is detached from the rest of the WSN. A software component called "mars" receives the data from the WSN and inserts the data into a database ("galaxy"). The VI-Server, running National Instruments LabVIEW, handles the requests for online visualization of the data. The requests to these visualization tools originate from a webserver, which is not shown in this sketch. The application builder software ("planemos") handles the update process of the sensor nodes with "miranda" applications.

Created by: admin. Last Modification: Monday 13 of February, 2012 13:56:42 CET by admin.