Vibrations measurement using wireless sensor network

Abstract

Laboratory prototype of a wireless sensor network (WSN) for vibrations measurements on buildings was developed. The system is comprised of sensor devices (nodes) each having main processor board, accelerometer board, batteries, radio modem, and optionally a liquid crystal display. Personal computer (PC) acts as a base station of the system. Sensor devices (nodes) are powered by rechargeable batteries. Each node spends most of its time in a sleep mode (low power consumption). They are awakened and synchronized by beacon signal from the base station, and then they perform measurements simultaneously during the predefined time interval, compress the data on spot, and send it to the base station for modal or other analysis. Embedded RTOS is specifically developed for this purpose, and allows different modes of operation, with large number of parameters, by varying which the results can be optimized for different applications. Star network topology is used, since accurate time stamping is critical for modal analysis application which is primary objective of this WSN. A number of presented measures have been taken to ensure synchronicity of results such as processors calibration using high precision frequency counter and testing of deviation of radio beacon signal detection time. Accelerometers have been tested for cross-axial sensitivity. Radio modems range (probability of packet transfer) has been tested in urban environment (strong interference) and coding of transmitted signals was applied in order to improve transfer efficiency. .

Nedestruktivno praćenje stanja građevinskih objekata se bazira na merenju vibracija objekata pri dinamičkim ispitivanjima ili u toku njihove eksploatacije. U ovu svrhu se sve više koriste mreže bežičnih senzora koje čine fleksibilan i jeftin merni sistem, jer nema razvlačenja kablova velikih dužina za povezivanje senzora. U ovom radu je opisan sistem za bežično merenje vibracija na objektima razvijen na Građevinskom fakultetu u Beogradu. Predstavljeni su struktura i karakteristike mernog sistema baziranog na elektronskim komponentama male potrošnje i originalnom softveru.