Design and analysis of sensor system for vibration measurments in civil engineering

Nadzor stanja objekata ili structural health monitoring (SHM) obuhvata merne tehnike kojima se vrši akvizicija podataka relevantnih za otkrivanje oštećenja i procenu upotrebljivosti raznih vrsta struktura. SHM se najčešće primenjuje u građevinskoj struci, za određivanje stanja zgrada i kapitalnih infrastrukturnih objekata, kao što su mostovi, tornjevi, brane, tuneli, itd. Razlozi za nagli razvoj SHM u poslednjih par decenija su povećane potrebe za ispitivanjem ostarelih objekata, novi zahtevi za izgradnjom jeftinijih a kompleksnijih objekata na težim tipovima terena (što zahteva nadzor i za vreme gradnje i za vreme eksploatacije), i rast zahteva sigurnosnih i drugih standarda. S druge strane, tehnološki razvoj i pojeftinjenje bežičnih tehnologija i mikroelektromehaničkih (MEMS) senzora je uslovio da SHM postane dostupan širokom spektru korisnika. U radu je opisan bežični senzorski sistem prvenstveno dizajniran za merenje vibracija na građevinskim objektima. SHM kapitalnih građevinskih objekata se najčešće vrši analizom modova oscilacija, što podrazumeva upoređivanje amplituda i faza pojedinih harmonika signala u različitim tačkama. U ovu svrhu se skoro isključivo koriste bežični sistemi, koji imaju izražene prednosti u odnosu na žičane. Nije potrebno nepraktično i skupo razvlačenje kablova, ceo sistem i pojedinačni senzori su lakši za premeštanje, i senzori se lakše mogu postaviti na teško pristupačna mesta. Postoje i mane, a to su manja brzina prenosa podataka, osetljivost na smetnje različitog porekla, uključujući otvorenost medijuma za nameran napad sa strane, i problemi sa ograničenošću napajanja. Senzorski uređaji su realizovani u surface-mount tehnologiji (SMT). Koriste MEMS akcelerometre za merenje ubrzanja. Njihova potrošnja je mala što odgovara zahtevima baterijski napajanih bežičnih uređaja. Napravljen je solarni panel koji služi za energetsko dopunjavanje senzorskih uređaja u slučaju da se ovi postavljaju na mesta sa prirodnom svetlošću dovoljnog intenziteta. Korišćeni su radio modemi domaće proizvodnje za komunikaciju...Structural Health Monitoring (SHM) involves measurement techniques used in damage detection and estimation of usability of different kinds of structures. SHM is usually performed in civil engineering, to determine states of buildings and capital infrastructural objects, such as bridges, towers, dams and tunnels. Reasons for the rapid development of SHM in the past two decades are increasing needs to monitor aging structures, new requests to build cheaper and more complex objects on heavier terrain (which often demands monitoring during both construction and exploitation), and growing demands implied by safety and other standards. On the other hand, technological advances and price decrease in the areas of wireless technologies and micro-electro-mechanical (MEMS) sensors caused SHM techniques to become widely available. A wireless sensor system primarily designed to measure vibrations of civil engineering structures is described. SHM of capital civil engineering objects is often performed by modal analysis of vibrations, which includes comparison of amplitudes and phases of specific signal harmonics in different points. Wireless systems are commonly used for this, since they have significant advantages over the wired ones. There is no need to use impractical and expensive large cables, both the whole system and sensor nodes can be easily relocated, and sensors are easier placed at hard-to-reach spots. There are shortcomings as well, mainly lower data transfer bit rate, sensibility to different electromagnetic interferences, including openness of the medium for attack, and limited energy supply. Sensor devices of the developed system are made in surfacemount technology (SMT). They use MEMS accelerometers, with small energy consumption, suitable for battery powered wireless systems. A solar panel was constructed to harvest sun power and supply the devices with additional energy, in case they are placed on spots with sufficient intensity natural light. Radio modems of domestic production were used for communication..