Abstract
Wireless sensor networks have attracted great attention for applications in structural health monitoring due to their ease of use, flexibility of deployment, and cost-effectiveness. This paper presents a software framework for WiFi-based wireless sensor networks composed of low-cost mass market single-board computers. A number of specific system-level software components were developed to enable robust data acquisition, data processing, sensor network communication, and timing with a focus on structural health monitoring (SHM) applications. The framework was validated on Raspberry Pi computers, and its performance was studied in detail. The paper presents several characteristics of the measurement quality such as sampling accuracy and time synchronization and discusses the specific limitations of the system. The implementation includes a complementary smartphone application that is utilized for data acquisition, visualization, and analysis. A prototypical implementation further demonstrates the feasibility of integrating smartphones as data acquisition nodes into the network, utilizing their internal sensors. The measurement system was employed in several monitoring campaigns, three of which are documented in detail. The suitability of the system is evaluated based on comparisons of target quantities with reference measurements. The results indicate that the presented system can robustly achieve a measurement performance commensurate with that required in many typical SHM tasks such as modal identification. As such, it represents a cost-effective alternative to more traditional monitoring solutions.
Highlights
The mechanical properties of structures change over the course of their lifetime
The frequencies that could be identified with the smartphone and the Raspberry Pi (RPi) measurement system agreed well with differences for higher modes typically being less than 1%
Thereby, the external sensor MPU-6050 was connected to the RPi, and the smartphone was used as a central control unit
Summary
The mechanical properties of structures change over the course of their lifetime. Changes related to deterioration such as damage may be safety-relevant and need to be detected. Besides the application for vibration measurements, other wireless monitoring systems employing cost-effective microcomputers and microcontrollers in combination with specific piezoelectric sensors (PZTs) have been developed to identify local damage in reinforced concrete elements. The presented work concentrates on the properties and advantages of the software framework designed for single-board computers to measure vibrations via sensors attached to microcontrollers or nested in mobile devices Such modern devices include smartphones and tablets equipped with considerable computational resources and large memory capacity. As past studies have already shown, the sensor resolution and sampling rate, which result from differences in accelerometers and sensor driver software configuration, affect the properties of measurement data directly [6] Based on this fact, sensor characteristics are further investigated with respect to the hardware used. The authors make the software framework available alongside this publication under the name RasPyre [20] which can be found on the website of the authors
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