Sensor Device Capable of Autonomously Keeping Accurate Time Information Using a Chip Scale Atomic Clock for Earthquake Observation and Structural Health Monitoring of Buildings

Abstract

Sensor devices were developed in this study for use in seismic observation to understand damage conditions after earthquakes and structural health monitoring for building and civil infrastructure maintenance. To be used, the sensor devices must be densely installed over a large area and measurement data with synchronized time must be obtained. It is preferable that the sensor devices themselves maintain accurate time information even when no network or Global Positioning System (GPS) signals are available. As a result, a sensor device was created that maintains accurate time information autonomously by employing a Chip Scale Atomic Clock (CSAC), which consumes ultra-low power, can be mounted on a small board, and is an ultra-high precision clock. This paper describes the CSAC and a mechanism for using the CSAC to add highly accurate time information to measured data. Following that, the study outlines the development process from prototype to practical device, as well as improvement results to address challenges identified in actual bridge use. A new procedure for time synchronization between devices is presented in this paper. Furthermore, the communication system of measurement data that was recently constructed using "fluentd," an open source software for data collection, is detailed. Eventually, the paper demonstrates the applicability of the developed sensor device through a case study in which seismic observation and structural health monitoring were implemented by installing the improved devices in a real-world building. The practical device developed in this research securing autonomous time synchronization made it possible to monitor the structural health of the building based on the evaluation of inter-story deformation.