Development of Wireless Acceleration Measurement System Applied to Structural Health Monitoring

Abstract

Newly developed low-cost MEMS based acceleration sensors exhibit enough accuracy and stability to monitor the shaking of structures caused by an earthquake. We have developed a practical shaking monitoring system using the MEMS-based acceleration sensors and a 920-MHz multihop radio communication method that can offer reliable radio wave communication even in buildings. In this kind of system, the base clock of each sensor unit must be highly synchronized to the master clock to minimize the acceleration-induced phase synchronization error. In the proposed system, such error among multiple sensor units can be limited to three milliseconds.

Development of a Wireless Acceleration Measurement System

“…Equation ( 4) shows the relationship between the frequency and the period. Equation (5) shows the relationship between the phase differences and the time lag, such that by combining equations ( 4) and ( 5), we obtain equation (6), which shows that if there is a time lag between NICE, the phase difference changes with the frequency. Here, the phase difference is calculated by passing a straight line through the origin and assigning to each frequency slope of the time lag times 360.…”