The goal of this work is to develop and deploy a network of long life, low-cost wireless strain sensors to monitor civil structures. Previous work on RF sensor nodes which transmit periodically to a central receiver using time division multiple access (TDMA) has been reported [1]. With a low power sleep mode and 30 minute sampling interval, this system is estimated to operate for 5 years on one 3.6V Li-Ion AA battery.

However, deployment of the TDMA system on structures underscored the need for a high-speed wireless sensor network with user-triggered and event-triggered data streaming capabilities. To this end, this prompted the development of a second generation datalogging transceiver (75 Kbps , 2MB memory). These systems provide 1KHz, 3-channel data in continuous streaming mode or 2KHz, 3-channel data in data logging mode. The node preserves battery life by entering a low power sleep state. The node periodically awakens and listens for commands, or wakes via event-triggered interrupt.

This high-speed system was installed on a heavily trafficked bridge in Vermont. Displacement sensors were attached to steel girders for static and dynamic strain measurement. Strain data were acquired via a wireless link. The wireless system is designed to remain long term on the bridge for interrogation under normal and controlled operating conditions.