Automation of Data Collection for Pwas-based Structural Health Monitoring

Crack detection through piezoelectric wafer active sensors (PWAS) [1] is emerging as an effective and powerful technique in structural health monitoring (SHM). Because of the piezoelectric properties of the PWAS, they act as both transmitters and receivers of guided Lamb waves for such applications. With arrays of PWAS attached to the structure, excitation signals are sent to one of the PWAS and wave signals from the structure are received at all the PWAS. The signals are analyzed to detect the position of cracks. One important issue associated with the PWAS-assisted SHM is the connectivity between the PWAS arrays and the measurement instruments. An automatic signal switch is necessary to send the excitation signals to PWAS and acquire the response signal from another PWAS. Such a program-controlled switch can quickly and precisely execute the data collection in a way which is more efficient and reliable than the manual switching operations. In this paper, we present an innovative design of a LabVIEW controlled auto signal switch for PWAS-assisted SHM. The hardware circuit construction and the control LabVIEW program are discussed. As a conduit between the phase array of PWAS and the signal instruments (signal generators, oscilloscopes etc.), the auto signal switch provides a convenient way to switch excitation and echo signals automatically to the selected sensors with the help of GUI in the control LabVIEW program. The control program is easy to implement and can be integrated into an upper level program that executes the whole task of signal acquisition and analysis. Because of the concise design of the hardware, the concept of the auto signal switch can be extended to other application cases such as the electromechanical (E/M) impedance [2] measurement for SHM. Introduction