Piezoelectric Wafer Active Sensors (PWAS) are a viable option for monitoring the structural integrity of pressure vessels and piping systems. They are inexpensive, small and unobtrusive sensors which can be permanently attached to structures for long term monitoring without interfering with operations, such as operating in areas with limited head space. PWAS are used to inspect the structure through several methods which include; pitch catch or pulse echo wave propagation, and electromechanical impedance spectroscopy. Since the PWAS could be exposed to a range of environmental and/or operating conditions while attached to the structure, the change in the properties and electromechanical characteristics of the sensor must be known at a given condition. Accordingly, there is a need for a testing system which can measure the PWAS properties while exposing the sensor to a wide range of temperatures.
The focus in this paper is on elevated temperatures, but the same methodology could be used for low temperature or environmental testing. The requirements which were imposed on the design include: providing an electrical connection from each electrode to the exterior of an industrial oven; allow the sensor to expand and contract both in plane and out of plane; withstand an extended duration at elevated temperatures; the equipment must not influence the measured quantities. The challenges include how to place the sensor in an oven and make electrical contact while allowing free motion, how to implement wiring and electrical connections at elevated temperatures, how to allow the thermal expansion of components and account for thermal mismatching, and how to maintain electrical isolation of the two electrodes. This paper discusses how these requirements were met and challenges overcome, as well as experimental validation of the system.