Pressure Gage Measurements in a Dry to Wet Environment

Pressure gages are used in many fluid measurements applications. One such application is the measurement of wave impact pressures on structures. This application poses a unique problem of measuring pressures in a “wet to dry” environment. Often there is a thermal drift component in the pressure readings that makes it difficult to extract the actual pressure rise due to wave loading. These types of measurements also require high response rates to measure the detail of the short duration impacts, usually on the order of one to twenty kilohertz. Several bench tests were carried out in at the Naval Surface Warfare Center, Carderock Division, in 2008 to investigate various types of gages to find a robust gage that could withstand this type of application. Three different gages were used in this investigation. The first sensor (gage 1) is a dynamics general purpose ICP (integrated circuit piezoelectric) pressure sensor, capable of making very high frequency dynamic pressure measurements, rated to 200 psi. The second sensor (gage 2) is a voltage compensated, media isolated piezoresistive sensor, rated to 15 psi. This gage had a pressure port which was filled with water during testing to eliminate air compression effects. The third sensor (gage 3) is a semiconductor pressure gage rated to 25 psi (172.4 kPa). A water “drop” test setup was constructed of 2 inch (5.1 cm) PVC pipe. The pressure gages were mounted to the bottom of the setup facing up, and the pipe was filled from the top, with a quick acting gate valve located 2 feet (0.61 m) from the pressure sensors. Once the pipe was filled with the desired amount of water, the gate valve was opened as quickly as possible, and the impact force was measured. Vent pipes were mounted to a “cross” fitting in the vertical pipe which allowed for the air to escape. Several water “drop” tests were performed with this setup. From these tests, the thermal drift of gage 1 is evident. Gage 3 exhibits similar behavior. Gage 2 captures the water pressure impact, and then returns to a small positive static pressure as a result of the water that is sitting above it. Of the three sensors, gage 2 appears to be the most temperature stable.