Pressure Transducer Performance and Measurement Trade-Offs in a Transient, High Temperature, Combustion Environment.

Abstract : At the U.S. Army Research Laboratory (ARL), a series of tests were performed in a 120mm cannon to characterize the effects of transducer type, transducer port configuration, thermal protection media, and severe mechanical forces on the amplitude and frequency response of the pressure measurement. A ring of five pressure transducer ports (72 deg apart)) was machined 2.6 m from the rear face of a 12Omm gun trade. The physical configuration of the transducer ports consisted of three single-diameter ports with varying standoff distances, a conventional two-diameter port, and blind port. As the projectile passed the longitudinal position the pressure transducers were exposed to a transient, high temperature environment which allowed the investigators to study the fidelity of the pressure measurement under transient, high temperature, mechanically adverse gun conditions. These tests demonstrated that the use of single-diameter pressure ports with cavity depths of 0.254 mm (0.010 in) and 0.711 mm (0.028 in) win more accurately characterize the oscillatory nature of the pressure measurement than would the use of a single-diameter port with a cavity depth of 1.6O0mm (0.063 in). In addition, the combustion chamber of the weapon was also highly instrumented with pressure transducers in an attempt to evaluate the effects of various transducer types and thermal protection greases on the magnitude of the pressure measurement. This study showed that the Kistler 6211 pressure transducer (quartz) reads about 5% higher than the E30MA pressure transducer (normaline) in both the forward and rear of the chamber. No conclusion could be reached as to which gage gives the more correct quasi-steady-state pressure level