Predictive criteria for the optimisation of a vibrating-reed transducer

Abstract

The optimisation of a vibrating-reed technique which is capable of measuring various properties such as fluid pressure, density, viscosity and mass under aggressive environments is described. The unit operates simply by utilising a stiff reed which is clamped securely at an intermediate point along its length. One end, mounted with an inert concentrated mass is exposed to the test environment, while the other is mechanically excited so that the system is sinusoidally vibrated at its first modal resonant frequency. Changes in the resonant conditions then reveal information about the physical properties of the fluid under test. The finite-element method of analysis adopted for a cylindrical reed reveals that optimum operating conditions in terms of output response are achieved with maximum reed diameter, minimum reed length and minimum mass ratio of the attached mass to that of the reed. The stability criteria on the other hand indicate that most stable operation corresponds to the clamping of the reed as far away as possible from its centre. The analysis also considers the effect of choosing different reed materials and shapes on the system's resolution and sensitivity. Most of the theoretical predictions are also confirmed by experimental evidence.