Implementation of a density sensitive structure in the torsionally oscillating resonant pipe viscosity sensor

We present an improved version of a torsionally oscillating resonant pipe viscosity sensor. The new design offers the possibility to sense both, viscosity and density independently and at the same time. The first version of the sensor allowed only sensing the viscosity-density product, where the two values were not separable without additional knowledge or measurements. For the new design, density sensitive structures were additionally implemented into the pipe system. These structures force the fluid to follow the torsional oscillation of the pipe, therefore, in this region the fluid influences the behavior of the resonant structure like an additional mass. This leads to a frequency shift which is mainly density dependent. Due to this behavior it is now possible to use a higher order model to extract both viscosity and density out of one single measurement. We present the newly introduced sensor design, compare it to the first sensor design, describe the additional density sensitive structures and explain how the sensor was designed and evaluated using the Finite Element Method (FEM). We show how different values of viscosity and density influence the resonance frequency and the damping characteristics of the sensor. To prove the concept, we apply a calibrated higher order model to the simulation results and provide a first accuracy estimation.