Resonant steel tuning forks for precise inline viscosity and mass density measurements in harsh environments

The principle of using steel tuning forks for viscosity and mass density measurements is investigated. From recorded fre- quency responses of fully immersed tuning forks, resonance frequencies and quality factors are evaluated and related to the liquids mass densities and viscosities. The benefit of these resonators is their mechanical rigidity which allows the appli- cation in harsh environments and mechanical cleaning processes without detuning or damaging the device. The setup was particularly devised that only the resonator itself but no excitation or read-out mechanisms get wetted by the sample liquid. The results obtained with a circular cross-sectioned tuning fork in different liquids are shown and discussed.