Balanced Torsionally Oscillating Pipe used as a Viscosity Sensor

We present a robust viscosity measurement system based on a torsionally oscillating pipe. The sensitive surface of the sensor performs periodic movements in the fluid to be sensed, generating a shear wave that penetrates the fluid. Due to this interaction, the resonance characteristic of the structure is affected, in particular the quality factor decreases with increasing viscosity. The pipe is mounted at its center where it features a nodal point of the preferred resonant mode reducing temperature issues while simultaneously enabling high quality factors. A mathematical model is presented illustrating how different parameters influence the sensitivity of the sensor. Longtime measurements were performed to demonstrate the time stability of the sensor setup.