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E. Benes, R. Schnitzer, S. Radel, M. Paroha, M. Gröschl:
"Viscosity sensor based on a biconvex quartz crystal thickness shear resonator in a novel stress-free holder";
Vortrag: 3rd Congress of the Alps Adria Acoustics Association, Hotel Weitzer, Graz; 27.09.2007; in: "Proc. 3rd Congress of the Alps Adria Acoustics Association", Hrsg: Joanneum Research, (2007), 8 S.

The paper describes a quartz crystal sensor for the measurement of the density-viscosity product of
liquids. The sensor element consists of a biconvex polished quartz crystal thickness shear resonator in a holder
with novel stress-free clamping of the crystal. The AT-cut quartz crystal is vibrating in a thickness-shear fundamental
mode at 2.77 MHz. The measurement values of the sensor are the fundamental resonance frequency f and
the associated resonance Q-value. For Newtonian liquids, these measurement values are analytically dependent
on the density-viscosity product of the liquid in contact with the sensing surfaces. The sensor features high
absolute accuracy and reproducibility without the need of calibration and without any fitting parameter. The
sensor covers a viscosity range from almost zero (air) up to 2000 Pas. It is restricted to electrically insulating
liquids with pressures of up to 1 MPa. Non-Newtonian behavior can be identified and the complex mechanical
impedance of non-Newtonian fluids can be determined at very high shear rates (10/-7 s/-1). The flange mounted
immersion sensor was employed successfully in rough industrial environment for on-line monitoring and controlling
viscosity and temperature of lacquer in cable marker machines. High viscosity resolution could be demonstrated
by adding small amounts of solvent (0.5 vol.%). The corresponding small decreases in lacquer viscosity
could be monitored. This work was financially supported by the European Commission within the GROWTH
shared-cost RTD funding scheme, project QxSens No. GRD1-2001-41816. http://www.qxsens.net

Viscosity, density, temperature, sensor, piezoelectric resonator, ultrasound, quartz crystal, virtual