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R. Thalhammer, S. Braun, B. Devcic-Kuhar, G. Karlowatz, M. Gröschl, F. Trampler, E. Benes, H. Nowotny, M. Kostal:
"Viscosity monitoring with a quartz crystal resonator";
J. Electrical Engineering, 54 (2003), 5-6; 140 - 143.

The paper describes a novel quartz crystal sensor for measurement of the density-viscosity product of Newtonian liquids. The sensorelement consists of two plano-convex AT-cut quartz crystals vibrating in a thickness-shear mode with the liquid sample in between. This special set-up allows suppression of disturbing resonances in the liquid layer. Such resonances are generated in the common single-plate arrangements due to compressional waves caused by spurious out-of-plane displacements of the shear vibrating finite plate. The primary rneasurands of the sensor are the fundamental resonance frequency and the associated resonance Q-value, which are influenced by the viscously entrained liquid contacting the quartz surface. The sensor was employed successfully in on-line monitoring of waffles dough viscosity.

Keywords: resonant sensors, viscosity sensor, viscosity monitor, viscosity-density product, dough-viscosity