VISCOSITY MONITORING WITH A QUARTZ CRYSTAL RESONATOR

Rudolf Thalhammer - Stefan Braun - Branka Devcic-Kuhar - Gerhard Karlowatz - Martin Gröschl - Felix Trampler - Ewald Benes - Helmut Nowotny - Milan Košťál

   The paper describes a novel quartz crystal sensor for measurement of the density-viscosity product of Newtonian liquids. The sensor element 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 measurands 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

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