VISCOSITY MONITORING WITH A QUARTZ CRYSTAL RESONATOR

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 flnite plate. The primary measurands of the sensor are the fundamental resonance frequency and the associated resonance Q-value, which are in∞uenced by the viscously entrained liquid contacting the quartz surface. The sensor was employed successfully in on-line monitoring of wa†es dough viscosity. K e y w o r d s: resonant sensors, viscosity sensor, viscosity monitor, viscosity-density product, dough-viscosity