Micro-rheometer for inline oil quality detection

A miniaturised high-shear rheometer using GaPO₄ resonators is described; it allows the detection of the rheological behaviour of Newtonian and non-Newtonian fluids. The sensor system that has been developed combines a torsional mode and a thickness shear mode resonator. When the resonators are immersed in a liquid, the frequency and the Q-value change: the higher the viscosity of the liquid, the lower the Q-value and the resonant frequency of the resonators. In order to measure in more viscous liquids, where excitation of the resonators by an oscillator is impossible, it is necessary to develop a special type of sensor electronics. The solution. presented is a low cost impedance analyser; its basic design and concept are outlined as well as first results in applying the sensor system in various non-Newtonian reference oils.