A resonant rolling sphere viscometer using magnetic actuation and readout

We present a viscosity measurement principle based on a metallic sphere rolling on a plane on a circular trajectory. The sphere is magnetically positioned and driven using a permanent magnet and four actuation coils placed below the rolling surface. This measurement principle is particularly suited for the characterization of thin fluid films and therefore also for cases where small sample volumes are available. We describe our prototype setup consisting of three parts: the probing body (sphere), the actuation part, and the readout part. For the readout two differential transformer arrangements are used, yielding a total of required five coils: one pair of readout coils for one direction and another pair perpendicular to it for the orthogonal direction. The fifth coil is used as primary coil in the differential transformer readout setup where the aforementioned coil pairs act as secondary coils. In this contribution we describe the sensor setup, outline the actuation and readout process and present first measurements.