Joe Flow - Rheometers: How and what do they measure?
To understand rheological measurements it is often helpful to learn more about the rheometer setup and how it works.
To measure the rheological properties of your sample with a rotational and oscillatory rheometer requires determination of the torque and deflection angle of the measuring bob. Your sample provides resistance or a reset torque to the setting. The resulting deflection angle is then measured by the rheometer's encoder. The speed is calculated from the deflection angle and the time.
However, as the user you are usually more interested in the rheological parameters. How do you get these? Rheological parameters are calculated from the measured values torque, deflection angle and speed using conversion factors. All further parameters, such as viscosity, are not measured but calculated.