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.

Rheometers: How and What do they Measure?

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 (see Table 1). All further parameters, such as viscosity, are not measured but calculated.

Table 1. Measuring values and rheological parameters with the conversion factors.

Measurement values	Conversion factor	Rheological parameter
Torque M [mNm]	CSS factor	Shear stress τ [Pa]
Deflection angle φ [µrad]	CSD factor	Deformation γ [%]
Speed n [min-1]	CSR factor	Shear rate [s-1]

Rheometer Design

Rotational and oscillatory rheometers are set up as shown in Figure 1. The measuring head contains the drive motor and encoder which measure and set the torque, deflection angle and speed.

Figure 1. Setup of a modern air-bearing rotational and oscillatory rheometer with the most important components

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This information has been sourced, reviewed and adapted from materials provided by Anton Paar GmbH.

For more information on this source, please visit Anton Paar GmbH.