Measurement intervals can be set freely allowing for continuous 24-hour measurement or measurement of any long term viscosity change. These viscometers are able to easily measure the state transition from sol to gel as there is no need to change sensors during measurement. The SV-10/SV-10A series of tuning fork vibro viscometers are capable of continuous measurement over a range of viscosities from the extremely low (0.3 mPa Simplified calibration function (for SV-10)Ĭlick here to see the complete accessory list.Įxample Measurements with the Tuning Fork Vibro Viscometer (SV/SV-A Series) Windows Communication Tools WinCT-Viscosity provided as standardzĮxcellent repeatability (1% of the measured value by standard deviation)Įxtremely high sensitivity (detects a viscosity as low as 0.3 mPa Simultaneous measurements of temperature and viscosity The values measured by the rheometer (deflection angle, torque, and phase shift) together with the conversion factors for the measuring system now give all necessary data to calculate the required rheological parameters such as the storage modulus G’ or loss modulus G’’.Wide-range, continuous measurement without replacing the sensor plates This time delay is called the phase shift δ. However, because jello has viscoelastic properties the response wave is time-delayed compared to the set oscillation. Also here, the rheometer determines the deflection of the measuring bob and the required torque. Instead, oscillatory tests with set sinusoidal oscillation of the measuring system and the sample are carried out. In this case a rotational test would not be very useful. If jello was in the shear gap instead of ketchup, the aim of the test would be, for example, to investigate the viscoelastic behavior and the characterization of the undestroyed structure at rest. The viscosity values are calculated from the rheological parameters which are independent of the instrument: As with the calculation of the shear stress, for the calculation of the rheological parameter ‘shear rate’ the influence of the measuring system is considered using a conversion factor: If in this case ketchup is measured in two different measuring systems, one with a large shear gap and one with a narrow shear gap, the same rotational speed results in a lower shear rate in the system with the large gap than in the system with the narrow gap. The same is true for the shear rate, which correlates with the speed. It is therefore easier to work with the rheological parameters. As the rheological parameter shear stress τ is calculated from the torque in relation to the shearing surface, the shear stress is therefore independent of the used measuring system. ![]() If a small measuring system is used, a smaller torque is needed to obtain the required speed. If the ketchup is measured with a large measuring system, a large torque is required because the shear surface is large. The viscosity η is then calculated in the rheometer software according to the viscosity law from the quotients of the shear stress τ and shear rate $\dot$.Īs mentioned, the shear stress correlates with the torque. The user sets the shear rate profile – the different speeds of rotation – and the rheometer determines the required shear stress. When measuring ketchup for instance, its viscosity should be measured with a shear-rate-controlled rotational test. All further parameters, such as viscosity, are not measured but calculated. Rheological parameters are calculated from the measured values torque, deflection angle, and speed using conversion factors (see Table 1). However, the rheometer user is usually more interested in the rheological parameters. In fact, it is always the current – and therefore the torque – which is provided and the parameter of either speed or torque is set via a quick controller. In a measurement, modern rheometers can set either the torque or the speed – the other parameter is then measured. The speed is calculated from the deflection angle and the time. The sample provides resistance or a reset torque to the setting and the resulting deflection angle is then measured very precisely by the rheometer’s encoder. ![]() This means that in a viscosity measurement the rheometer presets a certain current that correlates to a defined torque. They measure the torque and the deflection angle of the measuring bob. To measure the rheological properties of a material, rheometers are used.
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