photo courtesy of Fungilab
Rotational Viscometers and How They Work
Viscometers are used to measure the viscosity of sample substances. There are several different types of viscometers, and each measure viscosity in a unique way.
A rotational viscometer measures the torque required to turn a spindle in a fluid at a known speed, as a function of the viscosity of that fluid.
The torque required to turn the spindle is quantified as the shear stress acting across the surface area of the spindle. The fixed speed of the viscometer defines the shear rate.
Rotational viscometers can be used to test both Newtonian and non-Newtonians fluids, and measures a wide range of viscosity.
The Fungilab Rotational Viscometer
This rotary viscometer is designed to meet your budget and specification requirements, and is capable of measuring both Newtonian and Non-Newtonian fluids at a wide viscosity range.
It comes in four models - Alpha Series, Smart Series, Expert Series, and Premium Series - with the Alpha Series being the most basic, and the Premium Series the most advanced.
Each model has three "types": Type L is for a low viscosity range, Type R is for a regular viscosity range, and Type H is for a high viscosity range. See the Measuring Ranges PDF for more information.
Factors to Consider:
When measuring viscosity, it is important that the temperature of the sample remains constant throughout the testing. Changes in temperature can change the viscosity of any type of fluid.
Speed and torque ranges affect the viscostiy measurement range of a rotational viscometer. Each model of the Fungilab Rotational Viscometer offers several viscosity range options.
Spindles and Speeds
Choosing the right spindle and speed is a bit of a trial and error process. Each spindle measures a different range of viscosity. It is important to note that viscosity range is inversely proportional to the size of the spindle and to the rotational speed.
Fungilab suggests using a spindle and speed that will obtain a torque reading between 15 and 95%, with a percentage higher than 50% being most recommended.
To obtain a more precise measurement, it is important to know how the fluid sample will behave depending on fluctuations of shear rate. Note that there are several types of Non-Newtonain fluids - pseudoplastic, dilatant, plastic, thixotropic and rheopectic. (Get the infographic "Newtonian vs. Non-Newtonian Fluids" to learn more.)
Fungilab recommends using a 600 ml sample. Using too little of a sample can affect the viscosity reading. if you need a smaller sample we offer an adapter for testing 8-13 ml of fluid.