A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a viscometer can be considered as a special type of rheometer.[1] Viscometers only measure under one flow condition.

In general, either the fluid remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is a measure of the viscosity. The flow conditions must have a sufficiently small value of Reynolds number for there to be laminar flow.

At 20.00 degrees Celsius the dynamic viscosity (kinematic viscosity x density) of water is 1.0038 mPa·s and its kinematic viscosity (product of flow time x Factor) is 1.0022 mm2/s. These values are used for calibrating certain types of viscometers.

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ViscoTron process viscometers measure the viscosity of liquids continually and precisely in-line. ViscoTron sensors have virtually no moving parts and are maintenance free. Torsional oscillation viscometers are surface loading devices. These devices measure the viscosity at the interface between the liquid and the solid surface. The sensor bulb twists back and forth at the sensors natural resonance. The drive shaft is welded to the sensor and moves the sensor, resulting in a micron size motion at the sensor surface. The compliant sheath, which is also welded to the sensor and the opposing static plane, acts as a spring for the resonance. This completely welded construction hermetically seals the internal mechanism from the process and provides high integrity of the sensor. The vibration on the sensor surface can barely be felt.

ViscoTron sensors utilize a constant amplitude torsional oscillation principle to measure the viscosity. The power required to achieve the constant amplitude is a measure for the viscosity. This technology allows for the large range ability of our ViscoTron systems.