An Introduction to Viscometers
Viscometers are instruments that measure the fluid flow and viscosity of liquids. The viscosity of a liquid can affect its performance, whether this is pumping or piping it, or how it performs for dipping and coating. 
Measuring viscosity and flow properties also applies to the production of familiar consumer items such as food and drink, toothpaste, cosmetics and shampoo.
What Does a Viscometer Do?
Viscometers measure the viscosity and flow properties of liquids, and have a wide variety of applications, measuring these properties in a different substances and materials.
Monitoring the viscosity of jams and syrups in the production of food condiments, to ensure batches are consistent
Analysing milk’s flow properties when designing piping systems for it
Measuring how motor oil flows when under different temperature conditions
Testing the viscosity of inks for inkjet printers.
Viscosity is important in the lubrication of machines. If it is too low, there will be too much contact, and therefore wear, between internal components. If it is too high, it can force the machine to work harder, to overcome the lubricant’s own internal resistance to flow.
What is Viscosity?
Viscosity is the measure of how resistant a material is to motion when you apply force to it.
For example, if you squeeze a tube of toothpaste, how easily does the contents come out of the end of the tube?
There is a formula for measuring viscosity:
Viscosity = sheer stress/shear rate.
You express the result of this formula in centipoise (cP). Centipoise is the equivalent of 1 mPa s (millipascal second).
This applies to absolute viscosity. For kinematic viscosity, the measurement is different, as we will explain later.
Sheer stress is the force per unit area that you need to move one layer of fluid in relation to another
Shear rate is the measure of the change in speed in the movement of intermediate layers, in respect of each other.
For many liquids, the stress that causes flow is directly proportional to the rate of shear strain. The sheer stress divided by the shear rate is constant for a given fluid, at a specific temperature.
This constant is the dynamic or absolute viscosity. But you can also simply refer to it as the viscosity of a material.
A simple way of seeing viscosity is as the thickness of a fluid, but when you look at fluids with different densities, the clearest way of describing viscosity is as resistance to flow.
Why is Measuring Viscosity Important?
The process conditions of materials is important, both in their production and for their end-use.
The viscosity of a material is also a useful indirect measure of its properties, such as molecular weight and density. These material properties can affect flow behaviour.
Measuring viscosity is a valuable part of quality control and batch consistency.
It is also important to measure viscosity because not all fluids behave in the same way.
Broadly, there are two types:
Newtonian, and
Non-Newtonian.
Newtonian refers to Newton’s Law of Viscosity, which is the established formula for measuring it.
In Newtonian fluids, the viscosity remains constant, regardless of changes to the shear rate.
Examples of typical Newtonian fluids include water and motor oil.
But, in non-Newtonian fluids, the viscosity fluctuates. 
An everyday example of a non-Newtonian fluid is tomato ketchup, which, when you shake the bottle, becomes runnier. Ketchup has shear thinning properties, because its viscosity decreases as you increase the shear stress.
Kinematic and Absolute Viscosity. There are two ways of expressing viscosity:
Kinematic
Absolute
You measure kinematic viscosity by observing a fluid’s resistance to flow under the force of gravity.
You measure absolute viscosity by measuring this resistance to flow under an external and controlled force.
The measurement of these two expressions of viscosity are different too.
Kinematic viscosity is measured in centistokes (CSt)
Absolute viscosity is measured in centipoise (cP).

The measures viscosity by means of a torsional resonator, one end of which is immersed in the fluid under test. The more viscous the fluid, the higher the mechanical damping of the resonator. By measuring the damping, the product of viscosity x density may be calculated by rheonics' proprietary algorithms. The resonator is both excited and sensed by means of an electromagnetic transducer mounted in the sensor's body. Thanks to rheonics' patented symmetric resonator design, the transducer is isolated from the fluid in a hermetically sealed capsule, while maintaining excellent mechanical isolation from the sensor's mounting. Damping is measured by the rheonics patented sensing and evaluation electronics. Based proven gated phase-locked loop technology, the electronics unit offers stable and repeatable, high-accuracy readings over the full range of specified temperatures and fluid properties.