The kinematic viscosity [m²/s] is the ratio between the dynamic viscosity [Pa.s = 1 kg/m·s] and the density of a fluid [kg/m³].
 
The SI unit of the kinematic viscosity is m²/s. Other units are: 1 St (Stoke) = 1 cm²/s = 10⁻⁴ m²/s. 1 cSt (centiStoke) = 1 mm²/s = 10⁻⁶m²/s.
 
Water at 20 °C has a kinematic viscosity of about 1 cSt.

One way is to measure a fluid’s resistance to flow when an external force is applied. This is dynamic viscosity.        

The other way is to measure the resistive flow of a fluid under the weight of gravity. The result is kinematic viscosity. 
Put another way, kinematic viscosity is the measure of a fluid’s inherent resistance to flow when no external force, except gravity, is acting on it.

Measuring Kinematic Viscosity 

There are several ways to find the kinematic viscosity of a fluid, but the most common method is determining the time it takes a fluid to flow through a capillary tube. The time is converted directly to kinematic viscosity using a calibration constant provided for the specific tube.

The unit of measure of kinematic viscosity is Centistokes (cSt).

A basic difference between the dynamic and kinematic viscosity measurements is density. 
Density actually provides a way to convert between a kinematic and a dynamic viscosity measurement. The formula for the conversion is:

• Kinematic (cSt) x Density = Dynamic (cP)
• Dynamic (cP) / Density = Kinematic (cSt)

For a given sample, with a density greater than one, dynamic viscosity will always be the higher number.

Need a Refresher on Density?

Density is the ratio of the mass (or weight) of the sample divided by the volume of the sample. Think about an ice cube and a cube of steel. They may be the same size, but the steel cube weighs more than the ice cube. Therefore, we say that steel has a greater density than ice cube.

The mass (or weight) of a fluid is determined by gravity. In the kinematic measuring method, gravity is the only force that acts on the sample.

Different viscosities for Vortex Flow Meters

The LIQUI-VIEW Base series operate on the vortex principle. 
The obstruction (bluff body) placed in the flow of the liquid sheds vortices downstream at a frequency proportional to the velocity of the liquid. 
A piezoelectric sensor detects the vortices and creates electrical pulses which are proportional to the liquid flow rate.

LIQUI-VIEW Base provides the output either with pulse output or analog output (4-20 mA).

The LIQUI-VIEW instruments are able to work up to 1.8 cSt with an accuracy of <2%RD 
With a viscosity of 1.8 - 4cSt the measuring accuracy is 3%FS, between 4 - 14 cSt the accuracy will be around 4% FS.

* Viscosity changes with temperature, cSt above is average viscosity

> Liquid Vortex Flow Meter

• Flow range 0.5 l/min up to 150 l/min
• Output Analog (4..20mA) or Frequency output
• Display Local display showing current flow rate
• Low pressure drop 
• Maintenance free no moving parts
• Pressure 12 bar pressure rating
• Compact, light-weight, cost-effective construction

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