ABSTRACT
There is not any clear distinction between physical and chemical measurements, but it is a good idea to separate these as there are some differences. One difference is that 'broad sensitivity' (a sensor reacting on many parameters) is considered to be good for a chemical sensor but bad for a physical sensor (in which sensitivity to other parameters than the desired is considered as disturbances). The most common way to measure pH in the process industry is to use an electrode containing an ion membrane made of glass. Special attention must be paid when dealing with liquids having very low conductivity. Turbidity tells you how clear a liquid is. There are two types of viscosities: kinematic and dynamic. The kinematic viscosity is the dynamic viscosity divided by the density. 'Specific gravity' is another concept related to density, now comparing to a reference.
