As a general rule, refractometers measure the concentration of any dissolved material in a liquid. A typical measured medium is a binary solution, but it can also be a mixture of more than two components. In multi-component solutions this is a checksum; if one of the components is wrong, the overall refractive index value changes.
The potential applications in different industries are countless. Although the manufacturing process, environment and processing medium vary from industry to industry, all basic unit operations and control strategies are roughly the same despite of the end product.
This guide, courtesy of K-Patents, is a summary to give you an idea how the refractometer is used in different operations within a process manufacturing facility.