Vaisala Process Refractometers are commonly used to determine the concentration of a dissolved solids by making an optical measurement of a solution's refractive index (nD).

Vaisala refractometer sensor measures the refractive index nD and the temperature of the process medium. The measurement is based on the refraction of light in the process medium, i.e. the critical angle of refraction using a yellow LED light source with the same wavelength (580 nm) as the sodium D line (hence nD).

The measured refractive index nD and temperature of the process medium are sent via the interconnecting cable to the Indicating transmitter. The Indicating transmitter calculates the concentration of the process liquid based on the refractive index and temperature, taking pre-defined process conditions into account.

The output of the transmitter is a 4 to 20mA DC output signal proportional to process solution concentration, liquid density, Brix or other scale that has been selected for the instrument. Process data can also be downloaded to a computer via an Ethernet cable.

The basic Process Refractometer system consists of one or two sensors connected to an Indicating transmitter. However, there are different sensor models, each model is adapted for different industrial requirements.

Learn more about Refractive Index Measurement Principle (pdf)