Determining Refractive Index Using PR21 Process Refractometer

The process refractometer PR21 of A.KRÜSS Optronic, Hamburg, is a universal measuring instrument for determining the refractive index and therefore the concentration of a substance in liquid in a temperature range of -6 to +160°C. It can be installed into the walls of pipes, cauldrons or storage tanks without having to observe any special requirements. This allows controlling and managing processes, for instance monitoring the purity of liquids or concentration of solutions by carrying out measurements in the production plant itself.

It is possible to digitally program the PR21 using a PC, in order to adapt it to the specific respective application. It can be connected directly to computers via Ethernet or an optional profibus interface, in order to record measured values or to control the process. A further option is the use of a display during operation that can be installed at the measuring site or on an instrument panel in the control room. The universality and flexibility of the PR21 make it an integral part of the production plant.

The PR21 uses a LED with a wavelength of 589.3 nm as source of light. This corresponds to the sodium D line. The measuring range spans 1.33 to 1.70 nD, allowing programming of an application-specific measurement range of 0.15 nD. Two versions with different measuring accuracies are available. The standard version measures precisely down to 0.0002 nD, corresponding to 0.1% Brix, the high-precision version PR21H to 0.00002 nD respectively 0.02% Brix.

Since the density of liquids depends on their temperature, it is necessary to correct the determined measured value with the aid of parallel temperature measurement and a material-specific correction scale. The temperature range of both PR21 versions extends from -4°C to +60°C. Both versions are also available in a water-cooled version for high temperature measurements up to 160°C.

Using PR21 Process Refractometer for Individual and Periodic Interval Measurements

The PR21 can be used both for individual measurements as well as for periodic interval measurements. The measurement result can be output in nD and % Brix. In the basic model, correction scales for saccharose, inverse sugar, glucose, and fructose are pre-programmed. On request, A. KRÜSS Optronic can also supply differently programmed versions, such as e.g. to monitor exhaust gas additives for the AddBlue® process. This allows the device to be used immediately without reprogramming. It is furthermore very easy to program the PR21 for any material in the field.

All parts exposed to the process medium are made of stainless steel. A. KRÜSS Optronic can also supply models with increased chemical resistance for use in particularly aggressive environments.

Data Interfaces Available on PR21 Process Refractometer

The PR21 is equipped with several data interfaces for programming and communication with a process computer. An Ethernet connection is the standard interface for direct connection to a PC. Digital displays can be controlled via a serial RS-232 interface. Furthermore, 0 and/or 4 to 20mA current loops are available to measure the refractive index and temperature. A profibus interface is optionally available.

At shipment, the PR21 is prepared for the most frequent applications in the food and beverage industry. Programming for other applications can be carried out with a standard PC. This only requires establishing an Ethernet connection between the PC and the PR21. This is followed by entering all parameters into the Internet browser using clearly arranged menus. No special software is required.

Typical Applications of PR21 Process Refractometer

Typical application areas of the PR21 are food and beverage production, for instance when monitoring sugar solutions. Various equipment versions are also used in the chemical and petrochemical industry, in pulp and paper industry plants, in the textile industry and in the metal working industry.

This information has been sourced, reviewed and adapted from materials provided by A.KRÜSS Optronic GmbH.

For more information on this source, please visit A.KRÜSS Optronic GmbH.