In-line Process Refractometers

for liquid concentration measurement

K-Patents measurement products

Vaisala K-PATENTS? Process Refractometer

Vaisala K-PATENTS Process Refractometers are used for in-line liquid measurements for the purpose of process control and industrial automation. We invest heavily in research and development, maintaining a worldwide reputation for innovation, reliability and high quality.?

Customer reviews:
“We were amazed how reliable and stable the measurement is despite the high vibration of the membranes.”
– Whey protein concentrate plant, New Zealand.

“Previously, we produced approximately one million liters of waste product per year during product changeover on product filling lines. Instead of measuring volumetric flow and turbidity, we installed a TS meter on the filling lines and were able to cut our 15 min product changeover time to the legal minimum of 5 min, reducing waste by two thirds.”
– Dairy, Europe.

“Digital process refractometer was found to be an economic and environmentally friendly alternative to traditional measurement methods as it reduces time and resource consumption”.?
– Pharmaceutical plant, Austria ? ? ? ? ? ? ??

Industrial process refractometer in pharmaceutical manufacturing

Vaisala K-PATENTS Process Refractometers are commonly used to determine liquid concentration. This measurement has been an important element in the processing industries, for example, the chemical and refining, pulp and paper, food and beverage, sugar and pharmaceutical industries for more than a century.

The performance of all types of refining, manufacturing and quality control operations can be dramatically improved with our digital refractometer technology.

For instance, the in-line concentration measurement can be used as a real-time predictive tool for the final concentration. A quick and accurate response is needed to optimize production. Cost reduction is possible by reducing the variation of mean average of the product concentration. The cost saving is related to the value of the component being measured.

Process refractometer critical angle measurement

Completely digital measurement

The measurement principle of the Vaisala K-PATENTS process refractometer is a critical angle measurement. There are three main components in the refractometer; a light source, a prism, and an image detector. ?

The light source sends light rays in different angles to the prism and process interface. Rays with a steep angle are partly reflected to the image detector and partly refracted to the process. Rays with a low angle are totally reflected to the detector. The angle from which the total reflection starts is called the critical angle.?

The CCD camera detects a bright field and a dark field corresponding to partly reflected light and totally reflected light. The position of the borderline between the bright and the dark area correlates with the critical angle which is a function of the refractive index, and therefore correlates with the concentration of the solution.

A built-in temperature sensor measures the temperature T on the interface of the process liquid. The sensor converts the refractive index nD and temperature T into concentration units. Vaisala K-PATENTS refractometer can indicate different scales, for example Brix, liquid density or concentration by weight. The diagnostics program ensures that the measurement is reliable.

Learn more about the Refractive Index Measurement Principle (pdf).
Read the blog on the Refractometer technology

Installed process refractometer

Three generations of refractometers

Currently, we have 3 refractometer technology platforms in production. Most recent and advanced is the PR-43 platform where up to 4 refractometers can be connected to one user interface via Ethernet or 4-20 mA connection.?

The range of refractometer applications is wide as most liquid processes require continuous monitoring of concentration to help maintain quality and reduce costs. Vaisala serves the target industries according to their different nature and technology requirements to ensure a high standard of products and services.

Click on the industry of your interest to learn about the refractometer models and applications.

Automotive >>
Aviation >>
Chemical >>
Food and beverage >>
Metal machining >>
Mining >>
Oil refining and petrochemical >>
Pharmaceutical and biotechnology >>
Pulp and paper >>
Semiconductor >>
Sugar >>
Sweeteners >>

MI with user

Refractometer system

Vaisala K-PATENTS Refractometer can be used as a stand-alone device that measures, refines, manages and indicates concentration units and diagnostic information.?

The refractometer can be used with a graphical user interface. User interface options range from a rugged, multichannel, industrial computer, to a compact, lightweight interface to a web-based version, allowing the user to select their preferred way to access and use the refractometer measurement and diagnostics data.

The refractometer has a built-in web server with a homepage where the instrument can be configured, monitored, verified, and diagnosed via an Ethernet connection.?

Because of the identical calibration for refractive index measurement, each refractometer can be freely interchanged without optical recalibration. Units do not require any recalibration or regular maintenance.

Key Benefits

Full measurement range

The refractometer works over the full measurement range of Refractive Index (nD) 1.3200 – 1.5300, which corresponds to 0-100 Brix. Optional measurement ranges available.


Built-in CORE-Optics element eliminating the risk of leakages and drifts.

Completely digital system

Color, bubbles, particles, flow, temperature or pressure changes do not affect operation or accuracy.

Withstands low and high process temperatures

Compact model -40°C...130°C (-40°F...266°F), probe model: 40°C...150°C (-40°F...302°F).

Temperature compensated measurement output

The refractometer has a built-in PT-1000 temperature sensor for fast process temperature measurement and automatic temperature compensation.

Compatible with CIP and SIP cleaning

The refractometer withstands CIP (clean-in-place) and SIP (sterilization-in-place) processes and cleaning and rinsing of facilities.

Highly accurate

The accuracy of the in-line measurement is comparable to the accuracy of the production laboratory.

Easy on-site instrument verification

The refractometers are delivered calibrated from the factory in Finland with NIST traceable standard Refractive Index liquids. This allows easy instrument verification within user’s own quality assurance system using standard liquids and a built-in...

Easy installation

The refractometer can be installed in the main processing line, bypass line or vessel either directly or via a large variety of cost-effective and easy to mount flow cell options, and no by-pass arrangements are required. Installation in vessels with...


The refractometer requires no regular maintenance as there are no moving parts or components that would have to be changed regularly. This means a low cost of ownership.

Product approvals and certifications

All instruments are developed considering the industry specific regulations and safety aspects. Product approvals and certificates allow manufacturing and supply of products in compliance with ATEX, CSA, FM, IEC, CRN, KEMA, DEKRA AND SANITARY 3-A, EHEDG.

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To ensure continuous support before and after purchase of our products, we offer local application consultation, training, maintenance and support expertise locally via our authorized sales distributors as well as by the Headquarters and local service centers.