Liquid concentration measurement

Liquid measurement with inline process refractometers

Vaisala Polaris process refractometers are used for inline liquid measurements to enable efficient process control and industrial automation. They are stand-alone and smart devices that measure and indicate concentration units and diagnostic information. They provide 4-20 mA or Modbus RTU outputs to connect directly to the control system. All process refractometers can also be connected with the Indigo520 for process refractometers for physical user interface and expansion of features. 

The Vaisala Polaris refractometers represent the latest, 5th -generation product line. Process refractometers became part of Vaisala in 2019, following the acquisition of K-PATENTS, a leading innovator with over 40 years of experience in designing and manufacturing industrial process refractometers to cater to a wide range of applications. 

Our significant investments in research and development have earned us global recognition for delivering innovative, dependable, and top-quality products.

Accurate, drift-free measurements for liquid concentration

Vaisala Polaris process refractometers are widely utilized to determine liquid concentration or density. This measurement has been an important element in the processing industries for over a century. Our advanced digital refractometer technology can significantly enhance the performance of refining, manufacturing, and quality control operations.

Real-time concentration measurements obtained through our inline refractometers can be used as a valuable predictive tool for achieving optimal 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. 

Customer reviews:

“The measurement is reliable and stable despite of heavy membrane vibration.”


– Whey protein concentrate plant, New Zealand

“Our annual waste at filling line was million liters. Replacing volumetric flow and turbidity meters with in-line refractometers, helped us to cut the changeover time to a legal minimum of 5 min, reducing waste by two thirds.”

– Dairy, Europe

“Real-time process refractometer is a great alternative to titrators saving time and materials”.

– Pharmaceutical plant, Austria

Full system of Indigo520 transmitter and process refractometer

The Vaisala Polaris paired with the Indigo520 transmitter for process refractometers makes an impressive duo, offering compelling features to suit all users. Indigo520 enables data logging, prism wash control, adjustment of settings and measurement parameters, and Indigo service updates. 

The Indigo520 for process refractometers offers versatile system connectivity by two selected analog or digital inputs for process refractometers and other Indigo-compatible probes, four configurable analog outputs to alarm relays, and ModBus TCP/IP digital protocol. 

Completely digital measurement principle based on physics

The refractometer operates on the principle of critical angle measurement. Inside the refractometer, there is a light source, a prism, and an image detector. Light rays with varying angles are emitted 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 critical angle is the angle at which the total reflection begins. 

The CCD camera inside the refractometer detects a bright field and a dark field corresponding to partly and totally reflected light, respectively. The position of the borderline between these fields indicates the critical angle, which is proportional to the refractive index and thus the solution's concentration. As the measurement principle is based on physics and the law of refraction, it is drift-free. 

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 Polaris process 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) and the law of refraction.

5 generations of refractometers

Latest: Vaisala Polaris™ process refractometer product family


Refractometer models and applications by industry

Process refractometers help to achieve desired product specifications with improved product quality while optimizing the process and saving on energy consumption, raw materials, water, steam, and chemicals. 


Inline concentration measurement of acids, alkaline solutions, alcohols, hydrocarbons, solvents, and various other solutions in chemical industry

Measure changes in concentrations of liquid chemicals in the harshest conditions of chemical processing industry. See the typical processes and applications where the inline refractometer can be used for product quality and process control. 

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Food and beverage

Inline Brix, total dissolved solids, or other other liquid concentrations for dairy, whey, brewing, juices, soft drinks, meat and fish products, ingredients, and fruit and vegetables processing.

Stable inline liquid concentration measurements for instant productivity and material gains, and simplified process operation. Learn more from the application examples.

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Oil refining and petrochemical

Loading and unloading operations, sulfuric acid alkylation, amine gas treating, gas dehydration, and lube oil production

Eliminate sampling, improve product consistency and operations safety and optimize the process with the help of Vaisala Polaris process refractometometers.   

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Pharmaceutical and biotechnology

Active Pharmaceutical Ingredients (API) development and production, Pharmaceutical fermentation, Vaccine and penicillin production, Protein concentration and filtration

The Polaris Process Refractometer provides continuous, accurate, and repeatable measurements to optimize R&D and production processes. 

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Pulp and paper

Black liquor, green liquor, brown stock washing, filtrates, and other liquids in chemical recovery line and fiberline

Optimize processes in the pulp and paper industry

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KOH (Potassium hydroxide), H2SO4 (Sulfuric acid), HF (Hydrofluoric acid), NH4OH (Ammonium hydroxide), HCl (Hydrochloric acid), IPA (Isopropyl alcohol), EKC, CMP slurries, and others

Real-time concentration monitoring of wet chemical processes, including wafer manufacturing, etching, and cleaning 

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Cane and beet sugar crystallization control

Inline process refractometer for advanced supersaturation control and ensuring fine crystal formation and growth. Learn how to optimize cane and beet sugar refining and milling processes to achieve substantial energy conservation.

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Total dissolved solids (TDS) measurement in the production of starch sweeteners and sugar substitutes such as glucose (dextrose), fructose glucose syrup, corn syrup, and sorbitol.

Inline liquid concentration measurement for liquid and crystal sweeteners manufacturing. Learn how to use the inline process refractometer to optimize downstream processes and comply with tight final product specifications.

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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 eliminates 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 Pt1000 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.

Read more from our accuracy statement here 

Easy on-site instrument verification

The refractometers are delivered calibrated 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 verification procedure.

Easy installation

Installation in the main processing line or vessel directly or via variety of flow cells; no by-pass arrangements are required. Also in vessels with mixers or scrapers is possible. Engineered custom solutions available.


The refractometer requires no regular maintenance as there are no wear and tear 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.


Liquid measurement related products

Vaisala Polaris PR53GP

Vaisala Polaris™ PR53GP Process Refractometer

Measure concentrations of sugars/Brix, acids, alkaline solutions, alcohols, hydrocarbons, solvents, and various other solutions directly in pipeline and tanks, in production transport and quality control in sugar, chemical, petrochemical, and other industries.

Support material of the previous generations

Manuals, approvals, certificates, safety instructions, and videos 

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