An inline refractometer is a real-time concentration measurement instrument based on the principle of optical refraction. When light passes from one medium into another, its path is deflected; this angle of deflection is directly related to the content of soluble solids in the liquid.
The Inline Refractometer measures and displays parameters required by users, such as concentration (%) and Brix. It can be directly installed on pipelines or reactors to enable real-time, continuous, and online monitoring of liquid concentration during the production process. Compared to traditional manual sampling methods, the inline refractometer completely eliminates sampling delays and human error.
| Measuring Principle | Critical angle of total internal reflection. Readings are not affected by bubbles, suspended solids or sample color. |
| Robust Construction | Sapphire prism with 316L stainless steel housing. Resists corrosion and is rated to 1.5 MPa. |
| Temperature Compensation | A built-in sensor tracks process temperature in real time and automatically compensates readings to a reference temperature. |
| Low Maintenance | Modular design with no wearing parts, so it needs very little routine service. |
| Model | CRN50 | CRN52 | CRN56 |
|---|---|---|---|
| Measured Parameters | Refractive index, temperature, concentration, Brix (or other scales) | ||
| Displayed Parameters | Refractive index (nD), Brix (temperature-compensated per sucrose), concentration (Conc), temperature (°C) | ||
| Data Processing | Probe status diagnostics, RI calibration and adjustment, user self-modeling, multi-point temperature compensation, concentration curve correction | ||
| Concentration Range | 0.0–90% Brix | 0.0–100% Brix | |
| Refractive Index Range | 1.33299–1.51782 | 1.33299–1.57041 | |
| Process Temperature | 0–60 °C | 0–70 °C | -10–100 °C |
| Cleaning Temperature | -30–120 °C, supports CIP (clean-in-place) and SIP (sterilize-in-place) | ||
| Resolution | 0.01%; refractive index 0.00001; temperature 0.1 °C | ||
| Accuracy | ±0.1%; refractive index 0.0001; temperature 0.5 °C | ||
| Process Connection | Compact clamp (optional flange: DN25 / DN50 / DN65 / DN80) | ||
| Wetted Materials | SS316L + high-strength optical glass | SS316L + sapphire (optional: PTFE, Hastelloy, titanium, tantalum) | |
| Power Supply | Standard: 24 VDC; optional: 100–240 VAC, 50/60 Hz, 30 VA | ||
| Cable Length | Standard 2 m, extendable up to 200 m | ||
| Display | 1.4-inch on-board display | ||
| Signal Output | 4–20 mA / RS485 / RS232 / USB | ||
| Ingress Protection | Wetted part IP68 | ||
| Pressure Rating | ≤1.5 MPa | ||
| Explosion Protection | Ex ia IIC T6 Ga | ||
| Net Weight | ≈1.0 kg | ||
| Cleaning Options | CRN5-C1 ultrasonic cleaning assembly; CRN5-C2 high-pressure flushing assembly | ||
| Installation Options | Small-bore pipe adapter, tee / cross (with sight window), sanitary adapter, etc., customized to installation conditions | ||
Optional Accessories
Compact clamp-style mount; available in sizes: DN25/DN50/DN65/DN80.
Total length: 121.45 mm; distance from clamp face to rear: 114.45 mm;
Probe extension length: 26.15 mm; finned housing length: 63.50 mm;
Clamp outer diameter: Φ77.50 mm; probe diameter: Φ31.00 mm (with options for Φ56.00 / Φ48.00 mm);
Electrical connection: GX20 12-pin aviation connector; display window height: 14.86 mm.
Measurements with an inline refractometer begin with the propagation of light. Light emitted by a high-brightness LED is guided through a low-loss optical fiber and introduced from a specific side of the prism. Inside the prism, the light follows a carefully designed reflection path until it reaches the interface between the prism and the liquid being measured. At this critical interface, the propagation behavior of light differs significantly due to the varying refractive indices of the two liquids.
According to optical principles, when light travels from a denser medium to a less dense medium, total internal reflection occurs at a specific angle of incidence.
In an online refractometer, some light rays satisfy the conditions for total internal reflection and are completely reflected to the other side of the prism. Furthermore, the position of the total internal reflection light changes as the critical angle varies, since the critical angle is closely related to the liquid’s refractive index; even slight changes in the liquid’s refractive index directly cause corresponding changes in the critical angle.
To accurately capture changes in the position of the total reflection light, the online refractometer employs a linear array CCD. It precisely detects the position of the light-dark boundary of the total reflection light, with each specific position uniquely corresponding to a specific refractive index value.
It is worth noting that there is a clear correlation between the solution concentration and the position of the light-dark boundary: as the solution concentration increases, the light-dark boundary shifts further to the left.
The online refractometer uses optical methods to measure the critical angle of the solution and employs a hybrid analog-digital principle to determine the solution’s concentration. A light source inside the sensor emits light at different angles toward the prism and the interface with the solution being measured.
Due to the different angles of incidence, the light behaves differently at the interface: some light is totally reflected, some is partially reflected, and most is refracted into the solution being measured, thereby creating a unique optical image consisting of bright and dark regions at the interface.
The angle of incidence corresponding to the boundary line between the dark and bright zones is defined as the “critical angle.” Changes in the critical angle directly alter the brightness-to-darkness ratio detected by the CCD sensor; this ratio is, in fact, a function of the refractive index.
Given the stable correlation between solution concentration and refractive index, the solution’s concentration can be accurately determined by precisely measuring the critical angle.
During signal detection and processing, the online refractometer uses a digital CCD (charge-coupled device) to meticulously detect the optical image and the boundary shadow line. It converts complex image information point by point into electrical signals that are easy to process. Through precise analysis of these electrical signals, the exact position of the boundary shadow line is determined, thereby accurately measuring the refractive index nD.
At the same time, the probe incorporates a high-precision temperature sensor that measures the temperature of the medium at the interface in real time.
After acquiring data on the refractive index nD and temperature T, the transmitter automatically performs temperature compensation based on a preset algorithm, thereby precisely calculating and intuitively displaying the concentration value of the liquid.
The preliminarily processed electrical signals undergo further gain amplification and are then converted into various practical parameters, such as mass concentration, solids content, Brix, density, and refractive index. These parameters are not only clearly displayed locally on the instrument but can also be transmitted over long distances via remote transmission technology, providing robust support for real-time monitoring and automated control in industrial production processes.
Thanks to its high accuracy, real-time performance, and stability, the Inline Refractometer has found widespread application in numerous fields.
In the food and beverage industry, it can be used to monitor concentration during the production of products such as sucrose, fruit puree, jelly, soft drinks, fructose, milk, beer, glucose, fruit juice, and bone broth, ensuring stable and consistent product quality.
In the chemical industry, it is suitable for concentration testing of various chemical raw materials and products, such as sulfuric acid, hydrochloric acid, phosphoric acid, sodium hydroxide, ammonia water, urea, surfactants, ethylene glycol, hydrogen peroxide, sodium hypochlorite, methanol, and ethanol, thereby ensuring the safe and efficient operation of chemical production.
In other industries, such as the concentration measurement of cutting fluids, coolants, DMF, DMAC, PVOH, traditional Chinese medicine concentrates, emulsions, slurries, polyurethanes, alcohol extracts, sodium carbonate, glycerin, gelatin, and collagen peptides, it also plays a vital role in helping various industries improve production efficiency and product quality.
With their advanced measurement principles and wide range of applications, online refractometers have become indispensable tools in modern industrial production and scientific research.
The inline refractometer reads only the liquid touching the prism window. A good installation keeps that window fully covered by a moving, bubble-free sample.
The sample must fill the pipe and cover the prism surface. Positions ① to ③ are recommended. Positions ④ and ⑤ are not allowed.
Never install the probe with the prism facing down, whether on a pipe or a tank. On a horizontal line, gas collects at the top of the pipe. In a vertical line with downward flow, the pipe may not run full.
On large and medium pipes, insert the probe at an angle with the tip facing the flow. On 2-inch and smaller lines, use a flanged spool piece so the tip sits in the flow path. On vessels, mount through the wall at a point where the liquid is moving.
Zhang Wei, possesses 20 years of experience as an automation instrumentation engineer, specializing in the research, design, installation, commissioning, and maintenance of automation instruments.
Face to various instrument communication protocols (such as Modbus, Profibus, etc.), with solid hardware circuit design and software programming skills (proficient in C language and PLC programming). Has extensive project experience; projects he has led and participated in have all achieved outstanding results, improving product accuracy, reducing costs, and increasing production efficiency.
Possesses excellent communication and coordination skills and a strong team spirit, enabling him to quickly respond to customer needs and provide high-quality automation instrumentation solutions.