In chemical, petrochemical, refinery, sugar and process industries, liquid concentration measurement is a critical parameter for production efficiency, quality control and process safety. Many applications involve aggressive chemicals, hydrocarbons, acids, alkaline solutions or solvents, and some of these processes are located in potentially explosive environments.
The Vaisala Polaris PR53GPEX Probe Process Refractometer is designed for these demanding applications. With optical refractive index measurement, ATEX and IECEx compliance, Zone 0 and Zone 2 options, robust stainless steel construction and built-in analog and digital outputs, PR53GPEX provides reliable inline concentration measurement directly in the process stream.
What Is PR53GPEX?
The PR53GPEX is a general-purpose probe process refractometer designed for potentially explosive environments. It is used to measure liquid concentrations in pipelines or tanks.
Typical measured applications include sugars / Brix, acids, alkaline solutions, hydrocarbons, solvents and various other liquid solutions. The device is suitable for production and quality-control applications in the sugar, chemical, petrochemical and other process industries.
Because it is installed directly into the process, PR53GPEX enables continuous real-time concentration measurement without the need for manual sampling or laboratory delay.
Optical Measurement Principle
PR53GPEX measures concentration using refractive index, also known as RI. Refractive index is an optical property of liquids and responds to dissolved material in the process medium.
The measurement is continuous and inline. The refractometer measures the RI of the liquid and converts it into concentration units such as Brix, acid concentration, sodium hydroxide concentration or other configured concentration curves.
A major advantage of optical RI measurement is that it is not affected by bubbles, particles, suspended solids, fibers or liquid color. This makes PR53GPEX suitable for process liquids where traditional measurement methods may be disturbed by optical appearance, turbidity or process impurities.
Designed for Potentially Explosive Environments
One of the key strengths of the PR53GPEX is its suitability for hazardous areas. The PR53EX series can be installed directly into hazardous environments where flammable gas, vapor or mist may be present.
The product has two Ex certified options: Zone 0 and Zone 2.
For Zone 0 environments, a galvanic isolator is installed between the potentially explosive area and the refractometer to ensure safe operation. This makes the device suitable for applications where continuous exposure to potentially explosive environments must be considered.
PR53GPEX is compliant with ATEX and IECEx, supporting use in international hazardous-area installations.
Ex Classification
The datasheet lists Ex classification for Europe and international applications.
For Europe ATEX Zone 0, the certification is EESF 25 ATEX 025X, with classification II 1G Ex ia IIC T4…150 °C (T3) Ga, IP66.
For Europe ATEX Zone 2, the certification is EESF 25 ATEX 013X, with classification II 3G Ex ec IIC T4…150 °C (T3) Gc, IP66.
For international IECEx applications, Zone 0 and Zone 2 classifications are also listed, including Ex ia IIC T4…150 °C (T3) Ga and Ex ec IIC T4…150 °C (T3) Gc.
These certifications make the PR53GPEX suitable for demanding chemical and petrochemical environments where explosion protection is required.
Refinery Probe Head Option
The PR53GPEX can be ordered with a refinery probe head option. This option is designed to support the specific requirements of refining and petroleum industry applications.
Typical refinery applications include acid in alkylation, glycol or amines in gas processing, and multi-product interfaces such as crude oil, fuel oil and diesel in transfer operations.
The refinery probe head is machined from a single piece of metal. This allows weld-free pressure-bearing components, which is especially important in demanding petroleum and refinery processes.
Measurement Performance
The PR53GPEX has a refractive index measurement range of 1.32–1.53 nD, corresponding to 0–100 °Bx.
Accuracy is specified as ±0.00014 nD, equivalent to approximately 0.1 °Bx. Repeatability is ±0.000017 nD, and resolution is ±0.000001 nD.
The measurement cycle is 1 measurement per second, and the response time is 10 seconds with default damping.
Long-term stability is specified as maximum 0.1% of full scale per year, supporting stable process control over long operating periods.
Temperature Measurement
The PR53GPEX also includes temperature measurement. Temperature accuracy at 20 °C / 68 °F is ±0.3 °C / 0.54 °F.
The temperature sensor class is F0.15 according to IEC 60751, and the temperature coefficient is ±0.002 °C / °C.
Temperature measurement is important because concentration calculations often require temperature compensation. By measuring process temperature directly, the refractometer supports accurate and stable concentration output under changing process conditions.
Process Conditions
PR53GPEX is designed for demanding process environments. The process temperature range is -40 °C to +150 °C.
The design temperature is +180 °C, defined as a maximum momentary temperature peak. The design pressure is 40 bar, maximum at +20 °C, with operating pressure depending on the process connection rating.
The datasheet also includes process pressure curves for different connection types such as DIN flange, ANSI flange, JIS flange and L coupling. These curves help users evaluate allowable process pressure according to temperature and connection selection.
Operating Environment
The device can be used indoors and outdoors and is suitable for wet locations.
The operating temperature range is -40 °C to +60 °C, and the storage temperature range is -40 °C to +65 °C.
Operating humidity is 0–100% RH, and storage humidity is 0–100% RH non-condensing.
The enclosure has IP66 protection and UL 50E Type 4X rating. These ratings support installation in industrial and washdown environments.
Outputs and Communication
PR53GPEX includes built-in analog and digital outputs. Output parameters include refractive index, temperature, concentration and quality factor.
The analog mA output is configurable and follows NAMUR NE 43. The ia variant uses sinking isolated output, while the ec variant uses sourcing isolated output.
The mA range is 3.8–20.5 mA. Maximum load is 800 Ω for the ia variant and 600 Ω for the ec variant.
Digital communication is provided through RS-485 Modbus RTU, with maximum digital cable run of 300 m / approximately 1000 ft.
The device also supports HART communication, giving users flexible integration options for process automation systems.
Power Supply
For Zone 2 only, the supply is 24 VDC nominal, with operating voltage range of 9–30 VDC.
Power consumption is less than 1 W, making the device suitable for continuous industrial operation with low energy demand.
For intrinsically safe Zone 0 installations, the datasheet lists intrinsically safe parameters for VIN, RS-485 and analog output terminals.
Compatibility with Vaisala Indigo520
PR53GPEX can be interfaced directly or connected to a Vaisala Indigo520 transmitter.
When connected to Indigo520, users gain access to additional functions such as data storage, graphical interface, analog interface and digital interface.
Indigo520 is required when the application or installation position requires a wash system to control the process. Settings, measurement parameters and service updates can be managed directly from Indigo520 or through a USB cable using Vaisala software.
The PR53GPEX can also be connected to the Indigo80 handheld indicator, which is useful for portable diagnostics and field service.
Mechanical Construction
The wetted refractometer head material is EN 1.4404 / AISI 316L stainless steel. The surface roughness is Ra 0.8 µm.
The prism is sapphire monocrystalline, 99.996% Al₂O₃, and the prism gasket is modified PTFE. These materials support durability in demanding chemical and process conditions.
Non-wetted parts also use high-quality stainless steel materials. The housing is EN 1.4404 / AISI 316L, while screws are also AISI 316L. Cable glands and blanking plugs are AISI 303.
Material certificates and manufacturer declarations are included for specified components.
Process Connections and Mounting
PR53GPEX is available with clamp and flange connections. The datasheet includes dimensions for 2" flange, 3" flange, L coupling 88.9 mm / 3.5 in, L coupling clamp and the refinery probe head.
For a 2" flange version, the insertion depth is 110 mm. For a 3" flange version, the insertion depth is 130 mm.
Flange dimensions are available for ANSI, DIN and JIS standards, making the product adaptable to different plant standards and installation requirements.
Accessories
Several accessories are available for PR53GPEX. These include a USB adapter for the service port, instrument cables in different lengths, a cooling cover, RS-485 isolator and analog signaling / power isolator.
The cooling cover may be recommended or mandatory depending on the combination of ambient temperature and process temperature.
Calibration accessories are also available, including a verification kit, calibration kit, high-range special kit and sample holder with cover.
These accessories support commissioning, verification, diagnostics and long-term service.
Typical Application Areas
PR53GPEX is suitable for concentration measurement in potentially explosive areas across several industries.
Typical applications include sugar / Brix measurement, acid concentration, sodium hydroxide concentration, alkaline solutions, hydrocarbons, solvents, chemical processing, petrochemical production, refinery operations, gas processing, alkylation acid monitoring and multi-product interface detection.
Because the measurement is not affected by bubbles, particles, suspended solids or color, it can be used in many process streams where stable inline concentration measurement is required.
Why Choose PR53GPEX?
PR53GPEX is a strong choice when the application requires accurate inline concentration measurement in hazardous environments.
It combines optical refractive index technology, ATEX and IECEx certification, Zone 0 and Zone 2 options, robust AISI 316L construction, sapphire prism, Modbus RTU, HART, 4–20 mA output and Indigo520 compatibility.
Its no-moving-part design reduces maintenance requirements, while long-term stability supports continuous process control and quality assurance.
Conclusion
The Vaisala Polaris PR53GPEX Probe Process Refractometer is a robust inline concentration measurement solution for potentially explosive environments. With refractive index measurement, ATEX and IECEx certification, Zone 0 and Zone 2 options, 1.32–1.53 nD measurement range, 0.1 °Bx accuracy, -40 °C to +150 °C process temperature, 40 bar design pressure, IP66 / Type 4X protection, and built-in 4–20 mA, HART and Modbus RTU outputs, it provides reliable performance for demanding process industries.
For sugar, chemical, petrochemical, refinery and hazardous-area applications, PR53GPEX delivers continuous, accurate and stable concentration measurement directly in the process stream.