MEASURING REFRACTIVE INDEX nD IN ZONE 0 AT A TERPINEOL PRODUCTION PLANT

In chemical manufacturing plants, measurement accuracy is only one part of the equation. When a measuring instrument must be installed in an area where flammable gas/vapor mixtures may form, explosion protection and compliance with hazardous area classification become mandatory requirements.

This was precisely the challenge faced by a Terpineol production plant in Hà Nam, Vietnam, which needed to measure the refractive index nD of essential oil in a Zone 0 area.

The selected solution was the Vaisala Polaris™ PR53GCEX – an inline process refractometer designed for applications in potentially explosive environments, supporting Zone 0 configurations and meeting ATEX/IECEx requirements according to the applicable certified configuration.

1. The Real Challenge: Measuring nD in a Zone 0 Area

When measurement accuracy and safety requirements must be met simultaneously

During the Terpineol production process, the plant needed to monitor the refractive index (Refractive Index – RI/nD)of the essential oil.

Refractive index is an important parameter for monitoring the characteristics of a liquid and can be used as a basis for calculating concentration when combined with an appropriate concentration model.

However, the question is not simply:

“Can the instrument measure nD?”

It is also:

“Can the instrument be used safely in a Zone 0 area?”

Zone 0 is an area where a flammable gas/vapor mixture may be present continuously or for long periods. Therefore, electrical equipment installed in this area must meet the appropriate explosion protection requirements and use the correct certified configuration.

For the plant, selecting a conventional measuring instrument could create risks related to:

• Operational safety.
• Compliance with hazardous area classification requirements.
• Measurement continuity.
• Equipment control and management requirements in potentially explosive areas.

The challenge: a solution was required to measure refractive index nD directly in the process while remaining suitable for a Zone 0 environment.

2. The Solution: Vaisala Polaris™ PR53GCEX Process Refractometer

To address the above challenge, Filterfine Vietnam provided a solution using the Vaisala Polaris™ PR53GCEX – an inline process refractometer designed for potentially explosive environments.

The Vaisala PR53GCEX is designed to measure liquid concentration in a process pipeline based on the refractive index of the medium. The instrument is suitable for a wide range of chemical applications, including acids, alkaline solutions, alcohols, hydrocarbons, solvents, and various other solutions.

In particular, the PR53EX series includes versions certified for use in ATEX/IECEx Zone 0 and Zone 2. With the configuration intended for Zone 0, the instrument is designed to meet the requirements applicable to electrical equipment installed in hazardous areas.

From “Can It Measure?” to “Can It Measure Safely?”

Instead of taking samples out of the hazardous area for manual measurement, an inline process refractometer can be integrated directly into the process pipeline, providing measurement data directly from the process.

This approach helps reduce reliance on manual sampling operations and supports more stable process monitoring.

3. How Does the PR53GCEX Measure Refractive Index nD?

The Vaisala Polaris PR53 uses an optical refractive index measurement principle to determine the refractive index of the process medium.

For the PR53 series, the published refractive index measurement range is:

1.32–1.53 nD

Resolution: 0.000001 nD
Accuracy: ±0.00014 nD

The instrument also measures the temperature of the process medium. The measurement data can be used to calculate concentration through a predefined concentration model.

This is particularly useful in chemical manufacturing processes where companies need to continuously monitor process parameters instead of relying solely on laboratory testing of individual samples.

4. Why Is the PR53GCEX Suitable for the Terpineol Plant Application?

① Meets Hazardous Environment Requirements

This is the most important factor in the project.

The PR53GCEX is available in configurations certified under ATEX/IECEx for Zone 0, with the applicable configuration specified as Ex ia IIC T4…150 °C (T3) Ga IP66.

As a result, measuring nD in a hazardous area is no longer only a question of measurement accuracy, but is addressed simultaneously from the perspective of equipment safety.

② Direct Inline Process Measurement

The PR53GCEX is an inline process refractometer that can be installed on a process pipeline.

The instrument directly measures the refractive index and temperature of the process medium. A concentration model can then be used to calculate the corresponding concentration.

③ Optical Measurement Principle with No Moving Parts

The measurement method is based on the refraction of light through the liquid medium, allowing direct and continuous measurement.

This is an important advantage when the instrument is used in industrial processes that require continuous monitoring.

How Is the PR53GCEX Installed in Zone 0?

For a Zone 0 configuration, the PR53EX uses the Ex ia version together with an intrinsically safe cable. An isolator is installed between the hazardous area and the instrument; if an Indigo520 or Indigo80 is used, it is installed in the safe area.

5. Results of the Solution

Starting from the initial requirement:

Measuring the refractive index nD of essential oil in a Zone 0 area

the Vaisala PR53GCEX solution provides the plant with an approach for direct, continuous measurement suitable for hazardous environments, while meeting the requirement for refractive index measurement within the process.

The challenge is addressed across 3 key areas:

MEASUREMENT
Monitoring refractive index nD using an optical measurement principle.

SAFETY
Using a PR53EX configuration suitable for potentially explosive environments and Zone 0 according to the applicable certification.

INTEGRATION
Measurement data can be integrated into process monitoring/control systems through supported signals and communication protocols.

6. Filterfine Vietnam – Vaisala Representative in Vietnam

For high-performance process measurement instruments, selecting the right equipment is only the first step.

As a provider of Vaisala measurement solutions in Vietnam, Filterfine Vietnam supports customers from defining measurement requirements through to equipment implementation and operation.

For applications in hazardous environments, the technical team needs to consider multiple factors simultaneously, including:

• The process medium to be measured.
• The required nD/RI measurement range.
• Process temperature and pressure.
• Wetted materials.
• Installation location.
• Hazardous area classification: Zone 0/Zone 1/Zone 2.
• ATEX/IECEx requirements.
• Signal transmission and control system integration requirements.

7. Filterfine Vietnam After-Sales Service

An accurate measuring instrument can only deliver its full value when it is properly installed, configured, and maintained.

Filterfine Vietnam provides after-sales support for Vaisala measurement solutions, including:

🔧 Technical Consulting

Analysis of the application, process medium, operating conditions, and measurement requirements to support the selection of a suitable configuration.

⚙️ Installation & Operation Support

Guidance on installation, configuration, and commissioning according to application requirements.

📊 Measurement & Calibration Support

Support for equipment condition checks, measurement verification, and related calibration requirements.

🛠️ Maintenance & Troubleshooting Support

Ongoing support throughout equipment operation, including technical diagnosis and troubleshooting when issues arise.

🤝 Long-Term Partnership

Rather than simply supplying equipment, Filterfine focuses on providing comprehensive solutions that help businesses maintain measurement data reliability and process stability.

Conclusion: When Safety and Accuracy Must Go Hand in Hand

The case study at the Terpineol production plant in Hà Nam, Vietnam demonstrates a typical challenge in the chemical industry:

Not every measuring instrument capable of measuring nD can be used in a Zone 0 area.

For areas with explosion hazards, equipment must be selected based on both measurement requirements and the safety requirements of the installation area.

With the Vaisala Polaris™ PR53GCEX, businesses can access a solution for direct inline refractive index measurement while using a configuration certified for hazardous environments according to the applicable equipment configuration.

Are you looking to measure nD/RI or chemical concentration in an ATEX/IECEx hazardous area?

Filterfine Vietnam can advise on a suitable Vaisala configuration based on your process medium, operating conditions, and hazardous area classification.

📞 Hotline: 0961.152.844
🌐 Website: Filterfine Vietnam