How It Works
The science behind inline water measurement
All Zelentech instruments are based on capacitance measurement — the same physical principle used in laboratory instruments, adapted for continuous inline use in industrial pipelines and process systems. This page explains how it works, why inline measurement is better than sampling, and how our approach compares to alternative technologies.
The Measurement Principle
Water and oil have dramatically different dielectric constants (permittivity). Pure oil has a dielectric constant of approximately 2, while water has a dielectric constant of approximately 80. This 40× difference makes capacitance measurement an exceptionally sensitive method for detecting water in oil.
A Zelentech sensor consists of two electrodes that form a capacitor, with the process fluid flowing between them. As water content changes, the dielectric constant of the fluid mixture changes proportionally, altering the capacitance. The instrument’s electronics measure this capacitance change with high precision and convert it to a water content reading.
Advanced temperature compensation algorithms account for the temperature dependence of both the oil and water dielectric constants, ensuring accurate measurement across the full operating range.
Why Add Inline Monitoring
Continuous
Inline measurement provides a reading every second — filling the gaps between scheduled samples and capturing transient events like water slugs, separator carry-over, and seal failures as they happen.
Representative
The sensor measures the actual process stream as it flows through the pipe. No sampling valve, sample line, or sample container to introduce error or change the water-oil distribution.
Reduces Handling Error
Grab samples are subject to container contamination, poor mixing, and settling during transport. Continuous inline data provides a reliable baseline that complements periodic lab verification.
Real-Time Response
Live readings enable closed-loop control, automatic divert on high water content, and immediate alarm response — acting on process changes between scheduled sampling intervals.
Safe
Reduces the need to open valves, collect samples, and transport containers of hazardous fluids in classified areas. The ATEX/IECEx certified instrument monitors continuously without operator exposure.
Cost Effective
Reduces the frequency and cost of manual sample collection, transport, and laboratory analysis — while providing far more data points per day than any sampling programme.
Zelentech vs. Alternative Technologies
Capacitance Zelentech
How it works: Measures the dielectric constant of the oil-water mixture between two electrodes.
Strengths: High sensitivity across full range. Measures total water (dissolved + free + emulsified). No consumables, no radioactive sources, no optical windows. Works in all oil types.
Best for: Crude oil pipelines, industrial oils, vegetable oils, glycol — any liquid where water content needs continuous monitoring.
Microwave / RF
How it works: Measures microwave absorption or phase shift through the fluid.
Strengths: Good for high-salinity crude oil where capacitance readings can be affected by dissolved salts. Handles high water cuts well.
Limitations: More expensive. Larger physical size. More complex calibration. Less suited to industrial oils and low water cut applications.
Water Activity / Relative Humidity
How it works: Measures the equilibrium water vapour pressure above the oil (water activity).
Strengths: Good for monitoring dissolved water trends in clean transformer and turbine oils at very low levels.
Limitations: Only measures dissolved water. Cannot detect free or emulsified water — fails precisely when contamination is most dangerous (above saturation point). Reports relative saturation, not actual water content.
Near-Infrared (NIR)
How it works: Shines NIR light through the fluid and measures absorption at water-specific wavelengths.
Strengths: Very accurate in laboratory settings. Good for clean, transparent fluids.
Limitations: Optical windows foul in crude oil and dirty process streams. Not practical for inline use in most field applications. Primarily a laboratory technology.
Reference Methods — Lab & Field
Karl Fischer Titration
How it works: Chemical reaction that consumes water in a sample, measured electrochemically.
Strengths: The definitive reference method for water content. Extremely accurate. Used for calibration and certification.
Limitations: Batch laboratory method — not real-time, not inline. Requires trained operators, consumable reagents, and 15–30 minutes per test. Used to validate, not replace, inline instruments.
ASTM D4007 — Centrifuge BS&W
How it works: Equal volumes of crude oil and water-saturated toluene are mixed in a cone-shaped centrifuge tube and spun at high speed. The heavier water and sediment phase separates to the pointed bottom, where the volume is read directly from the graduated scale.
Strengths: Widely used field and lab method for crude oil BS&W determination. Portable centrifuges allow on-site testing at wellheads, tank farms, and custody transfer points. Results in 10–15 minutes. Simple, well-understood by field operators.
Limitations: Manual grab sample required — not continuous. Results depend on sample quality, solvent ratio, and centrifuge speed. Does not detect dissolved water or emulsions that resist separation. Typically resolves to 0.1% at best. Used alongside inline instruments, not as a replacement.
Hazardous Area Certifications
Most water-in-oil measurement applications are in hazardous areas where flammable gases or vapours may be present. Zelentech instruments carry hazardous area certifications for global deployment — from international IECEx through regional schemes in Europe, Brazil, and the Middle East.
All certificates are based on the flameproof enclosure protection concept (Ex db) rated for Gas Group IIC (including hydrogen) and Temperature Class T4 (≤135 °C surface temperature), suitable for Zone 1 and Zone 2 installations.
IECEx — International
IECEx QPS 19.0007X Issue 2 — Ex db IIC T4 Gb
The international certification scheme recognised in over 30 countries. IECEx forms the technical basis for most national schemes, including ATEX, INMETRO, and ECAS. One test report, globally accepted.
ATEX — European Union
CML 19ATEX1356X — Ex db IIC T4 Gb
EU Directive 2014/34/EU for equipment used in explosive atmospheres. Required for all EU and EEA member states. Type examination by CML B.V. (Notified Body 2776).
INMETRO — Brazil
LMP 24.0560X — Ex db IIC T4 Gb
Brazilian national certification under INMETRO Portaria 115/2022. Required for hazardous area equipment installed in Brazil. Issued by LMP Certificações.
ECAS — United Arab Emirates
26-02-184073 / E26-02-192048 / NB0002
Emirates Conformity Assessment Scheme for hazardous area equipment. Required for installation in the UAE oil & gas sector. Issued by SGS under the Ministry of Industry and Advanced Technology.
cQPSus — North America
LR1538-1 — Ex db IIC T4 Gb
QPS Evaluation Services certification for Canada and the United States. Evaluated to CSA C22.2 No. 60079-0, -1 and UL 60079-0, -1. Based on the IECEx test report, providing market access across North America.
ISO 9001:2015 — Quality Management
QS-17-1531
Certified quality management system for design, manufacturing, and supply of fluid measuring instruments. SAC-accredited certification by EQA IMS Certification.
Communication Outputs
Zelentech instruments support the three most common industrial communication protocols, allowing integration with virtually any DCS, SCADA, PLC, or flow computer system:
4–20mA Analog
Industry-standard analog output. The water cut reading is mapped linearly to the 4–20mA range. Simple, reliable, and compatible with all industrial systems. Loop powered — no external power supply needed.
HART
Highway Addressable Remote Transducer protocol superimposed on the 4–20mA signal. Enables digital configuration, diagnostics, and multivariable data (water cut + temperature) over the same two wires.
Modbus RTU
Serial digital protocol for connection to PLCs and RTUs. Provides water cut, temperature, and diagnostic data over RS-485. Supports multiple instruments on a single bus.
Questions About Our Technology?
Our engineering team can help you understand which measurement approach is right for your application.