CUBIC INSTRUMENTS TDLAS-Based Online Dew Point Analyzer

Overview

The CUBIC INSTRUMENTS TDLAS-Based Online Dew Point Analyzer is a high-performance, in-situ optical moisture analyzer engineered for continuous, real-time measurement of water vapor concentration in industrial process gases. Utilizing Tunable Diode Laser Absorption Spectroscopy (TDLAS), the instrument achieves selective, interference-free detection of H₂O molecules by targeting a fundamental rotational-vibrational absorption line near 1.39 µm. This first-principles spectroscopic method eliminates cross-sensitivity to background gas composition—critical in complex hydrocarbon streams such as natural gas, LNG feed gas, and NGL recovery off-gas—where traditional chilled-mirror or capacitive sensors suffer from condensation artifacts, contamination drift, or calibration instability. Designed for integration into hazardous-area process loops, the analyzer delivers trace-level water quantification (0–6000 ppmv) with sub-ppmv resolution and metrological traceability to NIST-traceable standards. Its non-contact, no-moving-parts architecture ensures long-term stability (>2 years mean time between maintenance) and immunity to particulate fouling or pressure-induced mechanical hysteresis.

Key Features

• True in-situ TDLAS measurement—no sample extraction, no conditioning, no zero/span drift due to ambient humidity or temperature gradients
• High selectivity for H₂O: immune to CO₂, CH₄, H₂S, C₂H₆, and other common process gas constituents
• Fast response time (<2 s T₉₀) enabling dynamic dew point monitoring during cryogenic startup/shutdown sequences
• Intrinsically safe and explosion-proof design certified to Ex db IIC T6 Gb and Ex tb IIIC T80°C Db for Zone 1/21 deployment
• IP66-rated enclosure suitable for outdoor installation in refinery, LNG train, or offshore platform environments
• Dual output modes: simultaneous 4–20 mA analog (linearized to ppmv or °C_dp) and digital communication via RS-485 (Modbus RTU) and Ethernet (Modbus TCP)
• Onboard diagnostics including laser power monitoring, signal-to-noise ratio logging, and cell contamination alerting

Sample Compatibility & Compliance

The analyzer is validated for direct installation in pressurized gas streams across the hydrocarbon processing value chain—including acid gas removal units, molecular sieve dryers, cold box inlet/outlet lines, and LNG liquefaction trains. It complies with ISO 8573-3:2010 for compressed air purity class assessment and supports traceability to ASTM D6675 (Standard Test Method for Water Vapor Content of Natural Gas Using Laser Absorption Spectroscopy). The measurement cell operates at controlled internal pressure (800–1200 mbara), decoupling readings from upstream fluctuations. All wetted materials—316L stainless steel flow path, fused silica optical windows, and gold-coated mirrors—are compatible with sour gas (up to 100 ppmv H₂S) and low-temperature service (−60°C dew point capability). Full compliance with IEC 61508 SIL2 functional safety requirements is achievable when integrated with certified SIS logic solvers.

Software & Data Management

The embedded firmware supports configurable alarm thresholds (high/low, latching/non-latching) with relay outputs and event-triggered data logging. Optional CUBIC Cloud Connect module enables secure remote access, historical trend visualization, and automated report generation (PDF/CSV) aligned with 21 CFR Part 11 audit trail requirements. Data export includes timestamped raw absorbance spectra, calibrated ppmv values, dew point temperature (°C), and diagnostic metadata—enabling root-cause analysis of moisture excursions. Firmware updates are performed over-the-air via HTTPS with SHA-256 signature verification. Configuration is managed through a browser-based GUI supporting multi-language localization (English, Spanish, Arabic, Chinese).

Applications

• Continuous moisture monitoring upstream of cryogenic separation units to prevent hydrate formation and heat exchanger fouling
• Verification of molecular sieve bed breakthrough in natural gas dehydration skids
• Quality assurance of pipeline specification compliance (e.g., GPA 2145, ISO 13686)
• Real-time control of glycol regeneration efficiency in TEG contactors
• Monitoring of inert gas blanketing systems in pharmaceutical nitrogen supply networks
• Validation of purge gas dryness prior to catalyst charging in petrochemical reactors

FAQ

Does this analyzer require periodic calibration with certified gas standards?
No—TDLAS is an absolute measurement technique based on quantum mechanical line strength. Calibration is factory-performed using NIST-traceable reference cells; field verification requires only zero-check with ultra-dry nitrogen (≤0.1 ppmv) every 6 months.
Can it measure dew point below −70°C?
Yes—the instrument reports dew point down to −80°C (equivalent to ~0.5 ppmv at 1 atm), with full accuracy maintained across the entire 0–6000 ppmv range.
Is the optical path susceptible to window fogging or coating in high-hydrocarbon environments?
No—the measurement cell employs heated optical windows (maintained >20°C above process dew point) and laminar flow design to prevent condensate nucleation or hydrocarbon deposition.
What cybersecurity protocols are implemented for Ethernet-connected units?
TLS 1.2 encryption, role-based user authentication (admin/operator/viewer), disabled default credentials, and configurable firewall rules per IEC 62443-3-3 Level 2.
Is third-party system integration supported beyond Modbus?
Yes—OPC UA server option available; custom API integration via RESTful endpoints with JSON payload support.