CMC iTMA-202 Electrolytic Dew Point Analyzer for Chlorine and Corrosive Gases

Overview

The CMC iTMA-202 is a high-stability, online electrolytic dew point analyzer engineered for continuous, absolute moisture measurement in aggressive and reactive process gases—particularly chlorine (Cl₂), hydrogen chloride (HCl), sulfur dioxide (SO₂), hydrogen sulfide (H₂S), and other high-purity acid or oxidizing gases. It employs the internationally recognized phosphorus pentoxide (P₂O₅) electrolytic principle: water vapor in the sample gas is quantitatively decomposed at a thin-film H₃PO₄-coated electrode pair (typically Pt or Rh wire), generating hydrogen and oxygen. The resulting electrolytic current is stoichiometrically proportional to the water concentration, enabling trace-level detection without reliance on calibration drift or external reference standards. Unlike chilled-mirror or capacitive sensors, the P₂O₅ cell delivers true absolute measurement—no zero or span recalibration required under normal operation. Its robust glass-cell construction, microprocessor-controlled auto-ranging electronics, and integrated self-diagnostic routines ensure long-term reliability in demanding chemical, semiconductor, and specialty gas production environments.

Key Features

• True absolute moisture measurement via P₂O₅ electrolysis—no periodic recalibration needed
• Ultra-fast response: T₉₀ < 1 second; T₅₀ < 8 seconds—enabling real-time process control
• Four selectable measurement ranges (0–10 ppm to 0–2500 ppm) with automatic or manual switching
• Full-scale accuracy of ±1% and repeatability of ±0.1%, validated across temperature and pressure variations
• Integrated touchscreen interface with configurable language support (including English, German, Chinese)
• NAMUR-compliant output architecture: two programmable relay alarms and fully isolated 4–20 mA analog output
• Onboard self-test at power-on and continuous sensor health monitoring
• Electrode regeneration capability—restores membrane integrity without instrument downtime
• Optimized for low-flow, low-pressure sampling: 20 NL/h at 0.1–0.5 barg, compatible with standard gas sampling manifolds

Sample Compatibility & Compliance

The iTMA-202 is specifically validated for use with corrosive, non-reactive, and flammable gases including Cl₂, HCl, SO₂, H₂S, F₂, O₃, SF₆, freons, natural gas, and high-purity inert carriers (Ar, Kr, Xe, He, N₂). It excludes only gases known to chemically attack phosphoric acid films (e.g., strong alkalis or reducing agents with catalytic activity toward P₂O₅). All wetted components—including the sensor cell, inlet fitting, and internal flow path—are constructed from chemically resistant materials (borosilicate glass, platinum/rhodium electrodes, PTFE seals) to prevent adsorption, condensation, or catalytic interference. The analyzer meets NAMUR NE 21 and NE 43 recommendations for signal conditioning and fault signaling. While not intrinsically safe certified, it is suitable for installation in Zone 2/Class I, Div. 2 areas when paired with appropriate barrier systems. Data logging and configuration adhere to GLP-aligned practices, supporting audit-ready operation in regulated manufacturing (e.g., ISO 8573-3, ASTM D6673, IEC 61511).

Software & Data Management

The embedded firmware provides full local control via the 5.7″ resistive touchscreen, supporting real-time trend visualization, alarm history, sensor status logs, and range-switching events. Configuration parameters—including analog output scaling, alarm thresholds, sampling interval, and language selection—are stored in non-volatile memory. Optional RS-485 Modbus RTU communication enables integration into SCADA or DCS platforms for centralized data acquisition. No proprietary software is required for basic operation; however, CMC’s optional PC-based configuration utility (iTMA ConfigTool v3.x) supports advanced diagnostics, firmware updates, and export of CSV-formatted measurement logs. All timestamped events—including power cycles, range changes, and alarm triggers—are retained with millisecond resolution. The system complies with FDA 21 CFR Part 11 requirements when deployed with user-access controls and electronic signature protocols enabled via external authentication infrastructure.

Applications

• Chlor-alkali plant off-gas monitoring: real-time Cl₂ drying verification prior to liquefaction or cylinder filling
• HCl synthesis and purification lines—ensuring compliance with ISO 8573-3 Class 1 (≤0.1 ppmv H₂O) specifications
• SF₆ reclamation and recycling systems in high-voltage switchgear maintenance
• Electronic-grade specialty gas production (e.g., etchant gases for semiconductor fabs)
• Hydrogen sulfide abatement unit effluent monitoring per EPA Method 18 and ISO 10156
• Continuous quality assurance in bulk gas delivery systems serving pharmaceutical cleanrooms
• Research applications involving reactive gas kinetics where water contamination must be held below 1 ppmv

FAQ

How does the P₂O₅ sensor achieve absolute measurement without calibration?
The electrolytic decomposition of water follows Faraday’s law: each mole of H₂O yields a fixed charge (2 × 96,485 C/mol). The instrument measures this current directly, referencing only fundamental constants—not empirical calibration curves.
Can the iTMA-202 measure moisture in wet chlorine gas containing hydrochloric acid mist?
Yes—provided the sample is filtered to remove liquid aerosols (<0.3 µm particulate filter recommended) and cooled to avoid condensation upstream of the sensor. The P₂O₅ cell tolerates trace HCl vapor but not free-phase acid.
What maintenance is required for long-term stability?
Annual verification using a certified moisture standard gas is recommended. Electrode regeneration (via built-in current pulse sequence) extends sensor life beyond 24 months in typical Cl₂ service.
Is the 4–20 mA output linear across all ranges?
Yes—the analog output scales linearly to the active measurement range (e.g., 4 mA = 0 ppm, 20 mA = full-scale value), automatically adjusting during range switches.
Does the analyzer support HART communication?
No—only Modbus RTU over RS-485 is supported. HART compatibility requires external protocol converters.