WTW TriOxmatic 700IQ Electrochemical Dissolved Oxygen Sensor

Overview

The WTW TriOxmatic 700IQ is a high-reliability, digital electrochemical dissolved oxygen (DO) sensor engineered for continuous, long-term deployment in demanding water and wastewater applications. Based on the Clark principle—first established in 1956—the sensor employs a potentiostatic three-electrode polarographic architecture: a gold cathode (working electrode), a silver counter electrode, and an isolated silver reference electrode. This configuration ensures stable reference potential, minimizes polarization drift, and enables precise control of the electrochemical reaction at the cathode surface. Unlike conventional two-electrode systems, the tri-electrode design allows real-time monitoring of electrolyte consumption and membrane integrity—critical for predictive maintenance in unattended online monitoring environments. The 50 µm hydrophobic Teflon® membrane delivers exceptional fouling resistance and mechanical durability, making the TriOxmatic 700IQ particularly suited for activated sludge basins, aeration tanks, and industrial effluent streams where particulate load and biofilm formation are prevalent.

Key Features

• Potentiostatic 3-electrode system with gold working electrode, silver counter electrode, and electrically isolated silver reference electrode—ensuring long-term signal stability and minimal zero drift.
• Integrated self-diagnostic functions: SensReg monitors electrolyte volume depletion; SensLeck detects membrane breaches or seal failure—both logged and reported via IQ Sensor Net interface.
• Digital IQ interface enables automatic storage of calibration parameters, sensor history, and diagnostic events—supporting audit-ready traceability per FDA 21 CFR Part 11 and EU Annex 11 requirements.
• Robust mechanical design with IP68-rated housing and corrosion-resistant materials (316L stainless steel probe body, PEEK sensor cap) for immersion in aggressive municipal and industrial wastewater.
• Low-maintenance operation: Pre-assembled, field-replaceable membrane caps with factory-filled electrolyte; no routine cleaning required under typical wastewater conditions.
• Extended service life: Optimized electrolyte formulation and low consumption rate support operational lifetimes exceeding 5 years under continuous use—validated per IEC 62271-1 reliability testing protocols.

Sample Compatibility & Compliance

The TriOxmatic 700IQ is validated for use in freshwater, seawater (with optional FDO variants), municipal wastewater, activated sludge, anaerobic digesters, and industrial process streams containing suspended solids, oils, or moderate sulfide concentrations. It complies with EN ISO 5814:2012 (water quality—determination of dissolved oxygen—electrochemical probe method), ASTM D888-22 (standard test methods for dissolved oxygen in water), and USP (oxygen content in purified water and water for injection). When integrated into IQ Sensor Net networks, the sensor supports GLP-compliant data handling—including electronic signatures, user access controls, and immutable audit trails—meeting regulatory expectations for environmental compliance reporting and wastewater treatment plant certification (e.g., EPA NPDES permits).

Software & Data Management

The sensor communicates exclusively via the proprietary IQ Sensor Net digital bus protocol, enabling plug-and-play integration with WTW’s IQ line of transmitters (e.g., IQ SENSOR NET Multi 740, IQ MONITOR 700). All calibration coefficients, sensor identification, firmware version, and diagnostic logs are stored onboard and automatically synchronized during connection. Data export supports CSV and XML formats compatible with SCADA systems (Modbus TCP/RTU, OPC UA gateways available via IQ Link module). Firmware updates are performed remotely over the network, eliminating site visits for routine maintenance. Calibration history—including date, operator ID, standard used (e.g., air-saturation or Winkler titration reference), and post-calibration verification—remains permanently accessible for internal QA review or external regulatory inspection.

Applications

• Real-time DO monitoring in aerobic bioreactors and activated sludge processes—enabling dynamic aeration control to optimize energy consumption and nitrogen removal efficiency.
• Effluent compliance monitoring at wastewater treatment plant outfalls—supporting continuous reporting to environmental agencies (e.g., EU Urban Wastewater Treatment Directive, US Clean Water Act).
• Industrial process water surveillance in food & beverage, pharmaceutical, and power generation facilities—where DO levels impact corrosion risk, microbial growth, or boiler feedwater purity.
• Long-term environmental monitoring in rivers, lakes, and reservoirs—leveraging low-drift performance and minimal zero-point migration for seasonal trend analysis.
• Integration into automated nutrient removal control loops (e.g., ORP-DO cascaded control in denitrification/anammox zones), when paired with compatible WTW multi-parameter probes (e.g., pH, conductivity, ammonium).

FAQ

What distinguishes the TriOxmatic 700IQ from conventional two-electrode DO sensors?
The tri-electrode architecture isolates the reference potential from current flow, eliminating reference electrode polarization—a primary source of drift and calibration instability in traditional designs.
Does the sensor require frequent membrane replacement or electrolyte refilling?
No. The factory-sealed, pre-filled membrane cap is designed for 12–24 months of continuous operation under typical wastewater conditions; replacement is tool-free and takes under 90 seconds.
Can the TriOxmatic 700IQ be used in low-flow or stagnant water applications?
It requires a minimum flow velocity of 0.5 cm/s for optimal response; for zero-flow or ultra-low-flow scenarios, the FDO 700IQ optical variant is recommended.
Is calibration traceable to national standards?
Yes—calibration can be performed using NIST-traceable air-saturation standards or certified Winkler titration reference samples; all calibration metadata is digitally archived with time-stamped operator credentials.
How does the sensor handle hydrogen sulfide interference?
While robust against moderate sulfide levels common in sewage, prolonged exposure to >2 mg/L H₂S may accelerate cathode passivation; in such cases, periodic air-purging or use of the FDO 700IQ optical sensor is advised.