WTW SenTix 940 pH Electrode

Overview

The WTW SenTix 940 is an intelligent, high-precision pH electrode engineered for demanding field and laboratory applications requiring robustness, traceable calibration history, and seamless interoperability across WTW’s IDS-compatible meter platforms—including the Multi 3630, pH 3310, and IQ Sensor Net systems. Based on a proven glass membrane sensing principle combined with a polymer gel electrolyte and fiber junction reference system, the SenTix 940 delivers stable, low-drift measurements across the full aqueous pH range (0.000–14.000) while eliminating liquid electrolyte leakage and minimizing clogging in turbid or particulate-laden samples. Its integrated NTC temperature sensor enables automatic temperature compensation (ATC) with ±0.1 °C accuracy, and its IDS architecture embeds non-volatile memory directly into the electrode connector—storing calibration coefficients, slope history, offset values, and user-defined metadata for full metrological traceability.

Key Features

• Intelligent Digital Sensor (IDS) interface: Stores calibration data, slope, offset, and usage history directly in the electrode head—ensuring consistent performance when connected to any compatible WTW meter.
• Polymer gel electrolyte: KCl-free, maintenance-free design eliminates refilling, leakage, and crystallization; suitable for long-term immersion and portable use.
• Fiber junction reference system: Provides stable, low-resistance contact with minimal sample contamination and high resistance to fouling in wastewater, soil extracts, and biological media.
• Integrated Pt1000 NTC temperature sensor: Enables precise ATC without external probes; calibrated to ±0.1 °C over 0–80 °C.
• Rugged PPE/PS composite shaft: Chemically resistant, impact-tolerant housing rated for continuous operation up to 80 °C.
• Optimized response dynamics: Achieves t₉₀ <15 s in standard buffers and maintains repeatability within ±0.004 pH units under GLP-compliant conditions.

Sample Compatibility & Compliance

The SenTix 940 is validated for routine and regulatory-grade pH measurement in environmental monitoring (e.g., surface water, groundwater, wastewater per ISO 10523 and ASTM D1293), food & beverage QC (per AOAC and USP ), aquaculture, and academic research. Its gel-filled construction complies with IEC 60746-1 for electrochemical sensors and meets essential requirements of EU Directive 2014/30/EU (EMC) and 2011/65/EU (RoHS). When used with WTW meters supporting audit trail functionality (e.g., Multi 3630 ID), the electrode supports 21 CFR Part 11-compliant workflows through time-stamped calibration logs, user authentication, and electronic signature-ready data export.

Software & Data Management

Calibration events—including date, operator ID, buffer values, measured mV/pH, slope (%), and offset (mV)—are automatically written to the electrode’s internal EEPROM upon completion. WTW’s LabX® software (via USB or Bluetooth) retrieves this metadata alongside real-time measurement data, enabling automated report generation, trend analysis, and compliance documentation. All stored parameters persist across instrument changes, ensuring method consistency during multi-user or multi-site deployments. Firmware updates and sensor diagnostics are performed via IDS-compatible host instruments without requiring disassembly or third-party tools.

Applications

• Field-based environmental sampling: Continuous pH logging in rivers, lakes, and effluent streams using portable IDS meters with GPS tagging.
• Process monitoring in municipal wastewater treatment plants: Immersion in aeration tanks and final effluent channels with minimal maintenance.
• Quality control of potable water and bottled beverages: Compliance with WHO Guidelines and national drinking water standards (e.g., EPA Method 150.1).
• Biological and cell culture media testing: Stable performance in protein-rich or low-ionic-strength solutions where conventional liquid-junction electrodes drift.
• Educational laboratories: Demonstrates fundamental electrochemical concepts including Nernst equation validation, junction potential effects, and calibration uncertainty propagation.

FAQ

How does the IDS memory improve measurement integrity?
It stores calibration constants and history directly on the electrode, preventing manual entry errors and ensuring that each meter applies the correct slope and offset—even after swapping between instruments or operators.
Can the SenTix 940 be used in high-salinity or seawater samples?
Yes—the fiber junction resists clogging and provides stable reference potential in saline matrices; however, frequent rinsing with deionized water post-measurement is recommended to prevent salt buildup.
What is the recommended recalibration frequency?
Under routine use, daily calibration is advised; intervals may be extended to 8–12 hours for stable, low-risk applications—provided the meter’s built-in calibration timer and slope monitoring features are enabled.
Is the electrode compatible with non-WTW meters?
No—it requires an IDS-enabled host instrument; analog-only or non-IDS pH meters cannot read or utilize its embedded calibration data.
How should the electrode be stored when not in use?
Always store upright in the supplied wet cap filled with pH 4 or 7 buffer solution; never store dry or in distilled water, as this accelerates glass membrane dehydration and reference junction desiccation.