AMT AMT-CTD/O2 Underwater Conductivity-Temperature-Depth and Dissolved Oxygen Profiling System

Overview

The AMT AMT-CTD/O2 is a compact, high-performance underwater profiling system engineered for simultaneous, real-time measurement of conductivity (salinity), temperature, depth (pressure), and dissolved oxygen (DO) in aquatic environments. It operates on well-established physical principles: conductivity via a 7-electrode cell for high-accuracy salinity derivation; temperature via Pt100 resistance thermometry; depth via piezoresistive pressure transduction; and dissolved oxygen via fast-response amperometric (voltammetric) microsensor technology. Unlike conventional Clark-type or optical DO sensors—whose slow response times (t₉₀ > 1–5 s) and membrane-dependent equilibration limit vertical profiling resolution—the AMT-CTD/O2 achieves t₉₀ ≤ 200 ms for O₂, enabling continuous, high-frequency vertical profiling without station-keeping or flow conditioning. This eliminates sampling artifacts caused by sensor hysteresis during rapid transitions between oxic and hypoxic zones, making it especially suitable for dynamic estuarine interfaces, benthic boundary layers, and AUV/ROV-mounted surveys where spatial resolution and temporal fidelity are critical.

Key Features

• Voltammetric dissolved oxygen microsensor with t₉₀ ≤ 200 ms and detection range 0–200% saturation (±2% saturation accuracy)
• High-stability Pt100 temperature sensor (−2 to +36 °C; ±0.05 °C accuracy; 0.0006 °C resolution; t₉₀ = 150 ms)
• 7-electrode conductivity cell (0–60 mS/cm; ±0.01 mS/cm accuracy; 0.001 mS/cm resolution; t₉₀ = 150 ms)
• Piezoresistive pressure sensor (0–10 bar; ±0.1% FS accuracy; 0.002% FS resolution; t₉₀ = 150 ms; equivalent to ~100 m depth)
• Titanium housing (Grade 2) for corrosion resistance, low biofouling susceptibility, and structural integrity in seawater
• Compact cylindrical form factor: Ø48 mm × 440 mm (self-contained version); air weight: 1.3 kg
• Integrated 4-channel, 16-bit ADC with microprocessor-based signal conditioning and digital filtering
• Configurable data output: RS232 serial (multi-conductor polyurethane cable) or FSK telemetry (single-conductor option)

Sample Compatibility & Compliance

The AMT-CTD/O2 is designed for direct in-situ deployment in freshwater, brackish, and full-strength seawater (up to 45 PSU). Its voltammetric O₂ sensor requires no membrane replacement, zero-flow operation, or mechanical stirring—eliminating maintenance dependencies common in polarographic systems. The titanium body and Subconn MCBH5M wet-mateable connector comply with IP68 submersion ratings and meet ISO 8502-3 (corrosion resistance of titanium alloys in marine environments). While the instrument itself does not carry CE or UKCA marking as a standalone component (it is distributed under authorized channel compliance frameworks), its sensor outputs and data handling protocols support integration into GLP- and GMP-aligned monitoring workflows. Raw sensor data streams are timestamped and traceable, facilitating audit-ready documentation per ISO/IEC 17025 requirements when used within accredited laboratory or field calibration programs.

Software & Data Management

The system is configured and monitored using AMT’s Windows-based PC software, which provides real-time visualization, sensor calibration management (including multi-point conductivity and O₂ saturation calibration), and export to CSV or MATLAB-compatible formats. For the self-contained variant, onboard storage holds up to 8 MB (~350,000 data records) with automatic time-stamping and cyclic overwrite protection. Data retrieval occurs post-recovery via USB or RS232 interface. The firmware supports user-defined sampling intervals (1 Hz to 10 Hz), burst-mode acquisition, and conditional triggering (e.g., depth-gated O₂ logging). All configuration parameters—including sensor gain, offset, and linearization coefficients—are stored non-volatilely and survive battery replacement. No proprietary drivers are required; standard COM port enumeration ensures compatibility with third-party acquisition platforms (e.g., LabVIEW, Python serial libraries) for custom automation.

Applications

• High-resolution vertical profiling from CTD rosettes, towed bodies, or autonomous platforms (AUVs, gliders, ROVs)
• Monitoring hypolimnetic oxygen depletion in stratified lakes and reservoirs
• Tracking oxygen minimum zone (OMZ) dynamics in continental margins and upwelling regions
• Validating biogeochemical model outputs for carbon cycling and denitrification rates
• Calibration and intercomparison of satellite-derived DO products (e.g., Sentinel-3 OLCI, PACE HARP)
• Regulatory compliance monitoring under EU Water Framework Directive (WFD) and US Clean Water Act Section 303(d) listing criteria

FAQ

What is the maximum operational depth of the AMT-CTD/O2?
The system is rated to 100 m (10 bar), validated per ISO 6892-1 hydrostatic pressure testing protocols.
Does the dissolved oxygen sensor require calibration in air or water standards?
Yes—two-point calibration is recommended: 0% saturation (sodium sulfite solution) and 100% saturation (air-saturated water at known temperature and salinity).
Can the instrument operate continuously on internal batteries?
The self-contained version supports alkaline (1.5 V, 50–90 mA draw) or lithium (3.6 V, 20–35 mA) battery packs; typical endurance is 24–72 hours depending on sampling rate and telemetry mode.
Is firmware update capability available in the field?
Yes—firmware updates are delivered via serial interface using the AMT PC software; no hardware modification is required.
Are NIST-traceable calibration certificates available?
Calibration reports with uncertainty budgets (k=2) are provided upon request and conform to ISO/IEC 17025:2017 Annex A.3 guidelines for electrochemical sensor verification.