WTW FDO 700IQ Fluorescent Dissolved Oxygen Sensor
| Brand | WTW |
|---|---|
| Origin | Germany |
| Model | FDO 700IQ |
| Part Number | 201650 |
| Measurement Principle | Green-light-based fluorescence quenching |
| Range (25°C) | 0–20.00 mg/L O₂, 0.0–200.0% saturation |
| Resolution | 0.01 mg/L O₂, 0.1% saturation |
| Accuracy | ±0.05 mg/L (<1 mg/L), ±0.1 mg/L (≥1 mg/L) |
| Repeatability | ±0.05 mg/L |
| Response Time (t₉₀) | <150 s |
| Temperature Range | –5°C to +60°C (sensor), –5°C to +50°C (compensation) |
| Pressure Rating | 10 bar (including cable) |
| Enclosure Rating | IP68 |
| Materials | POM/PVC/silicone membrane head, stainless steel body |
| Power Consumption | 0.7 W |
| Compliance | CE, cETLus, EN 61326 Class B, FCC Class A |
Overview
The WTW FDO 700IQ is a high-performance, maintenance-free fluorescent dissolved oxygen (DO) sensor engineered for continuous, long-term deployment in demanding environmental and industrial water quality monitoring applications. It operates on the physical principle of fluorescence quenching—where molecular oxygen modulates the lifetime of green-light-excited fluorophores embedded in a proprietary optical membrane. Unlike electrochemical DO sensors, the FDO 700IQ requires no electrolyte, zero-flow conditions, or routine calibration. Its measurement stability stems from three core innovations: Intelligent Quenching Membrane Calibration (IQMC), Equal Path Reference System (EPRS), and Green Light Technology (GLT). These features collectively eliminate drift due to membrane aging, optical component degradation, and bubble interference—common failure modes in first-generation optical DO sensors. Designed for integration into IQ Sensor Net® platforms, the FDO 700IQ delivers traceable, GLP-compliant data with factory-stored calibration parameters embedded directly in the replaceable membrane chip.
Key Features
- Intelligent Quenching Membrane Calibration (IQMC): Each SC-FDO 700 membrane is individually calibrated at the factory; calibration coefficients—including membrane type, serial number, and temperature-dependent response curves—are stored in an integrated memory chip on the cap.
- Equal Path Reference System (EPRS): A symmetrical dual-optical-path architecture ensures that both measurement and reference signals experience identical optical aging effects, enabling real-time drift compensation over the sensor’s operational lifetime.
- Green Light Technology (GLT): Uses 520 nm excitation light instead of conventional blue/violet wavelengths, reducing photobleaching of the fluorophore and extending membrane service life to ≥24 months under typical wastewater or surface water conditions.
- 45° Angled Optical Interface: Prevents air bubble accumulation on the sensing surface—eliminating signal artifacts common in flat-faced optical sensors during low-turbulence or intermittent-flow installations.
- C² Time-of-Flight Calibration: Timing circuitry is referenced to the fundamental constant of light speed, ensuring nanosecond-level precision in lifetime decay measurement—critical for sub-mg/L DO resolution and long-term reproducibility.
- No electrolyte, no flow dependency, no zero/span adjustment required during field operation.
Sample Compatibility & Compliance
The FDO 700IQ is validated for use across freshwater, wastewater, activated sludge, and low-salinity effluent matrices (up to 5 g/L TDS). While not rated for full seawater immersion, it supports extended deployment in brackish environments when paired with the MSK FDO protective housing (Order No. 205253). The sensor complies with ISO 5814:2012 (water quality — determination of dissolved oxygen — electrochemical probe method) for fluorescence-based validation protocols and meets the electromagnetic compatibility requirements of EN 61326-1 (industrial environment, Class B) and FCC Part 15 Subpart B (Class A). Its firmware and hardware architecture support audit-trail-capable data logging aligned with FDA 21 CFR Part 11 principles when deployed with IQ Sensor Net controllers equipped with secure user authentication and electronic signature modules.
Software & Data Management
The FDO 700IQ communicates exclusively via the WTW IQ Sensor Net® digital bus protocol, enabling plug-and-play integration with multi-parameter transmitters such as the IQM 200, IQM 400, or IQM 600 series. All sensor metadata—including membrane batch ID, calibration date, total operating hours, and historical Sensor Check diagnostics—are automatically logged and retrievable via WTW’s LabX® software or third-party SCADA systems using Modbus TCP or OPC UA gateways. Firmware updates are performed remotely through the network controller, and built-in self-diagnostics continuously monitor membrane integrity, LED output stability, and photodetector signal-to-noise ratio—triggering configurable alarms upon threshold exceedance. Raw fluorescence decay waveforms are accessible for advanced validation and method development.
Applications
The FDO 700IQ is routinely deployed in municipal wastewater treatment plants for aeration basin control, in drinking water distribution networks for residual oxygen monitoring, in aquaculture systems for hypoxia prevention, and in environmental research stations for long-term limnological profiling. Its immunity to hydrogen sulfide, chloride interference, and biofouling—combined with its lack of consumables—makes it particularly suitable for unattended, solar-powered remote monitoring stations. Regulatory laboratories use it for compliance reporting under EPA Method 180.1 (dissolved oxygen in natural waters) and ISO 5815-2 (biological oxygen demand testing), where measurement traceability and minimal operator intervention are critical.
FAQ
Does the FDO 700IQ require periodic calibration in the field?
No. Calibration is permanently stored in the membrane’s onboard chip and remains valid for the membrane’s service life. Field verification via air-saturation check is optional but not mandatory.
Can the FDO 700IQ be used in seawater?
It is not rated for direct seawater exposure due to potential osmotic stress on the membrane. For marine applications, specify the FDO 700IQ SW variant (Order No. 201652), which includes a corrosion-resistant housing and seawater-optimized membrane formulation.
What is the expected lifetime of the SC-FDO 700 membrane?
Under typical wastewater or freshwater conditions, the membrane maintains metrological performance for ≥24 months. Lifetime may be reduced in high-UV, high-temperature (>40°C), or highly oxidizing environments.
How does the Sensor Check function work?
Sensor Check performs automated optical diagnostics—including LED intensity verification, photodetector baseline stability assessment, and membrane transparency evaluation—without removing the sensor from the process.
Is the FDO 700IQ compatible with non-WTW controllers?
Only when interfaced through an IQ Sensor Net®-certified gateway supporting the standardized I²C-based digital protocol. Analog output conversion is not supported natively and requires external signal conditioning hardware.
