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Help CenterGerman WTW Dissolved Oxygen Sensor, Product Number 201300, Model FDO 925
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FDO® 925 IDS Optical Dissolved Oxygen Sensors – Product Introduction
Overview
The WTW FDO® 925 series represents a breakthrough in optical dissolved oxygen measurement, combining the intelligence of IDS (Intelligent Digital Sensor) technology with the renowned green-light fluorescence principle. These digital sensors deliver exceptionally fast, precise, and maintenance‑free DO readings across laboratory, field, and process applications. With four cable‑length variants and a rugged, slim design, the FDO® 925 family adapts perfectly to everything from BOD bottles to deep‑water profiling.
Key Features
Ultra‑Fast Response – T99 The FDO® 925 achieves a remarkable T99 response time of under 60 seconds – ideal for spot sampling, emergency measurements, and dynamic process control where speed matters.
Green Light Fluorescence Technology
WTW’s patented green‑light excitation ensures superior signal stability and extended sensor lifetime. The optical measuring principle consumes no oxygen, requires no flow, and is free from electrolyte depletion or membrane fouling issues common with conventional Clark‑type sensors.
Integrated Sensor Memory (IDS)
Each FDO® 925 sensor stores its factory‑calibrated cap data, serial number, and calibration history internally. When connected to any WTW MultiLine® meter (3510/3620/3630), the sensor is automatically recognised – no manual entry, no recalibration when switching instruments.
No Flow Dependence
Unlike polarographic sensors, the FDO® 925 provides stable readings even in stagnant water. This makes it ideal for low‑flow sampling, BOD bottle measurements, and quiescent water bodies where flow is minimal or intermittent.
Hydrogen Sulfide (H₂S) Immune
The optical principle is completely unaffected by H₂S, eliminating the poisoning and drift problems seen with electrochemical sensors in wastewater, sewage, or anoxic environments.
45° Sloped Membrane Cap
The unique angled membrane design effectively prevents bubble entrapment on the sensing surface, ensuring reliable readings even in aerated or vigorously stirred samples.
Rugged and Corrosion‑Resistant
The sensor body is constructed from POM (engineering plastic) and stainless steel, providing excellent mechanical strength and chemical resistance for demanding field and industrial conditions.
Kevlar‑Reinforced Cables
For deep‑water and rough‑terrain use, the longer cable versions are reinforced with Kevlar® fibres, offering extraordinary tensile strength and protection against abrasion or accidental pull‑out.
Available Models – Choose Your Cable Length
| Model | Cable Length | Application Focus |
|---|---|---|
| FDO 925 | 1.5 m | Standard lab and field use |
| FDO 925‑3 | 3.0 m | Slightly deeper sampling, tanks |
| FDO 925‑6 | 6.0 m | Deep lakes, rivers, and boreholes |
| FDO 925‑25 | 25 m | Profiling in deep water, long‑reach deployments |
Technical Specifications
| Parameter | Specification |
|---|---|
| Measuring principle | Optical fluorescence (green‑light excitation) |
| Concentration range | 0.00 – 20.00 mg/L (accuracy: ±0.5% of reading) |
| Saturation range | 0.0 – 200.0 % (accuracy: ±0.5% of reading) |
| Partial pressure range | 0.0 – 200 hPa (accuracy: ±0.5% of reading) |
| Temperature range | 0 – 50.0 °C (accuracy: ±0.2 °C) |
| Response time (T99) | |
| Membrane design | 45° sloped cap (bubble‑rejecting) |
| Sensor body material | POM, stainless steel |
| Dimensions (L × Ø) | 140 mm × 15.3 mm (±0.2 mm) |
| Cable lengths | 1.5 m, 3 m, 6 m, 25 m (Kevlar‑reinforced for ≥6 m) |
| Digital interface | IDS with integrated sensor memory |
| Interference immunity | Unaffected by H₂S, flow, or stirring |
Applications Across All Sectors
Laboratory & BOD Measurement
The slim profile (15.3 mm diameter) fits perfectly into standard BOD bottles, enabling direct DO measurement without sample transfer. The AutoRead function on MultiLine® meters automatically recognises stable endpoints, and the FDO® 925 can be calibrated to match the performance of WTW’s online FDO® 700 IQ for seamless lab‑to‑process data comparability.
Field & Deep‑Water Monitoring
With no flow dependence and rapid response, the FDO® 925 excels in lakes, rivers, groundwater wells, and estuaries. Optional protective guards (plastic or stainless steel) shield the sensor in harsh environments, while Kevlar‑reinforced cables (6 m and 25 m) allow reliable measurements at significant depths.
Wastewater Treatment Plants
The H₂S immunity and robust construction make the FDO® 925 a trusted tool for aeration tank monitoring, effluent control, and BOD testing in municipal and industrial wastewater facilities. The sensor delivers stable results even in fluctuating oxygen levels and contaminated matrices.
Aquaculture & Environmental Research
Precise low‑level DO measurements (below 1 mg/L) are fully supported, making the sensor suitable for fish farming, hypoxia studies, and natural water quality assessments where oxygen depletion is a concern.
Optional Accessories
Protective guards (plastic or stainless steel) – add mechanical protection and extra weight for stable deep‑water immersion.
Calibration caps – factory‑calibrated exchangeable caps simplify maintenance and ensure long‑term accuracy.
MultiLine® meters – pair with Multi 3510, 3620, or 3630 for full parameter flexibility.
Why Choose FDO® 925?
The FDO® 925 combines the proven advantages of optical DO technology – no flow dependence, no H₂S interference, and near‑zero maintenance – with the intelligence of WTW’s IDS platform. Its fast response, rugged build, and versatile cable options make it the go‑to sensor for professionals who demand reliable, accurate dissolved oxygen data in any environment – from the laboratory benchtop to the deepest lake.
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