Fluorescence Dissolved Oxygen Sensor
Fluorescence-based dissolved oxygen sensor utilizing luminescence lifetime detection for accurate, drift-resistant measurements in aquatic monitoring applications.
Louise Corscadden, PhD
Neuroscience · ConductScience
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The Fluorescence Dissolved Oxygen Sensor employs fluorescence lifetime detection technology to measure dissolved oxygen concentrations in aqueous samples. The sensor utilizes a green LED to excite luminescent material coated on the sensor surface, which emits red light upon relaxation. Oxygen molecules in the sample quench the fluorescence, creating an inverse relationship between fluorescence lifetime and dissolved oxygen concentration. This optical measurement principle eliminates the need for electrolyte replacement and provides stable, drift-resistant measurements across the 0-20.00 mg/L range.
The sensor integrates a DS18B20 digital temperature electrode for automatic temperature compensation and features IP68 waterproof rating for submersible applications. MODBUS/RS485 digital interface enables integration with data acquisition systems, while optional 4-20mA analog output provides compatibility with industrial process control equipment. The stainless steel 316 construction with organic silica gel sensing film ensures chemical resistance and longevity in challenging aquatic environments.
How It Works
The sensor operates on the principle of fluorescence quenching by molecular oxygen. A green LED illuminates the sensor tip, which is coated with an oxygen-sensitive luminescent material. The green light excites fluorescent molecules in the coating, causing them to emit red light as they return to their ground state. Dissolved oxygen molecules interact with the excited fluorophores through dynamic quenching, reducing both the intensity and lifetime of the fluorescence emission.
The instrument measures the time delay between the excitation pulse and fluorescence emission (fluorescence lifetime), which correlates inversely with dissolved oxygen concentration. Higher oxygen levels result in more frequent quenching interactions, shortening the fluorescence lifetime. A red LED provides an internal reference signal between measurement cycles to correct for variations in light source intensity and detector sensitivity. The integrated DS18B20 temperature sensor enables automatic temperature compensation, accounting for oxygen solubility changes with temperature.
The MODBUS/RS485 interface transmits digital measurement data, while the optional 4-20mA output provides analog signaling for process control applications. One or two-point calibration using air-saturated and zero-oxygen solutions establishes the measurement relationship for the specific sensing film and environmental conditions.
Features & Benefits
Measuring Range
- 0-20.00mg/L or 0-200%saturation level
Response Time
- 3-5min
Temperature Sensor
- DS18B20Digital temperature electrode
Working Temperature
- 5~40â
Working Pressure
- <5 bar
Digital Interface
- MODBUS/RS485
Analog Interface
- 4-20mA(optional)
Calibration
- One or Two calibration points
IP Grade
- IP68
Cable length
- 8 meters
Fluorescent Cap Shelf Life
- One year
Automation Level
- semi-automated
Brand
- ConductScience
Accuracy
- ±0.3mg/L or ±5%
Power/Voltage
- 12VDC±20%
Dimensions
- 34x222
Material
- The main body is stainless steel 316, and the sensitive film is organic silica gel.
Research Domain
- Analytical Chemistry
- Environmental Monitoring
- Food Science
- Materials Science
- Microbiology
- Pharmaceutical QC
Weight
- 0.26 kg
Dimensions
- L: 20.0 mm
- W: 10.0 mm
- H: 5.0 mm
| Feature | This Product | Typical Alternative | Advantage |
|---|---|---|---|
| Measurement Range | 0-20.00 mg/L or 0-200% saturation | Entry-level sensors often limited to 0-15 mg/L ranges | Extended range accommodates supersaturated conditions in biological systems and industrial processes |
| Accuracy Specification | ±0.3 mg/L or ±5% | Basic sensors typically offer ±0.5 mg/L accuracy | Higher precision enables detection of subtle oxygen changes in research applications |
| Communication Interface | MODBUS/RS485 with optional 4-20mA | Many sensors offer analog output only | Digital communication reduces signal degradation and enables remote configuration and diagnostics |
| Temperature Compensation | Integrated DS18B20 digital temperature sensor | Some sensors rely on external temperature probes | Built-in temperature sensing ensures accurate compensation and simplifies installation |
| Pressure Rating | Up to 5 bar operating pressure | Standard sensors often limited to atmospheric pressure applications | Enables deployment in pressurized systems and deeper water monitoring |
| Sensor Maintenance | One-year fluorescent cap replacement cycle | Clark electrodes require frequent electrolyte and membrane replacement | Reduced maintenance burden and more predictable operating costs for continuous monitoring |
This sensor combines fluorescence-based stability with comprehensive digital communication capabilities and integrated temperature compensation. The extended measurement range and pressure rating accommodate diverse research and industrial applications requiring reliable dissolved oxygen monitoring.
Practical Tips
Perform calibration in solutions at the same temperature as your target measurements to minimize temperature compensation errors.
Why: Temperature-matched calibration improves accuracy by reducing reliance on compensation algorithms.
Monitor fluorescent cap performance monthly using standard solutions and replace annually or when accuracy degrades beyond specifications.
Why: Proactive replacement prevents measurement drift and ensures consistent data quality throughout studies.
Ensure adequate water circulation around the sensor tip during measurements to prevent oxygen depletion in stagnant zones.
Why: Local oxygen depletion near the sensor can cause artificially low readings that don't represent bulk solution conditions.
If readings appear unstable, check for air bubbles on the fluorescent cap surface and ensure complete submersion of the sensing element.
Why: Air bubbles can interfere with fluorescence measurements and cause erratic readings.
Allow 3-5 minutes for sensor stabilization when oxygen levels change significantly before recording final measurements.
Why: The fluorescence-based measurement principle requires time for equilibrium between dissolved oxygen and the sensing film.
Verify proper electrical grounding when deploying in conductive solutions to prevent interference with sensitive electronics.
Why: Electrical interference can affect measurement accuracy and potentially damage the sensor electronics.
Store calibration solutions according to manufacturer specifications and prepare fresh standards monthly for critical applications.
Why: Degraded calibration standards compromise measurement accuracy and can introduce systematic errors.
Document environmental conditions during field deployments, including temperature, pH, and potential interfering substances.
Why: Environmental documentation enables proper data interpretation and helps identify sources of measurement variability.
Setup Guide
What’s in the Box
- Fluorescence dissolved oxygen sensor with 8-meter cable
- Power adapter (12VDC) (typical)
- Communication interface cable (typical)
- Calibration solutions (typical)
- User manual and calibration certificate (typical)
- Mounting hardware (typical)
Warranty
ConductScience provides standard one-year manufacturer warranty covering sensor electronics and mechanical components, with technical support for installation and operation guidance.
Compliance
References
Background reading relevant to this product:
How does temperature affect dissolved oxygen readings and compensation?
The integrated DS18B20 temperature sensor automatically compensates for oxygen solubility changes with temperature. Since oxygen solubility decreases with increasing temperature, the compensation algorithm adjusts readings to provide accurate concentration values across the 5-40°C operating range.
What is the typical lifetime of the fluorescent sensing element?
The fluorescent cap has a one-year shelf life under normal operating conditions. Replacement involves installing a new sensing cap and recalibrating the system using standard oxygen solutions.
Can the sensor operate in flowing water conditions?
Yes, the sensor can operate in flowing conditions and benefits from water circulation around the sensing element. The IP68 rating and stainless steel construction enable deployment in streams, rivers, and process flow systems up to 5 bar pressure.
How does this fluorescence method compare to traditional Clark electrode sensors?
Fluorescence sensors eliminate electrolyte consumption, membrane fouling, and stirring sensitivity issues associated with Clark electrodes. However, they typically have slower response times (3-5 minutes vs seconds) and may require more frequent calibration verification.
What calibration standards are recommended for accurate measurements?
Use air-saturated distilled water for single-point calibration or combine with sodium sulfite solution for zero-oxygen two-point calibration. Calibrate at the expected measurement temperature when possible.
How do interfering substances affect fluorescence measurements?
Heavy metals, hydrogen sulfide, and certain organic compounds may interfere with fluorescence. Consult product datasheet for specific interference studies and consider sample pretreatment if interfering substances are suspected.
What data output formats are available from the MODBUS interface?
The MODBUS/RS485 interface provides dissolved oxygen concentration, temperature readings, and sensor status information. Consult product datasheet for specific register mappings and communication protocols.
How should the sensor be stored between measurement campaigns?
Store the sensor in clean, distilled water or as specified in the user manual. Avoid exposure to freezing temperatures and ensure the fluorescent cap remains hydrated to maintain calibration stability.
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