Versions | Specifications | Optical D.O. (RDO^®)

Optical D.O. technology is revolutionizing water quality monitoring by eliminating the need for frequent membrane changes, stirring, and frequent calibration during deployments. The In-Situ^® optical Dissolved Oxygen sensor, called Rugged D.O. (RDO^®), utilizes advances in lifetime-based optical fluorescence technology to provide an extremely stable, precise and low maintenance dissolved oxygen sensor.  Unlike other optical D.O. sensors on the market, the RDO’s innovative design eliminates hydration and photobleaching effects.  In addition, the RDO’s 5-year lumiphore life delivers a lower cost of ownership by minimizing maintenance and calibration requirements.

Features:

No hydration effects Store wet or dry No conditioning necessary prior to use No photobleaching effects Not effected by ambient light 5 year lumiphore life No membrane to change No fill solution Minimal maintenance - replace sensor foil every 5 years or 5 million readings High precision and accuracy Low drift Excellent performance in anoxic conditions (0 ppm) Fast and stable response Low maintenance No flow requirements - no stirring Up to 1 year between calibrations dependent on water matrix Rugged Not "poisoned" by sulfides No cross sensitivity to: H2S, pH, CO2, NH3, SO4-, Cl-, MeOH, EtOH, various ionic species Performs in most water monitoring applications Not subject to "thermal shocking"

Two options are available: Titanium Delrin®

30-DAY NO RISK GUARANTEE - If you don't like it after 30-days just return for full credit.

Optical Technology addresses age-old problems with electrochemical D.O. sensors.
Stirring, membrane replacement, maintenance, maintenance, maintenance.
Dissolved Oxygen (D.O.) is the single most important parameter monitored when examining aquatic biology and related processes. Until recently the ability to accurately monitor dissolved oxygen levels over long periods of time was limited. Electrochemical sensors (Clark, Galvanic) require sample stirring and are functionally limited by the durability of their membrane and electrode, while galvanic diffusion types offer characteristically slow response. Optical dissolved oxygen technology eliminates the need for stirrin, frequent membrane replacements and calibration.

The optical technology incorporated in the RDO^® sensor centers around the field-proven methodology of Lifetime-based Luminescent Dissolved Oxygen detection. This solid-state method uses LEDs to excite a fluorescent material, while an optical receptor gauges the duration, or lifetime, of the event. The duration of fluorescence is inversely proportional to the amount of dissolved oxygen in the water.

Environmental Industry interest in the RDO^® sensor is centered around the fact, that in many instances, the RDO^® can remain deployed through entire testing seasons, spanning months, without calibration; at the same time retaining its accuracy in even the harshest of fouling environments, without the need for stirring.

All dissolved oxygen sensors are subject to interference from active bio-fouling. Optical sensors may be affected in that the actual D.O. levels in the water near the sensing element can become locally elevated or depressed. Unlike electrochemical sensors which will need a replacement of the membrane and filling solution, followed by a calibration, the optical sensor can simply be cleaned and redeployed; the calibration is unaffected.

The data on the left is from a traditional Clark-electrode, while the one on the right is from an In-Situ^® RDO^® sensor. Surprisingly, this data is from the same water sample. So why the difference? Optical D.O. is inherently more stable, has little to no drift, and higher precision than a Clark style D.O. electrode.

Why Optical D.O.?
The new RDO^® sensor is to the Clark cell what the computer was to the typewriter. Now you can:

• Eliminate the need for complex sensor storage and conditioning
• Reliably measure oxygen concentration with accuracy and precision
• Eliminate the need for flow/stirring
• Eliminate the need for changing membranes and fill solution
• Eliminate unwanted temperature effects
  

Method

Winkler Titration Method

Optical Fluorescence Method

Polarographic Electrochemical Method

Galvanic Electrochemical Method

Average Initial Error

(reference method)

0.2 mg/L

0.5 mg/L

0.2 mg/L

How accurate was it at the beginning?

Frequency of Initial Errors < 0.2 mg/L

(reference method)

50%

40%

10%

Frequency of Initial Errors > 2.0 mg/L

(reference method)

0%

10%

60%

Individual Precision

0.22%

0.11%

0.11%

0.15%

Typical Drift during first week, mg/L

(reference method)

0.4 mg/L

0.7 mg/L

1.0 mg/L

How bad was the drift?

Variability of Drift

(reference method)

0.6 mg/L

3.9 mg/L

0.7 mg/L

Optical D.O. Technology - how does it work?

	The sensing element (lumiphore) is activated, or excited when illuminated with a blue light
	When activated, the lumiphore emits red light in an intensity that is inversely proportional to the amount of oxygen present in the water
	There is also a time delay between the peak emission of blue light and peak response of fluoresced red light. The amount of delay is inversely proportional to the amount of oxygen present.
	This time delay can be expressed as a phase shift between the wave patterns of incident blue light and the fluoresced red light
	In-Situ® optical D.O. sensor is not affected by sample color or turbidity

All of the optics and electronics are solid-state with no moving parts

1. Magnitude -- Measures peak height of luminescence. Accuracy is impacted over time as the lumiphore degrades due to photobleaching by ambient light

2. Time Domain --Measures the decay rate of the luminescence but the signal to noise ratio can limit the sensor range.

3. Phase Domain -- Phase domain measures the phase difference based on the entire signal and references wave forms across a population of pulses. This method delivers the highest accuracy and widest operating range. This is the method used by the In-Situ^® RDO^®.

Item

Specification

Accuracy and precision

+/- 0.1 mg/L from 0-10 mg/L; +/- 1% of reading from 10-20 mg/L

Operating range

0-20 mg/L or 0-450% saturation

Temperature range (operating)
Temperature range (storage)

0 to 40 °C
-40 to 80 °C

Salinity range

Up to 42 ppt

pH range

0-12 pH

Typical response limit

>25 mg/L

Response Time

T90 = 12 seconds

Technology

Lumiphore impregnated foil matrix, dynamic luminescence quenching technique using phase domain detection. The In-Situ^® optical D.O. technology does not require hydration before use or during storage.

Calibration

1 or 2 point

Typical calibration duration

12 months (clean water)

Known interferences

Interferences (cross-sensitivity) are found for gaseous sulfur dioxide (SO₂) and gaseous chlorine (Cl₂).

The sensors can be used in methanol- and ethanol -water mixtures as well as in pure methanol and ethanol. The In-Situ^® optical D.O. sensor should not be used in other organic solvents, such as acetone, chloroform or methylene chloride, which may swell the foil matrix and destroy it.

There exists no cross sensitivity for carbon dioxide (CO₂), ammonia (NH₃), pH, any ionic species like sulfide (S₂^- ), sulfate (SO₄^2-), chloride (Cl^-) or hydrogen sulfide (H₂S). The In-Situ^® optical D.O. sensor will not be damaged by hydrogen sulfide (H₂S) and it is not cross-sensitive to it. If H₂S is present the oxygen concentration should be zero or very close to zero since oxygen (O₂) and H₂S rarely coexists, especially over longer time periods. 

Material

Delrin^®

Sensor foil technology

Platinum porphyrin lumiphore embedded in polyester

Typical sensor foil life

5 years or 5 million measurements

Dimensions, RDO^® sensor
RDO^® sensor adapter assembly

36mm (1.4 in) OD, 89mm (3.5 in) long
88.4mm (3.5 in) OD, 20.3cm (8.0 in) long