The O2 sensors consist of quenchable fluorescence dyes embedded in sol gels and polymers that are deposited on the tips of optical fibers, or coated as thin films on flat substrates. Our AP chemistry is ideal for stable operation and immunity from interference from water vapor. Our HCR chemistry works in the harshest organic solvents including jet fuels, kerosene, acetone and toluene. Our newest sensor is the MR series, fast response and totally hydrophobic -- ideal for measuring O2 in gases.
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Optical O2 Sensors, drift free fiber optic Oxygen Sensors Zero Drift Sensors are the most stable, optical based oxygen sensors available anywhere.
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Oxygen Sensors -- Fluorescence Quenching
Our O2 (molecular oxygen) sensors use the quenching of fluorescence by collision of molecular oxygen with a fluorophore that is trapped in an oxygen permeable sol gel or polymer. This technique is superior to polarographic electrodes in that O2 is not consumed. The sensing material can be coated on the tip of an optical fiber, or deposited as a thin film on flat substrates (patches and probe caps). We have a variety of sizes and shapes but they all work by the same principle. The NEOFOX "reader" is a phase fluorometer, which pulses a blue LED and measures the red fluorescence decay lifetime (tau) of the return signal. There are three chemistries available, ZERO-DRIFT AP for general purpose use in gases and aqueous based samples, MR hydrophobic sensor designed for fast response in gases, and HCR for use in aggressive hydrocarbon solvents such as toluene, alcohol, acetone and aviation fuels.
ZERO-DRIFT AP Chemistry This is our best sensor yet! Our breakthrough multi-layered formulation has virtually no drift due to photo-bleaching. It is not influenced by water vapor, and It is very resistant to prolonged exposure to elevated storage and operating temperatures.
HCR Chemistry HCR is formulated to work in organic solvents, which interfere with standard formulations. It features excellent adhesion in alcohols, jet fuels, toluene, acetone and many other hydrocarbons. We can test our probe in your solvent to validate its use. Just give us a call.
MR Chemistry MR sensors are based on very hydrophobic sol gels, so the influence of water vapor on readings is eliminated without any degradation in response rate. It is ideal for measuring pO2 in gas mixtures where fast response is required.
Sensing chemicals with Light, how it works!
Oxygen is sensed from the fluorescence decay rate of a trapped metal-organic fluorphore. A blue LED pulse is sent down the fiber to the tip, or to a patch with a polymer or sol-gel matrix encapsulated fluorophore. The blue light causes a red fluorescence. The red fluorescence decays over micro-seconds of time. Collision with O2 molecules causes quenching, and a faster decay rate. If the LED is modulated, the fluorescence signal is also modulated but with a phase delay that is related to the lifetime. In the absence of O2 the lifetime is long, as the partial pressure of O2 increases, the lifetime gets shorter. The relationship between lifetime and pO2 follows a Stern-Volmer relationship. Tau(0) is the lifetime in the absence of O2, Tau is the lifetime in the sample, pO2 is the partial pressure of O2 and Ksv is the sensor calibration coefficient.
In practice, the linear form of the Stern-Volmer equation above is not accurate over a large range of pO2 values. Instead the calibration data is fit to a quadratic equation, and at least 3 calibration points are required.
If temperature compensation is required, then a calibration matrix at at least 3 pO2 levels and two temperatures are required.
We offer factory calibrations for the probes, or you can do the calibrations yourself. Generally you will need a source of gases with known O2 concentrations, and a water bath, incubator or some other means to control temperature. We can help you design your calibration apparatus, so feel free to call us.
Our chemistries are extremely stable, and once calibrated should maintain calibration for a long time period. However, damage to the probe material, switching to a new set of optical fibers or other pertubations could cause a "shift" in calibration. When that happens a simple single point "reset" can be performed.
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