Ocean Optics OOISensors - Manual (Page 49)

3: Oxygen Sensors
Calibration Requirements for Oxygen Sensors
The following section explains the principles of calibration for oxygen sensors, as well as the algorithms
required in the calibration procedures.
For accurate oxygen measurements of a sample, you must first calibrate the oxygen system. There are two
major considerations when calibrating the Fiber Optic Sensors System:
• Temperature: Determine if you need to compensate for changes in temperature in the sample. If so,
you must calibrate the Fiber Optic Sensors System accordingly. (Sample Temperature Duration <± 3
ºC)
• Algorithm: Determine which algorithm you will use for the calibration. The Linear (Stern-Volmer)
algorithm requires at least two standards of known oxygen concentration while the Second Order
Polynomial algorithm requires at least three standard of known oxygen concentration.
Calibration curves are generated from your standards and the algorithms to calculate concentration values
for unknown samples. The Second Order Polynomial algorithm provides a better curve fit. Thus, this
algorithm returns accurate data during oxygen measurements, particularly when working in a broad
oxygen concentration range.
Note
A linear calibration is good from 0 to 30% O2. Higher values of O2 require a second order fit.
Linear (Stern-Volmer) Algorithm
The Stern-Volmer algorithm requires at least two standards of known oxygen concentration. The first
standard must have 0% oxygen concentration and the last standard must have a concentration in the high
end of the concentration range in which you will be working. The fluorescence intensity can be expressed
in terms of the Stern-Volmer equation where the fluorescence is related quantitatively to the partial
pressure of oxygen:
For a given media, and at a constant total pressure and temperature, the partial pressure of oxygen is
proportional to oxygen mole fraction.
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