Ocean Optics OOISensors - Manual (Page 51)

3: Oxygen Sensors
Compensating for Temperature with the Second Order Polynomial Algorithm
If you decide to compensate for temperature, the relationship between the Second Order Polynomial
algorithm and temperature are defined as:
I
0
= a
0
+ b
0
* T + c
0
* T 2
K
1
= a
1
+ b
1
* T + c
1
* T 2
K
2
= a
2
+ b
2
* T + c
2
* T 2
Theory - Henry’s Law
It is possible to calibrate the Fiber Optic Sensors System in gas and then use the system in liquid or vice
versa. In theory, the Fiber Optic Sensors System detects the partial pressure of oxygen. In order to convert
partial pressure to concentration, you can use Henry’s Law. When the temperature is constant, the weight
of a gas that dissolves in a liquid is proportional to the pressure exerted by the gas on the liquid.
Therefore, the pressure of the gas above a solution is proportional to the concentration of the gas in the
solution. The concentration (mole %) can be calculated if the absolute pressure is known:
Oxygen mole fraction = oxygen partial pressure / absolute pressure
Since the Fiber Optic Sensors System detects partial pressure of oxygen, the response in a gas
environment is similar to a liquid environment in equilibrium with gas. Therefore, it is possible to
calibrate the Fiber Optic Sensors System in gas and then use the system with liquid samples and vice
versa if you utilize Henry's Law.
However, Henry's Law does not apply to gases that are extremely soluble in water. The solubility of
oxygen in water at different temperatures is shown below:
Oxygen Solubility in Water at Differing Temperatures
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