G 1690 / G 1690T
Measurement Basics | 5
B-H86.0.31.DK2-1.0
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5
Measurement Basics
5.1
Oxygen principles
The oxygen sensor used provides an output signal which is proportional to the oxygen
partial pressure (p
O
2
).
5.1.1
Oxygen partial pressure and oxygen concentration
_
The partial pressure is the pressure of one component in a mixture of different compo-
nents. The sum of all partial pressures is the same as the total pressure of the mixture
(Dalton's law).
For air, the absolute air pressure (p
abs
), e.g. 1013 hPa, would be the sum of the partial
pressures of each individual component (N
2
, O
2
, Ar, ...).
The oxygen concentration is the percentage by volume of oxygen in the air mixture.
As a rule, this is 20.95 % by volume for dry air.
5.1.2
Maximum operational depth (MOD)
_
In order to slow down the accumulation of nitrogen in the body and thus reduce the risk
of decompression sickness, nitrogen-air mixtures with enriched oxygen concentration
(NITROX) is used in diving. However, with these mixtures, the maximum possible
diving depth is reduced (the oxygen partial pressure increases extremely at depth).
The oxygen partial pressure should be within the limits of 0.16 ... 1.40 bar.
The following calculation is performed in the device based on the measurement and
the user inputs of oxygen partial pressure (p
O
2
) and the absolute air pressure (p
abs
):
𝑀𝑂𝐷 [𝑚
𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟
] = 10 [
𝑚
𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟
𝑏𝑎𝑟
] × (
𝑝
𝑂
2
𝑐
− 𝑝
𝑎𝑏𝑠
) [
𝑏𝑎𝑟
%𝑂
2
]
𝑀𝑂𝐷 [𝑓𝑡
𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟
] = 33 [
𝑓𝑡
𝑠𝑒𝑎𝑤𝑎𝑡𝑒𝑟
𝑎𝑡𝑚
] × (
𝑝
𝑂
2
𝐶
𝑂
2
− 𝑝
𝑎𝑏𝑠
) [
𝑎𝑡𝑚
%𝑂
2
]
