TD 269 OPERATING MANUAL
OXYGEN OPTODE 4330, 4831, 4835
June 2017
page 53 of 93
The temperature in °C is calculated from raw data (RawTemp) by use of a polynomial similar to the above
with coefficients stored in the TempCoef property.
Based on the calibrated phase (CalPhase) and temperature (Temperature) the partial pressure of O
2
is
calculated by use of a two dimensional polynomial:
27
27
2
2
1
1
0
0
27
2
1
0
...
n
m
n
m
n
m
n
m
ph
t
C
ph
t
C
ph
t
C
ph
t
C
p
⋅
⋅
+
+
⋅
⋅
+
⋅
⋅
+
⋅
⋅
=
∆
where the polynomial coefficients C
0
to C
13
are stored in the property
FoilCoefA
and C
14
to C
27
are stored
in
FoilCoefB
. The temperature exponents, m
0..27
, are stored as
FoilPolyDegT
and phase exponents, n
0..27
,
are stored as
FoilPolyDegO
.
From the partial pressure the air saturation is then calculated as:
( )
( )
[
]
NomAirMix
t
p
ess
NomAir
p
ion
AirSaturat
vapour
⋅
−
⋅
∆
=
Pr
100
%
where
NomAirPress
is a property for the nominal air pressure, usually 1013.25 hPa, and
NomAirMix
is
the nominal O2 content in air, by default 0.20946.
The
p
vapour
(t)
is the vapour pressure calculated from temperature by the following equation:
)
.
(t+
*
.
-
.
t+
.
-
.
(
vapour
e
(t)
p
15
273
ln
681
4
15
273
9
6690
57
52
=
If the property
Enable HumidityComp
is set ‘No’ the
p
vapour
(t)
will be set to zero.
The oxygen concentration is finally calculated as:
100
659
.
44
)
(
2
*
ion
AirSaturat
C
M
ion
Concentrat
O
⋅
⋅
=
µ
where C
*
is the oxygen solubility (cm
3
/dm
3
) calculated from the Garcia and Gordon equation of 1992:
( )
(
)
2
0
3
3
2
2
1
0
5
5
4
4
3
3
2
2
1
0
*
ln
S
C
T
B
T
B
T
B
B
S
T
A
T
A
T
A
T
A
T
A
A
C
S
S
S
S
S
S
S
S
+
+
+
+
+
+
+
+
+
+
=
where:
T
s
= scaled temperature
+
−
=
t
t
15
.
273
15
.
298
ln
t
= Temperature,
°C
