63
8014084/ZWT7/V3-1/2020-06 | SICK
O P E R A T I N G I N S T R U C T I O N S | TRANSIC111LP
Subject to change without notice
SETTING AMBIENT PARAMETERS
5
Water content of background gas
The dependency on water content is expressed as absolute humidity in g/m
3
H
2
O because
relative humidity is strongly dependent on the temperature.
▸
Calculate the absolute humidity in g/m
3
H
2
O with the following equations:
0511-060
0511-061
Example for calculating absolute humidity in g/m
3
:
Gas temperature is 40°C and relative humidity is 90%.
1
First calculate the water vapor pressure
P
W
: P
W
(hPa) = P
WS
(40 °C) × 90/100 = 66.5
2
Use this result to calculate absolute humidity:
H
2
O (g/m
3
) = 216.679 × 66.5 / (273.15 + 40 °C) = 46.0
The Table below gives a quick overview of the values for converting temperature and
relative humidity into absolute humidity as well as the effect these conditions have on the
O
2
measured value of the device.
The water content of the background gas influences the oxygen measuring result:
1
The water molecules contained by the background gas displace a certain amount of
oxygen molecules.
2
Collisions between the water and oxygen molecules affect the shape of the oxygen
absorption lines.
H
2
O (g/m
3
)
C
P
W
¥
T
§
=
T
=
gas temperature in K (= 273.15 + T °C)
P
W
=
water vapor pressure in hPa
C
=
216.679 gK/J
P
W
P
WS
RH (%)
¥
100
§
=
RH(%) = relative humidity and P
WS
= saturation pressure of the water vapor, or
P
WS
1000 x 10
28.59051
8.2log
T
–
0.0024804
T
3142 T
§
–
+
=
T
= as specified above
Effect of humidity on measured O
2
values
(% of measured value)
T °C
%RH
g/m
3
H
2
O
Dependency
Dilution
−
20
50
0.5
0.0
−
0.1
−
20
90
1.0
0.0
−
0.1
0
50
2.4
−
0.1
−
0.3
0
90
4.4
−
0.2
−
0.5
25
50
11.5
−
0.4
−
1.6
25
90
20.7
−
0.7
−
2.8
40
50
25.6
−
0.9
−
3.6
40
90
46.0
−
1.6
−
6.6
60
50
64.9
−
2.1
−
9.8
60
90
116.8
−
3.6
−
17.7
80
50
145.5
−
4.2
−
23.4
80
90
262.0
−
6.3
−
42.1
Table 10: Table to convert temperature and relative humidity to absolute humidity
