SICK TRANSIC111LP - Page 63

63
8014084/ZWT7/V3-1/2020-06 | SICK OPERATING INSTRUCTIONS | 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
) CP
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
0502.4 −0.1 −0.3
0904.4 −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