SICK TRANSIC Extractive TRANSIC151LP, Operating Instructions Manual, Page: 42 / 84

42 8015383/ZUQ7/V1-3/2020-06 | SICK O P E R A T I N G I N S T R U C T I O N S | TRANSIC151LP
Subject to change without notice
5
SETTING AMBIENT PARAMETERS
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
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.
The first effect is the dilution of the oxygen concentration of the measured gas (water
displaces oxygen so there is a lower oxygen concentration in the measured gas). This is not
compensated during measurement. Only the second effect is due to the measuring
principle and can be compensated.
The dependency due to the measuring principle is shown in the 4th column of “Table to con-
vert temperature and relative humidity to absolute humidity” . This is compensated and
eliminated when a value is specified for H
2
O compensation.
The 5th column of “Table to convert temperature and relative humidity to absolute humid-
ity” shows the dilution effect. This effect is much stronger than the measuring principle
effect. This is also valid for the water content compensation because it is the actual
decrease of oxygen content in the measured gas due to water displacing oxygen in the gas
mixture.
NOTE: Deactivating humidity and CO
2
compensation
▸
Set the values for the water and CO
2
content of the background gas to zero (factory
setting).
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
§
=
r.h.(%) = 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
The water content of the background gas influences the oxygen measuring result.