COSA Xentaur Hygrocontrol Type 72 - Manual (Page 24)

Series 72 Manual page 20
11.4 Protection of Transmitter Electronics
To give highest protection against the surrounding atmosphere, our transmitter
housings are according to IP 65. Avoid atmospheres of more then 80 %RH, as
condensation could occur with rapid temperature changes.
11.5 Influence of Temperature on Humidity
To detect rel. Humidity, the sensor has to be in equilibrium with the atmosphere
- this cannot be done spontaneously! It is up to you, to choose a position of the
sensor, where the equilibrium may be reached as quick as possible. Take into
consideration that also Temperature has a great influence on rel. Humidity! At
Room Temperature and 50 %RH, a temperature change of 1°C will cause a
change of rel. Humidity by 3%. This is the reason, why all instruments use a
combination of Humidity and Temperature Sensors for detection of rel.
Humidities. Only if Temperature has stabilized, proper values of rel. Humidity
may be expected.
Different tube materials of sensors have an influence on temperature
stabilisation by their different thermal mass and conductivity. SS - 316 tubes
predict higher times to achieve equilibrium of temperature as PTFE or PP tubes
- be aware of this problem and choose a proper material.
Avoid errors by unproper installation of the sensor as for example:
- Influence by Heat: direct Sun, Heaters, unknown Air Streems
etc.
- Influence by Water: Vapors, dropping or spraying Water etc.
- Influence by Pollution: Dust, Aerosoles, Chemicals etc.
11.6 Humidity Measurements over Ice
Don't forget that our sensors are calibrated for conditions of vapor pressure over
liquid water. If you are measuring rel. Humidities over ice, you will get an error
which is strictly dependent on the differece of saturation pressure of vapor over
ice compared with the saturation pressure of vapor over chilled water. The
following table shows the results of a measurement of saturated vapor over ice
at different temperatures below zero.
Table 3: Display at 100% RH over Ice at different Temperatures
TEMPERATURE (°C) PSF (MBAR) PSE (MBAR) M (%RH)
0
6,11 6,11 100,0
-5 4,22 4,02 95,3
-10 2,87 2,60 90,6
-15 1,91 1,66 86,9
-20 1,26 1,03 81,7
-25
0,81 0,64 79,0
-30 0,49 0,37 75,5