COSA Xentaur Hygrocontrol Type 83 - Manual (Page 12)

HYGROCONTROL Manual for Type 83 Page - 11 -
6.3 Resistance against Chemical Attack
Our sensors are well known for their resistance against most
chemical attacks. To give the user some information over the
additional errors which are arising from some chemicals, we listed
our experiences over the last 10 years. (See the table at the end of
this manual).
Be aware, that the given concentrations are valid for a single
chemical in normal atmosphere (room temperature) only. As
temperature has to be taken into consideration too, you cannot
expect to get proper predictions out of the table - please contact our
technical staff for more information.
6.4 Protection of Transmitter Electronics
To give highest protection against the surrounding atmosphere, our
transmitter housings type "B" are according to IP 65. Avoid
atmospheres of more than 80 %RH, as condensation could occur
with rapid temperature changes.
6.5 Influence of Temperature on Humidity
To detect relative 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 quickly as possible. Take into consideration that also
Temperature has a great influence on relative Humidity! At Room
Temperature and 50 %RH, a temperature change of 1°C will cause a
change of relative Humidity by 3%. This is the reason, why all
instruments use a combination of Humidity and Temperature
Sensors for detection of relative Humidity. Only if Temperature has
stabilized, proper values of relative Humidity may be expected.
Different tube materials of sensors have an influence on temperature
stabilization 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 improper installation of the sensor as for example:
- Influence by Heat: direct Sun, Heaters, and unknown Air Streams etc.
- Influence by Water: Vapours, dropping or spraying Water etc.
- Influence by Pollution: Dust, Aerosols, Chemicals etc.
6 .6 Humidity Measurements over Ice
Don't forget that our sensors are calibrated for conditions of vapour
pressure over liquid water. If you are measuring relative Humidity over
ice, you will get an error which is strictly dependent on the difference
of saturation pressure of vapour over ice compared with the saturation
pressure of vapour over chilled water. The following table shows the