COSA Xentaur Hygrocontrol Type 72 - Manual (Page 23)

Series 72 Manual page 19
11.1 Direct Contact with Liquids
Avoid in any case direct contact between the humidity sensor and any liquid.
The sensor may only detect the humidity in the atmosphere over the surface of
a liquid or a solid material.
Even if the sensor will not be changed in his characteristic by direct contact with
water and will measure correct values after being dryed, you should avoid
immersion or condensation. Some gases in the atmosphere could form acids
and corrosional attack will cause damages of the sensor with time.
11.2 Filters
11.2.1 Protection against high Air Velocities
As our humidity sensor has a very tiny mass together with a great surface area,
it is necessary to protect him against high gas velocities. Different filters are
available which give protection according to the list below:
- Protection Basket (SS-316): Up to 1 m/sec
- Sinterfilter (SS-316): Up to 30 m/sec
- Teflonfilter (sintered PTFE) Up to 50 m/sec
- Axialfilter (SS-316 with PTFE Membrane): Up to 30 m/sec (axial direction)
Up to 50 m/sec (tangential
direct.)
11.2.2 Protection against Dust and Aerosoles
Normally the Sinterfilter (SS-316) - which has pores of approx. 18/1000 mm -
will be used for protection against dust and particles. If quick response time of
the sensor is needed, an Axialfilter is preferable, but then no particles of high
speed should be able to hit the PTFE Membrane. As this membrane is only
65/1000 mm thick - with pores of 1/1000 mm only - it could be destroyed.
If humidity measurements are done in atmospheres containing Aerosoles like
solvents, oils or greases, a Teflonfilter (pores are approx. 1/1000 mm) should
be used for protection of the sensor. The smooth surface of the PTFE will not
be contaminated so fast as other filters. High concentration of Aerosoles will
predict a cleaning of the Teflonfilter from time to time. This may be done easily
with an Ultrasonic Bath.
11.3 Resistance against Chemical Attack
Our sensors are wellknown for their resistance against most chemical attacks.
To give the user some informations 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 informations.