COSA Xentaur Hygrocontrol Type 86 Ex - Manual (Page 23)

4. Practical Instructions and Limits
Besides the temperature limits specified for all our transmitters, probe
heads and sensors, you should observe the following rules when using our
instruments:
4.1 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.
4.2 Filters
4.2.1 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 flow)
Up to 50 m/sec (tangential flow
4.2.2 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.
HYGROCONTROL Manual for Type 86 Ex Page
22