COSA Xentaur Hygrocontrol Type 83 - Manual (Page 11)

HYGROCONTROL Manual for Type 83 Page - 10 -
6. 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:
6.1 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 dried,
you should avoid immersion or condensation. Some gases in the
atmosphere could form acids and corrosion attack will cause
damages of the sensor with time.
6.2 Filters
6.2.1 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
- Sinter filter (SS-316): Up to 30 m/sec
- Teflon filter (sintered PTFE) up to 50 m/sec
- Axial filter (SS-316 with PTFE Membrane): Up to 30 m/sec (axial direction)
Up to 50 m/sec (tangential)
6 .2.2 Protection against Dust and Aerosols
Normally the Sinter filter (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 axial filter 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
Aerosols like solvents, oils or greases, a Teflon filter (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 Aerosols will predict a cleaning of the
Teflon filter from time to time. This may be done easily with an
Ultrasonic Bath.