User manual

OPERATING INSTRUCTION
Technical changes reserved
0141 0315-199 09/2014
Humidity reference cells
for adjustment of humidity sensors
The operating principle is based on a saturated salt solution over which a particular value of relative humidity gets adjusted. For this purpose,
it is important, that the solution is properly saturated i.e. both un-dissolved salt in crystalline form is available in the solution and liquid is also
visible above that.
The cells have a mechanically stable and leak-proof construction. The inner
wall forms a membrane (also referred to as the diaphragm) which separates
the test chamber from the salt solution. The diaphragm is a micro-porous,
water vapour permeable wall, which restricts contact of test objects with the
salt solution. The sealing is also effective for a short time use in “overhead“.
The outer wall of the cell is made up of transparent plastic material. Hence,
the level of liquid and also saturation of the solution can be judged and
monitored from outside.
The saturated salt solution is present between the inner wall and the outer
wall. The water vapour (or more exactly the water vapour partial pressure
over the salt solution) penetrates through the diaphragm in the inner space
of the test container and forms a water vapour air mixture of relative humi
dity specic to the salt.
The reference cells are used for checking and adjustment of capacitive, resistive and electrolytic humidity sensors and probes.
The reference cells are not suitable for application in psychrometers, dew point mirrors or other thermal working measurement systems
due to its type of construction.
The cells are to be used only within the temperature range of 20 °C to 40 °C. Rapid change in temperature or pressure and mechanical
shocks should be avoided otherwise the cell or the diaphragm can get damaged.
The reference cells must be checked before use. Due to sudden change in temperature or pressure, some salt solution can ooze out of
the diaphragm. This is a normal physical phenomenon and is not considered as a defect. Hence, the required functioning is not affected.
CAUTION ! In any case, the split out liquid should be absolutely removed and inner space should be cleaned with a dry cloth as per the
safety guidelines. If there is still some liquid inside, , it can damage the sensor, metal housing or electronics of the sensor through inadver-
tent contact or salt corrosion!
Leaking cells, e.g. due to damaged diaphragm, are subject to be replaced.
The salt solution must be always in saturated condition i.e. both crystalline salt and liquid should be visible at the base of the reference cells.
In an unsaturated salt solution (i.e. either only liquid is visible without crystals or only dry crystalline salt is visible) a dened value of relative
humidity can no longer be warrantyd.
Before application, the cells should be briey tossed.
3. Operating principle
4. Application guidelines
4.1 Intended use
4.2 Checks before application
B+B Thermo-Technik GmbH | Heinrich-Hertz-Straße 4 | D-78166 Donaueschingen
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