User manual

OPERATING INSTRUCTION
Technical changes reserved
0141 0315-199 09/2014
Humidity reference cells
for adjustment of humidity sensors
In the most frequently used Lithium chloride, Magnesium-chloride and Sodium-chloride salts, the effect of temperature on humidity values
is practically nil. Details of temperature dependence are as per the humidity tables provided in the appendix section of this documentation.
To apply this, the ambient temperature of the salt container is to be measured with a thermometer and humidity value is to be worked out
from the tables through interpolation.
With proper use, under laboratory conditions, an accuracy of up to ±1 % RH can be achieved at the test point. During applications in open
eld, a temperature stable environment is important for attaining the desired accuracy. An additional error of ±2 % RH should be taken into
account.
The accuracy possible for the total system considerably depends on the characteristics of the sensor elements used (hysteresis effect,
linearity error, secondary drift, consistency).
Since the capacitive sensor elements show typical backlash characteristics for both offset and gain value, the adjustment should be always
done at two points.
Even if very good results are achieved with the reference cells, application errors should never be totally ruled out. To be safe, an additional
comparative measurement should always be carried out with a certied reference device.
If possible, the sensing units should be kept inside the reference cells without the sinter guard lters. If necessary, get details from the
manufacturer of sensors as to how the cap is to be removed. While using with the protection cap, a clear increase in stabilisation time
should be anticipated.
CAUTION ! After removing the protection cap, the delicate humidity sensor is in exposed condition and can get damaged by inappropriate
handling. The sensor surface should not be touched. Finger prints or scratches on the surface may lead to deviations or malfunctioning.
CAUTION ! The sensor should be inserted in the cell only to the extent that it does not touch the base otherwise both sensor or diaphragm
can get damaged.
The humidity sensor must be in error free condition. Damaged, scratched or broken humidity sensors must be referred to the works for
replacement!
The sensor should not show any dust deposits or other contaminations. The humidity sensors are water resistant. If the sensor gets dirty, it can
be cleaned with distilled water of max 65 °C. In addition, the sensor is to be rinsed in water for approximately 1 Minute. After that, the sensing
element should be dried for 24 hours at 80 °C. Subsequently, the sensor should be kept under ambient conditions (30 % - 70
% RH) for 48 h
before using again.
CAUTION! There is electronics circuitry inside the sensor housing which can get damaged due to contact with water. Therefore only the
sensor should be immersed in water and not the complete sensing unit.
!
4.5 Temperature dependence
4.7 Removing the protection cap
4.8 Humidity sensor checking
4.9 Humidity sensor cleaning
!
4.6 Tolerance and accuracy
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