Vaisala HMT360N - Manual (Page 22)

User's Guide ______________________________________________________________________
20 __________________________________________________________________ M210744EN-C
Selecting Location
Select a place with stable conditions for mounting the transmitter. Do
not expose the transmitter to direct sunlight or rain. A rain shield is
available and it is recommended for direct outdoor installations. When
mounting the probe, select a place representing the process conditions.
Checking the Temperature Reading
The actual temperature of the process can be measured with a reference
instrument to be compared with the transmitter reading. The heat
transfer is less evident if you remove the protective filter of the sensor
for a short-term test. However, never use the sensor long periods
without the filter as this may cause a faster contamination of the sensor.
The transmitter fulfils the specified EMC regulations with the
protective filter on the probe.
In humidity measurement and especially in calibration and adjustment
it is essential that temperature of the probe and measuring environment
is the same. Even a small difference in temperature between the
environment and the probe causes an error. As the curve below shows,
if the temperature is +20 °C and the relative humidity 100 %RH, a
difference of ±1 °C between the environment and the probe causes an
error of ±6 %RH.
The graph below illustrates the measurement error at 100 %RH when
the difference between the ambient and sensor temperature is 1 °C.
WARNING During the installation work of the probes in gas group IIC areas
(requiring category I devices), it has to be guaranteed that even in fault
cases sparks generated by impacts or friction on the surface of the
housing can never occur.