Vaisala HMT360 - Manual (Page 24)

User’s Guide ______________________________________________________________________
22 ___________________________________________________________________ M010056EN-J
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.
0507-036 Figure 5 Measurement Error at 100 %RH