Vaisala PTU300 - Manual (Page 46)

User's Guide _______________________________________________________________________
44 ___________________________________________________________________ M210796EN-G
Probe Mounting
In humidity measurement and especially in calibration 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.
0507-023
Figure 24 Measurement Error at 100 %RH
General Instructions for Probes with
Cable
Mount the probes with a cable with the probe horizontally; this way, any
water condensing on the tube cannot flow onto the sensor.
When there is no alternative but to install the probe in the process
vertically, the point of entry must be carefully insulated. The cable must
also be allowed to hang loosely as this prevents any condensed water
from running onto the probe along the cable.