Vaisala PTU300 User's Guide download pdf (Page 42)

USER'S GUIDE____________________________________________________________________

40 __________________________________________________________________ M210796EN-E

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.

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Vaisala PTU300 User's Guide Page 42