IN-E-HL20-V1_16
Rotronic AG
Bassersdorf, Switzerland
Document code
Unit
HygroLog HL20 and HL21 data logger:
User Guide
Instruction Manual
Document Type
Page
16
of 23
Document title
3.5 Practical advice for measuring temperature and humidity
The most common source of error when measuring relative humidity is a difference between the
temperature of the probe and the temperature of the environment. At a humidity condition of 50
%RH, a temperature difference of 1
°
C (1.8
°
F) typically results in an error of 3 %RH on relative
humidity.
When using the data logger, it is good practice to allow for sufficient for temperature equilibration
with the environment. The larger the initial temperature difference between the probe and the
environment to be measured, the more time temperature equilibration requires. This can be
monitored with the optional display.
In extreme situations, condensation may occur on the sensors when the data logger is colder than
the environment. As long as the humidity / temperature limits of the humidity sensor are not
exceeded, condensation does not alter the calibration of the sensor. However, the sensor has to
dry out before it can provide a valid measurement.
Non-moving air is an excellent insulator. When there is no air movement, surprising differences in
temperature and humidity can noted over short distances. Air movement at the probe generally
results in measurements that are both faster and more accurate.
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IN-E-HL20-V1_16
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