ROTRONIC HygroLog HL20 - Manual (Page 13)

IN-E-HL20-V1_12
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
HygroLog HL20 and HL21 data logger:
User Guide Instruction Manual
Document Type
Page 13 of 17
Document title
© 2010-2011; Rotronic AG IN-E-HL20-V1_12
The ROTRONIC HW4 software is required to view the measured or calculated data on a PC
monitor. Connect the da
ta logger to the HW4 PC as explained under “Initial Start-up”. HW4 is
also required to download and save the recorded data to disk. For additional instructions, see
document E-M-HW4v3-F2-018.
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.
4. Maintenance
4.1 Periodic calibration check
Both the Pt 100 RTD temperature sensor and associated electronics are very stable and
should not require any calibration after the initial factory adjustment.
Long term stability of the ROTRONIC Hygromer humidity sensor is typically better than 1
%RH per year. For maximum accuracy, calibration of the HL20 should be verified every 6 to
12 months. Applications where the data logger is exposed to significant pollution may require
more frequent verifications.
Note: calibrating and adjusting the data logger typically require a humidity-temperature
generator or other specialized equipment that may not be available to all users.