E-M-HyLabC1-V1
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
HygroLab C1 bench-top indicator:
User Guide
Instruction Manual
Document Type
Page
12 of 28
Document title
© 2011; Rotronic AG E-M-HyLabC1-V1
3.7 Practical advice for measuring 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.
It is always good practice to monitor the display for temperature stability. The probe should be given sufficient
time to equilibrate with the environment to be measured. The larger the initial temperature difference between
the probe and the environment to be measured, the more time temperature equilibration requires. This time
can be shortened, and errors avoided, by using the probe configuration that fits best for your application.
In extreme situations, condensation may occur on the sensors when the probe 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 Aw Measurement
When enabled to measure water activity, the HygroLab C1 automatically displays humidity as Aw (1.000 a
w
=
100 %RH) and offers the following options:
• AwE mode: the HygroLab C1 waits for the full equilibration of the measured product and probe. For most
products, this takes from 30 to 60 minutes. The HygroLab C1 automatically detects equilibrium conditions
(humidity and temperature) and ends the measurement at that time by freezing the display.
• AwQuick mode
: the HygroLab C1 uses an algorithm to accelerate the water activity measurement and
provides a result in typically 5 minutes. The measurement ends automatically and the display is frozen. When
temperature conditions are stable (both at the product and probe), the value measured with the AwQuick
mode is generally within ± 0.005 aw of the value that would be obtained by waiting for full equilibration of the
product and probe
.
NOTE: See technical paper E-T-AW (Measuring Water Activity) for basic information on water activity and its
applications.
4.1 Enabling Aw Measurement
To enable the HygroLab C1 to measure water activity:
o Press the MENU key and select “Aw Settings”. Press ENTER to activate the menu.
o With the “Enable Aw” menu item highlighted, press ENTER and use the UP or DOWN arrow key to
select ON. Press ENTER to confirm the selection.
o Optional: Use the DOWN arrow key to select the “SaveResult” menu item and press ENTER. Use
the UP or DOWN arrow key to select either ON or OFF. Press ENTER to confirm the selection
o Use the DOWN arrow key to select the “Mode” menu item and press ENTER. Use the UP or DOWN
arrow key to select either AwQuick or AWE. Press ENTER to confirm the selection.
o The settings for either the AwQuick or AWE function can be changed after using the UP or DOWN
arrow key to highlight the setting and by pressing on ENTER. Use the UP or DOWN arrow key to
change each digit. Press ENTER to move the cursor to the right. When done, press ENTER to save
the value.
o Press MENU twice to fully exit the menu.
(51 pages)
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