Many devices, whether newly purchased or long unused, may be out
of calibration or have never been properly calibrated. For some,
verifying their accuracy may be a matter of curiosity, while for
others, it is a practical necessity. To ensure their accuracy, it
is essential to verify and, if necessary, adjust their readings.
Inaccurate humidity measurements can lead to incorrect
environmental assessments, affecting everything from scientific
experiments to home climate control.
This guide demonstrates how to use the Dry
Bulb and Wet Bulb method to measure humidity accurately
and calibrate a hygrometer using the CHEMIX School software. By
following a simple step-by-step process, you can determine the
relative humidity and adjust your hygrometer or take note of any
discrepancies for future reference.
4-Step Guide for Single Thermometer Dry-Bulb Wet-Bulb
Measurement
Follow these steps to measure humidity using a single
thermometer:
Measure and record the ambient temperature (Dry-Bulb)
using a thermometer.
Wrap a cloth around the thermometer sensor.
Moisten the cloth with distilled water at ambient
temperature.
Blow air over the damp cloth using a fan. Observe and
record the stabilized wet-bulb temperature.
Fig. CHEMIX School - Hygrometer Calibration
Using the Software
The software includes a calculator for
computing Dry-Bulb, Wet-Bulb, and Humidity values:
Dry Bulb: Input the recorded ambient
temperature.
Wet Bulb: Input the stabilized wet-bulb
temperature after blowing air.
Humidity: The software calculates relative
humidity based on the Dry-Bulb and Wet-Bulb values.
Dew Point: The calculator also determines the
dew point based on user inputs.
Experiment Management
The software allows users to name and save different experiment
settings and notes:
Name (experiment): Enter a name for the
current experiment.
Experiment List Box: A list of saved
experiments.
Edit List Box Frame:
Save: Store current settings as a
"Before" or "After" entry.
Replace: Update the selected entry with
new settings.
Delete: Remove an entry from the list.
A large editable text field is available for
additional notes and observations.
Conducting the Experiment
This experiment demonstrates how to use the Dry Bulb and
Wet Bulb method to measure humidity and calibrate a
hygrometer.
Materials Needed
Baking thermometer
Cloth
Small amount of glue
Fan
Preparation
Wrap the cloth tightly around the
thermometer’s metal rod.
Use a small amount of glue to secure the
cloth in place. Textile glue is probably the best option. Be
sure to read the glue label for proper use.
Ensure the cloth can slide smoothly over the
thermometer sensor without obstruction.
Measurement Process
A PC fan is tested to create airflow over
the cloth.
The temperature sensor is positioned inside
the metal rod.
A wooden block can help elevate the
thermometer for better positioning.
The dry-bulb temperature stabilizes,
representing ambient room temperature.
Adjust the cloth so it fully covers the
sensor located inside the metal rod. The sensor is located
approximately 2 cm from the tip of the hollow metal rod.
Moisten the cloth with distilled water at
ambient temperature.
Turn on the fan to direct airflow over the
thermometer.
Observe the temperature drop as the water
evaporates.
Recording the Data
The temperature decrease due to evaporation
is observed.
The process takes normally approximately 3 minutes
to complete.
The next step is calculating relative humidity
using the software.
Calculating Relative Humidity
Insert the dry-bulb temperature.
Insert the wet-bulb temperature.
The software calculates relative humidity
and dew point.
The temperature unit can be adjusted if needed.
Calibrating a Hygrometer
If the hygrometer does not allow adjustment,
note the error and place a visible reminder on
the device. This helps account for discrepancies when reading
humidity levels.
