Uncertainty Analysis in Humidity Measurements by the Psychrometer Method

Area of Science:

• Environmental Science
• Metrology
• Atmospheric Science

Background:

• Relative humidity (RH) is commonly measured indirectly using psychrometers.
• Psychrometers utilize dry and wet bulb temperature sensors for RH estimation.
• Understanding measurement uncertainty is crucial for accurate environmental monitoring.

Purpose of the Study:

• To evaluate the measurement uncertainty of relative humidity using psychrometers.
• To compare the predictive accuracy of different empirical equations for RH calculation.
• To develop an improved method for determining the psychrometer constant.

Main Methods:

• Indirect RH measurement using a psychrometer with dry and wet bulb sensors.
• Evaluation of six empirical equations for RH calculation.
• Regression analysis to establish a new equation for the psychrometer constant.
• Analysis of measurement uncertainty influenced by temperature sensor accuracy.

Main Results:

• The Penman equation demonstrated the best predictive ability for RH within a 15-50 °C range.
• Increased wet bulb depression led to higher errors at fixed dry bulb temperatures.
• A newly derived equation for the psychrometer constant achieved an average predictive error of <0.1% for RH.
• Wet bulb temperature uncertainty was identified as the primary contributor to RH measurement uncertainty.

Conclusions:

• The developed psychrometer constant equation offers high accuracy for RH measurement.
• Accurate dry and wet bulb temperature readings are essential for minimizing RH uncertainty.
• Psychrometer-based RH measurements can be significantly improved with optimized constants and error analysis.