Air Humidity Measurement

Author: Hans-Jürgen Schwarz

back to Climatic measurements

Overview of the chapter for measuring humidity

• Physical Principles
  • Dalton´s Law
  • Water Vapor Partial Pressure in the air
• Measurand
  • Dewpoint
  • Saturation Humidity
  • Relative Humidity
  • Absolute Humidity
  • Mixing Ratio
• Moisture measurement methods
  • Dewpoint
  • Psychrometric Measuring Methods
  • Capacitive Measuring Methods
  • Hygrometric Measuring Methods
    • Hair Measuring Element
    • Plastic Measuring Element
  • LiCl-Dewpoint Hygrometer
  • Electrolytic Hygrometer
  • Infrared Hygrometer
  • Bi-Strip Hygrometer (Feather Hygrometer)
  • Aluminium Oxide Sensor
  • Resistive Sensors
• Comparison of the Measuring Method
• Measuring Humidity in Practice

Introduction

Air is a mixture of gases. The main components are summarized in table 1. In addition to these components, the air always contains a small amount of water, which exists in three states of matter:

• solid: ice, hail, snow
• liquid: rain, fog, dew
• gas: water vapor

Table 1: Composition of the air

Gas	Symbol	Content in Vol. %
Nitrogen Oxigen Argon	N2 O2 Ar	78 21 0,8
Krypton Xenon Neon Helium Hydrogen Carbon dioxide Methane Ozone	Kr Xe Ne He H2 CO2 CH4 O3	Trace gases

Water is the only gas in the atmosphere that is present in its three states of matter. For the building trade, this leads to some undesirable phenomena such as condensation, corrosion and frost. In addition to temperature, humidity is the main indicator for describing the climate. Relative humidity, for example, influences our wellbeing to a great extent.