Humidity

Relative humidity (%RH) describes the relative amount of water vapour present in the air in relation to the amount the air can absorb at the current temperature. More formally, relative humidity is defined as the ratio of the partial pressure of water vapor to its maximum value (saturation) at the same temperature.

Measuring humidity

We calibrate instruments for Relative humidity in climate chambers by comparison with a calculated relative humidity. We measure air temperature with precision thermometer in unit degrees Celsius (°C) and humidity with a chilled mirror in measurement size dew point/freezing point which is also indicated in degrees Celsius (°C). These measurements are used to calculate relative humidity with the Wexler/Sonntag vapor pressure formula.

Instruments for relative humidity are used, among other things, for:

• monitor industrial processes that are sensitive to moisture
• measurements for meteorology and climatology
• in agriculture for irrigation of fields and regulation of humidity in greenhouses
• monitoring of humidity in laboratories, offices, kindergartens and other places where we spend time

The Norwegian Metrology Service’s work with humidity

The Norwegian Metrology Service develops and maintains national references.  This means, among other things:

• traceability to national references for dew point and temperature
• calibration of instruments for laboratories, industry and others
• development and improvement of measurement methods
• international collaboration with metrology institutes to ensure competence and global comparability