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Humidity and Thermal State Behaviour

Working Group 3.41

Gas Humidity

Gas Humidity describes the amount of water in a gas. The humidity is specified and disseminated in different units, e.g. dew-point/frost-point temperature, relative humidity or volume fraction.

The humidity is measured with so-called hygrometers which are based on different working principles. A summary of important kinds of hygrometers is given at the following Opens internal link in current windowLink.

The validation and traceability of gas humidity scale is done by so-called humidity generators. A selection of humidity generators which are used for traceability of the property humidity is given at the following Opens internal link in current windowLink.


The metrological traceability to the national standard is offered for hygrometers of the different working principles and for a selection of commercial humidity generators.

Opens external link in new windowCalibration and measurement capabilities

Please address requests about calibration and questions about the topic gas humidity to our e-mail address Opens window for sending emailgasfeuchte(at)ptb.de

Research and Development

Research and development activities in the field of gas humidity cover the following topics:

  • development of a new primary standard for the range of frost-point/dew-point temperatures from -40°C up to +95°C
  • development of mobile gas humidity generators based on the principle of permeation
  • activities in the field of trace humidity
  • activities in the field of different gas matrices, e.g. energy gases or biogas
  • development and application in the field of humidity transfer standards on the basis of laser spectroscopy (TDLAS)
  • traceability of atmospheric humidity measurement on research airplanes (HALO, Learjet, etc.)
  • development and application of fast laser hygrometers for the dynamic characterization of commercial hygrometers


Contribution in following committees:

  • DKD-Fachausschuss Temperatur und Feuchte
  • VDI/VDE-GMA FA 2.53 Gasfeuchtemessung
  • Technical Committee for Thermometry (EURAMET TC-T)
  • Consultive Committee for Thermometry (CCT)

General Literature Gas Humidity

  • Hardy, R.: ITS-90 Formulations for Vapor Pressure, Frostpoint Temperature, Dewpoint Temperature and Enhancement Factors in the Range -100 to 100 °C; Proceedings of Third International Symposium on Humidity and Moisture; edited by National Physical Laboratory (NPL), London, 1998, pp. 214-221.
  • Sonntag, D.: Important New Values of the Physical Constants of 1986, Vapor Pressure Formulations based on the ITS-90 and Psychrometer Formulae; Z. Meteorol., 70 (5), 1990, pp. 340-344.
  • Wexler, A.: Vapor Pressure Formulation for Water in Range 0 to 100 °C. A Revision; J. Research NBS, A. Physics and Chemistry, 80A, 1976, pp. 775-785.
  • Greenspan, L.: Functional Equations for Enhancement Factors for CO2-free Moist Air; J. Research NBS, A. Physics and Chemistry, 80A, 1976, pp. 41-44.
  • Harrison, L. P.: Fundamental Concepts and Definitions Relating to Humidity, in Wexler, A., Wildhack, W. A. (Eds.), Humidity and Moisture Vol. 3 Fundamentals and Standards, Reinhold Publishing, New York 1965, pp. 3-69.