Title: time constant
Long Title: IUPAC Gold Book - time constant
DOI: 10.1351/goldbook.T06376
Status: current
Index: quantity

Definition
If the output of a detector changes exponentially with time, the time required for it to change from its initial value by the fraction \(1 - \exp(-t/\tau _{\rm{c}})\) (for \(t=\tau _{\rm{c}}\)) of the final value, is called the time constant.

Source
- PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1751 (https://doi.org/10.1351/pac199567101745)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/T06376/html
- json: https://goldbook.iupac.org/terms/view/T06376/json
- xml: https://goldbook.iupac.org/terms/view/T06376/xml

Citation: Citation: 'time constant' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.T06376
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-04-27T14:53:10+00:00