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Dew-Frost Error and the Chilled-Mirror Hygrometer

Technical Guide 24

Chilled mirror hygrometers provide accurate measurements of humidity as long as the state of the condensate (frost or dew) is known. Large errors are common when the mirror temperature lies between 0 °C and ‑25 °C, since the condensate can be frost or supercooled dew, or even a mixed state. This technical guide explains how to account for, and partially correct, the error in a chilled-mirror hygrometer measurement, when it is not possible to unambiguously identify the condensate.

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