Calibration of hygrometers at fluctuating and transient conditions
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Hygrometers are normally calibrated under stable conditions. Relative humidity values in the climatic chamber fluctuate quite much at medium levels. In this work it was measured how much the relative humidity fluctuation in the climatic chamber affects the calibration of hygrometers. Also the time constants of different hygrometers were measured and the hygrometers were calibrated at drifting relative humidity values. Even though the relative humidity values fluctuate in the climatic chamber at medium levels, this fluctuation has a minor effect in calibration. Even the slowest hygrometers can be calibrated under fluctuating conditions. Under drifting conditions the accuracy of calibration depends on the speed of the drift and the time constant of the hygrometer. The calibration of slowest hygrometers at drift speeds 0.5 %/min and 1 %/min can lead to significant lag errors.