AN EXPERIMENTAL-VERIFICATION OF SATURATED SALT SOLUTION-BASED HUMIDITY FIXED-POINTS

The high instability and hysterisis of the relative humidity sensors c urrently available on the market render necessary simple and economic calibration methodologies that can be used as secondary or working sta ndards. The chemical equilibrium-type systems based on saturated aqueo us salt solutions, even though simple and economical, are not always m etrologically satisfactory For calibration. They can, in fact, be unre liable, when fundamental requirements are neglected; also, unacceptabl e discrepancies continue to exist in the equilibrium relative humidity reference data of saturated aqueous salt solutions furnished by both literature and standards. To highlight the factors that increase the r eliability of calibrations with saturated aqueous salt solutions, the authors of this paper have redetermined the equilibrium relative humid ity reference data of 11 saturated acqueous salt solutions at ambient pressure and temperature. The solutions chosen were the ones generally used as fixed points to obtain a relative humidity calibration scale.