engleski

New Submersed Chamber for Calibration of Relative Humidity Instruments at HMI/FSB-LPM

This paper gives a detailed description of a new chamber designed for calibration of relative humidity (RH) instruments at Laboratory for Process Measurement(HMI/FSB- LPM).Tothepresenttime, thecalibrations ofRHinstrumentsatthe HMI/FSB-LPM were done by comparison method using a climatic chamber of large volume and calibrated dew point hygrometer with an additional thermometer. Since 2010, HMI/FSB-LPMincooperation withCentreforMetrologyand Accreditation in Finland (MIKES) developed the two primary dew point generators which cover the dew point temperature range between −70 ◦C and 60 ◦C. In order to utilize these facilitiesforcalibrationsoftheRHinstruments, the newchamberwasdesigned, manufactured and installed in the existing system, aiming to extend its range and reduce the related calibration uncertainties. The chamber construction allows its use in a thermostatic bath of larger volume as well as in the climatic chambers. In the scope of this paper, performances of the new chamber were tested while it was submersed in a thermostated bath. The chamber can simultaneously accommodate up to three RH sensors. In order to keep the design of the chamber simple, only cylindrical RH sensors detachable from display units can be calibrated. Possible optimizations are alsodiscussed, andimprovements inthedesignproposed.Byusingthenewchamber, HMI/FSB-LPM reduced the expanded calibration uncertainties (level of confidence 95%, coverage factor k = 2) from 0.6%rh to 0.25%rh at 30%rh (23 ◦C), and from 0.8%rh to 0.53%rh at 70%rh (23◦C).

Comparison calibration ; Relative humidity ; RH test chamber

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