Case study Realistic and best uncertainties with humidity instruments

Transcription

1 Case study Realistic and best uncertainties with humidity instruments Domen Hudoklin September 2014 Brdo, Slovenia

2 Humidity calibrations Dewpoint primary - against dewpoint generator secondary - against precision dew-point sensor (chilled mirror hygrometer) Relative humidity reference value: dewpoint + temperature reference RH probe Other (mass fraction - upper air, )

3 Traceability scheme LMK case Other NMI pressure meter LMK primary dew-point generator PGR-LMK-01 LT bath LMK primary dew-point generator PGR-LMK-02 HT bath precision resistance bridge precision ref.resistor thermometer SPRT LMK primary realisation of temperature -50 C to 20 C 0,028 C to 0,049 C 20 C to 95 C 0,05 C precision dew-point sensors humidity generator IPRT thermometers -10 C to 70 C 0,03 C -10 C to 70 C 0,12 C unit under cal. (dew-point sensor) unit under cal. 10% to 95% 0,5 % to 1,6 % (rel. humidity sensor)

4 CMC - Calibration and Measurement Capability a CMC is a calibration and measurement capability available to customers under normal conditions: as published in the BIPM key comparison database (KCDB) of the CIPM MRA; or as described in the laboratory s scope of accreditation granted by a signatory to the ILAC Arrangement * BIPM/RMO-ILAC/RAB Working Party, The CMC-BMC Issue: Developments since the Nashville statement, 2007 (

5 BIPM KCDB CMCs - dewpoint

6 BIPM KCDB CMCs - dewpoint

7 Combining different uncertainties In RH calibrations, if the reference is dew-point sensor, then the temperature and dew-point contributions have to be considered separately. u u t t 2 u t d t d 2

8 Temperature dependence of relative humidity D / % t / C / %

9 BIPM KCDB CMCs relative humidity at 95%rh, 98%rh

10 BIPM KCDB CMCs relative humidity at 10%rh (and 0.5%rh)

11 Humidity calibrations Sources of uncertainties: generation of humidity uncertainty of reference value uncertainty of calibration method UUT correlations (generation UUT, )

12 4. UUT Unit under test temporal variation hysteresis resolution curve-fitting loading effect drift (to be added by the end user) reproducibility the influence of UUT to calibration environment (self-heat, humidification psychrometer) uncertainty of electrical devices (bridge, resistor,...)

13 Expanded uncertainty contribution of the UUT LMK case for period of 1 month