Metrological Traceability in Meteorological Sensors: Examples & Illustrations

1. METROLOGICAL TRACEABILITY FOR METEOROLOGICAL SENSORS ILLUSTRATED THROUGH EXAMPLES MirunaDOBRE– SMD (Belgium)Stephanie BELL– NPL (United Kingdom)Doloresdel CAMPO– CEM (Spain)MarttiHEINONEN- MIKES (Finland)Domen HUDOKLIN– LMK (Slovenia)GiuseppinaLOPARDO, AndreaMERLONE – INRIM (Italy) http://economie.fgov.be

2. Why do I need traceability? International Vocabulary for Metrology (VIM) definition: “property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty”. • Confidence in the • Quality of my measurement and • Equivalence to other similar measurements http://www.bipm.org/en/publications/guides/vim.html

3. International agreement (CGPM decision) The unbroken chain of calibrations Maintained by National Measurement Institute ( unit realization) Compared with primary standard (calibration at NMi) Compared with secondary standard (calibration at accredited or final user’s lab) Compared with working standard (in-field or lab. calibration) http://economie.fgov.be

4. A measurement has metrological traceability if: • An unbroken and documented chain of calibrations links the instrument to an internationally agreed reference; • Each chain link has documented uncertainty estimations; • The final user has procedures to ensure that the instrument maintains its calibration with associated uncertainties over time; • The influence factors affecting the measurement are quantified and a total measurement uncertainty is calculated, documented and reported with the result. http://economie.fgov.be

5. The unit definition and its practical realization USA ismembersince 1875 • Signed by 17 countries on 20 May 1875 • Today 56 Member States and 37 Associates www.bipm.org 7 base units The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. Many derived units The pascal, unit of pressure or stress, is the force applied per unit area. www.bipm.org http://economie.fgov.be

6. Thermometry practical reference standards Discrete reference scale: Fixed point cell Interpolation instrument: Standard platinum resistance thermometer http://www.bipm.org/en/publications/mep_kelvin/ http://economie.fgov.be

7. ITS 90 http://www.nmij.jp/english/library/units/temperature/ http://economie.fgov.be

8. Unbroken chain of calibrations for temperature measurements For measurements in air see for example the calibration of climaticchambers guide: www.dkd.eu/dokumente/.../dkd_r_5_7_e.pdf Measurement in lab. and in liquid http://economie.fgov.be

9. Traceability scheme for resistance thermometry measurements Traceability/uncertaintycalculation startfrom the mathematicalmodel Traceabilityfor the measurandY = traceability for all the input quantitiesxi http://www.bipm.org/en/publications/guides/gum.html http://economie.fgov.be

10. Humidity quantities - what is the measurand? • Humidity is a general term encompassing: • Vapourpressure (partial pressure) of water (in units of pressure) • Dew-point temperature [and frost point] (in units of temperature) • Composition (dimensionless) • Relative humidity (dimensionless) but symbol %rh used (also %hr, %ur, %rF, etc) - not very standardised! • And other less-used parameters http://economie.fgov.be

11. Humidity primary standards • By measurements: gravimetric hygrometer • By realizations: a system that can produce a gas stream of known humidity • By saturation at defined pressure(s) and temperature(s) • By gas blending, … http://economie.fgov.be

12. Humidity primary standards Humidity = mass of water vapor in a unit volume of moist air at a given temperature and pressure. • Absolute humidity generator operation: • Saturate the gas with water at a known temperature and pressure. • The mole fraction x of water vapor in the gas is • For 2-p expand till atmosphere, for divided flow mix withknownamounts of dry gas (traceableflowmeters) water vapor pressure enhancement factor uncertainty due to formulae calculations http://economie.fgov.be

13. Humidity primary standards http://economie.fgov.be

14. Traceability scheme for humidity measurements http://economie.fgov.be

15. Traceability scheme for humidity measurements http://economie.fgov.be

16. Mass reference Length reference Temperature reference m A p Important influence Primary standards in pressure measurement Laser interferometric manometer Piston gauge http://economie.fgov.be

17. Primary standards in pressure measurement • Othereffectsaffectingmeasurementresult: • dilatation of piston and cylinder due to temperature and pressure; • surface tension effects around piston; • air buoyancy over masses; • liquid column head, • …. http://economie.fgov.be

18. A measurement has metrological traceability if: • An unbroken and documented chain of calibrations links the instrument to an internationally agreed reference; • Each chain link has documented uncertainty estimations; • The final user has procedures to ensure that the instrument maintains its calibration with associated uncertainties over time; • The influence factors affecting the measurement are quantified and a total measurement uncertainty is calculated, documented and reported with the result. http://economie.fgov.be

19. Questions? Askyour National Metrological Institute! http://www.bipm.org/en/practical_info/useful_links/nmi.html http://economie.fgov.be