http://economie.fgov.be
Miruna DOBRE – SMD (Belgium)Stephanie BELL – NPL (United Kingdom)
Dolores del CAMPO – CEM (Spain)Martti HEINONEN - MIKES (Finland) Domen HUDOKLIN – LMK (Slovenia)
Giuseppina LOPARDO , Andrea MERLONE – INRIM (Italy)
METROLOGICAL TRACEABILITY
FOR METEOROLOGICAL SENSORS
ILLUSTRATED THROUGH
EXAMPLES
Why do I need traceability?
International Vocabulary for Metrology (VIM) definition: “property of a measurement result whereby the result can be related to a referencereference through a documented unbroken chain of calibrationschain of calibrations, each contributing to the measurement uncertaintymeasurement uncertainty”.
1. Confidence in the
2. Quality of my measurement and
3. Equivalence to other similar measurements
http://www.bipm.org/en/publications/guides/vim.html
http://economie.fgov.be
Maintained by National Measurement Institute
( unit realization)
Maintained by National Measurement Institute
( unit realization)
Compared with primary standard (calibration at NMi)
Compared with primary standard (calibration at NMi)
Compared with secondary standard
(calibration at accredited or final user’s lab)
Compared with secondary standard
(calibration at accredited or final user’s lab) Compared with
working standard (in-field or lab.
calibration)
Compared with working standard
(in-field or lab. calibration)
International agreement
(CGPM decision)
International agreement
(CGPM decision)
The unbroken chain of calibrations
http://economie.fgov.be
A measurement has metrological traceability if:
1. An unbroken and documented chain of calibrations links the
instrument to an internationally agreed reference;
2. Each chain link has documented uncertainty estimations;
3. The final user has procedures to ensure that the instrument
maintains its calibration with associated uncertainties over
time;
4. 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
The unit definition and its practical realization
7 base unitsThe kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
Many derived unitsThe pascal, unit of pressure or stress, is the force applied per unit area.
Derived quantity Name SymbolExpressed in terms of other SI units
Expressed in terms of SI base units
pressure, stress pascal Pa N/m2 m–1 kg s–2
www.bipm.org
www.bipm.org
• Signed by 17 countries on 20 May 1875• Today 56 Member States and 37
Associates
USA is member
since 1875
http://economie.fgov.be
Discrete reference scale: Fixed point cell
Interpolation instrument: Standard platinum resistance thermometer
http://www.bipm.org/en/publications/mep_kelvin/
Thermometry practical reference standards
http://economie.fgov.be
http://www.nmij.jp/english/library/units/temperature/
ITS 90
http://economie.fgov.be
Unbroken chain of calibrationsfor temperature measurements
Measurement in lab. and in liquid
For measurements in air see for example the calibration of climatic chambers guide:
www.dkd.eu/dokumente/.../dkd_r_5_7_e.pdf
http://economie.fgov.be
Traceability scheme for resistance thermometry measurements
nxxxfY ...,, ,21Traceability/uncertainty calculation start from the mathematical model
Traceability for the measurand Y = traceability for all the input quantities xi
rWWfT
XRR
CR
TRW
s
01.090
http://www.bipm.org/en/publications/guides/gum.html
http://economie.fgov.be
Humidity quantities -what is the measurand?
Humidity is a general term encompassing:
•Vapour pressure (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
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
Absolute humidity generator operation:
1.Saturate the gas with water at a known temperature and pressure. The mole fraction x of water vapor in the gas is
2.For 2-p expand till atmosphere, for divided flow mix with known amounts of dry gas (traceable flowmeters)
ssss PPTfTex ,
Humidity = mass mass of water vapor in a unit volumevolume of moist air at a given temperaturetemperature and pressurepressure.
water vapor pressure enhancement factor
uncertainty due to formulae calculations
Humidity primary standards
http://economie.fgov.be
Humidity primary standards
http://economie.fgov.be
Traceability scheme for humidity measurements
http://economie.fgov.be
Traceability scheme for humidity measurements
http://economie.fgov.be
Primary standards in pressure measurement
Hgp
m
p
A
Agmp
Temperature reference
Important influence
Mass reference
Length reference
Laser interferometric manometer
Piston gauge
http://economie.fgov.be
Other effects affecting measurement result:
•dilatation of piston and cylinder due to temperature and pressure;•surface tension effects around piston;•air buoyancy over masses;• liquid column head,•….
Primary standards in pressure measurement
http://economie.fgov.be
A measurement has metrological traceability if:
1. An unbroken and documented chain of calibrations links the
instrument to an internationally agreed reference;
2. Each chain link has documented uncertainty estimations;
3. The final user has procedures to ensure that the instrument
maintains its calibration with associated uncertainties over
time;
4. 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
http://www.bipm.org/en/practical_info/useful_links/nmi.html
Questions?
Ask your National Metrological Institute!
Top Related