Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
articles:nist_traceability [2019/01/26 14:47]
rrandall [An "unbroken chain of calibrations" to what?]
articles:nist_traceability [2019/06/12 22:32] (current)
rrandall [Conclusion]
Line 66: Line 66:
 ===== What are SI Units? ===== ===== What are SI Units? =====
 {{ :​articles:​2018-si.png?​direct&​130|}} {{ :​articles:​2018-si.png?​direct&​130|}}
-Adopted by the [[https://​en.wikipedia.org/​wiki/​General_Conference_on_Weights_and_Measures|General Conference on Weights and Measures (CGPM)]] in 1960, the "​[[https://​www.bipm.org/​en/​measurement-units/​|International System of Units]]"​ (//Système International d'​Unités//,​ with the international abbreviation SI) consists of 7 base units that define 22 derived units. ​With the exception of the kilogram, the base SI units are all derived from intrinsic (i.e., invariant) constants of nature, such as the speed of light in vacuum and the [[https://​en.wikipedia.org/​wiki/​Boltzmann_constant|Boltzmann constant]] (which serves as the basis for the Kelvin temperature scale). According to Dr. Chris Sutton, "​[[https://​www.sciencelearn.org.nz/​resources/​1872-non-si-units|the SI system of units allows for complete coverage of all scientific measurements]]"​. \\+Adopted by the [[https://​en.wikipedia.org/​wiki/​General_Conference_on_Weights_and_Measures|General Conference on Weights and Measures (CGPM)]] in 1960, the "​[[https://​www.bipm.org/​en/​measurement-units/​|International System of Units]]"​ (//Système International d'​Unités//,​ with the international abbreviation SI) consists of 7 base units that define 22 derived units. ​The base SI units are all derived from intrinsic (i.e., invariant) constants of nature, such as the speed of light in vacuum and the [[https://​en.wikipedia.org/​wiki/​Boltzmann_constant|Boltzmann constant]] (which serves as the basis for the Kelvin temperature scale). According to Dr. Chris Sutton, "​[[https://​www.sciencelearn.org.nz/​resources/​1872-non-si-units|the SI system of units allows for complete coverage of all scientific measurements]]"​. \\
  
 The SI Units are defined in the [[https://​www.bipm.org/​en/​publications/​si-brochure/​|SI Brochure]], which is published by the [[https://​www.bipm.org/​en/​about-us/​|“Bureau International des Poids et Mesures” (BIPM)]], located in France. The SI Units are defined in the [[https://​www.bipm.org/​en/​publications/​si-brochure/​|SI Brochure]], which is published by the [[https://​www.bipm.org/​en/​about-us/​|“Bureau International des Poids et Mesures” (BIPM)]], located in France.
- 
-SI Units are also explained on the NIST web site at: https://​www.nist.gov/​pml/​weights-and-measures/​metric-si/​si-units 
  
 Because SI units are derived from intrinsic (i.e., invariant) constants of nature, "​intrinsic measurement standards"​ exist. This is acknowledged in ISO 17025:2017, sec. 6.5.2, which provides 3 (three) different methodologies for achieving metrological traceability. And is further clarified in ISO 17025:2017, "Annex A: Metrological traceability"​. \\ Because SI units are derived from intrinsic (i.e., invariant) constants of nature, "​intrinsic measurement standards"​ exist. This is acknowledged in ISO 17025:2017, sec. 6.5.2, which provides 3 (three) different methodologies for achieving metrological traceability. And is further clarified in ISO 17025:2017, "Annex A: Metrological traceability"​. \\
Line 80: Line 78:
 b) a documented unbroken chain of calibrations going back to stated and appropriate references (appropriate references include national or international standards, and __intrinsic standards__);// ​ b) a documented unbroken chain of calibrations going back to stated and appropriate references (appropriate references include national or international standards, and __intrinsic standards__);// ​
 </​WRAP>​ </​WRAP>​
 +
 +SI Units are also explained on the NIST web site at: https://​www.nist.gov/​pml/​weights-and-measures/​metric-si/​si-units and in "​[[https://​www.nist.gov/​pml/​special-publication-330|NIST Special Publication 330 -  The International System of Units (SI)]]"​. Both NIST sources will likely be updated soon to reflect the new definitions to the SI that went into effect on May 20, 2019. 
 ===== What are "​intrinsic"​ standards? ===== ===== What are "​intrinsic"​ standards? =====
  
Line 113: Line 113:
 While ISO 9001:2015, AS9100:2016 (Rev. D) and ISO 17025:2017 all mention "​International Standards",​ I am aware of only four (4) "​international standards"​ (as opposed to SI //units//); three of which are listed as examples in the "​Bureau International des Poids et Mesures"​ (BIPM) [[https://​www.bipm.org/​utils/​common/​documents/​jcgm/​JCGM_200_2012.pdf|JCGM 200:2012, "​International vocabulary of metrology – Basic and general concepts and associated terms (VIM)"​]] (3rd edition), sec. 5.2, "​international measurement standard"​. However, there are probably others. Those that I am aware of include: \\ While ISO 9001:2015, AS9100:2016 (Rev. D) and ISO 17025:2017 all mention "​International Standards",​ I am aware of only four (4) "​international standards"​ (as opposed to SI //units//); three of which are listed as examples in the "​Bureau International des Poids et Mesures"​ (BIPM) [[https://​www.bipm.org/​utils/​common/​documents/​jcgm/​JCGM_200_2012.pdf|JCGM 200:2012, "​International vocabulary of metrology – Basic and general concepts and associated terms (VIM)"​]] (3rd edition), sec. 5.2, "​international measurement standard"​. However, there are probably others. Those that I am aware of include: \\
 \\ \\
-**1 - The international prototype of the kilogram** \\+**1 - The international prototype of the kilogram ​(OBSOLETE as of May 20, 2019)** \\
 All of the SI units are based on physical constants of nature EXCEPT the kilogram. The kilogram is the unit of mass; which nominally has the same mass as one litre of water at the freezing point. ​ All of the SI units are based on physical constants of nature EXCEPT the kilogram. The kilogram is the unit of mass; which nominally has the same mass as one litre of water at the freezing point. ​
 The only SI unit "​physical artifact"​ (i.e., not defined by a fundamental,​ natural constant), the international prototype kilogram (IPK), was certified in 1889, and consists of a cylinder of platinum-iridium. The IPK is maintained by the [[https://​www.bipm.org/​en/​publications/​si-brochure/​kilogram.html|BIPM]]. The only SI unit "​physical artifact"​ (i.e., not defined by a fundamental,​ natural constant), the international prototype kilogram (IPK), was certified in 1889, and consists of a cylinder of platinum-iridium. The IPK is maintained by the [[https://​www.bipm.org/​en/​publications/​si-brochure/​kilogram.html|BIPM]].
  
-<​note>​Because the IPKs stability has been a matter of significant concern, during November 2018, the world’s measurement experts voted and unanimously approved a revision of the SI that establishes a measurement system entirely based on physical constants of nature. The changes ​will take effect on [[http://​www.worldmetrologyday.org|World Metrology Day]], May 20, 2019. See [[https://​www.theverge.com/​2018/​11/​13/​18087002/​kilogram-new-definition-kg-metric-unit-ipk-measurement|The Kilogram is Dead; Long Live the Kilogram]]</​note>​+<​note>​Because the IPKs stability has been a matter of significant concern, during November 2018, the world’s measurement experts voted and unanimously approved a revision of the SI that establishes a measurement system entirely based on physical constants of nature. The changes ​took effect on [[http://​www.worldmetrologyday.org|World Metrology Day]], May 20, 2019; which  commemorates the anniversary of the signing of the Metre Convention in 1875. See [[https://​www.theverge.com/​2018/​11/​13/​18087002/​kilogram-new-definition-kg-metric-unit-ipk-measurement|The Kilogram is Dead; Long Live the Kilogram]]</​note>​
 **2 - Chorionic Gonadotrophin (Biological standard)** \\ **2 - Chorionic Gonadotrophin (Biological standard)** \\
 Defined by the [[http://​apps.who.int/​iris/​bitstream/​handle/​10665/​70154/​WHO_BS_09.2107_eng.pdf|World Health Organization (WHO)]] in the 4th international standard 1999, as 75/589, 650 International Units per ampoule. Defined by the [[http://​apps.who.int/​iris/​bitstream/​handle/​10665/​70154/​WHO_BS_09.2107_eng.pdf|World Health Organization (WHO)]] in the 4th international standard 1999, as 75/589, 650 International Units per ampoule.
Line 135: Line 135:
 </​WRAP>​ </​WRAP>​
  
-Unless required by statute or regulation (i.e., for Legal Metrology), mandating "NIST traceability"​ unnecessarily "​limits"​ the sources for metrological traceability,​ excluding other NMIs and/or accredited commercial metrology laboratories.+Unless required by statute or regulation (i.e., for [[https://​www.oiml.org/​en/​about/​legal-metrology|Legal Metrology]]), mandating "NIST traceability"​ unnecessarily "​limits"​ the sources for metrological traceability,​ excluding other NMIs and/or accredited commercial metrology laboratories.