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 [2018/12/14 12:34]
rrandall [What are SI Units?]
articles:nist_traceability [2019/01/26 14:47] (current)
rrandall [An "unbroken chain of calibrations" to what?]
Line 41: Line 41:
 a. calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards __traceable to international or national measurement standards; when no such standards exist, the basis used for calibration or verification shall be retained as documented information__;//"​ a. calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards __traceable to international or national measurement standards; when no such standards exist, the basis used for calibration or verification shall be retained as documented information__;//"​
 </​WRAP>​ </​WRAP>​
-Unfortunately,​ the language in ISO 9001:2015 & AS9100:2016 (Rev. D) is antiquated in stating its requirements for "​measurement traceability"​. In contrast, ISO 17025:2017 is much more modern and technically correct in stating:\\+Unfortunately,​ the language in ISO 9001:2015 & AS9100:2016 (Rev. D) is extremely ​antiquated in stating its requirements for "​measurement traceability"​. In contrast, ISO 17025:2017 is much more modern and technically correct in stating:\\
 <WRAP center round box 80%> <WRAP center round box 80%>
 **ISO 17025:2017, “General requirements for the competence of testing and calibration laboratories”** \\ **ISO 17025:2017, “General requirements for the competence of testing and calibration laboratories”** \\
Line 62: Line 62:
 \\ \\
 [[http://​www.isobudgets.com/​measurement-traceability-complying-iso-17025-requirements/​|{{ :​articles:​measurement-traceability-pyramid-600px.jpg?​direct }}]] [[http://​www.isobudgets.com/​measurement-traceability-complying-iso-17025-requirements/​|{{ :​articles:​measurement-traceability-pyramid-600px.jpg?​direct }}]]
 +
 +I describe the above pyramid as "//​typical//"​ because, contrary to the antiquated language of ISO 9001:2015 & AS9100:​2016,​ it is possible to “bypass” the National Metrology Institutes (NMIs) to obtain traceability to SI units. Using the example of DC volts, [[https://​www.fluke.com|Fluke]],​ a world leader in the field of metrology, owns a [[https://​nvlpubs.nist.gov/​nistpubs/​jres/​095/​jresv95n3p219_A1b.pdf|Josephson voltage system]], which they can use to realize the SI Units directly.
 ===== What are SI Units? ===== ===== What are SI Units? =====
 {{ :​articles:​2018-si.png?​direct&​130|}} {{ :​articles:​2018-si.png?​direct&​130|}}
-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. 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]]"​. \\
  
 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.
Line 76: Line 78:
 A.2 Establishing metrological traceability** \\ A.2 Establishing metrological traceability** \\
 //A.2.1 Metrological traceability is established by considering,​ and then ensuring, the following: \\ //A.2.1 Metrological traceability is established by considering,​ and then ensuring, the following: \\
-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__);// ​
----- +
-Source: [[https://​ilac.org/?​ddownload=840|ILAC-P10:​01/​2013,​ "ILAC Policy on the Traceability of Measurement Results"​]]" ​+
 </​WRAP>​ </​WRAP>​
 ===== What are "​intrinsic"​ standards? ===== ===== What are "​intrinsic"​ standards? =====
Line 107: Line 107:
 </​WRAP>​ </​WRAP>​
  
-Let's use the example of DC volts. ​[[https://​www.fluke.com|Fluke]], a world leader in the field of metrology, ​owns a [[https://​nvlpubs.nist.gov/​nistpubs/​jres/​095/​jresv95n3p219_A1b.pdf|Josephson voltage system]], which they can use to realize the SI directly. Even though they don't send an instrument to NIST for calibration,​ they [[https://​www.fluke.com/​en-us/​learn/​blog/​electrical/​the-volt-makes-a-stop-at-the-fluke-metrology-lab|compare their Josephson voltage system to an identical Josephson Voltage system maintained by NIST]]. ​+As mentioned earlier, ​[[https://​www.fluke.com|Fluke]] owns a [[https://​nvlpubs.nist.gov/​nistpubs/​jres/​095/​jresv95n3p219_A1b.pdf|Josephson voltage system]], which they can use to realize the SI Units directly ​for DC Volts. Even though they don't send an instrument to NIST for calibration,​ they [[https://​www.fluke.com/​en-us/​learn/​blog/​electrical/​the-volt-makes-a-stop-at-the-fluke-metrology-lab|compare their Josephson voltage system to an identical Josephson Voltage system maintained by NIST]]. ​
  
-Fluke performs this comparison because, just as the requirements for “measurement traceability” contained in ISO 9001:2015 & AS9100:2016 (Rev. D) are antiquated, so is U.S. law in this area. U.S. Law has designated that NIST holds the national standards of measurement,​ and NIST has defined the U.S. legal volt to be produced from its one particular Josephson voltage system, so it is the national standard.+Fluke performs this comparison because, just as the requirements for “measurement traceability” contained in ISO 9001:2015 & AS9100:2016 (Rev. D) are antiquated, so is U.S. law in this area. U.S. Law has designated that NIST holds the national standards of measurement,​ and NIST has defined the U.S. legal volt to be produced from its one particular Josephson voltage system, so it is the national standard. However, this is only pertinent to the area of "legal metrology"​ (Ref.: [[https://​www.oiml.org/​en/​about/​legal-metrology|International Organization of Legal Metrology]]).
 ===== What are "​International Standards"?​ ===== ===== What are "​International Standards"?​ =====
 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: \\
Line 125: Line 125:
 ===== Conclusion ===== ===== Conclusion =====
  
-Specifying that a calibration service provider __must__ supply "NIST Traceable"​ calibration certifications not only reveals a lack of understanding "​metrological traceability",​ it ignores the reality that many calibrations,​ from accredited metrology laboratories,​ may be traceable to SI units through other means (e.g., intrinsic measurement standards).+Specifying that a calibration service provider __must__ supply "NIST Traceable"​ calibration certifications not only reveals a lack of understanding "​metrological traceability",​ it ignores the reality that many calibrations, ​whether ​from NMIs (e.g., the [[https://​www.nrc-cnrc.gc.ca/​eng/​solutions/​advisory/​calibration_index.html|NRC]] in Canada, [[http://​www.cenam.mx/​eng/​|CENAM]] in Mexico, [[https://​www.ptb.de/​cms/​en.html|PTB]] in Germany,) or accredited ​commercial ​metrology laboratories,​ may be traceable to SI units through other means (e.g., intrinsic measurement standards).
  
 This is politely pointed out by the [[https://​ilac.org|ILAC – International Laboratory Accreditation Cooperation"​]]. This is politely pointed out by the [[https://​ilac.org|ILAC – International Laboratory Accreditation Cooperation"​]].
Line 135: Line 135:
 </​WRAP>​ </​WRAP>​
  
-Further, mandating "NIST traceability"​ unnecessarily "​limits"​ the sources for metrological traceability ​through ​other NMIs, such as the [[https://​www.nrc-cnrc.gc.ca/​eng/​solutions/​advisory/​calibration_index.html|NRC]] in Canada, [[http://​www.cenam.mx/​eng/​|CENAM]] in Mexico, [[https://​www.ptb.de/​cms/​en.html|PTB]] in Germany, the [[http://​nml.gov.ph|NML]] in the Philippines, ​or NIM in China. This use of other NMIs may be due to location, but could also be a diligent ​metrology ​laboratory seeking out and utilizing the NMI providing the world’s best uncertainty for a particular parameter.+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.