Pub Date : 1900-01-01DOI: 10.51843/wsproceedings.2020.12
S. Giblin
We broach a seldom-discussed topic in precision metrology; how subtle errors in calibration processes are discovered and remedied. We examine a case study at the National Physical Laboratory (NPL), UK, involving the calibration of DC standard resistors of value 100 MΩ and 1 GΩ. Due to an oversight in the assessment of error sources in the cryogenic current comparator (CCC) ratio bridge used for resistance calibrations, results from the period 2001 to 2015 were in error by approximately 0.7 parts per million (ppm), with quoted uncertainties (k=2) of 0.4 ppm and 1.6 ppm respectively. International inter-comparisons did not detect the error, mainly because the uncertainty due to the transportation drift of the comparison standards was too large to resolve it. Likewise, research into single-electron current standards relied on traceability to 1 GΩ, and did not detect the error because at this resistance value it was on the borderline of statistical significance. The key event was a comparison between PTB (Germany) and NPL (UK) of a new small-current measuring instrument, the ultrastable low-noise current amplifier (ULCA). The NPL measurements took place over one week in early 2015 and involved calibrating the transresistance gain (nominally 109 V/A) of the ULCA. At that time, the transport stability of the ULCA was not well established. Nevertheless, calibrations of the ULCA at NPL using a 100 MΩ resistor were sufficiently discrepant with the PTB calibrations to motivate a thorough investigation into the NPL traceability chain, which uncovered the error. All recipients of erroneous calibration certificates were notified, but their responses indicated that the size of the error did not impact their business significantly. This instructive episode illustrates a positive interplay between calibration and research activities and shows that cutting-edge calibration uncertainties must be supported by a vigorous research programme. It is also important for NMIs to maintain a comfortable buffer (at least a factor of 10) between their claimed uncertainty and the uncertainty that their customers require, so that small errors can be resolved without significant impact on measurement stakeholders.
{"title":"Discovery and rectification of an error in high resistance traceability at NPL: a case study in how metrology works","authors":"S. Giblin","doi":"10.51843/wsproceedings.2020.12","DOIUrl":"https://doi.org/10.51843/wsproceedings.2020.12","url":null,"abstract":"We broach a seldom-discussed topic in precision metrology; how subtle errors in calibration processes are discovered and remedied. We examine a case study at the National Physical Laboratory (NPL), UK, involving the calibration of DC standard resistors of value 100 MΩ and 1 GΩ. Due to an oversight in the assessment of error sources in the cryogenic current comparator (CCC) ratio bridge used for resistance calibrations, results from the period 2001 to 2015 were in error by approximately 0.7 parts per million (ppm), with quoted uncertainties (k=2) of 0.4 ppm and 1.6 ppm respectively. International inter-comparisons did not detect the error, mainly because the uncertainty due to the transportation drift of the comparison standards was too large to resolve it. Likewise, research into single-electron current standards relied on traceability to 1 GΩ, and did not detect the error because at this resistance value it was on the borderline of statistical significance. The key event was a comparison between PTB (Germany) and NPL (UK) of a new small-current measuring instrument, the ultrastable low-noise current amplifier (ULCA). The NPL measurements took place over one week in early 2015 and involved calibrating the transresistance gain (nominally 109 V/A) of the ULCA. At that time, the transport stability of the ULCA was not well established. Nevertheless, calibrations of the ULCA at NPL using a 100 MΩ resistor were sufficiently discrepant with the PTB calibrations to motivate a thorough investigation into the NPL traceability chain, which uncovered the error. All recipients of erroneous calibration certificates were notified, but their responses indicated that the size of the error did not impact their business significantly. This instructive episode illustrates a positive interplay between calibration and research activities and shows that cutting-edge calibration uncertainties must be supported by a vigorous research programme. It is also important for NMIs to maintain a comfortable buffer (at least a factor of 10) between their claimed uncertainty and the uncertainty that their customers require, so that small errors can be resolved without significant impact on measurement stakeholders.","PeriodicalId":422993,"journal":{"name":"NCSL International Workshop & Symposium Conference Proceedings 2020","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130632180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.51843/wsproceedings.2020.03
Chi-Hsuan Lin, Wei-Hong Hsu
According to different calibration systems and characteristic of calibrated items, there are different factors influence measurement results. This paper discusses the factors that influence measurement results in dew-point meter calibration with two-pressure humidity generator measurement system at National Measurement Laboratory (NML). In this analysis, four control factors have been chosen, including the relative humidity, the flow rate of standard gas source input, the flow rate through the dew-point meter, and the waiting time before reading data from the dew-point meter. Taguchi method is used to find out the best combination of the factors and their levels. A suitable orthogonal array was selected and experiments were conducted under the different temperature. By calculating the mean square deviation (MSD) and the signal-to-noise (S/N) ratio, the best combination can be found. After the experiments, the lab staff can easily find out the best combination without experimenting full factorial design, and improve the reliability of measurement effectively.
{"title":"Application of the Taguchi Method to Dew-point Meter Calibration","authors":"Chi-Hsuan Lin, Wei-Hong Hsu","doi":"10.51843/wsproceedings.2020.03","DOIUrl":"https://doi.org/10.51843/wsproceedings.2020.03","url":null,"abstract":"According to different calibration systems and characteristic of calibrated items, there are different factors influence measurement results. This paper discusses the factors that influence measurement results in dew-point meter calibration with two-pressure humidity generator measurement system at National Measurement Laboratory (NML). In this analysis, four control factors have been chosen, including the relative humidity, the flow rate of standard gas source input, the flow rate through the dew-point meter, and the waiting time before reading data from the dew-point meter. Taguchi method is used to find out the best combination of the factors and their levels. A suitable orthogonal array was selected and experiments were conducted under the different temperature. By calculating the mean square deviation (MSD) and the signal-to-noise (S/N) ratio, the best combination can be found. After the experiments, the lab staff can easily find out the best combination without experimenting full factorial design, and improve the reliability of measurement effectively.","PeriodicalId":422993,"journal":{"name":"NCSL International Workshop & Symposium Conference Proceedings 2020","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121952914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.51843/wsproceedings.2020.13
N. Fletcher, Jonathan Williams, S. Rozhko, A. Tzalenchuk, J. Janssen, Becky King, Connor D. Shelly, Kieran Edmonds
The redefinition of the SI base units ampere and kilogram in 2019 formalized the use of the quantum Hall effect (QHE) to provide resistance traceability (the SI ohm) from the fundamental constants h and e. Traditionally, realization of the ohm via the QHE has required large complex liquid helium cryostats (including a high field superconducting magnet), and been largely confined to National Measurement Institutes. In recent years, graphene has been demonstrated as an ideal material for QHE samples, offering access to the quantum resistance reference (RK=h/e2) at lower magnetic fields and higher temperatures than previously possible. We present a system that builds on this technological advance, combined with liquid helium-free (closed cycle) cryogenic cooling techniques. The system integrates both a graphene QHE reference and a Cryogenic Current Comparator (CCC) instrument into a single compact enclosure. Resistance bridges based around a CCC offer the ultimate accuracy and noise performance for comparisons of conventional room temperature standard resistors to the QHE reference, and for scaling between different decade values, but this technology has not previously been demonstrated without the use of liquid helium. Our CCC system also integrates a second cryogenic SQUID detector to operate as the critical nanovoltmeter in the bridge electronics. We use a latest generation polymer-encapsulated molecular doped epigraphene sample optimized for operation at the 5 T field of our compact magnet, which does not require any user tuning of device properties on repeated cool-down cycles. Combined with the cryogen-free cooling, this gives a truly ‘turn-key’ system, making the quantum resistance reference and CCC accuracy available 24/7 in the metrology laboratory with no regular user intervention. The system is designed for both the realisation of the ohm at 100 Ω and regular calibration of standard resistors in the range 1 Ω to 10 kΩ, with combined relative standard uncertainties down to 0.01 ppm in the best cases.
{"title":"A Compact Self-Contained Cryogen-Free Instrument for the Realization of the Ohm in the Revised SI","authors":"N. Fletcher, Jonathan Williams, S. Rozhko, A. Tzalenchuk, J. Janssen, Becky King, Connor D. Shelly, Kieran Edmonds","doi":"10.51843/wsproceedings.2020.13","DOIUrl":"https://doi.org/10.51843/wsproceedings.2020.13","url":null,"abstract":"The redefinition of the SI base units ampere and kilogram in 2019 formalized the use of the quantum Hall effect (QHE) to provide resistance traceability (the SI ohm) from the fundamental constants h and e. Traditionally, realization of the ohm via the QHE has required large complex liquid helium cryostats (including a high field superconducting magnet), and been largely confined to National Measurement Institutes. In recent years, graphene has been demonstrated as an ideal material for QHE samples, offering access to the quantum resistance reference (RK=h/e2) at lower magnetic fields and higher temperatures than previously possible. We present a system that builds on this technological advance, combined with liquid helium-free (closed cycle) cryogenic cooling techniques. The system integrates both a graphene QHE reference and a Cryogenic Current Comparator (CCC) instrument into a single compact enclosure. Resistance bridges based around a CCC offer the ultimate accuracy and noise performance for comparisons of conventional room temperature standard resistors to the QHE reference, and for scaling between different decade values, but this technology has not previously been demonstrated without the use of liquid helium. Our CCC system also integrates a second cryogenic SQUID detector to operate as the critical nanovoltmeter in the bridge electronics. We use a latest generation polymer-encapsulated molecular doped epigraphene sample optimized for operation at the 5 T field of our compact magnet, which does not require any user tuning of device properties on repeated cool-down cycles. Combined with the cryogen-free cooling, this gives a truly ‘turn-key’ system, making the quantum resistance reference and CCC accuracy available 24/7 in the metrology laboratory with no regular user intervention. The system is designed for both the realisation of the ohm at 100 Ω and regular calibration of standard resistors in the range 1 Ω to 10 kΩ, with combined relative standard uncertainties down to 0.01 ppm in the best cases.","PeriodicalId":422993,"journal":{"name":"NCSL International Workshop & Symposium Conference Proceedings 2020","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125941085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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