AFRIMETS Secretariat Private Bag X34 Lynnwood Ridge 0040 AFRIMETS Supplementary Comparison Programme Calibration of Gauge Blocks by Mechanical Comparison Method AFRIMETS.L S3 Final Report Giza, Egypt, March 2015 M. Amer, F. Abdel Aziz 1
Contents Page No. Abstract... 3 1. Introduction... 3 2. Aim of the Programme... 4 3. Participants... 4 4. Design of the Programme... 4 5. Reporting... 6 6. Measurement equipment used by the participants... 6 7. Stability of the travelling standards... 6 8. Analysis of results... 9 9. Reference Values... 11 10. Results as reported by the Participants... 12 11. Discussion of measurements results... 18 12. Conclusions... 21 13. List of References... 21 2
Abstract: A round robin comparison in calibration of gauge blocks by mechanical comparison method between NMIs of Arab countries in addition to the NMI of South Africa was carried out during the period of November 2011 to July 2013, The Arab Federation for Metrology (AFM) identification number for this comparison is: ARABMET L.S.1. NIS-Egypt acted as the pilot laboratory. One set of gauge blocks, with nominal size: 1 mm, 5 mm, 10 mm, 40 mm, 90 mm were circulated. This comparison was registered in the BIPM KCDB in June 2012 as an AFRIMETS supplementary comparison under the identifier AFRIMETS.L-S3. The results obtained are represented in this report. Coordination of the programme has been done by the AFM technical support unit. 1- Introduction: The Technical Support Unit (TSU) of the Arab Federation for Metrology (AFM) developed a questionnaire to assist the Arab Metrology Programme ARABMET to develop appropriate protocols and schedules for an intended intercomparisons schemes. In May 2011 the TSU distributed the questionnaire among Arab Metrology Institutions. Positive response was received from 5 Arab NMIs requesting the participation in two fields, namely Length and Mass Measurements. The comparison programme proposed for length was of the Round Robin type on Gauge Blocks calibration, up to 100 mm, by mechanical means. It was then decided that the AFM, the observer member of the Intra-Africa Metrology System (AFRIMETS), would extend its invitation to the National Metrology Institutes, NMIs to participate in measurement comparison programmes in the prescribed metrological fields. The comparison programmes were designed, organized and coordinated by AFM TSU under technical support of the National Institute for Standards (NIS) of Egypt being an active member of both the Programme and the Federation at the time. The comparison programme was open for NMIs of the members and non members Arab states of the Federation. The comparisons were to be conducted following appropriate measurement protocols. The objectives of the comparison programmes are to provide the participating laboratories with the means for comparing their measurement results, opportunities for technical capability improvements and recognition of Calibration and Measurements Capabilities (CMCs). AFM, being an observer member of the AFRIMETS, worked through concerned AFRIMETS authorities to submit the comparison programmes for registration as AFRIMETS supplementary comparisons on the BIPM KCDB. Thus, the National Metrology Institute of South Africa (NMISA) has been invited to join the round robin scheme. Five gauge blocks, with nominal size 1 mm, 5 mm, 10 mm, 40 mm and 90 mm are chosen as the artifacts for the comparison. All of them are made of steel according to ISO 3650:1998. The Engineering and Surface Metrology laboratory (ESML) of NIS - Egypt provided the travelling standards and the comparison protocol. The measurements in this comparison were carried out from November 2011 to July 2013. 3
The measurements were carried out according to a protocol approved by the concerned Regional Metrology Organization technical authorities, namely AFRIMETS.TCL. 2- Aim of the Programme: The aim of this comparison is to give confidence in the technical capacity of the AFM members and non members as a step towards the publication of CMCs in the BIPM KCDB to gain international Statement of Equivalence in accordance with the mutual recognition arrangement (CIPM MRA). The participation of NIS - Egypt and NMISA South Africa would help in achieving these goals through their active participation in Sub Regional Metrology Organizations (SRMOs) members of AFRIMETS. The comparison gives objective evidence on the technical competence of the participated laboratories, and it assists in identifying opportunities to improve the metrological capacity of the Laboratories. 3- Participants: Table 3.1 shows the participating NMIs, their affiliations and the planned time schedule. Country - Laboratory Abbreviation 1- EGYPT - National Institute of Standards NIS-ESML 2- IRAQ - Central Organisation for Standardisation and Quality Control - COSQC 3- SYRIA - National Standards and Calibration Laboratory - NSCL 4- JORDAN - Jordan National Metrology Institute - JNMI 5- TUNISIA - Central Laboratory for Testing and Analysis- Metrology Center - LCAE-CME 6- SOUTH AFRICA - National Metrology Institute of South Africa - NMISA SOUTH AFRICA - National Metrology Institute of South Africa - NMISA 1- EGYPT - National Institute of Standards NIS-ESML Date Planned November 2011 December 2011 January 2012 February 2012 March 2012 April 2012 May 2012 Metrology region Pilot Lab; AFM Member, AFRIMETS Member (NEWMET), APMP associate member and EURAMET Corresponding Member AFM Member AFM Member and APMP Associate Member AFM Member and APMP Associate Member AFRIMETS Member (MAGMET) Coach Lab. AFRIMETS Member (SADCMET) and APMP Associate Member Pilot Lab; AFM Member, AFRIMETS Member (NEWMET), APMP Associate Member and EURAMET Corresponding Member 4
4- Design of the Programme: The program was designed according to the guidelines for CIPM (Comité International des Poids et Mesures) key comparisons. Five travelling gauge blocks of nominal size 1 mm, 5 mm, 10 mm, 40 mm and 90 mm were provided as artifact by NIS-ESML. They are made of steel according to ISO 3650:1998. The travelling standards were circulated between the participants as shown in table 4.1. As pilot laboratory, NIS-ESML of Egypt determined the length deviation of the travelling standards at the beginning and the end of the comparison. The transportation sequence and measurements of the travelling standards has been done as shown in figure 4.1. NIS-ESML of Egypt acted as the pilot laboratory regarding the measurements which were conducted starting in November 2011 at NIS-ESML. Then the artifact moved to Institute number 2 and so on. No significant accident has been reported during the comparison. However, the artifacts stayed for a longer period than planned at NIS-ESML at the end of the round waiting for their measurement standard to be calibrated to ensure traceability to SI units. Serial NMI Country Artefact Received Report Delivered 1 NIS Egypt November 2011 15 March 2012 2 COSQC Iraq 14 December 2011 7 February 2012 3 NSCL Syria 21 January 2012 26 February 2012 4 JNMI Jordan 11 March 2012 15 March 2012 5 LCAE Tunis 6 June 2012 10 December 2012 6 NMISA - South Africa 17 October 2012 16 November 2012 7 NIS Egypt 30 November 2012 7 July 2013 Table 4.1:- Sequence of the measurements 5
NSCL - Syria COSQC - Iraq NIS- Egypt JNMI - Jordan NMISA - South Africa LCAE - Tunis Figure (4.1) shows the transportation sequence and measurements of the travelling standards. 5- Reporting: The measurement results were sent to the AFM in a final report. A list of the equipment used as gauge block comparator, environmental conditions, details of measurement procedure and uncertainty analysis were included as well as the reference standard used in order to see the traceability at each laboratory. 6- Measurement Equipment used by Participants: Lab Measurement Device Tip material NIS-ESML Mitutoyo, GBCD-250 COSQC MAHR 826 NSCL JNMI Tsugami - ECHD Mitutoyo, GBCD250 LCAE MAHR 826 Tungsten Carbide Tungsten Carbide Tungsten Carbide Tungsten Carbide Tungsten Carbide Tip diameter Upper tip Lower tip Measuring Force Upper Lower tip tip 40 mm 10 mm 0.8 N 0.3 N 3 mm 3 mm 0.75 N 0.6 N 20 mm - 3.2 N - 40 mm 10 mm 0.8 N 0.3 N 3 mm 3 mm 0.75 N 0.6 N NMISA TESA Tungsten 40 mm 40 mm 0.63 N 0.63 N 6
Deviation from nominal length, nm AFRIMETS L.S3 Table 6.1.: Measurement equipment used in comparison 7- Stability of the traveling standards: The pilot laboratory NIS-ESML of Egypt assures the stability of the traveling standards during a period of months before beginning of the laboratory measurements. Statement on the instability has been found, so that, the measured gauge block length values of the traveling standards were stable during this period. The travelling standards were circulated among five participating laboratories without any incident that required any return to the pilot laboratory to re-measure the travelling standards. Figures 7.1 to 7.5 show graphs indicating the stability of gauge blocks. 7.1. Stability of 1 mm gauge block 50 40 30 20 10 0-10 -20-30 1 mm gauge block NIS- Nov.2011 NIS - July 2013 Figure 7.1. Stability of 1 mm gauge block 7.2. Stability of 5 mm gauge block 7
Deviation from nominal length, nm AFRIMETS L.S3 Figure 7.2. Stability of 5 mm gauge block 7.3. Stability of 10 mm gauge block 120 10 mm gauge block 100 80 60 40 20 0-20 NIS- Nov.2011 NIS - July 2013 7.4. Stability of 40 mm gauge block Figure 7.3. Stability of 10 mm gauge block 8
Deviation from nominal length, nm AFRIMETS L.S3 Figure 7.4. Stability of 40 mm gauge block 7.5. Stability of 90 mm gauge block 100 90 mm gauge block 50 0-50 -100-150 NIS- Nov.2011 NIS - July 2013 Figure 7.5. Stability of 90 mm gauge block 9
8. Analysis of results: The weighted mean is used as the reference value in the comparison. For each laboratory (i) the normalized weight, wi was calculated by the following formula: w i = c. 1 u 2 (x i ) (1) where u(xi) is the standard uncertainty given by the laboratory i and C is the normalizing factor and is calculated by the following formula: c = where n is the number of the laboratories. The weighted mean (reference value) is: 1 1 n i=1 u 2 (x i ) (2) x w = The uncertainty of the deviation from the weighted mean is: n i=1 w i. x i (3) u(x i x w) = u 2 (x i ) 2 u int (x w) (4) To avoid bias, only the first set of measurements from the pilot laboratory was included in reference value determination and the analysis of the results of each participant can be done by calculating the deviation of the given result from the weighted mean and the uncertainty of this deviation. The statistical consistency of the results with the uncertainties given by the participants can be checked by the E n value for each laboratory. E n = x i x w 2 u 2 2 (x i ) u int (x w) (k = 2) (5) where x i x w is the deviation from the weighted mean for a result of a laboratory, u int is the so called internal standard deviation that is based on the estimated standard uncertainties as reported by the participants: u int (x w) = C (6) E n values for consistent measurement results are expected to be between -1 and 1 for a coverage factor of k = 2. 10
The statistical consistency of the comparison can be analyzed by the so called Birge ratio test. The Birge ratio compares the observed spread of the results with the spread expected from the individual reported uncertainties. The Birge ratio is: R B = u ext (x w) u int (x w) (7) where u ext is the so called external standard deviation and can be calculated by the following formula: u ext (x w) = 1 I 1. I (x i x w) 2 i=1 u 2 (x i ) 1 I i=1 u 2 (x i ). (8) where I is the number of the results that are taken in the calculation. For an infinite population size, the Birge ratio has an expectation value of R B = 1, when considering standard uncertainties. For a coverage factor of k = 2, the expectation value is increased and the data in a comparison are consistent provided that R B < 1 + 8/(I 1). (9) For a limited population size, the Birge criterion is given by: R B Crit = 1 + 8/(I 1) (10) If the calculation of a gauge shows inconsistent dataset, the largest consistent subset is determined by elimination, starting with excluding the result having the largest E n value that makes the largest contribution to the overall chi-squared value. The iteration runs until R B < R B crit. For six laboratories, R B is equal to 1.5. The criterion is recalculated if any results are excluded. A Birge ratio much larger than the criterion implies that some data contain systematic offsets or alternately that some uncertainties have been underestimated. A ratio much less than the criterion implies that uncertainties have been overestimated. The results will point to calculations that may need further investigation and possibly reassessment. The reference value will be selected that best reflects the population. For a population with a number of results of E n greater than 1 and the Birge ratio greater than the Birge criterion, the result with the largest E n was removed and the weighted mean, the 11
uncertainty of the mean, all E n values, the Birge ratio and Birge criterion were recalculated. This iteration process was repeated until the Birge ratio became less than the Birge criterion and the exclusion process was stopped. When a result x i is excluded from the reference value, it is not correlated to it and its E n value is calculated by: E n = x i x w 2 u 2 2 (x i ) u int (x w) (11) 9 Reference Value: In this comparison, to meet the requirements of the Mutual Recognition Arrangement, the Key Comparison Reference Values (KCRV) has been evaluated according to the method described in section 8. The weighted mean was determined and the deviations from the weighted mean were calculated. The uncertainty of the weighted mean is based on the internal standard deviation of the final measurement results. The stability measurements of the gauge blocks, performed by the pilot laboratory were excluded. The results of the pilot laboratory contribute only once in the calculation of the reference values. Table 9.1 shows the Key Comparison Reference Values and their standard uncertainties. Table 9.1 Key Comparison Reference Values and associated standard uncertainty (k = 1). Nominal Length (mm) Reference value (nm) 1 25.6 13.7 5 66.2 14.4 10 42.9 15.5 40-57.2 22.5 90-55.1 36.5 Reference value uncertainty (nm) 10 Results as reported by the Participants: On receipt of the reports from all participants the coordinator asked the participants to revise their results regarding the units and uncertainties quoted. Among the received answers, the JNMI asked to withdraw the results of 40 mm and 90 mm gauge blocks for technical reasons. This withdrawal of results was made before Draft A was released, i.e. with the results still blind. 12
Overview of measurement results as they were reported by the participating laboratories is given in Table 10.1. Weighted mean and its difference from reported results were calculated, along with corresponding E n values (k = 2), for each gauge block. A statistical consistency check was performed as described in section 8. Results of 90 mm gauge block which belongs to COSQC were excluded from calculation in order to form a consistent subset, and their E n values are given according to: E n = x i x w 2 u 2 2 (x i )+u int (x w) (12) NIS- ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c 1 mm 10 28.7 50 48.2 34 27 30 90 28 30 20 30 5 mm 70 31.5 80 48.1 53 29 70 90 56 32 80 30 10 mm 60 35.1 20 48.1 47 35 10 90 17 34 60 30 40 mm -40 56.4-10 48.3-59 49 NA NA -126 45-30 55 90 mm -20 91.9 100 49.3-121 91 NA NA -45 64-50 61 Table 10.1. Reported measurement results, in nm, k = 1 10.1. Results of 1 mm gauge block Table 10.1.1. Results as reported by the participants Nominal 1 mm NIS- ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c 10 28.7 50 48.2 34 27 30 90 28 30 20 30 13
Deviaation from nominal length, nm AFRIMETS L.S3 160 140 120 100 80 60 40 20 0-20 -40-60 -80 1mm gauge block standard uncertainty (k = 1) NIS COSQC NSCL JNMI LCAE NMISA Figure 10.1.1. Graphical representation of results Table 10.1.2. Results calculated from participant s values 1 mm X i - X w E n NIS- ESML -15.6-0.31 u int, nm 13.66 COSQC 24.4 0.26 u ext, nm 5.08 NSCL 8.38 0.18 R B 0.37 JNMI 4.38 0.02 X w, nm 25.62 LCAE 2.38 0.04 NMISA -5.62-0.11 10.2. Results of 5 mm gauge block Table 10.2.1. Results as reported by the participants Nominal 5 mm NIS-ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c 70 31.5 80 48.1 53 29 70 90 56 32 80 30 14
Deviaation from nominal length, nm AFRIMETS L.S3 200 180 160 140 120 100 80 60 40 20 0-20 -40 5mm gauge block standard uncertainty (k = 1) NIS COSQC NSCL JNMI LCAE NMISA Figure 10.2.1. Graphical representation of results Table 10.2.2. Results calculated from participant s values 5 mm X i - X w E n NIS- ESML 3.8 0.07 u int, nm 14.38 COSQC 13.8 0.15 u ext, nm 5.06 NSCL -13.2-0.26 R B 0.35 JNMI 3.8 0.02 X w, nm 66.2 LCAE -10.2-0.18 NMISA 13.8 0.26 10.3. Results of 10 mm gauge block Table 10.3.1. Results as reported by the participants Nominal 10 mm NIS- ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c 60 35.1 20 48.1 47 35 10 90 17 34 60 30 15
Deviaation from nominal length, nm AFRIMETS L.S3 140 120 100 80 60 40 20 0-20 -40-60 -80-100 10mm gauge block standard uncertainty (k = 1) NIS COSQC NSCL JNMI LCAE NMISA Figure 10.3.1. Graphical representation of results Table 10.3.2. Results calculated from participant s values 10 mm X i - X w E n NIS- ESML 17.1 0.27 u int, nm 15.51 COSQC -22.9-0.25 u ext, nm 8.54 NSCL 4.1 0.07 R B 0.55 JNMI -32.9-0.19 X w, nm 42.9 LCAE -25.9-0.43 NMISA 17.1 0.33 10.4. Results of 40 mm gauge block Table 10.4.1. Results as reported by the participants Nominal 40 mm NIS- ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c -40 56.4-10 48.3-59 49 NA NA -126 45-30 55 16
Deviaation from nominal length, nm AFRIMETS L.S3 80 40 0-40 -80-120 -160-200 40mm gauge block standard uncertainty (k = 1) NIS COSQC NSCL JNMI LCAE NMISA Figure 10.4.1. Graphical representation of results Table 10.4.2. Results calculated from participant s values 40 mm X i - X w E n NIS- ESML 17.2 0.17 u int, nm 22.45 COSQC 47.2 0.55 u ext, nm 21.39 NSCL -1.8-0.02 R B 0.95 JNMI - - X w, nm -57.2 LCAE -68.8-0.88 NMISA 27.23 0.27 10.5. Results of 90 mm gauge block Table 10.5.1. Results as reported by the participants Nominal 90 mm NIS- ESML COSQC NSCL JNMI LCAE NMISA L u c L u c L u c L u c L u c L u c -20 91.9 100 49.3-121 91 NA NA -45 64-50 61 17
Deviaation from nominal length, nm AFRIMETS L.S3 220 180 140 100 60 20-20 -60-100 -140-180 -220-260 90mm gauge block standard uncertainty (k = 1) NIS COSQC NSCL JNMI LCAE NMISA Figure 10.5.1. Graphical representation of results for 90 mm gauge block with standard uncertainty (k = 1) Table 10.5.2. Results calculated from participants values 90 mm X i - X w E n NIS -ESML -19.8-0.11 u int, nm 29.32 COSQC 100.2 1.27 u ext, nm 39.05 NSCL -120.83-0.70 R B 1.33 JNMI - - X w, nm -0.17 LCAE -44.83-0.39 NMISA -49.83-0.47 Table 10.5.3. Results calculated from largest consistent subset 90 mm X i - X w E n NIS - ESML 35.1 0.21 u int, nm 36.47 COSQC 155.1 1.27 u ext, nm 17.64 NSCL -65.95-0.40 R B 0.48 JNMI - - X w, nm -55.05 LCAE 10.05 0.10 NMISA 5.05 0.05 18
In table 10.5.2., the results calculated from all the participants values. After the statistical consistency check was performed as described in section 8. Results of 90 mm gauge block which belongs to COSQC were excluded from calculation in order to form a consistent subset and the results in table 10.5.3 are calculated. 11 - Discussion of measurement results: Table 11.1 shows the differences of measured values with respect to Key Comparison Reference Values and the expanded (k = 2) uncertainties of these differences, calculated by: U(x i x ref) = 2 u 2 (x i ) u 2 (x ref) (12) where u(xi) is the standard uncertainty of the laboratory result xi and u(xref) is the standard uncertainty of the reference value xref. Table 11.1 Differences of measured values and KCRV s, with expanded uncertainties (k = 2) Gauge block \ Lab NIS ESML COSQC NSCL JNMI LCAE NMISA 1 mm x i -x ref -15.6 24.4 8.4 4.4 2.4-5.6 U(x i -x ref ) 50.5 92.4 46.6 177.9 53.4 53.4 5 mm x i -x ref 3.8 13.8-13.19 3.81-10.19 13.81 U(x i -x ref ) 56.2 91.8 50.4 177.7 57.2 52.7 10 mm x i -x ref 17.1-22.9 4.13-32.87-25.87 17.13 U(x i -x ref ) 63.0 91.1 62.8 177.3 60.5 51.4 40 mm x i -x ref 17.2 47.2-1.8 --- -68.8 27.2 U(x i -x ref ) 103.5 85.5 87.1 --- 78.0 100.4 90 mm x i -x ref 35.1 155.1-65.9 --- 10.1 5.1 U(x i -x ref ) 168.7 122.6 166.7 --- 105.2 97.8 Figures 11.1 through 11.5 show the graphs of Degrees of Equivalence for the five gauge blocks. 19
250.00 200.00 150.00 100.00 50.00 0.00-50.00-100.00-150.00-200.00 NIS COSQC NSCL JNMI LCAE NMISA Figure 11.1 Degrees of Equivalence for 1 mm gauge block with expanded uncertainty (k = 2) 250 200 150 100 50 0-50 -100-150 -200 NIS COSQC NSCL JNMI LCAE NMISA Figure 11.2 Degrees of Equivalence for 5 mm gauge block with expanded uncertainty (k = 2) 20
200 150 100 50 0-50 -100-150 -200-250 NIS COSQC NSCL JNMI LCAE NMISA Figure 11.3 Degrees of Equivalence for 10 mm gauge block with expanded uncertainty (k = 2) 200 150 100 50 0-50 -100-150 -200 NIS COSQC NSCL JNMI LCAE NMISA Figure 11.4 Degrees of Equivalence for 40 mm gauge block with expanded uncertainty (k = 2) 21
300 250 200 150 100 50 0-50 -100-150 -200 NIS COSQC NSCL JNMI LCAE NMISA Figure 11.5 Degrees of Equivalence for 90 mm gauge block with expanded uncertainty (k = 2) 12 Conclusion: Participation of NMISA of South Africa, a non member of Arab Federation for Metrology (AFM), enriched the inter-comparison programme and contributed to its recognition on the international level. Measurements reports provided by participants show a well established scientific discipline in length metrology in the participant laboratories. Data, equipments, procedures followed and traceability listed in the participant s reports show a very good infra- structure for length metrology in the participant laboratories except for NSCL where a single probe comparator was used which does not comply with ISO 3650:1998. The inter-comparison programme assures the ability of the participant laboratories to provide a world class results in length metrology except for COSQC for 90 mm gauge block, also, JNMI does not participate for 40 mm and 90 mm gauge blocks. 13 List of References 1. ISO 3650:1998(E), Geometrical Product Specification (GPS) Length Standards Gauge Blocks, International Organization for Standardization, Geneva, Switzerland. 2. Guide to the Expression of Uncertainty in Measurement (JCGM 100:2008, GUM 1995 with minor corrections) 3. Decker J.E., Brown N. et al., Recent recommendations of Consultative Committee for Length (CCL) regarding strategies for evaluating key comparison data. Metrologia 43 (2006) L51-L55. 4. EURAMET comparison of gauge blocks by interferometry, EURAMET #1138,EURAMET.L-K1.2,, Zagreb, December 2011, V. Mudronja, M. Katic. 22
5. Asia-Pacific Metrology Programme; developing Economies Committee (DEC) Intercomparison on gauge blocks by Mechanical Comparison Method (APMP.L-S3; 2006 2009) 6. Measurement comparisons in the CIPM MRA; CIPM MRA-D-05 Version 1.2. 7. International comparison of surface roughness, APMP.L-K8, final report, NMIA 2013, Andrew Baker. 23