FIVE PROFICIENCY TESTING PROGRAMS FOR THE JCSS WEIGHT CALIBRATION LABORATORIES

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1 Measurement of Mass, Force and Torque (APMF 2013) International Journal of Modern Physics: Conference Series Vol. 24 (2013) (10 pages) The Authors DOI: /S FIVE PROFICIENCY TESTING PROGRAMS FOR THE JCSS WEIGHT CALIBRATION LABORATORIES MASAAKI UEKI *, JIANXIN SUN and KAZUNAGA UEDA Mass and Force Standards Section, NMIJ/ASIT, Umezono, Tsukuba, Ibaraki , Japan * m.ueki@aist.go.jp The Japan Calibration Service System (JCSS) organized in 1993 accredits the measurement capability of calibration laboratories and ensures the traceability to the national measurement standards. As an essential part of accreditation of the measurement capability of calibration laboratories for the weights, the International Accreditation Japan (IAJapan) of National Institute of Technology and Evaluation has been operating the JCSS proficiency testing programs with the technical support of the National Metrology Institute of Japan (NMIJ/AIST). Up to now, five proficiency testing programs have been carried out for the JCSS weight calibration laboratories in the range of 2 mg to 10 kg. The proficiency testing programs organized by the IAJapan were carried out in accordance with ISO/IEC Guide 43 (JIS Q 17043), and the NMIJ was responsible for the technical aspect as a reference laboratory. This paper describes the methods of the five proficiency testing programs during the period from 1997 to 2009, and outlines assessment of the measurement capability of the JCSS weight calibration laboratories. Keywords: Mass standard; calibration; proficiency testing; weight calibration laboratory. 1. Introduction The Japan Calibration Service System had been organized in 1993 according to the revision of the Measurement Law of Japan, and the International Accreditation of Japan (IAJapan) of National Institute of Technology and Evaluation operates the JCSS as an accreditation body. Accredited calibration laboratories of the JCSS are regularly confirmed by the periodical examinations to satisfy the general requirements on the proficiency of test and calibration laboratories (ISO/IEC (JIS Q 17025)). Calibration results on the JCSS calibration certificates are secured to be traceable to the national measurement standards. More than 200 calibration laboratories have been registered in 24 measurement divisions such as mass, electricity, concentration (reference materials), as of March, 2013, and information on these calibration laboratories are open on the home page of the IAJapan ( This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 3.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited

2 M. Ueki, J. Sun & K. Ueda The JCSS proficiency testing is one of the essential activities for operating the JCSS adequately. In the proficiency testing program, participating laboratories make calibrations of a traveling standard with a reference value assigned by the reference laboratory, and from the compatibility between the reference value and reported calibration results of the participants, the calibration capability of the individual participants are evaluated. The JCSS calibration laboratories participate regularly in the JCSS proficiency testing program in order to identify their registered calibration capabilities. The reliability in mass measurements is secured by means of referring the mass values of calibrated weights. Since the first JCSS proficiency testing program for these weight calibration laboratories was carried out in 1997, those programs have been carried out seven times in total, until 2012 in the mass range of 2 mg to 1000 kg. In this 2013, the 8th one is scheduled. In these proficiency testing programs for weight calibration laboratories, the National Metrology Institute of Japan (NMIJ/AIST) has been responsible, as a reference laboratory, for such technical parts as management of travelling standards, assignment of reference value, etc. This paper describes the five JCSS proficiency testing programs which had been carried out in 1997 to 2009 for weight calibration laboratories in the range of 2 mg to 10 kg. The technical features for confirming the capability of the weight calibrations introduced into these proficiency testing programs will be also reported. 2. Method of proficiency testing The testing method adopted in the five testing programs satisfies the requirements of ISO/IEC GUIDE 43:1997 (latter ISO/IEC 17043: ) and JIS Q (later JIS Q ) Proficiency testing by inter-laboratory comparisons and allows to evaluate the capability of weight calibrations. It was defined as follows Traveling standard weights Austenitic stainless steel weights of single-piece type without any adjusting cavity have been used for the traveling standards. Fig. 1 shows the traveling standard weights in the milligram range used for the proficiency testing in 2003 and the ones of cylindrical shape with a lifting nob used for the 2009 proficiency testing. The volumes, magnetic susceptibilities, residual magnetizations and surface roughnesses of these traveling weights of 1g to 10 kg in the nominal mass have been preliminarily measured by the NMIJ. The volumes of the traveling weights were measured by acoustic volumeters 3-4 with the expanded uncertainty of cm 3 to 0.75 cm 3, and these volume values were informed to the participants for evaluating the calibration uncertainties. The magnetic susceptibilities, residual magnetizations and surface roughnesses of the traveling weights were measured by BIPM susceptometers 5 for the magnetism and by visual inspection for the surfaces, comparing with standard specimens. It confirmed that these measurement results were all less than the maximum values required for class E 1 weights, given by OIML R111 5 (JIS B 7609). The traveling standard weights were respectively identified

3 Five Proficiency Testing Programs for the JCSS Weight Calibration Laboratories by markings on their surfaces by laser markers for both the cylindrical and flat-sheet weights, and by some bends at the end for the weights of wires. The nominal masses and the numbers of the traveling weights used for the individual proficiency testing programs have been selected in principle one piece for each digit of respective series of weights. The compositions of the traveling standard weights used for the individual proficiency testing programs will be described later. Sheet weight 2 kg 2 mg 20 mg 200 mg Wire weight (i) Sheet and wire weights from 2 mg to 200 mg. (ii) Cylindrical weights from 1 g to 2 kg. Fig. 1. Traveling standard weights for the 2003 and 2009 proficiency testing programs Calibrating process The calibrating work process is as follows. A participating calibration laboratory receives the travelling weights on Friday, and after waiting two days, Saturday and Sunday, for thermal equilibrium, it starts the calibration work on Monday. After finishing the calibrations, the weights are transported to a next participant before the day of second Friday, two weeks later from the received day. In order to monitor any change in the masses of weights and to avoid any trouble on the transportations in the course of the proficiency testing, each participant has to confirm any scratch or stain on the surfaces of the weights at the times of receiving and sending and to record examined results on a fixed form of Inspection of surface conditions of the travelling weights. The mass calibrations of the weights by the participants are carried out according to the procedure ruled in the written calibration manual. It is not allowed to deviate from the defined procedures, for example, to make more number of measurements, or to use measuring instruments of a higher performance or a higher resolution. 50 g 200 g 1 g

4 M. Ueki, J. Sun & K. Ueda Table 1. Calibration report form with an example. Nominal mass No. Calibration result Expanded uncertainty (95%) Instrument Mass comparator Reference N.M., No. u (m cr) 1) (k =1) T : Calibration conditions H :%RH P :kpa ρ a :kg/m 3 20 g X mg mg MC-XXX 20 g S mg 22.1 to to to to ) 1) Standard uncertainty of of the the reference weight weight Report of calibration results The results of the weight calibrations have been recorded in a report form as shown in Table 1 and reported to the secretariat within 10 days after finishing the calibrations. Additional information of three documents has been also presented; Copies of the calibration certificates of reference weights used for estimation of the calibration results, Budget sheets of the uncertainties that describe estimating processes of the uncertainties, and Inspecting records of the surface conditions of the travelling weights at receiving and sending them. It is prohibited to make any intentional change of the calibration results and any information exchange of the ones among the participants Mass stabilities of the traveling weights The stability of the traveling weights is an important factor for these proficiency testing programs. To keep the mass stabilities, the petal-type methods have been adopted to circulate the weights; the reference laboratory makes the calibrations at starting and finishing of each petal loop, and during these two calibrations, four participants at the most make their calibrations in order. In addition, the reference laboratory repeats the calibrations even in the duration between the respective petal loops as many times as possible, in order to watch any change of the masses of the weights. The reference values of the traveling weights are taken from the mean values of the two calibration results obtained before and after the corresponding petal loop, and the deviations of these two results from the mean value are taken as the uncertainty of mass changes of the weights and included into the uncertainty factors of the calibration results of the participants. Even if any significant change of the masses of the traveling weights happens to arise, the effect of the mass changes is minimized in this petal-type method, without affecting the proficiency evaluations of the participants Capability evaluation The technical capability has been evaluated by the E n number, which is one of the statistical methods defined in the Annex A of ISO/IEC GUIDE 43-2:1997. The E n number is calculated by Eq. (1),

5 Five Proficiency Testing Programs for the JCSS Weight Calibration Laboratories E n = Lab Ref U + U 2 2 Lab Ref. (1) Here, Lab is the calibration value of a participating laboratory, Ref is the reference value of the reference laboratory, and U Lab and U Ref are the expanded uncertainties of the calibration value and the reference value, respectively. In the proficiency testing of weight calibrations, the E n number is calculated excepting common uncertainty components, taking account of the correlation between the mass values of the traveling standard weight and the reference weight of the participant which are both calibrated by the NMIJ. The expanded uncertainty U Lab is calculated by Eq. (2), U = k u + u + u + u + u. (2) Lab r _ Lab rstb _ Lab w _ Lab b _ Lab ba _ Lab Here, k is the coverage factor, u r_lab is the standard uncertainty of the reference value of the participant excepting the correlated uncertainty components, u rstd_lab is the standard uncertainty of the stability of the reference value of the participant, u w_lab and u b_lab are the standard uncertainties of the weighing process and the air-buoyancy correction in the calibration of the traveling weight by the participant, respectively, and u ba_lab is the standard uncertainty of the balance used by the participant. The JCSS proficiency testing reports have been prepared using laboratory codes, assigned randomly to the participants, and the secrecy of information has been kept, such as the results of evaluation of calibration capabilities of the participants, the reported values of calibration results and so on. 3. Proficiency testing programs performed The JCSS proficiency testing programs for the calibration laboratories of weights in the range up to 20 kg have been carried out five times in total for the duration from 1997 to 2009, and the details are as follows First testing program in 1997 From January, 1997 to December, 1997, the 8 participating laboratories classified into two groups had performed the round-robin comparisons using 2 sets of weights. The weights of five different masses, that is, 1 g, 10 g, 100 g and 1 kg in nominal mass, 2 pieces each, made by different manufacturers and having different densities of weight materials. Namely 10 weights in total had been calibrated Second testing program in 2000 From October, 2000 to December, 2000, the 11 participating laboratories classified into three groups had performed the round-robin comparisons using 3 sets of weights. The

6 M. Ueki, J. Sun & K. Ueda traveling weights are composed of 2 sets of 8 weights, which are of 5 g, 50 g, 500 g and 5 kg in nominal mass, two pieces each, and one set of 8 weights, which are of 2 g, 20 g, 200 g and 2 kg in nominal mass, two pieces each Third testing program in 2003 From September, 2003 to February, 2004, the 16 participating laboratories classified into 4 groups had performed the round-robin comparisons using 2 sets of weights. The traveling weights are composed of 2 sets of 6 weights, which are of 2 mg, 20 mg and 200 mg in nominal mass, 2 pieces each, being made by different manufacturers and having flat sheets and wires, respectively, in the shape. For the 2 mg weights, there was some doubt in the mass stability due to any environmental change at their transportation, and its calibration data were, therefore, taken as trial and made arbitrary in reporting Forth testing program in 2006 From September, 2006 to February, 2007, the 16 participating laboratories classified into 4 groups had performed the round-robin comparisons using 2 sets of weights. The traveling weights are composed of 2 sets of 3 weights, which are of 2 g, 20 g and 2 kg in nominal mass, one piece each, being made by different manufacturers and having different densities of weight materials. From this forth testing program, another proficiency testing to evaluate the technical capabilities of measuring the four characteristics of weights, namely 1) volume, 2) magnetic susceptibility, 3) magnetization and 4) surface roughness had been performed in parallel. For September, 2006 to March, 2007, the 5 participating laboratories had performed the round-robin comparisons. The traveling weights are composed of 2 sets, A and B, of 3 weights, which are of 5 g, 100 g and 1 kg in nominal mass, one piece each. Considering any possibility of magnetization of the weights during the circulating period, a star-type method had been adopted for this testing, being circulated as NMIJ laboratory X NMIJ laboratory Y NMIJ laboratory Z NMIJ. The weights of B set were kept at NMIJ during the circulation, and observed on their stabilities of the weight characteristics Fifth testing program in 2009 From July, 2009 to November, 2009, the 29 participating laboratories classified into 8 groups had performed the round-robin comparisons by the petal-type method. The traveling weights are composed of 4 sets of 5 weights, which are of 200 mg, 1 g, 50 g, 200 g and 2 kg in nominal mass, one piece each. Some weight calibration laboratories prescribe, in their regulated calibration manuals, two or more kinds of the calibration procedures, in which their own reference or working standards are used for the calibration services, depending on the required accuracies. In this fifth testing program, these calibration laboratories had been reported two calibration

7 Five Proficiency Testing Programs for the JCSS Weight Calibration Laboratories results for each the traveling standard weights in accordance with the first level and the second level of these calibration procedures, respectively. These additional testing programs had been planned to examine and confirm the maintenances of working standards in the participating laboratories. 4. Evaluation of calibration capability Some examples of evaluating the calibration capability in the JCSS proficiency testing programs will be given in the following Calibrations of milligram weights in the conventional masses The capability evaluations of weight calibrations in the third testing program in 2003 are shown for the weights in the milligram range in Fig. 2. The ordinate in the figure gives the deviations of the calibration results from the first value obtained by the NMIJ, and these deviations for 13 calibration results of the NMIJ and those of the participants are shown along with their expanded uncertainties given by the error bars. As seen in the figures, significant changes in the masses are observed for the flat sheet weights of 20 mg and 200 mg at the early stage of the circulation. These changes arise in all of the 6 flatsheet weights of 2 sets circulated, in the same tendency during the first petal loop. Namely, for the calibration results of the NMIJ, the mass degreases of 1.2 µg to 3.0 µg at the largest are observed between the two results, R04 and R05, just before and after the first petal loop, respectively. After these changes, the results, R05 to R13, keep stable without showing any significant change. The other results for the confirming weights and wire ones obtained in this third testing program are all stable and any significant changes are not found in the results, R01 to R13. Deviation (µg) mg Sheet weight Wire weight Deviation (µg) mg Sheet weight Wire weight -12 R01 R02 R03 R04 Lab1 Lab2 Lab3 Lab4 R05 R06 R07 Lab5 Lab6 R08 R09 R10 R11 Lab7 Lab8 R12 R13-12 R01 R02 R03 R04 Lab1 Lab2 Lab3 Lab4 R05 R06 R07 Lab5 Lab6 R08 R09 R10 R11 Lab7 Lab8 R12 R13 Deviation (µg) mg Sheet weight Wire weight -12 R01 R02 R03 R04 Lab1 Lab2 Lab3 Lab4 R05 R06 R07 Lab5 Lab6 R08 R09 R10 R11 Lab7 Lab8 R12 R13 Fig. 2. Calibration results for traveling standards reported from the participants and the reference laboratory

8 M. Ueki, J. Sun & K. Ueda As described above, there happened some degreases in the mass for the 6 flat-sheet traveling weights after their first transportation due to some reason. These sudden decreases in the masses of weights are supposed to be surely due to a separation of adhered materials. At the NMIJ, newly-prepared traveling weights have been cleaned and checked by cleanings with blower brushes, surface inspections and photographing, four replicated calibrations of the masses, and surface examinations before their transportations. It seems difficult to investigate the reason of the above mass changes in the past time. Considering the experiences of the changes in the weight masses, it will be suggested to examine and evaluate the traveling weights more severely, before starting the proficiency testing program. In fact, the reliability of these proficiency testing programs had been firmly ensured by the calibration results of the wire weights. Although the observed mass changes of 3.0 µg at the largest for the flat-sheet weights are significant for the calibration results of the NMIJ, these changes do not give any serious effect to judged results of the technical capabilities in the proficiency testing program, by adding those to the uncertainty, U Ref Calibrations of 200 g weights in the conventional mass The capability evaluations of the calibrations of the 200 g weights are shown as an example in Fig.3. The ordinate in the figure gives the absolute values of the deviations of the calibrated values of the participants from the reference value, along with the expanded uncertainties, U Lab, of these calibrated values calculated from Eq. (2), given by error bars. The abscissa gives the code numbers of the 15 participants. The reported value of the participant 2 gives a significant deviation from the reference value, corresponding to 0.00 mg in Fig. 3, and its E n number is obtained as The calibration result of this participant was judged as an outlier. In the whole of the five JCSS proficiency testing programs as mentioned before, most of the participating calibration laboratories have been confirmed to have the required technical capabilities, but a few number of the reported results were judged as the outliers, exceeding E n = Lab-Ref (mg) Participant Number Fig. 3. Calibration results of 200 g traveling standard weight from the participants

9 Five Proficiency Testing Programs for the JCSS Weight Calibration Laboratories 4.3. Weight calibrations in the true mass The calibration services carried out by the JCSS weight calibration laboratories are, in general, for the calibrations in the conventional masses prescribed in the OIML D28. Some calibration laboratories, however, have also accredited or are going to plan the calibration services in the true masses. In the JCSS proficiency testing programs, calibration reports of the true masses are also accepted, being made with reference to the density values of the traveling standards obtained and made public by the reference laboratory, and the calibration capabilities of the weights in the true mass are evaluated. At the early stage of the JCSS proficiency testing programs, there were some examples that the calibration laboratories, having no problems in the report of calibration results in the conventional mass, had reported the outliers for the calibrations of the same traveling standards in the true mass. These laboratories had some misunderstandings of the air buoyancy corrections, and the corrective actions were made so that correct calibrations for the true masses have been performed afterward Characteristics evaluation of weights In the proficiency testing program in 2009, the measurement results and their expanded uncertainties of the volumes, magnetic susceptibilities, residual magnetizations and surface roughness for 6 weights of 20 g, 200 g and 2 kg in the nominal mass, two pieces each, had been also requested to report, and the measurement capabilities of these characteristics of the participants had been evaluated by the E n numbers. The instruments used for of the three characteristics measurements adopted by the reference laboratory (NMIJ/AIST) and the expanded uncertainties of these measurements were as follows. (i) Volumes (a) 20-g weights; instrument: Hydrostatic weighing system (AT106 [1 µg/111 g]) expanded uncertainty of volume = cm 3. (b) 200-g weights; instrument: Aerostatic weighing system (CC1000S-L [1 µg/1 kg]) expanded uncertainty of volume = cm 3. (c) 2-kg weights; instrument: Aerostatic weighing system (CC10000U-L [10 µg/10 kg]) expanded uncertainty of volume = cm 3. (ii) Magnetic susceptibilities and residual magnetizations instrument: BIPM susceptometer, expanded uncertainty of magnetic susceptibility = to , expanded uncertainty of residual magnetization = 0.50 µt. For the measurement capabilities of the weight characteristics, some reports of a participating laboratory had the En numbers exceeding 1.0, being judged as the outliers. This laboratory was requested to investigate the cause of the outliers and to take any corrective action on this problem. In addition, the case of scratching the traveling standard weights on the surfaces had arisen at working for the characteristics measurements. It is the responsibility for the calibration laboratory to recover the original

10 M. Ueki, J. Sun & K. Ueda state of the weights. Against the case of scratching, the laboratory had been strongly requested to investigate the cause of the accident and to take the corrective action for protecting the weights from any damage. 5. Summary For the weight calibration laboratories in the mass range of 1 mg to 20 kg, the JCSS proficiency testing programs to evaluate the capabilities of mass calibrations had been carried out five times for the duration of 1993 to 2009, under the management of IAJapan. In these proficiency testing programs, the calibration results of the weights exceeding 500 in number had been reported from the 80 calibration laboratories in total, and their calibration capabilities had been evaluated. As a result, the absolute values of the E n number had exceeded 1.0 only in a few cases of the reported calibration results, being judged as the outliers. The JCSS calibration laboratories who had reported these results of the outliers had been compulsorily required to investigate the cause of the outliers and to take corrective actions. The IAJapan had confirmed that the said laboratories had taken the corrective actions adequately and realized the weight calibration services as registered to the JCSS. There are also increasing needs for on-site calibrations of weights, the present state of which are under study. It will be needed, in near future, to extend the JCSS proficiency testing program to the area of these on-site calibrations. Standard weights calibrated by the JCSS calibration laboratories are broadly disseminated in Japan, and the reliability of mass metrology even in daily uses will be surely improved with the linkage to the traceability system of the mass standards. References 1. International Organization for Standardization, Conformity assessment General requirement for proficiency testing, ISO/IEC (2010). 2. Japanese Industrial Standard, Conformity assessment General requirement for proficiency testing, JIS Q (2011) in Japanese. 3. T. Kobata M. Ueki A. Ooiwa and Y. Ishii, Measurement of the volume of weights using an acoustic volumete and the reliability of such measurement, Metrologia 41 (2004), p.s M. Ueki T. Kobata K. Ueda and A. Ooiwa, Automated volume measurement for weights using acoustic volumeter, in IMEKO TC3 Proc. (2007). 5. M. Ueki Jian-Xin Sun and K. Ueda, Evaluation of the magnetic properties of weights at NMIJ, in APMF2007 Proc. (2007). 6. International recommendation, Weights of classes E 1, E 2, F 1, F 2, M 1, M 1-2, M 2, M 2-3 and M 3, OIML R111 (2004)