NMISA A discussion on Force ILC's and methods to improve results. 13 October 2015 Speaker: S.T.S. Dlamini Author: C.H. Gouws

Transcription

1 NMISA A discussion on Force ILC's and methods to improve results. 13 October 2015 Speaker: S.T.S. Dlamini Author: C.H. Gouws

2 INDEX INTRODUCTION Background Why the need for this discussion ACCREDITATION Testing communities view on accreditation and ILC s Where does SANAS ILC s fit into the bigger picture? How to evaluate competence and quality? NLA FORCE ILC SCHEME Protocol Results Concerns SUGESSTIONS Calibration Good Practices SUMMARY

3 INTRODUCTION Background In 2013/2014 the NLA coordinated an inter-laboratory comparison (Proficiency Testing Scheme) in the field of force metrology. This offered SANAS accredited Force calibration laboratories to comply with SANAS R which states SANAS shall ensure that their accredited facilities participate in proficiency testing or other comparison programmes, where available and appropriate. Why is there a need for a discussion Unfortunately the report released by NLA indicated that not a single lab was able to obtain an En value 1 through the whole calibration range.

4 ACCREDITATION (1) Testing communities view on Accreditation and ILC s Viewed as just another requirement which must be fulfilled in order to get and maintain accreditation. Participation in PT scheme is treated as something to do as quickly and with the least amount of effort possible. Overall it s treated with disdain, contempt and with suspicion. But ILC s are one of the most important methods of proving competency and evaluating the technical ability of a laboratory.

5 ACCREDITATION (2) Where does SANAS ILC s fit into the bigger picture? SANAS is the only nationally recognized steward of this accreditation system within South Africa SADCAS is the main accreditation body in the SADC region. SADCAS forms part of a larger accreditation body the AFRAC. AFRAC forms part of a larger umbrella body, ILAC. ILAC provides an internationally harmonised guideline for certain activities and evaluations, a.k.a. accreditation, to be performed. Thus, SANAS has the responsibility to ensure that testing and calibration laboratories conform to the standards and guidelines of ILAC. ILAC International Laboratory Accreditation Cooperation AFRAC African Accreditation Cooperation SADCAS Southern African Development Community Cooperation in Accreditation SANAS South African National Accreditation System

6 ACCREDITATION (3) How to evaluate competence and quality? For SANAS to conform to the measurement and testing standard guidelines which are imposed by ISO/IEC and ILAC- P9:06/2014, SANAS R48-03 states: SANAS shall ensure that their accredited facilities participate in proficiency testing or other comparison programmes, where available and appropriate.. To summarise, SANAS only require ILC s and PT schemes to ensure the technical validity of measurements performed by laboratories. These results are not only nationally comparable but also internationally. Thus ILC s are used to, validate, ensure quality of and even improve measurement results produced by each laboratory and should be seen as a tool rather than a punishment.

7 NLA FORCE ILC SCHEME (1) Protocol The detailed procedure for performing the measurements was described in the procedure number NLA-ILC-P In summary, the procedure calls for the participants to use their normal day to day calibration procedure to calibrate the ILC artefact which consisted of a Loadcell and Readout unit combination. Measurements had to be performed at the following nominal forces: 50 ; 100 ; 150 ; 200 ; 250 ; 300 ; 350 ; 400 ; 450 and 500.

8 NLA FORCE ILC SCHEME (2) Results Summary Of all the participants of the ILC, not a single lab was able to achieve an E n value 1 for the whole calibration range. Only a single lab was able to achieve E n value 1 for 9/10 calibration points. Average number measurement with a E n value 1 for all participants are 2 measurements of the 10 measurements.

9 Absolute Normalised Error (En) NLA FORCE ILC SCHEME (3) Results E n Value Absolute Normalised Error Over Whole Range b52r xpu1 8dxq 9ngy 17uf sd9v cf7w

10 NLA FORCE ILC SCHEME (4) Results Conclusion It has always been a widely held view within the Force calibration and testing community that the community is one of competency yet this ILC completely contradict this view. Whilst the objective of the ILC demonstrating the competence of the Force calibration laboratories who participated, was not successfully met, the objective of highlighting areas of concern within this community definitely was achieved. One of the main concerns that came to light while investigating the report and the participants calibration methods was the calibration practices adopted by the calibration and testing laboratories when calibrating force transducers.

11 NLA FORCE ILC SCHEME (5) Concerns Practices and Methods Insufficient attention being spent on alignment Multiple people calibrating the same transducers for the same calibration certificate Incorrect use of swivel heads/plates, loading buttons and loading platens. Using faulty/substandard equipment to calibrate the transducer. Rushing through the calibration/ilc to complete it as fast as possible. Using reference transducers with questionable traceability or the misinterpretation of the information contained in the calibration certificate for the reference transducers. Not having the correct equipment for the calibration. Competence and Attitude Accepting all results as always true. No implementation of intermediate check measurements. Negative attitude towards the ILC calibration. Untrained personnel doing the ILC calibration.

12 NLA FORCE ILC SCHEME (6) Concerns Ex. Alignment Alignment is one of the most important factors that need to be considered when performing a Force calibration. F z = F in cos α 1 = 0,015 % 2 = 0,06 % 3 = 0,14 % 4 = 0,24 % 5 = 0,38 % This clearly indicates that if the calibrating laboratory had made a small alignment error, the accuracy of their results could be drastically affected.

13 NLA FORCE ILC SCHEME (7) Concerns Ex. Alignment (Cont.) Basic tips for alignment: Transducer is centered to the principle force application axis of the machine. Alignment between the laboratory standard loadcell and the unit under test loadcell. When using some form of alignment platens, such as swivel heads, ensure they are clean and free of dirt to enable them to easily swivel and align themselves. When using swivel heads to align the force transducer, only use one swivel plate per installation. Incorrect type of loading button is used during the calibration. Incorrect use of loading buttons during calibration. This list is not comprehensive and it is the responsibility of each laboratory to further investigate other possible misalignment causes.

14 NLA FORCE ILC SCHEME (8) Concerns Participants Complaints/Concerns Though the following comments are not all the concerns regarding the scheme, these are the most pressing ones presented by some of the participants: The readout which was in mv/v was confusing to some of the participants. To such an extent that they were uncertain about the results they submitted. The calibration period was too short or was in a very difficult time for the participants. Could not participate in full range of the calibration due to large calibration range. The scheme running was out of the expertise and experience of the lab but due to low number of PT schemes, was forced to partake. Some laboratories partook in second round measurements while others did not know they could improve on their results.

15 SUGGESTIONS Calibration/ILC Good Practices These include but are not limited to: A single, competent metrologist should perform one calibration at a time. Analyse the raw data measurement results before issuing a certificate, use the Common Sense Principle. The use of intermediate check measurements should be implemented to maintain confidence in the measurement results being generated. The correct, calibrated and functional equipment must be used to perform the calibration Calibrations must not be rushed. There is never enough time to do the measurement correctly the first time, but there is always enough time to repeat the measurement later applies here. The procedures set out in SANAS and ISO standards such as ISO376 and ISO7500 should be followed as far as possible.

16 SUMMARY The ILC has exposed the industries short fallings and thus also all of South Africa s industry dependent on force measurements. Testing and calibration laboratories has to investigate possible causes for their poor results in the ILC. They then have to develop new methods/procedures to address these shortcomings. There might be radical changes required within the testing laboratories, but hope remains in that the ILC has now given direction for improvements of procedure, methods and quality of results and thus improvement of South Africa s quality of products. It can now be used as the tool it is meant to be within the testing and calibrating community.

17 QUESTIONS?