Interlaboratory Comparisons NMi - Accuracy you can trust A basis for reliable measurements NMi VSL B.V.
Laboratories continually strive to ensure the quality of instruments, procedures, and capabilities. No matter how carefully they conduct these internal checks, systematic deviations often go unnoticed. It is therefore important that they regularly compare their measurement results with those of other laboratories. Participation in interlaboratory comparisons is a key criterion for accreditation, but is also a vital investment in reliability, operational certitude, and staff confidence. NMi Van Swinden Laboratory offers a wide array of interlaboratory comparisons and proficiency testing programs. Convenient, capable, to-the-point, and eminently reliable these are the cornerstones of NMi s reputation. Extensive experience NMi Van Swinden Laboratory has more than 30 years experience in interlaboratory comparisons. We conduct interlaboratory comparisons and proficiency testing programs in many different fields from pressure, mass and viscosity to chemical analyses, and from temperature and humidity to electricity, length and gas flow. NMi is accredited to conduct comparisons and proficiency testing programs in many of these fields. As the Dutch national institute for metrology, NMi participates in key comparisons with national metrology institutes throughout the world. We are therefore well acquainted with the demands of participation in such programs. For instance, we know just how important it is for laboratories to receive advance warning on when test materials will arrive. And we know how important it is to receive clear, comprehensive, and prudent reports on results. NMi is accredited to conduct interlaboratory comparisons and proficiency testing programs. We have gained an international reputation as an independent national metrology institute. Metrology Traceability Accreditation Interlaboratory Comparison Calibration Quality System Standardisation Procedure How do we compare? Interlaboratory comparisons offer a broad assessment of measurement accuracy. This not only extends to a laboratory s measurement standards, but also to underlying procedures. Incorrect procedures can cause systematic deviations in the measurements. Examples include erroneous readings or a too short time of evaporation for specific samples. The participating laboratories are each sent a sample, an artefact, or a measurement instrument on which measurements have to be performed or deviations have to be determined using their standard procedures. An E n value is then calculated for each laboratory, based on comparison of the lab s measurements with reference values (Y and Y ref ), in combination with the reported uncertainties for these two values (U and U ref ). E n = ( Y-Y ref )/ U 2 +U 2 ref If the absolute value of E n is less than or equal to 1, the lab s results are in agreement with the reference values. However, if the absolute value of E n is greater than 1, the laboratory must determine the cause of the systematic deviations, which may result from improper standards, instruments or procedures. In some comparisons, a Z-score is calculated in addition to the E n value.
Interlaboratory comparisons and proficiency testing programs enable laboratories to operate with confidence and help resolving conflicts. They allow measurements to be compared. Confidence Measurement precision is a hidden quality at all laboratories. It usually only attracts attention if measurements fail to match those of other laboratories, indicating that there may be some kind of problem. Prior to that, no news is good news. Affirmation of accuracy does, however, help to keep lab staff sharp and motivated. Interlaboratory comparisons provide this affirmation. This serves as a positive impulse for staff at larger laboratories, but also for those at smaller calibration laboratories, that often operate as little islands within major corporations. In short, comparisons provide a welldeserved sense of self-confidence. Resolving conflict Interlaboratory comparisons offer great transparency, especially if they are conducted regularly. Systematic deviations can be spotted at an early stage and swiftly rectified. When measurements differ, proficiency testing reports provide a firm foundation for proving that the cause of such variations must lie elsewhere. This saves time, reduces stress, and minimizes liability risks. Traceability Participation in NMi interlaboratory comparisons also allows laboratories to check for flaws in their traceability chain. In general, laboratories from various countries participate in the NMi s interlaboratory comparisons and proficiency testing programs. This has the added advantage of providing an international benchmark for participants. NMi offers practical solutions to everyday concerns. We offer robust, efficient and reliable execution of existing programs. And we have the flexibility to offer you more, wherever necessary. That is why so many leading companies rely on NMi. Robust and practical Participants in NMi s interlaboratory comparisons are assured of careful preparation and organization. We apply our expertise and experience in selecting appropriate artefacts (for physics-related programs) and in producing stable and homogenous samples (for testing chemical analyses). During our interlaboratory comparisons, an artefact may be sent from one lab to another 10 to 20 times over the course of several weeks. We ensure stability by selecting the best possible artefact and ensuring optimum packaging and transportation. Prior to a comparative study, we often confirm the stability of artefacts by monitoring fluctuations over a period of several months. We also incorporate well-timed checks into our intercomparisons.
Flexible and innovation-driven Laboratories that periodically participate in interlaboratory comparisons compile a valuable dossier, making quality improvements visible and placing deviations within a historical context. In addition to our reputation and reliability, this continuity is one of the main reasons why leading companies rely on NMi for interlaboratory comparisons. Another key factor is that we have the standards, expertise, and ambition to develop innovative interlaboratory comparisons and proficiency testing programs. NMi has the international contacts to assure widespread accreditation of such innovations. We are, for instance, closely involved in the formulation of national and international criteria for interlaboratory comparisons. That makes us an obvious choice for corporate trendsetters seeking to ensure and develop quality. Confidentiality The results of the interlaboratory comparisons are strictly confidential. The results will be presented to the other participants in an anonymous fashion. Each laboratory individually decides who else is allowed to learn about their performance. Any questions? If you would like further information about NMi s interlaboratory comparisons, please feel free to contact us at +31 (0)15 269 1500. NMi has factsheets outlining interlaboratory comparisons and proficiency testing programs for the following fields: Chemical analysis Electricity Pressure, mass, force, and viscosity Gas and liquid flow Temperature and humidity Length and geometry Optics and radiation Ionising standards
Information NMi VSL B.V. Thijsseweg 11 T (+31) 15 269 15 00 F (+31) 15 261 29 71 P.O. Box 654 2600 AR Delft The Netherlands E I nmi@nmi.nl www.nmi.nl