Intercomparison. Nine test laboratories - one task.
On December 3, 2015 the final meeting of the annual intercomparison took place in Slovenia. Participants of this intercomparison are laboratories from Luxembourg, France, Belgium, Tunese, Slovenia and Germany. Intercomparisons are obliged by national authorities. In Germany this authority is the Deutsche Akkreditierungsstelle GmbH (DAkkS - Germany’s National Accreditation Body).
In 2015 ZERA arranged this comparison. The devices to be compared – a Reference Meter of type MT3000 and a current and voltage source MT551 – have been tested under identical laboratory conditions at the beginning as well as at the ending of the comparison. The test occurs under predefined load conditions – in every participating laboratory.
At the end of the year, when all results of every single laboratory are available, all load points are compared in consideration of the specified measurement uncertainty (MU). Very important is in this case, how near the measuring results (error values) are to the (predefined) weighted average and that the weighted average is always in the range of the measurement uncertainty.
Start and final test procedure of the intercomparison resp. the difference of the accuracy give information about how the device has been influenced. By the different locations, the device has been used at, the device has been exposed in an increasing way to vibrations (caused by transportation) and variations in temperature. This can influence the long term stability and the accuracy of the device and thereby might result in an adjustment/calibration.
Many laboratories take part to the intercomparison for several years. Improvements in measurement quality of each single laboratory can be certified by comparing these results over the years. The improvements in a current range can be determined exactly by the predefined load points.
Laboratories' participation at intercomparisons can be a great benefit in consideration of reliability and quality.
"An .... intercomparison resp. interlaboratory test... is a method of external quality assurance for measurement procedures as well as measuring and test laboratories. In general identical tests will be examined by ... identical procedures. Comparing the results allows a general statement about its measurement quality of the involved laboratories ... Accredited laboratories have to participate at intercomparisons regularly according to DIN EN ISO/IEC 17025 or within the scope of the state certification procedures in order to assure the quality of the results and to prove its competence."