Ensuring the unity and metrological traceability of measurement results becomes the key component necessary to reach market confidence in the results of calibrations, tests or measurements. Important aspect of maintaining the ability of the laboratory to receive metrological traceability and reliable measurement results is to determine the maximum permissible period between two calibrations of the standards and measuring instruments that provides the acceptable accuracy of measurements during their operation. Each test or calibration laboratory that aspires to comply the requirements DSTU ISO/IEC 17025 should establish calibration interval for current standards and equipment and/or introduce criteria for determining the necessity of calibrations. Substantiated solution of the mentioned problem is this paper issue.
To provide the metrological traceability of measurement results, the developed method of establishing the necessity of time intervals of standards and other measuring instruments calibrations is elaborated below. The development implies the conjugated consideration of Shewhart control charts and statistical processing time series instrument, namely, the movable averages. Example of implementing the movable averages is considered for solving the particular tasks.
Application of several movable averages of the same type or the different types, with the same or different parameters of smoothing, their intersection (or lack thereof) and forecasting instruments (modeling, extrapolation, etc.) may be the basis of a method which would allow to substantiate the development of criteria for determining the need for calibration standards and measuring instruments, or to change already established calibration intervals.
It is revealed that the application of Shewhart control charts with the drawing of movable average lines on them, under certain conditions, can provide timely signals about the necessity to conduct calibration of the standards and measuring instruments used by the laboratories. Proposed approach allows create the forecasting instrument convenient for the test and calibration laboratories.
[1] Law of Ukraine «On Metrology and Metrological Activity», no.1314-VII, (in Ukranian), June 05, 2014.
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[7] Criteria, which must meet metrological centers, state enterprises belonging to the management of the Ministry of Economic Development and Trade of Ukraine and conduct metrological activity, and verification laboratories that are authorized or authorized to carry out the verification of legally regulated measurement instruments in use (in Ukranian).
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