ANALYSIS OF VERIFICATION AND CALIBRATION METHODOLOGIES OF MEASURING INSTRUMENTS

Abstract

The article focuses on the main problems of metrological confirmation of measuring instruments in accordance with international requirements and considers possible directions of their solution. One of the main tasks of metrology is assurance of the uniformity of measurements, that is, the state of measurements, in which their results are expressed in the legal units, and the characteristics of errors or uncertainty of measurements are known with a certain probability and do not exceed the established limits. The uniformity of measurements is ensured by the conformity of methods of measurements and measuring instruments to use for their intended purpose. In turn, the suitability of the measuring instruments to use for their intended purpose is determined by the conformity of their metrological characteristics with the established norms. Conformity assessment is the process of proving that the established requirements for a product, process, service, system, entity or body have been met. Metrological confirmation is a set of operations required to ensure that measuring equipment conforms to the requirements for its intended use. Metrological confirmation of measuring instruments generally includes their verification and calibration. Verification and calibration procedures of measuring instruments have both common features and certain differences. The procedure of the experimental part of the metrological confirmation of measuring instruments, both their verification and calibration, consists in comparing the indication ,1 ind х x of the measuring instrument, which is being verified, whether indication ,1 c х x of the measuring instrument, which is being calibrated, with the standard (reference) quantity value ,1 st х x . Consequently, in both procedures there is a common research object: in the verification procedure it is the indication ,1 ind х x of the measuring instrument, which needs to be verified; in the calibration procedure it is the indication ,1 c х x of the measuring instrument, which needs to be calibrated. Accordingly, the methods for implementing the verification and calibration procedures are practically identical. One of the key issues in the measuring instruments verification and calibration procedures is the question of estimating the accuracy and reliability of the obtained results. The error ,1 ind х x ∆ of the measuring instrument indication ,1 ind х x , which is being verified, is the measurand in the verification procedure, and it is determined as the result of indirect measurements. The combined standard uncertainty ( ) ,1 c ind x u x ∆ of the found error value ,1 ind х x ∆ is the accuracy estimate of the verification result. The actual quantity value ,1 act х x , that corresponds to the measuring instrument indication ,1 с х x , which is being calibrated, is the measurand in the calibration procedure. The expanded uncertainty ( ),1 P act х U x of the found actual value 1 act х x , with confidence level p is the accuracy estimate of the calibration result. The obtained values ,1 act х x and ( ),1 P act х U x with confidence level p are indicated in the calibration certificate of the measuring instrument.