Uncertainty analysis for determination of long-term drift and mounting position for pressure transmitter calibration

A reliable estimation of standard uncertainty can provide an assurance to instrument calibration process. This paper focuses on analyzing the influences of long-term drift of calibration standard and mounting position of instrument under test on standard uncertainty of pressure transmitter calibration in order to verify whether these factors are significant sources of Type B uncertainty. The mathematical model for estimating the standard uncertainty from major sources including two interested influence factors is developed. Based on the proposed model, the standard uncertainties were calculated using historical data of calibrated transmitters from a calibration laboratory in Thailand during the year 2014 to 2017. The influences of the long-term drift of the standard pressure source and standard instrument since their last calibration as well as the effects of the mounting position type of instrument under test can be examined from the estimated uncertainties. The analysis results show that the mounting position of the transmitter being calibrated should be considered during calibration process. The proposed uncertainty model is helpful for calibration stakeholders to understand more about the influences on standard uncertainty to achieve more reliable estimation when calibrating pressure transmitters with electrical output.