چكيده به لاتين
One of the most important subjects in accurate measurement of gas is uncertainty of flow meters as a measurement tool and one of the most important cases is uncertainty of measurement system, interactions and mutual effects of each component of measurement system .In this ,in addition to computing the uncertainty of a measurement station equipped with ultrasonic flow meter , the combined uncertainty of the Neka CGS station No.2 in accordance with ISO-5168 standard is calculated . The results showsfor flow rate 33146 and 89513 sm3/hr ,the overall uncertainty of the studied system is equal to 0.72 % . The most effective parameter on uncertainty related to the operation conditions of ultrasonic flow meter. After this, he pressure , meter calibration in high pressure , the ratio of the super compressibility coefficient, repeatability in operating conditions, temperature and a deviation of error in calibration conditions have the highest influence on uncertainty respectively . This indicates that in the limits of the uncertainties in the system elements,( especially of USM ) is not considered as the criterion , because the error summation of the measurement station is greater than the individual uncertainties. In addition according to the calculations, overall uncertainty of this system for10000&25000 sm3/hr are 3.5 and 1 percent respectively, this indicates the effect of flow rate on overall uncertainty of city gas stations in the flow rate of less than 20 % of the Qmax with ultrasonic flow meter is more considerable .
