eng Science and Education Publishing International Journal of Physics 2333-4886 2014-09-22 2 5 151 157 10.12691/ijp-2-5-4 IJP2014254 article Gunawan Marto msc.gunawan96@gmail.com 1 Harijono. A. Tjokronegoro 1 Edi Leksono 1 N Nugraha 1 Ghufron Zaid 2 Research Group of Engineering Physic Institut Teknologi Bandung, Jalan Ganesha 10 Bandung 40132, Indonesia Research Centre for Calibration, Instumentation dan Metrology (Pusli KIM-LIPI), Indonesia This paper explainsan enthalpy uncertainty ofnatural gas energy measurement (custody transfer) using orifice meter in non adiabatic condition. The method of uncertainty analysis used in this paper was developed based on theuncertainty analysis of natural gas flow measurement using orifice meter at adiabatic condition based on AGA 3, 1992 (which reference by No 10.). In addition of non adiabatic condition includes: critical pressure, critical temperature, realtime pressure, realtime temperature and generalized correlation constanta. The measurement of enthalpy uncertaintyis referring to the Guide to the Eexpression of Uncertainty Measurementof the Guide in MetrologyWorking Group 1 of Joint Committee for Guide In Metrology, 2011. Based on the energy flow in orifice meter is 1000 Mmbtud, The combined uncertainty of f enthalpy is 3.86 x 10-7 Mmbtud (3.86 x 10-8 %) while the expandeduncertainty analysis results 7.73 x 10-7 Mmbtud (7.73 x 10-8 %)with confidence level 95%. This number of uncertaintyis smaller than the Measurement Permissive Error specified by legal metrology organization 0.1667%. http://pubs.sciepub.com/ijp/2/5/4/ijp-2-5-4.pdf measurement uncertainty orifice meter adiabatic condition non-adiabatic condition Maximum Permissible Error (MPE)