Process Controls, Instrumentation and Automation the metering systems are installed and the parameters associated with metering system operation contribute to measurement uncertainty. Uncertainty analysis of a metering system should be performed during the detail design stage to understand the estimated uncertainly in the flow measurement. If the estimated uncertainty is beyond the acceptable limit, suitable actions like design changes, instrument selection, testing, etc., can be undertaken. Stages of uncertainty estimation. Uncertainty estimation is performed in the following stages: * Formulation-defining the output quantity; identifying the input quantities using the calculated output; developing a measurement model relating output to the input quantities; identifying elemental Instrument error (linearity/repeatability/stability) Variation in ambient temperature Validation acceptance tolerance/uncertainty in reference standard RTD sensor error Line pressure and temperature variation Uncertainty in pressure measurement Uncertainty in temperature measurement Uncertainty in density measurement Uncertainty in CPL, CTL Equ. (API Chap 11) Uncertainty in volume of water-draw tank Uncertainty in base prover volume Uncertainty in sampling system and BS&W measurement Uncertainty in calculated CPL/CPS (prover and meter) Uncertainty in calculated CTL/CTS (prover and meter) Uncertainty in K-factor calculation Uncertainty in indicated volume measurement Uncertainty in gross std. vol measurement Uncertainty in net std. vol measurement FIG. 2. A generic multistage measurement model of a liquid hydrocarbon measurement process. TABLE 1. A pressure measurement uncertainty budget table Source Sr. No. Symbol A 1 B ePATamb= 2 3 4 5 ePacc= ePstab3= ePcal = ePchk= of uncertainty C Ambient temperature effect Instrument error classhttp://www.HydrocarbonProcessing.com