Improvement of the measurement uncertainty of a high accuracy single sinker densimeter via setup modifications based on a state point uncertainty analysis

The single sinker densimeter with magnetic suspension coupling is one of the state of the art methods for the accurate measurement of fluid densities. The uncertainties of experimental pressure, density and temperature data, measured with a single sinker densimeter, were thoroughly evaluated following the uncertainty propagation law. The main uncertainty sources of each magnitude were determined. Based on this statistical study, several modifications were performed to reduce the uncertainty associated to each magnitude. Firstly two new PTR-25 probes were added. Secondly a new pressure transducer for the low pressure range was added. Finally the sinker of the densimeter was replaced by a bigger one to improve the balance reading. After these modifications the uncertainty of each magnitude was evaluated and validated with a Monte Carlo simulation. Results yielded a significant reduction of 44% in temperature uncertainty, more than 92% on pressure below 2 MPa, and more than 22% on density.

► State point (p, T, ρ) uncertainty of a technique to measure gas density is analyzed.
► Improvements based on an analysis of the uncertainty budget are proposed.
► Uncertainty analysis of the state point of the modified technique is performed.
► Results have been validated using the Monte Carlo method.
► Test measurements were performed, capability of the modified technique is evaluated.