Temperature robustness of oscillation-type density meters

Abstract

The temperature robustness of an oscillation-type density meter was investigated with the aim of examining the limitations of measurement uncertainty. We demonstrate that the measured density by such a device reveals a relaxational behavior after a temperature adjustment of the glass vibrating tube. From an analysis of the time-dependent measured density, we demonstrate that this behavior is neither caused by a time-dependent temperature of the oscillation tube due to convective heat transfer after temperature adjustment of the device, or by a time-dependent spring constant of the oscillation tube, since this effect is suppressed by a reference oscillation tube. Instead, we show that this behavior is inherently connected to the relaxational behavior of the volume of the tube which is governed by the elastic properties of glass. By rigorous analysis of the time characteristics of the measured density, we were able to determine the characteristic time constant of the relaxation at different temperatures, and consequently we further show that the characteristic time constant of the relaxation follows a temperature-activated behavior. A characteristic waiting time after a temperature adjustment of the device is also presented in order to keep the uncertainty as small as possible.