A novel vibrational sensor for high precision viscometry of liquids in wide ranges of temperature and pressure

This report describes how the insights from the two previous studies led to a newly designed viscosity sensor that centers around a torsionally vibrating piezoelectric quartz cylinder. The main features of the sensor are line conductor electrodes for improved piezoelectric excitation of the torsional vibration of the quartz cylinder and a novel suspension of the cylinder with significantly reduced vibrational losses. The quartz cylinder itself was machined with higher accuracy and much reduced surface roughness than before. The resulting sensor is more compact, easier to assemble, and offers greater access to the liquid whose viscosity is to be determined. The sensor was incorporated and calibrated in an experimental manifold for automated measurements in a wide temperature range from 200 to 420 K with pressures up to 100 MPa. The performance of the sensor is assessed by a detailed uncertainty analysis and validated by measurements of the aromatic hydrocarbon toluene, whose viscosity is considered to be known at standard reference quality. Representative measurement results for most of the experimental temperature range are presented at standard atmospheric pressure, while results for the entire pressure range are reported at two temperatures, 303.15 and 393.15 K, at which comparisons with literature data are possible. They confirm that with an achieved 0.2% the uncertainty development goal of the sensor of less than 1% has been exceeded and is approximately by an order of magnitude improved over previous such sensors, while the repeatability of the new sensor is 0.02%.