Basic calibration of the PTB's primary viscometers
|ISBN:||ISBN 3-89701-508-0 ; ISSN 1434-2391|
|Zusammenfassung:||The calibration of a set of five long-capillary Ubbelohde viscometers used as the starting point of the realisation of the PTB viscosity scale has been described.
From the measurement results for water the viscometer constant was calculated. A new method to evaluate the kinetic energy correction was applied. This correction was found to be significantly higher (up to factor 2) than the value calculated from the correlation given in . Individual surface tension correction factors were calculated from measurement results for water and nonane. With this procedure the viscosity of nonane was measured relativ to water by two U-tube viscometers. The relative uncertainty (coverage factor k=2) of the viscometer constant for the set of primary viscometers is 2,4·10.sup.-4.nosup. and the relative uncertainty of a viscosity measurement using these viscometers can be kept below 5·10.sup.-4.nosup.. The stated uncertainties do not include the uncertainty of the viscosity of water.