Comparison of density determinations of liquid samples

Project Description

Density determinations of liquid samples are performed by laboratories to provide a means of calibrating or checking liquid density measuring instruments such as oscillating density meters. The aim of this comparison is to compare the results of the density determinations of the participating laboratories.
The main reason for this project is to establish a link to CCM.D-K2 "Comparison of liquid density standards" carried out by the PTB and finished two years ago.
The laboratory of the PTB (DE) helped the Pilot Laboratory BEV (AT) with setting up the Technical Protocol.
To find a better link, it was decided to measure for this comparison samples of equal liquids as in CCM.D-K2: water, pentadecane, tetrachloroethylene and of an oil of high viscosity. The temperature range is from 5 °C up to 60 °C. The measurements should be carried out at atmospheric pressure by hydrostatic weighing of a solid density standard.
The stability of the used liquids is checked by the pilot laboratory by monitoring the density at 20 °C over a time interval of one month. Beginning of the year 2008 the liquids will be divided into samples that will be sent to all participants. After the measurements, the pilot laboratory will check whether the density of the samples has changed during the comparison.
The comparison is intended to be a regional key comparison according to the Mutual Recognition Arrangement.

Final Report 2012-06-30

The project has been completed and results are published in the KCDB.

Density determinations of liquid samples had been performed by laboratories to provide a means of calibrating or checking liquid density measuring instruments. The aim of this comparison was to compare the results of the density determinations of the participating laboratories.
The main reason for this project was to establish a link to CCM.D-K2 “Comparison of liquid density standards” carried out by the PTB and finished 2008.
In this comparison 8 reference values for the density of four liquids were determined: the density of water at 20 °C, of pentadecane at 15 °C, 20 °C, 40 °C and 60 °C, of tetrachloroethylene at 5 °C and 20 °C and of a viscosity oil at 20 °C. The measurements were carried out at atmospheric pressure by hydrostatic weighing of a solid density standard.
The stability of the density at 20 °C and the homogeneity of the used liquids were monitored over a time interval of one month by the pilot laboratory. The measurements of the participants have been finished in 2008; Feb 2009, after receiving of the last results, the formal process for the calculation and the visualization of the results started. Accompanied by discussions regarding the scattering of the results, reasons for these deviations, and the best praxis for a reference value the Draft A, the Draft B and the final draft of the report were communicated to the participants and finally was agreed by them.

The analysis of the discrepancies in the results have shown, that in the most of the cases the main cause of this scattering was not the method of the measurements itself, but rather the inappropriate handling of the liquid samples before and after the weighing.

In order to calculate the reference values for this comparison, the measurement results of the link laboratories (PTB and MKEH) have been corrected over their deviation to the reference values of CCM.D-K2.

Conclusion: The determination of the density of 4 different liquids at different temperatures of 15 participants is showing compared to the mean uncertainty a high scattering. It seems that the size of the deviation is completely different from laboratory to laboratory and depends more on the handling routines than to the principal of the measurements.

With this EURAMET comparison a link to the CCM.D-K2 “Comparison of liquid density standards” was successfully established. The measuring capabilities of the CMC claims based on this project shall be carefully investigated due to the discrepancies.

Progress Report 2010-02-23

Density determinations of liquid samples had been performed by laboratories to provide a means of calibrating or checking liquid density measuring instruments such as oscillating density meters. The aim of this comparison is to compare the results of the density determinations of the participating laboratories.
The main reason for this project was to establish a link to CCM.D-K2 "Comparison of liquid density standards" carried out by the PTB and finished 2008.
The measurements have been finished in 2008; Feb 2009 receiving of the last results and stability tests of the used liquids by the pilot laboratory by monitoring the density of 20 °C over a time interval of one month.
2009: work to link CCM.D-K2; EURAMET meeting 2010 Draft A