Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Measuring the density of ultra-pure water

19.12.2007
For oceanography – and there in particular for the description of ocean currents – accurate measurements of the density of sea water are of great importance. For this purpose, measuring instruments are needed which reach an uncertainty of approx. 0.001 kg/m3 (relative 1 · 10–6).

To be able to calibrate these measuring instruments, ultra-pure water is required as a reference fluid – the density of which can now be measured with the required accuracy over a large temperature range by means of the Magnetic Flotation Method which has been further developed at PTB.

Normally, the hydrostatic weighing method is used for measuring the density of liquids. Thereby, the density of the liquid is determined by means of Archimedes' principle from the buoyancy which is experienced by a sinker that plunges into the fluid. This method has several disadvantages which become apparent especially when water is to be measured. For this method, an open fluid tank is required into which the sinker – hanging on a wire – plunges. At the point where the wire passes through the surface of the liquid into the water, a meniscus forms which, in the case of water, is extremely difficult to be reproduced and therefore contributes significantly to the measurement uncertainty. Along the wire, a temperature gradient occurs which, too, increases the measurement uncertainty. Due to the open system, the gas content of the water is difficult to control, but it alters the density.

In order to eliminate these sources of uncertainty, an apparatus has been developed in which the wire has been replaced by a magnetic coupling. In this magnetic flotation system, a small magnet is mounted at the holder of the sinker. By means of this magnet, and with the aid of a controllable magnetic field produced by an electromagnet, the sinker is kept in a fixed position. The current needed for this purpose is a measure for the buoyancy that is experienced by the sinker. The fluid tank can almost be shut as the liquid is linked with the outside world only via a thin pipe by means of which the pressure can be regulated. In this way, it is possible to measure also with fully degassed water.

Thanks to the fact that the above-mentioned sources of uncertainty are avoided, measurements can be carried out with a repeatability standard deviation of approx. 2 · 10–7. The total measurement uncertainty of the water density measurement therefore reaches a value below 1 · 10–6. The measurements carried out with this new apparatus could confirm to a large extent the values delivered by foreign colleagues. However, there are still discrepancies in the temperature range around 4 °C, which is of great importance especially in oceanography. Therefore, there is still a great need for further research in this field.

Erika Schow | alfa
Further information:
http://www.ptb.de

More articles from Physics and Astronomy:

nachricht New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>