Mass comparator
A mass comparator is a very accurate, specialized scale that allows large masses to be compared accurately . They cannot be used outside the comparison range. The comparison area is relatively small.
Designs
The simplest and clearest design of a mass comparator is the double-shell beam balance .
Most of today's mass comparators are single-shell electronic scales and work with electromagnetic force compensation . The weight force generated by the masses in the earth's gravitational field is balanced (compensated) here by an oppositely directed electromagnetically generated force. The mass comparator often has a very limited measuring range which only shows the difference between the two weight forces (reference mass and comparison mass).
Application and accuracies
The most common application of mass comparators is the calibration of reference masses ( weights ). The national metrological institutes, such as the Physikalisch-Technische Bundesanstalt (PTB) in Germany, and calibration laboratories, based on a primary implementation of the unit kilogram, calibrate further reference masses to pass on the unit.
The relative standard deviation of such mass comparators is in the range <2 · 10 −9 . The best mass comparators of national metrological institutes (NMI) have relative standard deviations of 5 · 10 −12 .
literature
- Michael glasses: mass comparators. In: Michael glasses (ed.): Mass determination. John Wiley & Sons, 2008, ISBN 978-3-527-62494-2 , pp. 442-479. ( limited preview in Google Book search).
Individual evidence
Web links
- Mass comparators at PTB
- Mass metrology - precision is a question of the right equipment Brochure from Satorius AG on mass comparators (PDF file, 6.7 MB)
- Mass comparators Website of the Mettler-Toledo company