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Technische Universität Ilmenau and the Physikalisch-Technische Bundesanstalt (the National Metrology Institute of Germany) are developing a balance which is required for measuring the redefined kilogram that will be introduced in 2018. Called the Planck balance, this highly precise electronic weighing balance is not based on weights, but refers to the fundamental physical constant called Planck's constant. The balance will be used worldwide for calibrating other scales or balances so that they correspond to the system with this new method. The new balance will also be used in industry for measuring weights.
In many sectors, there is a significant demand for highly precise balances, including pharmaceutical companies for precise dosing of medical products, in official metrology service labs for calibrating scales for food, and in police departments, for the proof of toxic substances and in ballistics.
The original kilogram, a 4 cm cylinder made from platinum and iridium and stored under three glass domes in a safe near Paris since 1889, is becoming lighter. Over 100 years, it has lost 50 millionths of a gram. As all scales worldwide refer indirectly to this unique kilogram, they all weigh incorrectly, even if by minimal and negligible amounts. Although the original kilogram is becoming lighter, structurally identical copies of the prototype are used worldwide – which means that these copies are slowly becoming heavier relative to the prototype. Therefore, a new standard is required that does not change and cannot be damaged or lost.
In 2018, the new kilogram will be adopted at the 26th General Conference on Weights and Measures. It is not defined by an object or a physical mass, but by Planck's constant. The highly precise, continuously measuring Planck balance, developed by the German university Technische Universität Ilmenau, operates on the principle of electromagnetic force compensation. Simply put, a weight on one side is to be balanced by electrical force on the other. This electrical force is inextricably linked with the Planck's constant and can be directly referred to the new kilogram definition. As this balance is the first self-calibrating instrument of its kind, masses determined as reference or standard masses for calibrating scales and balances are no longer required. Another advantage of the Planck balance is its wide measuring range, from milligrams to one kilogram. At the end of the year, the first prototype of the balance will be available and ready for use.
At last, a balanced article.
(Score: 4, Insightful) by deadstick on Wednesday June 21 2017, @12:36PM (3 children)
How would that measure the mass of the sample? It seems to be measuring the weight and inferring the mass, using an assumed value for g.
If I'm reading it correctly, one "new" kilogram would have different masses at the North Pole and the Equator.
(Score: 1, Informative) by Anonymous Coward on Wednesday June 21 2017, @01:38PM (1 child)
By additionally measuring g at the very same place, and dividing the weight by the measured value of g. Note that you don't need to know the value of any mass to do that; the nice thing about movement in the Earth's gravitational field is that the masses of the moving objects all cancel out (well, as long as the mass of the object is small compared to the mass of the Earth, which should be a given for all conceivable experiments).
Correct, so far.
Wrong. There's no reason to assume a value of g when you can measure it.
(Score: 2) by darkfeline on Thursday June 22 2017, @03:30AM
How do you measure g without first having something of known mass (presumably, you would need to know g to measure the precise mass of said object)?
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(Score: 2) by Soylentbob on Wednesday June 21 2017, @02:21PM
Not sure. If they don't have any better idea, I'd assume instead of supporting the mass, the currents in the coils could be used to accelerate the mass. (Actually this is the same; supporting it against g means applying a force to it / applying an acceleration in the opposite direction. Once you have a current I1 which works to hold M in place, you add another current I2 and measure the additional acceleration generated by I2. From a2 and I2 you could infer the mass of the object.)