This tabletop device turns the quantum definition of a kilogram into a real mass

WEIGH IN Small enough to fit on a table, this mini Kibble balance measures smaller units of mass, such as a few grams, to an accuracy of a few ten-thousandths of a percent. A Lego figurine (top right) holds a 1-gram mass for scale. Leon Chao/NIST
The mini Kibble balance will measure 10 grams to a few ten-thousandths of a percent accuracy

By Emily Conover | ScienceNews

A tabletop device makes the new definition of the kilogram more accessible. Previously, the kilogram had been equal to the mass of a special metal cylinder kept in a vault near Paris. But researchers did away with that standard on May 20, pegging the kilogram instead to a quantum mechanical number known as the Planck constant (SN Online: 5/20/19).

Using that new definition, scientists at the National Institute of Standards and Technology in Gaithersburg, Md., created a scaled-down version of a device called a Kibble balance to directly measure masses of several grams via the Planck constant. When the prototype’s kinks are worked out, the apparatus should be accurate to a few ten-thousandths of a percent, researchers report in the June IEEE Transactions on Instrumentation and Measurement.

A full-scale Kibble balance requires its own laboratory space, costs millions of dollars to build and demands Ph.D.s to run it. But the new, suitcase-sized Kibble balance is just over half a meter tall, with a price tag around $50,000. That puts it within reach for pharmaceutical companies, for example, which must accurately dole out small drug dosages.

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