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

Its mass for the masses.

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 prototypes 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.

Traditional balances work by comparing the weights of masses in two different pans. But a Kibble balance compares a mass to the electromagnetic force needed to hold up that mass. Certain electromagnetic quantities, like voltage and resistance, can be tied back to quantum measurements involving the Planck constant, connecting that quantity to the objecRead More – Source
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