This Weird Machine Could Be the Most Accurate Measuring System Ever

Known as a Kibble balance, it can nail down a weight to several ten thousandths of a percent.

NIST kibble balance
J. L. Lee / NIST

Now that the kilogram is disassociated from its physical form, it can be measured anywhere. At least that's the theory behind a prototype of a device called a Kibble, built by scientists at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. It's been hypothesized for decades, but now it's close to reality.

They've reported on the device, called a Kibble, in detail in the June IEEE Transactions on Instrumentation and Measurement.

Outside of the U.S., England, and the handful of countries that use imperial measurements like feet and miles, the vast majority of the planet uses the International System of Units (SI) to measure things. Commonly referred to as the metric system, this system has for centuries used physical guides as to what exactly, say, a kilogram was.

But last month on World Metrology Day, everything changed. The physical standard was removed, replaced by Planck's constant.

"Upon fixing the Planck constant, mass can be directly realized at any level, deeming the kilogram only a historically unique benchmark," says lead author Leon Chao and his team at NIST in their paper's abstract.

The Kibble is the result of switching over to Planck's constant. Named after Bryan Kibble of the U.K.’s National Physical Laboratory (NPL), who conceptualized the device in 1975, a Kibble is an extremely accurate weighing machine. According to NIST, within a Kibble "the weight of a test mass is exactly offset by a force produced when an electrical current is run through a coil of wire immersed in a surrounding magnetic field."

Originally known as a "watt balance," a Kibble measures both current and voltage in the coil, the result of which is expressed in watts, the SI unit of power. That result is equivalent to the mechanical power of the mass being measured. Essentially, it links the mass being measured back to electromagnetic quantities through Planck's constant.

NIST, which is part of the Department of Commerce, has been developing Kibble balances since the 1980s. In fact, a couple of years ago, the team made one out of LEGOs.

mini nist kibble balance
The mini Kibble balance, also known as KIBB-g1.
Chao, et al. / NIST

But now that Planck's constant has become the universal constant for determining a kilogram, it has newfound value. While full-size Kibble balances can take up entire rooms, the new, smaller version is around 1.6 feet (0.5 meters) tall and will cost a cool $50,000. While that's a long way from having one on every desk, it's well within the budget for industries where extremely accurate measurements matter, like pharmaceuticals or complex machinery.

Chao says that the LEGO experience “subconsciously planted a seed" to create the miniature Kibble balance, known as KIBB-g1. It's still in a prototyping phase, with a focus on getting repeatable results.

But it's still a pretty incredible accomplishment. The metric system has its roots in the French Revolution, a response to how measurements differed from town to town, creating an ecosystem in which it was easy to get ripped off when measuring produce. Now, the most accurate system ever known could soon fit on a person's desk.

Source: ScienceNews

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