Operating Principles of the NIST 4 Watt Balance Source

The video tutorial explains the concept of balancing forces, comparing gravitational and electromagnetic methods. It introduces the Watt balance, a device that measures mass indirectly by determining the strength of a magnetic field and the current through a coil. The Watt balance operates in two modes: velocity mode, which measures field strength, and weighing mode, which balances the weight of a test mass using electromagnetic force. NIST's design uses a wheel instead of a balance beam, with laser sensors and interferometry ensuring precise measurements.

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