Design of the KRISS watt balance

We report the design of the KRISS watt balance, which includes a magnet, a guiding stage and a coil position measurement system. The KRISS watt balance incorporates a closed-type cylindrical permanent magnet and a motion guiding stage. For the magnet, a flux shunt is used to reduce flux changes due to temperature variations. A piston gauge is used to achieve linearity in the motion guiding stage. In the weighing mode, the residual force between the weight of the test mass and the Lorentz force generated in a coil is measured by a commercial weighing cell. In the dynamic mode, a linear motor in the motion guiding stage vertically translates the coil and the weighing cell. The in-plane motion of the coil is measured by position sensors, and the out-of-plane motion is measured by single-pass homodyne interferometers.