Recent renovations of dead-weight type force standard machines at NMIJ

• Calibration uncertainties have been improved by removing tare balancing mechanism.
• Extrapolation of calibration forces from kgf to N in 54 kN DWM has been eliminated.
• Capacity of the 54 kN DWM has been expanded to 100 kN.
• Weight actuation and rotation of force measuring instruments have been automated.

The older-generation dead-weight type force standard machines (DWMs) at the National Metrology Institute of Japan (NMIJ) were recently renovated with four aims: improving calibration uncertainty, enabling calibrations conforming to the latest standard, automating the calibration work, and reducing maintenance costs. Calibration uncertainties have been improved by removing eccentricity due to the incomplete tare balancing mechanism of the older 20 kN DWM and by eliminating extrapolation of calibration forces from kgf to N in the 54 kN DWM. Insufficient dead-weight division of the 54 kN DWM has been reformed to enable 8-step calibrations, along with expansion of its capacity to 100 kN. Working efficiency has been improved by automating dead-weight actuation and rotational position changes of force measuring instruments. Maintenance costs and labor have been reduced by electrifying the dead-weight actuation mechanism in the 54 kN DWM.