Confirmation of calibration capability of low-nominal capacity reference torque wrenches at NMIJ

Abstract

The calibration procedure for a reference torque wrench (RTW), which is a torque transducer in the form of a torque wrench, is based on the JMIF-016 (TTSG-W102) technical guideline in Japan. The mounting position of an RTW is set to three directions (0°, 120°, and 240°; case 1) when it is calibrated using dead weight torque standard machines (DWTSMs) with rated capacities of 1 kN·m (1-kN·m-DWTSM) and 20 kN·m (20-kN·m-DWTSM). However, the mounting position is set to three different directions (0°, 90° and 270°; case 2) when the 10-N·m-DWTSM is used. In this study, the effect of the difference of the RTW mounting position on the calibration results was investigated. Next, to confirm the equivalence of the RTW calibration capabilities of the 10-N·m- and 1-kN·m-DWTSMs, they were compared using two low-nominal capacity RTWs. The results obtained in cases 1 and 2 showed good agreement within the uncertainties. The recommended RTW calibration procedure is based on case 1. But, if an RTW cannot be mounted in the 120° and 240° directions because of the space problem, case 2 can be adopted as the RTW calibration procedure. The RTW calibration capability of the 10-N·m-DWTSM was found to be equivalent to that of the 1-kN·m-DWTSM in the range of 5 N·m to 10 N·m.