Range expansion of the reference torque wrench calibration service to 5 kN m at NMIJ

The reference torque wrench (RTW) calibration service within the range from 5 N m to 1 kN m has been provided to industry by the National Metrology Institute of Japan (NMIJ) in the National Institute of Advanced Industrial Science and Technology (AIST). Reflecting the strong demand from Japanese industry, the calibration range was extended to 5 kN m. First, a high-precision torque transducer in the form of a torque wrench with a rated capacity of 5 kN m was developed in order to establish a calibration method for such a large RTW. Second, the calibration method was investigated using a deadweight type torque standard machine with a rated capacity of 20 kN m as a reference standard. Aimed expanded calibration range is from 200 N m to 5 kN m. As a result of calibration experiment using three transducers having different rated capacities, a relative expanded uncertainty of less than 7.0 × 10⁻⁵ could be obtained at a certain calibration point in the best case.