Evaluation of actual sensitivity limit in a 10 N·m dead weight torque standard machine and stability of a new 1 N·m torque transducer

A 10 N·m dead weight torque standard machine (10-N·m-DWTSM) has been under development at NMIJ/AIST since 2006 to expand the range of the torque standard. Estimation of the sensitivity limit of the fulcrum is one of the most important issues to realize a precise reference torque of small capacity by using a dead weight torque standard machine. In this study, a torque transducer was installed on the 10-N·m-DWTSM in order to keep the moment-arm on the horizontal line (balancing). The sensitivity limit of the fulcrum under real calibration conditions was estimated by reading the change in the output from the torque measuring device (TMD: the torque transducer with a cable and an indicating device) when small weights were loaded or unloaded. The small weights used in the experiment were 0.5 mg, 1 mg, 10 mg, and 100 mg. Equivalent radial loads from 0.1 N·m to 10 N·m were imposed on the fulcrum during the sensitivity measurement.As a result, the sensitivity limit of the fulcrum was confirmed to be sufficient to load at least 0.5 mg. A relative sensitivity limit of the fulcrum of 2.5 × 10−5 and relative reproducibility of the sensitivity limit of the fulcrum of 1.7 × 10−6 could be obtained within the calibration range from 0.1 N·m to 10 N·m.It is also important to develop small-rated-capacity torque transducers that can be used as a transfer standard. Therefore, a transducer with a rated capacity of 1 N·m was developed in parallel with the development of the 10-N·m-DWTSM. The stability of the 1 N·m TMD has been evaluated over a period of 1 year.

► The sensitivity limit under real calibration conditions was investigated. ► The relative sensitivity limit of the fulcrum was 2.5 × 10−5. ► The calibration range of the 10-N·m-DWTSM was expanded down to 0.1 N·m. ► The stability of the 1 N·m transducer has been evaluated over a period of one year. ► The relative deviation of the last half year was less than 7.6 × 10−5.