Torque wrench calibration and uncertainty of measurement

Abstract

Torque wrenches (TW) are widely used in the automotive, aviation and building industry. TW are used to control torque in assembly and fastening operations. Regular calibration of torque tools guarantees traceability to international standards. At KEBS, a torque wrench calibrator with four interchangeable torque transducers and torque meters are used to calibrate both type I and type II torque wrenches as per ISO 6789:2003. In compliance to “Guide for evaluation of uncertainty in measurement” (GUM), it is a requirement that a complete measurement result should include its uncertainty, a proposed method with an example on how to estimate measurement uncertainties for torque wrenches is presented after taking into account the various influencing quantities. Uncertainty values of ± 2.54 N•m, ±1.15 N•m, and ±1.33 N•m are estimated at 20%, 60% and 100% respectively of a type II class A torque wrench with a nominal value of 1000 N•m. The paper aims to provide guideline information for TW calibration and uncertainty evaluation.