Evaluation of a dead weight torque machine by a generalized least square approach

Calibration of primary dead weight torque machines (DWTMs) is mainly a National Metrology Institutes (Is) task. However, traceability is obtained via dimensional and mass quantities and several secondary's laboratories have sufficient Best Measurement Capabilities (BMCs) to achieve acceptable uncertainty levels. This paper describes a method that combine length and mass measurements in a Generalized Least Squares (GLS) approach that avoid the evaluation of complex uncertainty contributions. The method was implemented on in-house developed DWTMs; the sensitivity limit is first examined for each momentum arm length. Several dimensional measurements were made with an Articulated Arm Coordinate Measuring Machine (AACMM). A set of mass measurements from different equilibrium combination were taken and all information was introduced in the GLS with the advantage of the consistency check via chi square test. Regardless of the uncertainties levels of case treated, this method can be applicable to any DWTM.