P1.9 - A Guide for Choosing the Right Calibration for Torque Transducers

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings SENSOR 2009, Volume II
P1 - Mechanical Sensors
G. Wegener, L. Stenner - Hottinger Baldwin Messtechnik GmbH, Darmstadt, Germany
265 - 270


Torque transducers (e.g. torque shafts, torque flanges) have become increasingly important during the last decades. Measuring torque is crucial for testing the performance of a wide range of rotating machinery. Some important examples are engine and transmission test stands in the automotive industry, testing of pumps or electric motors and many other mechanisms like steering gear. Another field of torque measurement is in torque tools used in assembly, from simple torque wrenches to rotary assembly tools (either electric or pneumatic). However the latter will not be covered by the present paper.
Basically, torque transducers like any other test and measurement equipment used in industry needs to be calibrated regularly. Traceable calibration for all testing equipment is a requirement of every serious quality management system. It is essential for meeting any standard of the ISO 9000 family. In some branches of industry, the requirements for a traceable calibration are even stricter. An example is ISO/TS 16949 used by the European and American automotive industry.
But even though undoubtedly in many cases a calibration is required, it remains open, which kind of calibration to choose in view of the variety of different types of calibrations for torque transducers. The most obvious criterion is the difference between accredited calibration and what is called a working standard calibration. In Germany accreditation for calibration laboratories is done by the DKD (“Deutscher Kalibrierdienst” = German Calibration Service). Similar institutions exist in all major industrial countries, e.g. COFRAC in France, UKAS in the United Kingdom and SIT in Italy.
The difference between an accredited and a working standard calibration is primarily a formal one, but there are also big technical differences. Usually, the calibration procedures (loading sequences) and the evaluation procedures are much more elaborate in the case of accredited calibrations. But the high metrological quality is also expensive. Therefore it is the aim of this contribution to define criteria which help users in their decision for a specific type of torque calibration. It will also show that a compromise which is quite attractive for many fields of application exists.