ANOMALIES IN THE NORMAL FORCE MEASUREMENT WHEN USING A FORCE REBALANCE TRANSDUCER

Torque and normal force measurements in torsional experiments provide a powerful technique for the efficient measurement of material propert ies. Over the past several decades NIST has been active in pioneering the use of such measurements for the characterization of polymer mater ial behaviors, particularly in transient experiments. In a recent seri es of tests using a force rebalance transducer, anomalies in normal fo rce measurements were observed. It was determined that the active natu re of the transducer, which leads to excellent zero stability, causes thermal heating and consequent expansion of the system. The transducer length changes are shown to be the cause of the normal force anomalie s and, in collaboration with the equipment manufacturer, suggestions f or working around the problem and potential transducer redesign are di scussed. (C) 1996 Society of Rheology.