Effect of strain gage misalignment on cross sensitivity of extended ring (ER) transducers

Abstract

The extended octagonal ring (EOR) and plain extended ring (ER) transducers are popular devices for multi-dimensional force and moment measurement in agricultural engineering research. Independent measurements of forces and moments are accomplished by strain gages strategically located in ring sections at either end of the devices. Much effort has been devoted to determining the optimal location of strain gages to minimize cross sensitivity. This paper presents a theoretical analysis using analytical equations derived for the plain extended ring transducer to determine the effect of strain gage misalignment on cross sensitivity. The analysis showed that a tangential misalignment of one degree for one strain gage in a four arm bridge would result in a cross sensitivity of approximately 0.004 N N-1 for the horizontal strain gage bridge to vertical loading, and 0.012 N N-1 for the vertical bridge to horizontal loading. Angular misalignment had little effect when the strain gages were located at the secondary strain nodes, but had a large effect when strain gages were located in regions of high strain resulting from secondary loading. Cross sensitivity was relatively independent of nominal angular location of the strain gage bridge except for a discontinuity near the primary strain nodes. The analysis demonstrates the importance of careful alignment of strain gages on extended ring transducers to minimize cross sensitivity.