Effect of load fixture design on sensitivity of an extended octagonal ring (EOR) transducer.

Abstract

Identical loading and support fixtures were fabricated to apply vertical compressive loads at two points with varying spacing on the faces of an Extended Octagonal Ring (EOR) transducer. A calibration apparatus employing an air cylinder fitted with a strain gage load cell was assembled to apply and measure vertical load on the EOR. Calibrations were performed to determine the effect of spacing between the two loading points on EOR sensitivity. At moderate load point spacings, a small decrease in EOR sensitivity was noted with increasing load point spacing. The EOR sensitivity rapidly decreased as the load points approached the ring sections, with approximately 40% reduction in sensitivity when the load points were near the sloped outer surface of the ring sections. Effect of non-flat loading and support fixtures was evaluated by calibrating the EOR with different torques applied to the mounting bolts and with varying load point spacings. Tension in the mounting bolts created an initial bending moment in the EOR at zero applied load. Bolt torque had little effect on EOR sensitivity at small load point spacings, but high bolt torque decreased the EOR sensitivity at large load point spacings. When the loading points were over the ring sections, the changing the bolt torque from zero to maximum changed the EOR offset (zero load signal) by an amount approximately equal to the EOR design capacity. These results demonstrate the importance of careful attention design of the load and support fixtures and calibration procedures for an EOR to achieve optimum performance.