A New Frame-Based Calibration Method for Extended Octagonal Ring Transducers

Abstract

HighlightsA simple frame was built to hold and apply uniaxial and biaxial loads to octagonal ring transducers for calibration.Similar results were obtained with the frame as with a universal tensile testing machine.The transducer outputs exhibited low cross-sensitivities and hysteresis (=0.4%), and R2 = 0.9998.The frame is portable and safe, and its concept can be adapted to take a wide range of non-gravitational loads.Abstract. An extended octagonal ring transducer (EORT) is a simple, single, and compact biaxial force measuring transducer, which is ideal for soil force measurement in tillage tool research. Calibration of EORTs is needed to ascertain their sensitivities and to determine an accurate calibration equation to convert voltage output to force measurement. Typically, calibration of EORTs involves the use of universal tensile testing machines, hydraulic systems and large gravitational loads (hanging weights) to apply loads. In this study, a simple calibration frame that enables application of non-gravitational loads was evaluated and used to hold and calibrate an EORT through both uniaxial and biaxial loading. The frame was suitable for both uniaxial and biaxial application of offset coincident force up to 3000 N and centered perpendicular force up to 1500 N. The EORT exhibited a strong linear relationship (R2 = 0.9998) between applied forces and voltage outputs, low hysteresis errors (=0.4%), and low cross-sensitivities (3.61% and 1.6% for coincident and perpendicular forces, respectively). Calibration equations developed from the primary bridge output data or from the biaxial loading data using the frame produced good force predictions, which also improved when taking into account the impacts of cross-sensitivity. The results confirmed that this calibration approach can integrate the interactions of output cross-sensitivity to deliver more accurate force prediction. Coefficients of determination of the relationships between applied and predicted forces were 0.9993 to 0.9996 and 0.9877 to 0.9984 for coincident and perpendicular forces, respectively. This calibration frame presents potential for safely applying large, non-gravitational loads in a contained and portable manner and its concept can easily be adapted to suit the scale of the transducer. Keywords: Biaxial loading, Cross-sensitivity, EORT calibration, Offset coincident force, Uniaxial loading.