The extended octagonal ring transducers are popular devices for force and moment measurements in agricultural engineering research due to its capability in measuring forces independently in two dimensions and resultant moment in one dimension. In this study design, construction and calibration of extended octagonal ring transducers are discussed. The transducers were designed to measure the two force components of the soil reaction with minimum cross-sensitivity. Strain distributions in the extended octagonal rings were analyzed using finite element method to locate optimal strain gauge positions to minimize cross-sensitivity between the two force components. A Data acquisition system consisted of a programmable DT800 data logger with 12 differential voltage and 16 frequency channels, and a PC for storing the data for further graphing and analysis. The system was tested for its sensitivity, cross-sensitivity, linearity and repeatability. The results of the calibration tests revealed that the system was well working for a range of draught and vertical forces up to 25 kN. The results showed a high degree of linearity between bridge output voltage and force applied. The minimum coefficient of determination, R2, was found to be 0.99. The interactions of the applied forces on the orthogonal force bridges were less than one percent. The system could best be used for the measurement of draught (horizontal) and vertical forces where medium size equipment is attached with a tractor.
