RT - Journal Article T1 - Development and Evaluation of a Three-Point Hitch Dynamometer and a Fifth Wheel for Mounted Implement Draft and Tractor Speed Measurements JF - JCPP YR - 2007 JO - JCPP VO - 11 IS - 1 UR - http://jcpp.iut.ac.ir/article-1-653-en.html SP - 147 EP - 163 K1 - Three-point hitch dynamometer K1 - Fifth wheel K1 - Draft K1 - Ground speed K1 - Mounted implement K1 - Drawbar power. AB - For measuring draft force and drawbar power requirements for mounted implements, precise instruments such as three-point hitch dynamometers and tractor speed measurement devices are needed. In this research, a frame-type three-point hitch dynamometer was built and evaluated. Forces applied to dynamometer are measured by three separate load cells located on a frame which can be attached to tractor’s three-point hitch. Each dynamometer’s load cell measures load using a strain gauge bridge circuit. Each load cell was calibrated by applying a known load and measuring bridge circuit’s output voltage. Dynamometer was calibrated by the application of known forces and measuring the output voltage of the strain gauge bridges. The calibration showed a high degree of linearity between the applied forces and the bridge outputs (R2 = 0.996). The hysteresis effect between loading and unloading as well as the effect of the position of the applied forces from the longitudinal axis of the dynamometer was small. For measuring actual tractor speed, a fifth wheel equipped with an encoder shaft was designed and built. The calibration on tarmac and soil surfaces showed a highly linear relation between measured forward speed and output of encoder’s rotation (R2 =0.994). The errors in speed measurements at low speed in field and at high speed (up to 12.5 km/h) on tarmac surface were approximately 3 and 8%, respectively. The data acquisition system, not only could display the instantaneous force and speed, it could also show force-time and force-distance curves on the system’s monitor. LA eng UL http://jcpp.iut.ac.ir/article-1-653-en.html M3 ER -