Orbach, A., "Electro-Hydraulic Draft Control (EDC) System Description for a Variety of Tractors," SAE Technical Paper 941764, 1994, doi:10.4271/941764.
A controller for a three point hitch is described. It includes five separate states which govern the operation and performance of the hitch. The control objective in each state is explained in detail. The actual transitions between the states, which are controlled based on external events, are given via a transition table and some examples. Such transitions are triggered by both; the operator and, in certain circumstances, by the conditions of the soil, tractor speed, etc. The controller is designed to allow adapting it to various tractors under different types of loading conditions, hydraulic cylinder volumes, and options available on the tractor.Controller operation is also adjusted based on battery voltage as well as the electro-hydraulic valve coil resistance. Failures, which are being continuously searched for, are divided into four categories which manipulate and modify the performance of the hitch.Finally, the draft state is explained in detail and examples of hitch operations with different implements are described. Field results are mapped and analyzed in the position/load domain.