Abstract: The electro-hydraulic proportion valve is used in the novel hoist for well logging to regulate the angular speed of the roller. The rolling radius is changing during well logging, and the line speed is also changing continuously. In order to keep the line speed constant , the angular speed should be regulated manually which is a heavy work, and also the output consistency is not satisfactory. Analyzing the characteristic of the hoist, a kind of digital controller of constant speed is designed using Dahlin arithmetic ,the model and formulas are presented. The stability of line speed in the designed digital control system keeps in good accord with the requirements of local well logging, the workload is decreased also, and it is a good application with higher quality and lower cost.

Key words: Digital control, Electro- hydaraulic proportion, Hoist, Speed