The SideCONTROL Positioner Type 8635 is an electropneumatic positioner for pneumatically actuated process valves with linear or part-turn actuators. It is excuted in two conductor technology. Signal processing, control and actuation of the internal positioning system are accomplished with microprocessor controlled electronics. The software function Autotune implemented therein enables automatic adaptation of the positioner to the control valve in use. The positioner is parametrized and operated comfortably via three operating keys and a plain-text display. It is possible to set up a decentralized control system if a process controller with PID characteristics is used. As an option, the SideCONTROL Positioner Type 8635 can be supplied with approval for use in the Ex area (Zone 1) according to ATEX. Because of its compact and robust design, the housing is suitable for use in chemical and process engineering.