Adjusting method and apparatus for automatic power adjustment of a movable barrier

A moving barrier operator includes a motor controller (10) and a motor (11) that control the selective movement of a movable barrier (12), and further includes an obstacle detector (14) which uses an automatically determined Uberkraftschwellwert to provide a reliable detection of a to allow obstacle in a wide range of operating conditions, including changing physical circumstances, aging components, temperature changes and engine running time. In a preferred embodiment, a characteristic value for the power system is frequently updated as a function of actual measured force requirements (and further compensated in accordance with various embodiments with respect to other conditions, such as temperature and engine running time). This characteristic force value is then used to determine a Uberkraftschwellwertes.