Abstract: A signal processing unit for use in process automation technology for mounting on a top-hat rail, comprising a housing for accommodating a plurality of plug-in cards, for example CPU card, I/O cards, power supply card, which can be connected with a display unit including a frame with a display, keyboard and circuit board, to form a control panel-mountable module. The signal processing unit is created by substituting an adaptation module for the display unit. The adaptation module is connected with the housing and serves for fastening to a top-hat rail. The adaptation module has a circuit board which is configured analogously to the circuit board of the display unit. Thus, the adaptation module allows for the conversion of a panel-mountable module to a top-hat rail module.