A Controllers operates through a coordination of its thermal or pressure or displacement sensing system and its air signal relay system. The controller’s sensing bulb or pressure connection or Displacer, installed within the process application, senses change within the measured variable and relays this information (input signal) to the controller. The controller mechanically compares the signal against a predetermined set point and sends a corrective air signal to a pneumatic control valve, which modulates process flow, thereby returning the application to the desired condition.