Abstract: There is disclosed a control system for use, for example, in facility management which controls an environmental parameter to maintain the parameter at a given set point. A PID Controller is coupled to a remote sensor for generating a feedback signal responsive to the parameter level sensed by the remote sensor. The PID Controller is responsive to being coupled to a field device for providing the field device with an automatic control signal having a level derived from the sum of integral, derivative, and proportional actions to the feedback or error signal to place the field device under automatic control, and is responsive to being decoupled from the field device when the field device is under manual control for either terminating the generation of the automatic control signal or providing an estimate of a manual control signal.