I am wondering about different categorizations of control loops. One categorization differentiates control loops with respect to what inputs they take:
- Open control loops.
- Closed control loops.
1a. Open control loops without external inputs.
1b. Open control loops with external inputs, also known as feedforward.
An example of 1a would be a temperature controller that simply switches on and off based on a timer. It has no actual knowledge of the conditions of the process it affects, but it's set-point (duration of on- and off-time) would ideally be based on some model of the process it affects.
An example of 1b would be the same temperature controller, only in this scheme, it also takes into account the opening and closing of the entrance door. Perhaps the on-time is increased as some function of how long the entrance door was open.
An example of 2 would be a thermostat taking into account the temperature of the room it affects.
Are there more categories within this categorization? Are there other categorizations? For example, in what categorization would cascade control be a distinct category?