Controllers and the Controlled

Controlling a variable means that a controller operates as part of a controlled system. What's controlled feeds back upon the controller but does not 'control' the controller. Feedback describes the moment-to-moment interaction between the controller and what's controlled. Feedback is continuous and changes over time as the system changes. Feedback filters through the controller's 'representation' of the interaction. Think of a fighter pilot watching the image of a laser bomb striking a target. The controller reads a composite image of its own actions superimposed upon an image of what's being controlled. The controller may even destroy what's controlled at the same instant as the system engenders a perception within the controller as when the pilot watches his bomb detonate on the cockpit screen.

To accomplish control, the controller changes some variables in the controlled system directly. At the same time, the controller senses the changes and feeds these back to what operates the controller. Each system's dynamics determine what the observed and controlled variables are. Uncontrollable disturbances may also influence the observed variables.

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