In this example, one application of the observer is to use the observed plant state (CO) to close the control loop, as shown in the diagram. The sensor output Y is no longer used to close the loop.

Industrial control systems can be categorized in two types: open-loop and closed-loop systems. The open-loop control system is a continuous control system that provides no feedback from its output.

Fig. 5 is a simple block diagram of the desired system. An example of a closed-loop system is the use of a thermistor for temperature feedback, with results shown in Fig. 6 .