Accounting for Factors that Influence a System (System Identification Toolkit)

The key to the system identification process is having some knowledge of the system for which you want to identify a model. This knowledge provides the basis for determining which signals are outputs, which in turn determines sensor placement, and which signals are inputs that you can use to excite the system. Simple tests might be necessary to determine influences, coupling, time delays, and time constants to aid in the modeling effort.

You also must consider signals that are not directly capable of being manipulated but still affect the system. You must include those signals as inputs to the system model. For example, consider the effect of wind gusts on the pitch dynamics of an airplane. The airplane responds in pitch to the elevator angle as a direct input. A wind gust affects the pitch of an airplane, which in turn influences the dynamics of the airplane, but the wind gust is not directly adjustable. To create an accurate model of the airplane, you might want to include wind gusts as an input variable.