1.3 Types of control system Control systems are classified in terms that described either the system itself or its variables These descriptive terms are mainly of the either-or form 1 An open-loop system is shown in Fig1-1-la and is characterized by the input entering directly into the control elements unaffected by the output the output is related to the input solely by the characteristics of the plant and control elements. In the closed-loop system of Fig 1-1 2b, however the input is modified by the actual output before entering the control elements 2022-2-3 92022-2-3 9 1.3 Types of control system Control systems are classified in terms that described either the system itself or its variables. These descriptive terms are mainly of the either-or form. 1 An open-loop system is shown in Fig1-1-1a and is characterized by the input entering directly into the control elements unaffected by the output ;the output is related to the input solely by the characteristics of the plant and control elements .In the closed-loop system of Fig.1-1- 2b,however the input is modified by the actual output before entering the control elements