01-01-2013, 04:29 PM
Block Diagrams and Transfer Functions
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Introduction:
In recent years, control systems have gained an increasingly importance in the development and advancement of the modern civilization and technology. Figure 1-1 shows the basic components of a control system. Disregard the complexity of the system, it consists of an input (objective), the control system and its output (result). Practically our day-to-day activities are affected by some type of control systems. There are two main branches of control systems: 1) Open-loop systems and 2) Closed-loop systems.
Open-loop systems:
The open-loop system is also called the non-feedback system. This is the simpler of the two systems. A simple example is illustrated by the speed control of an automobile as shown in Figure 1-2. In this open-loop system, there is no way to ensure the actual speed is close to the desired speed automatically. The actual speed might be way off the desired speed because of the wind speed and/or road conditions, such as up hill or down hill etc.
Closed-loop systems:
The closed-loop system is also called the feedback system. A simple closed-system is shown in Figure 1-3. It has a mechanism to ensure the actual speed is close to the desired speed automatically.
Block Diagrams:
Because of their simplicity and versatility, block diagrams are often used by control engineers to describe all types of systems. A block diagram can be used simply to represent the composition and interconnection of a system. Also, it can be used, together with transfer functions, to represent the cause-and-effect relationships throughout the system. Transfer Function is defined as the relationship between an input signal and an output signal to a device.