Block diagrams serve as a visual representation of the input-output relationships within a system. An illustrative example is a heating system, where the set temperature activates the furnace to warm the room to the desired level. Block diagrams are versatile, modeling linear systems through Laplace transform variables and nonlinear systems using time domain variables.

A block diagram typically includes essential elements such as comparators, blocks, and feedback loops. Each of these elements is represented by specific equations. Comparators function as junction points where signals are compared, performing fundamental mathematical operations like addition and subtraction. This comparison is crucial in control systems for generating error signals that drive corrective actions.

Blocks within a block diagram represent the system's equations in the time domain or as transfer functions in the frequency domain. In control systems, these blocks symbolize various components such as plants, controllers, actuators, and sensors. In the previous example, a comparator would compare the set temperature to the measured temperature, and cycle the furnace on and off, as appropriate. In another example, a plant represents the main process or system being controlled, while a controller adjusts the input to the plant-based on feedback. Actuators convert control signals into physical actions, and sensors measure the output, providing feedback to the system.

In a feedback control system, the controlled variable is continually compared with the reference input to produce an error signal. This error signal activates an actuator, which works to minimize the error. The sensor in the system converts the physical output back into a signal that can be compared with the reference input. Feedback can be either positive or negative, affecting the system's stability and response.

Block diagrams can feature elements of feedback control systems arranged in series or parallel configurations. The overall transfer function of the system is determined by combining the individual transfer functions of the blocks. This process involves algebraic manipulation of the block equations to derive the system's behavior. Understanding the transfer function is crucial for analyzing the system's performance and stability, ensuring it meets the desired specifications.