Name Definition An element of the control system responsible for

A system can be broadly defined as an converting control signals from the controller into
interconnected set of elements or components that physical action that affects the plant. Actuators
work together to achieve a common objective. provide the necessary motive power or mechanical
These components may include physical devices, movement to change the plant's state. Examples
ACTUATOR
What is a System? processes, information flows, and human include: Valves that regulate fluid flow, Motors
operators, all functioning cohesively to produce a that drive mechanical operations, Hydraulic and
desired output. Systems are designed to efficiently pneumatic devices used in industrial machinery.
transform inputs into outputs, following specific The actuator forms the link between the control
rules and conditions that define their behavior. signals and the physical operation of the plant.
A Control System is a framework or mechanism A device that measures the output or state of the
designed to command, regulate, or direct the plant and converts it into a signal that can be
behavior of other systems or processes to achieve interpreted by the controller. Sensors provide
a specific desired outcome. It continuously essential feedback about the plant’s performance
What is a Control monitors inputs, compares them to desired to ensure the system can make corrections as
System? setpoints or reference values, and makes SENSOR needed. Examples of sensors include:
adjustments to maintain the desired output. These Thermometers for temperature measurement,
adjustments help ensure stable, efficient, and Pressure sensors for fluid or gas systems, Encoders
accurate system operation under varying for measuring angular position in robotics. By
conditions. continuously monitoring key variables, sensors
The part of a control system that is being managed help maintain system accuracy and stability.
or controlled. It typically represents the primary Often referred to as the "brain" of the control
system or process whose behavior must be system, the controller manages the relationship
regulated to achieve a desired outcome. The plant between the input (reference) and output by
PLANT
can be any physical entity such as an industrial comparing the current output to the desired
CONTROLLER
machine, an electrical motor, or a heating system. setpoint. The controller generates appropriate
For example, in a temperature control system, the control signals to actuators to correct errors and
plant might be a furnace that heats a space. maintain stable performance. Controllers can
range from simple analog circuits to sophisticated
 digital systems, including: Proportional-Integral- that push the system away from its desired
Derivative (PID) controllers, Programmable Logic operating point.
Controllers (PLC), Microcontrollers and The technology and methodology used to operate
computers. The controller is responsible for a system or process automatically with minimal or
decision-making and system optimization. Automation no human intervention. Automation improves
The reference is the desired level of fluid that the system efficiency, consistency, and productivity
Example 1: Manual operator is instructed to maintain. The actuator is while reducing operational errors.
control system for the valve that opens or closes the fluid flow out. The process of conceptualizing, planning, and
regulating the level of
The sensor is the visual of the operator. The detailing the components and operation of a
the fluid in a tank.
controller is the operator. Design control system to meet defined objectives and
The reference is the position of the iron ball. The specifications. Effective design considers system
Example 2: Magnetic actuator is the electromagnet. The sensor is the gap performance, stability, and robustness.
Levitation. sensor. The controller is the program in the A detailed set of requirements that define what a
computer. system, component, or product is expected to be
The signal or excitation applied to a control system Specifications and do. Specifications often include performance
to drive its behavior or achieve a desired criteria, operational limits, and physical
Input operational state. Inputs can represent physical constraints.
quantities such as voltage, force, or setpoints for A virtual representation or model of a control
process control. system used to study, analyze, and predict system
Simulation
The response or result produced by a control behavior under different operating conditions by
system after processing the input. The output applying actual or simulated input signals.
Output reflects the system's behavior and can represent The process of fine-tuning control system
values such as position, speed, or temperature in parameters to achieve the best possible
Optimization
real-world applications. performance, typically balancing factors such as
Unwanted external or internal signals that cost, efficiency, stability, and accuracy.
negatively impact the performance or stability of a Graphical representations of control systems that
Disturbances
control system. Disturbances can be Block Diagrams illustrate the relationships between system
environmental factors, noise, or load variations components using unidirectional blocks. These
 blocks represent system elements and their transfer response to a bounded input. A system is
functions, making it easier to understand system considered unstable if its output grows without
structure and behavior. limit or behaves erratically.
A graphical tool used to represent and analyze the Multivariable Control A control system with more than one input or
relationships among variables in a system. It System output variable that requires simultaneous
Signal Flow Graph
consists of nodes connected by directed branches regulation. These systems often involve complex
(SFG)
and is particularly useful for visualizing complex interactions between multiple variables.
system dynamics. Trade-off The process of making compromises between
A measurement of the output of a system that is conflicting design criteria, such as balancing
sent back to the controller to adjust and correct the speed, accuracy, cost, and system complexity to
Feedback Signal
system’s performance, maintaining the desired achieve optimal performance.
output.
A feedback mechanism where the output signal is
fed back in such a way that it reduces or subtracts A type of control system where the output is not fed back
Negative Feedback into the system for monitoring or correction. This means
from the input signal. This helps improve system
the system operates based on a predefined set of
stability and reduce errors.
instructions without making adjustments based on the
A type of control system designed to maintain Open Loop System
actual output produced. Open loop systems are also
specific output values at fixed or nearly constant known as non-feedback systems because there is no
Regulator levels despite the presence of disturbances. mechanism to compare the actual output with the desired
Examples include voltage regulators and output.
temperature controllers. 1. No Feedback Mechanism: The system operates
A control system designed to manage mechanical without receiving any feedback from the output.
outputs such as position, velocity, or acceleration Key 2. Output is Not Monitored or Corrected: Since
Characteristics of feedback isn't provided, the output is not checked in real-
Servo System with high precision. Servo systems are commonly
Open Loop time.
used in robotics, aerospace, and manufacturing Systems 3. Predefined Operations: Open loop systems perform
applications. tasks based on a pre-programmed sequence of operations,
Stability The property of a control system that describes its often requiring no real-time adjustments.
ability to produce a bounded and predictable Examples of Open 1. Electric Fans: Run at constant or preset speeds
Loop Systems without adjusting for room conditions.
 2. Washing Machines: Fixed cycles that do not adjust
based on load. 3. Microwave Ovens: Heat food for a
fixed time regardless of its actual temperature.
A control system where the output is continuously
monitored and compared to the desired setpoint
Closed Loop
(reference). Feedback is used to make adjustments in real-
System
time, allowing for corrections to errors or disturbances
that might affect the output.
1. Feedback Mechanism: The output is constantly
Key measured and compared to the desired value.
Characteristics of 2. Output Correction: The controller adjusts the input to
Closed Loop minimize the error.
Systems 3. Real-time Monitoring:Sensors monitor and adjust the
system dynamically.
1. Automobile Steering Control: The driver
continuously adjusts the steering based on road position
feedback.
Examples of
2. Missile Launcher Control: Feedback adjusts the
Closed Loop
position dynamically to match the input.
Systems
3. Human Body Temperature Regulation: The
hypothalamus controls sweating and shivering based on
temperature feedback.
 Name Definition Produces fast and aggressive responses in mechanical
Quick Response systems. Example: In pneumatic systems, positive
Occurs when the output of a system amplifies or
and Actuation
reinforces the input or initial disturbance. In a positive feedback can quickly trigger action.
feedback loop, an increase in output leads to a further Employed to create oscillations or generate pulses in
Positive Feedback Switching and
increase in the system’s input, which can result in systems like clocks and timers. Example: Oscillators in
Oscillation
exponential growth or runaway behavior until an external electronics use positive feedback to cycle the output.
force intervenes. DISADVANTAGES
The key characteristic of positive feedback where the Instability and Can lead to uncontrollable behavior if not designed with
effect or output is amplified. Each iteration of feedback Risk of Runaway limits or safeguards. Example: In a motor, excessive
Amplification increases the system's deviation from the original Behavior positive feedback could result in spinning out of control.
setpoint. Example: In certain electronic circuits, positive Can drive components beyond their safe operating limits.
feedback is used to amplify signals. Potential for
Example: In power amplifiers, positive feedback can
Damage
Positive feedback can lead to instability if not carefully cause components to burn out.
controlled. If left unchecked, the system can run away or Systems relying on positive feedback can be difficult to
Instability oscillate, potentially damaging components. Example: A Difficulty in stabilize. Example: Mechanical control systems may
Control
mechanical system might experience runaway motion require damping or limiters.
due to positive feedback. APPLICATIONS
Positive feedback can result in exponential growth, Used in electronic circuits to amplify electrical signals.
where the system’s output increases at an accelerating Regenerative Example: In radio transmitters, positive feedback
Exponential
Amplifiers
Growth rate. Example: A small initial signal can be amplified increases signal strength.
repeatedly until it reaches a saturation point. Generates periodic waveforms in circuits. Example: A
ADVANTAGES Oscillators sine wave oscillator in a signal generator uses positive
Used in systems that require amplification or feedback to continuously produce a wave.
Signal enhancement of signals. Example: In audio amplifiers, Converts noisy or analog input signals into clean digital
Amplification positive feedback increases the amplitude of the input Schmitt Trigger output. Example: Used in digital circuits for reliable
signal. logic level interpretation.
 Uses positive feedback to switch between two stable Example: In a temperature control system for ovens,
Bistable Systems states. Example: Flip-flops store binary information in negative feedback keeps the temperature
(Flip-Flops)
memory chips. steady by adjusting the heating element whenever the
Used in mechanical engineering to "latch" a switch in measured temperature diverges from the
Relay Systems one position. Example: In pneumatic systems, a relay set point
maintains pressure in a tank. The system becomes more stable because negative
Occurs when the output of a system is used to reduce or feedback counteracts changes, preventing
Negative counteract the input. It helps maintain stability and rapid fluctuations and runaway behavior.
Feedback Enhanced
control by opposing the changes that occur. ○ Example: In electronic amplifiers, negative feedback
Stability
If the output moves away from the setpoint, negative prevents distortion and ensures the output is
How Negative stable by reducing the effects of non-linearities and
feedback corrects it by reducing the input or modifying
Feedback Works
system behavior. noise.
CHARACTERISTICS Negative feedback makes the system less sensitive to
Negative feedback continuously monitors the system's external disturbances or variations in
Error Correction: output and adjusts the input to minimize any Reduced system components, leading to consistent performance.
discrepancies from the setpoint. Sensitivity to ○ Example: In a robotic arm, negative feedback is used
Negative feedback works to stabilize systems by Disturbances to adjust motor speeds based on the arm’s
reducing the effect of any disturbances or fluctuations. position, compensating for any disturbances that may
Stabilization: affect its movement.
It helps to keep the system operating smoothly and
reliably, even in changing conditions. DISADVANTAGES
Negative feedback ensures that the system remains close ○ While negative feedback improves stability, it can
Maintaining reduce the system’s gain or amplification, which might
to equilibrium by counteracting deviations in
Equilibrium
the output, keeping the system balanced.. not be desirable in some applications where high gain is
Reduced Gain: necessary.
ADVANTAGES
Negative feedback increases the accuracy of a system by ○ Example: In audio amplifiers, using too much negative
Improved continuously adjusting the output to feedback can reduce the overall
Accuracy volume or intensity of the output signal.
match the desired value, reducing errors and variations
 ○ Implementing negative feedback can require additional Electronics: In power supply circuits, negative feedback
components, such as sensors, controllers, and feedback is used to stabilize the output
loops, which adds to the complexity of the system. voltage. When the output voltage deviates from the
○ Example: In closed-loop motor control systems, setpoint, feedback mechanisms
Complexity:
feedback devices like encoders or Power Supply adjust the current to bring the voltage back to the desired
tachometers are required, increasing the complexity Regulation: level.
compared to open-loop control systems. ○ Example: In a voltage regulator, negative feedback
ensures that a constant voltage is
○ Negative feedback systems may have a slower supplied to sensitive components like microprocessors
response time as they require continuous and sensors.
monitoring and adjustment, which might not be suitable
for systems requiring rapid or Mechanical and Electronics Engineering: In robotics,
Response Time:
immediate response. negative feedback controls the position and
○ Example: In some high-speed mechanical systems, the movement of actuators, motors, and joints. Feedback
time required for feedback from position sensors (e.g., encoders) allows the
adjustments may result in delayed reactions, which could system to adjust motor speeds to maintain precise
affect system performance. Control Systems movement.
in Robotics
APPLICATIONS ○
Mechanical Engineering: In heating, ventilation, and Example: In a robotic arm, the position of the arm is
air conditioning (HVAC) systems, constantly monitored, and the motors are adjusted
negative feedback is used to maintain a desired room via negative feedback to ensure the arm reaches and
temperature. Sensors detect the holds the correct position.
Temperature temperature and send feedback to the thermostat, which
Control in HVAC adjusts the heating or cooling Electronics: In audio systems, negative feedback
Systems elements accordingly. reduces distortion and ensures the output signal
○ Example: If the room gets too warm, the thermostat Audio Amplifiers: remains faithful to the input signal. This correction
activates the cooling system to enhances the quality of the sound, keeping the audio
reduce the temperature back to the desired value. output clean and accurate.
○
 Example: In a hi-fi audio amplifier, negative feedback ● Unintentional Positive Feedback: In real-world systems, there might
helps minimize harmonic distortion and feedback be unintentional positive feedback loops due to factors like component
noise, delivering clear sound imperfections or environmental conditions.
Recognizing these potential sources of positive feedback is vital for
Mechanical Engineering: In automated factories, troubleshooting and ensuring
negative feedback is used in processes such as reliable operation.
● Specific Applications: While generally avoided, positive feedback does
conveyor belts or robotic arms that perform assembly
have niche uses in control systems. For example, it can be used to create
tasks. Feedback sensors monitor the
oscillators or to implement certain types of control algorithms.
Automated position or speed, adjusting motors to ensure consistent
Understanding positive feedback allows engineers to design and utilize
Manufacturing operation. these specialized systems.
Systems: ○
Example: In an assembly line, negative feedback ensures BLOCK DIAGRAMS
that products are consistently placed in Block diagrams are simplified representations of complex systems, where
the correct positions for further processing, even if there each block represents a component or operation in the system.
are variations in the speed or load. The blocks are connected by arrows to represent the flow of signals or
information between components. In control systems, these diagrams
often include transfer functions that describe how each component in
Why discuss positive feedback if negative the system affects the input signal to produce an output. They are
feedback is more desirable in control systems? useful for visualizing the structure of a control system, the interactions
● Understanding System Behavior: Even though we usually aim for between components, and how the system processes signals.College of
negative feedback in closed-loop control, understanding positive feedback Engineering and Architecture
is crucial. It helps us analyze how a system might become unstable or Department of Electronics Engineering
oscillate. By knowing what positive feedback does, we can design systems ● Blocks: Represent system components or subsystems, often showing
that avoid it. their transfer functions (mathematical relationships between input and
● Stability Analysis: When designing a closed-loop system, we need to output).
ensure it's stable. This often involves analyzing the system's response to ● Arrows (Signal Paths): Show the flow of signals between blocks.
disturbances. Understanding how positive feedback ● Summing Points: Indicate where multiple signals are combined.
can amplify disturbances is essential for predicting and preventing ● Branch Points: Points where the signal splits to feed different parts of
instability. the
system.
 equations and analyzing complex networks.

BLOCK DIAGRAM VS SIGNAL FLOW GRAPH

● Focuses on the functional structure ● Focuses on the flow of signals and
of the system and shows components, the interrelationship between
their variables.
connections, and transfer functions.

● Primarily used for understanding ● More intuitive for analyzing and

system structure and analyzing the solving systems of linear equations.
overall system
response.
SIGNAL FLOW GRAPHS
Signal Flow Graphs are a graphical representation of the linear
● Good for high-level system design ● Often used when precise
relationships between variables in a system. They provide a way to
and control analysis. relationships between multiple
represent the flow of signals, where each node represents a
signals need to be understood
variable, and the directed edges represent the relationships
or when applying Mason’s Rule for
(multiplying by a transfer function) between the variables. Signal
finding transfer functions in complex
flow graphs are used to describe systems in a more intuitive and
system
graphical way. They can be particularly useful for solving systems of