COEG 304 Lecture 1: Control Systems

• Lecture 1 introduces instrumentation and control, specifically for course COEG 304 at Kathmandu University, with the lecture scheduled for March 14, 2025.

Table of Contents:

• The lecture will define control systems, provide their history and examples.
• The lecture will discuss the concept of feedback and closed-loop control.
• Then open-loop versus closed-loop systems, and linear time-invariant systems will be described.

Control Systems - What are they?

• Control systems manage, regulate, and direct the operation of another system.
• Also regulating itself as needed.
• Control systems maintain stability and desired performance.
• A control system consists of single or multiple devices working to command, direct, or adjust the behavior of other devices or systems.
• Inputs are continuously monitored with adjustments made to achieve efficient and stable operation.
• Functions can be carried out automatically or with human intervention.

Control Systems - Defined

• A control system manages the behavior of other systems through devices or algorithms.
• The system takes input, processes it, and affects the system’s behavior by producing an output.

Control System Composition

• Control systems include subsystems and processes/plants.
• These assemble to achieve a desired output and performance from a certain input.

Core Terminologies

• System: Interconnected elements and devices with a specific aim.
• Control System: Interconnected components in a configuration that provides a desired response.
• Process: It is a device, plant, or a system being controlled where the relationship between input and output represents the cause-and-effect.

Controlled and Manipulated Variables

• A controlled variable is a parameter or specific output in a system being regulated to achieve a desired performance.
• Control systems maintain the variable at a setpoint, irrespective of external influences.
• Example: In building temperature control, the goal to is maintain a comfortable 22°C temperature, whether it is hot or cold outside, or depending on the number of people inside.
• A manipulated variable is the adjustable input to the control system used to influence the controlled variable.
• It is altered by the control system to bring its controlled variable closer to a desired setpoint.
• Example: To control temperature, the manipulated variable is the amount of heated or chilled air supplied.

Control Disturbances

• Control disturbances are inputs or external factors that can directly impact the controlled variable, which the control system doesn't manipulate.
• They cause deviations from the desired setpoint, requiring that the system compensate to maintain stability.
• Example: Disturbances in a temperature control system include changes in outdoor temperature (external), or the number of people in a building (internal), or heat generated by appliances.
• These cause indoor fluctuations for which the system responds to maintain setpoint.

Advantages of Control Systems

• Control systems offer flexibility and adaptability.
• Control systems offer process optimization and informed decision-making.
• Control systems help with enhanced convenience and technology integration.
• Control systems add anomaly detection and enhanced safety.
• Predictive maintenance and remote monitoring are enabled by control systems.
• Robotic automation is enhanced.

Continuing Advantages of Control Systems

• Improved stability via continuous monitoring, input adjustment, output control, and oscillation prevention.
• Plant efficiency and profitability are enhanced while sustaining production and minimizing costs.

Types of Control Systems

• Natural control systems
• Artificial control systems

Examples of Control Systems

• Natural systems include the universe and the human body.
• Manmade systems include vehicles and aeroplanes.

More Control System Types

• Manual control systems involve operating components to manage aspects such as room temperature with a fan.
• Automatic control systems regulate aspects like room temperature via A/C.
• The hypothalamus controls body temperature.
• The body also regulates blood glucose.

Configurations of Control Systems

• Open loop
• Closed loop

Open Loop Control System

• This system features: Input, Input Transducer, Controller, Summing Junction interacting with Disturbance 1 and 2, Process/Plant, Output for Controlled Variable.

Open Loop Characteristics

• The reference input is not compared with measured output. There is a fixed operating condition for each reference.
• The system's accuracy is dependent on calibration.
• System performance is affected by disturbances, and variations in environmental conditions.

Closed Loop Control System

• This system integrates: Input, Input Transducer, Error/Actuating Signal, Controller, Summing Junction interacting with Disturbance 1 and 2, Process/Plant, Summing Junction, Output for Controlled Variable, and an Output Transducer/Sensor.

Traffic Light Controller

• Traffic flow control is a time dependent control system on roads.
• Traffic movement varies depending on the lights timing.
• Relays control both the duration and sequence, but it's predetermined and not responsive to the current traffic.

Servo System

• A servo system/servomechanism provides feedback control.
• Servo means slave/serving and mechanism means command, so the system is a slave to the command.
• Output is usually mechanical, defined by position, velocity, or acceleration.

Human as a system

• Input: information about surrounding
• Plant: human
• Controller: brain
• Output: position adjustment

Types of Control Systems

• Linear systems are those where the output varies linearly with the input, where the principle of superposition applies.
• Time-invariant systems have characteristics that don't change with time.
• Time-variant systems have characteristics that can vary with time.

Design Process

• Step 1: Determine physical system needs and specifications from requirements
• Step 2: Draw a functional block diagram.
• Step 3: Transform the physical system into a schematic.
• Step 4: Translate the schematic to block diagram, signal-flow diagram, or state-space representation.
• Step 5: Simplify the block diagram to a single block or closed system where there are multiple blocks.
• Step 6: Analyze, design, and test to ensure it is meeting the required specifications.

Ideal Control System Characteristics

• Accuracy.
• Sensitivity.
• Stability.
• Speed.
• Bandwidth.
• Minimal external disturbance or noise reaction.
• Minimal oscillations.

Readings

• Control Systems Engineering, N. Nise, Seventh Edition - Chapter 1
• Modern Control Systems Engineering, R. Dorf - Good for examples of control systems
• Control Systems Principles and Design by M.Gopal - Chapter 1, 3 (optional)

Assignments

• History of Control Systems
• Analog and Digital Control Systems
• Single Input Single Output and Multiple Input Multiple Output systems
• Control System Open-loop versus Closed loop systems
• Continuous Data vs. Discrete Data Systems
• Study the Antenna Azimuth as a case study: An Introduction to Position Control System