Introduction to a Closed Loop Control System

Summary

This script explains the function of a closed-loop system in maintaining a variable at a setpoint in a manufacturing process, using a heat exchanger as an example. It details the components of the system, including the controlled variable (water temperature), measurement device (thermal sensor), set point, error detector, controller, and actuator (flow valve). The script also discusses how disturbances affect the process and the role of closed-loop control in ensuring precise control within manufacturing.

Takeaways

• 🔧 The function of a closed-loop system is to monitor and maintain a variable at a desired setpoint in a manufacturing process.
• 🔄 An example given is a heat exchanger in a food processing operation, where heated water is supplied.
• 💧 Cold water enters the heat exchanger, warms up through steam-heated coils, and exits at the top.
• 📊 A block diagram is used to illustrate the operation, with blocks representing functions and lines indicating process flow.
• 🌡 The controlled variable is the water temperature leaving the tank, which is maintained at a set level.
• 📏 The measured variable is the actual water temperature, sensed by a thermal sensor to provide a feedback signal.
• 🎯 The set point is a predetermined desired condition for the control variable, like the water temperature.
• ⚖️ The error detector compares the set point with the feedback signal, producing an error signal if they differ.
• 🤖 The controller is the system's brain, receiving the error signal and adjusting the final control element to match the set point.
• 🚰 The actuator, such as a flow valve, controls the steam flow to adjust the manipulated variable, which is the amount of energy or steam.
• 🔍 Disturbances are changes in the process that affect the control variable, like sudden changes in water temperature or flow.
• 📚 Closed-loop control is essential in manufacturing systems where precise control of physical variables is required.

Q & A

What is the primary function of a closed-loop system in manufacturing?

The primary function of a closed-loop system is to monitor and automatically maintain a variable at a desired setpoint in a manufacturing process.

Can you provide an example of a closed-loop system in operation?

An example of a closed-loop system is a heat exchanger in a food processing operation, which supplies heated water and maintains water temperature at a set point.

What is the role of the controlled variable in a closed-loop system?

The controlled variable is the actual variable maintained in the process, such as the temperature of the water leaving the tank in the heat exchanger example.

What is the measured variable in the heat exchanger example?

In the heat exchanger example, the measured variable is the water temperature, which is monitored to ensure it matches the set point.

How does a measurement device contribute to a closed-loop system?

A measurement device, such as a thermal sensor in the heat exchanger, senses the measured variable and produces an output signal that represents the status of the controlled variable.

What is the purpose of the feedback signal in a closed-loop system?

The feedback signal from the sensor provides an electrical signal to the controller, indicating the current status of the controlled variable for comparison with the set point.

What is the significance of the set point in a closed-loop system?

The set point is the predetermined value of the desired condition of the control variable, such as the programmed water temperature leaving the tank in the heat exchanger.

What does an error detector do in a closed-loop system?

An error detector compares the set point to the feedback signal and produces an output proportional to the difference between them, known as the error signal.

What is the role of the controller in a closed-loop system?

The controller is the brain of the system; it receives the error signal as input and provides an output signal to the final control element or actuator to adjust the controlled variable to match the set point.

Can you explain the function of an actuator in a closed-loop system?

An actuator, such as a flow valve in the heat exchanger example, is the final control element that adjusts the manipulated variable, like steam flow, to control the process variable and achieve the set point.

What is a disturbance in the context of a closed-loop system?

A disturbance is a change in the manufacturing process that results in a change in the control variable, such as a sudden change or stop in water flow affecting the water temperature.

Why are closed-loop controls important in manufacturing systems?

Closed-loop controls are important in manufacturing systems where precise control is required to maintain process variables at set points, ensuring consistent product quality and efficiency.

Outlines

00:00

🔧 Closed-Loop System in Manufacturing

This paragraph introduces the concept of a closed-loop system in manufacturing, focusing on its role in maintaining a variable at a desired setpoint. The example of a heat exchanger is used to illustrate the system's operation, where heated water is supplied to a food processing operation. The paragraph details the components of a closed-loop system, including the controlled variable (water temperature leaving the tank), the measured variable (water temperature sensed by a thermal sensor), the feedback signal, set point, error signal, and the controller. It also explains the actuator's role in adjusting the manipulated variable (steam flow) to match the set point and mentions disturbances that can affect the process.

Keywords

💡Closed-loop system

A closed-loop system is a type of control system that continuously monitors and automatically adjusts a process variable to maintain it at a desired setpoint. In the context of the video, it is used to maintain the water temperature in a heat exchanger at a set level for a food processing operation. The system uses feedback from the process to make adjustments, ensuring precision and stability.

💡Heat exchanger

A heat exchanger is a device used to transfer heat between two or more fluids. In the script, it is used as an example to illustrate the operation of a closed-loop system. The heat exchanger supplies heated water to a food processing operation, where cold water is heated by steam coils before being pumped out, demonstrating the process control in action.

💡Controlled variable

The controlled variable is the process variable that the closed-loop system is designed to maintain at a specific value. In the video's example, the controlled variable is the temperature of the water leaving the tank. It is the actual variable that the system is actively monitoring and adjusting to meet the setpoint.

💡Measured variable

The measured variable is the actual value of the controlled variable as it is monitored by the system. In the context of the video, the measured variable is the water temperature, which is sensed by a thermal sensor and used to provide feedback to the controller.

💡Measurement device

A measurement device is the instrument used to detect and measure the value of the controlled variable. In the script, the thermal sensor that measures the water temperature in the heat exchanger is the measurement device, providing an electrical signal that represents the measured variable.

💡Feedback signal

The feedback signal is the output from the measurement device that indicates the status of the controlled variable. It is used by the controller to compare with the setpoint and determine the necessary adjustments. In the video, the feedback signal from the thermal sensor is crucial for the controller to maintain the water temperature.

💡Set point

The set point is the predetermined value for the control variable that the closed-loop system aims to achieve and maintain. In the video, the set point is the programmed water temperature leaving the tank, which the system works to achieve through adjustments.

💡Error detector

An error detector, or error signal, is the output from the controller that is proportional to the difference between the set point and the feedback signal. If the feedback signal matches the set point, the error signal is zero, indicating that the system is at the desired condition. In the video, the error detector plays a key role in identifying the need for adjustments.

💡Controller

The controller is the central component of the closed-loop system that receives the error signal and determines the necessary output signal to adjust the final control element. In the script, the controller is described as the 'brain' of the system, which uses the error signal to ensure the water temperature matches the set point.

💡Actuator

An actuator is the final control element in a closed-loop system that physically makes the adjustments needed to control the process variable. In the video, the flow valve is the actuator that controls the steam flow, thereby adjusting the manipulated variable to achieve the desired water temperature.

💡Manipulated variable

The manipulated variable is the variable that is adjusted by the actuator to achieve the desired control variable. In the context of the video, the manipulated variable is the amount of energy or steam flow controlled by the actuator to maintain the set water temperature.

💡Disturbance

A disturbance is an undesired change in the process that can affect the control variable. In the video, disturbances are changes such as sudden variations in water temperature or cessation of water flow, which the closed-loop system must compensate for to maintain the set point.

Highlights

A closed-loop system's function is to monitor and maintain a variable at a desired setpoint in a manufacturing process.

The example of a heat exchanger is used to illustrate the operation of a closed-loop system.

In the heat exchanger, heated water is supplied to a food processing operation.

Cold water enters the heat exchanger vessel and is heated by steam coils before exiting.

A block diagram represents the functions and process flow of a closed-loop system.

The controlled variable is the actual variable maintained in the process, such as water temperature.

The measured variable is the status of the controlled variable, monitored by a measurement device.

A thermal sensor is used to measure the water temperature in the heat exchanger.

The sensor provides an electrical feedback signal to the controller.

The set point is the predetermined value for the control variable, like the desired water temperature.

An error detector compares the set point to the feedback signal, producing an error signal.

If the feedback signal matches the set point, the error signal is zero.

The controller is the central component that processes the error signal and controls the actuator.

The actuator, such as a flow valve, controls the manipulated variable, like steam flow.

Disturbances are changes in the process that affect the control variable, like sudden temperature changes.

Closed-loop control is essential for precise control in manufacturing systems.

The terminology and concepts of closed-loop control are common in manufacturing where accuracy is crucial.

Transcripts

[Music]

the function of a closed-loop system is

to monitor and automatically maintain a

variable at a desired setpoint in a

manufacturing process

using an example of a heat exchanger the

operation of a closed loop system is

compared with a block diagram

the heat exchanger supplies heated water

to a food processing operation cold

water enters the bottom of the vessel

where the water temperature rises as it

passes through steam heated coils before

flowing out of the pump at the top

each block represents a function of the

operation lines connecting the blocks

indicate input and output signals of

each function with directional arrows

indicating the process flow

the controlled variable is the actual

variable maintained in the process in

this example the controlled variable is

the temperature of the water leaving the

tank

measured variable monitors the status of

the controlled variable water

temperature is the measured variable in

the process

the measurement device senses the

measured variable and produces an output

signal that represents the status of the

controlled variable the thermal sensor

that measures the water temperature in

the heat exchanger is the measurement

device

the sensor provides an electrical signal

to the controller and is defined as the

feedback signal in the block diagram

set point is the predetermined value of

the desired condition of the control

variable in the heat exchanger the set

point is the programmed value of the

water temperature leaving the tank

detector compares the set point to the

feedback signal and produces an output

proportional to the difference between

them

error signal is the output of the error

detector if the feedback signal and

setpoint are equal the error signal is

zero

the controller is the brain of the

system it receives an error signal as it

inputs and provides an output signal to

the final control element or actuator in

this example

a signal from the controller causes the

controlled variable to match the set

point using the actuator of the system

the flow valve represents the actuator

where steam flow is controlled

the amount of energy or steam in this

example altered by the actuator is the

manipulated variable

manufacturing process is the operation

of the heat exchanger to control the

physical variable

disturbance is defined as a change in

the manufacturing process resulting in a

change in the control variable

disturbances occur when the water

temperature suddenly changes or stops

flowing

closed-loop control and the associated

terminology are common within

manufacturing systems where precise

control is required

[Music]