Control System

What is an automatic control system?

What is a control system?

A control system can be described as a system that can control the output quantity. Basically, it is a device or a set of the device which can manage, command, and regulate the operation of the other device or a system that uses control loops. So this system can control and regulate the operation of another system. A system consists of different elements and devices that are interconnected to do a process. The control system is formed by the component interconnection and thus a system configuration is achieved and it will control the system. The major components of a control system are actuators, sensors, reference input, and the system. The system is the process or plant which needs to be controlled and the actuator would convert the control signal to a power signal. The sensor would measure the system output and the reference input represents the required output.

What is the need for an automatic control system?

A control system is needed to maintain a process at the required operating conditions safely and effectively. The control system is capable to maintain product quality. We would be able to get high-value products and also increase yield with the help of a control system. It can meet environmental safety regulations such as it can reduce pollution and also can ensure safety. With the help of automatic control systems, repeated works can be done really easily in many industrial processes.

What is a set point change and disturbance change?

Set point change

This is the predetermined value for the control variable, so if there is a change in the set point then, certain adjustments would be done in order to achieve the new operating conditions.

Disturbance change This is the change in the process because of a disturbance, so the control system must be capable to return the controlled variable to the set point.

What are the hardwares of a control system?


The sensor would measure the system variable, in the automatic control this would act as a signal source


The controller would do the comparison and the computation process

Control element

It is the equipment to do the control action in a process, the control element would receive signals from the controller and according to that, it will perform certain actions. In most cases, the control element would be the control valve

What are the functions of a control system?

The control system must be capable to do the measurement, and it compares the measured value to the required value. The control system should be able to compute the difference between the required value and the measured value. So while comparing the measured valve and the desired value, if the measured value is not close to the desired value then correction must be done and all these are the major functions of a control system.

What are the requirements of a control system?

  • The control system should be accurate
  • It must be really sensitive
  • It should not be sensitive to external noise but it must be sensitive to the input commands
  • It must be stable
  • It should have a good frequency response
  • The control system must operate very quickly

Why automatic control system or what is the purpose of an automatic control system?

  • Productivity can be increased
  • Quality can be increased
  • Energy optimization
  • Comfortable operation
  • The remote control can be done
  • The input can be controlled

The automatic control system will use, for the regulation and quality control of processes and the environment. The control system is used in many industrial processes, a process is a device, plant, or system which is under control. The process control is done by a control system, the control system would convert the variable to the required variable. There are manual and automatic control systems if a human operator is required to give input throughout the process then it is manual control. In an automatic control system, there will be a controller which can replace the human operator and this will be very useful and this controller is set to control the process accurately. In most cases, the function of the control system is to control the physical variables such as temperature, voltage, frequency, flow rate, current, position, speed, etc, and all these are called the controlled variables.

What is an automatic control system?

In a manual control system a machine will be operated by a person but in the case of an automatic control system machine will do the operation automatically. The automatic control system has a controller so it can perform the operation on its own. Basically, the control system is a combination of elements and subsystem which needs to maintain a quantity. The control system can maintain a process with the help of feedback control, this would help to maintain the specific variables close to the required values. So the control system can meet the requirement of the process by adjusting the selected variables in the system. The feedback control can make use of an output of the system to influence the input of the same system. The automatic control system would have electronic equipment and it uses current and voltage to communicate. Control will be implemented in the sensors, valves, and other equipment in the process.

What are the disturbance in a control system?

In a control system, the disturbance is a signal which would affect the system output value. There are two types of disturbance one is an internal disturbance that is generated within the system and the other one is external disturbance and which is generated outside the system.

What are the different types of control system?

Open loop system

This is also known as a non-feedback system, in this type of control system the control action is not dependent on the output of the system. In this type of control system, there is no feedback and it is really difficult to get the required output from this type of system. These systems are not capable to take into account the disturbances. So it can only make changes in the output by making changes in the input.

What are the advantages and disadvantages of an open loop control system?


  • Simple construction
  • Economical
  • Easy to maintain
  • Stable


  • Not accurate
  • It is no reliable
  • Any change in the output cannot be corrected automatically

Closed loop control system

In this type of control system, there is a sensor that would measure the output and it uses feedback of the sensed value to influence the control input variable. In this type of control system, the output would have an effect on the input quantity in a way that it can maintain the required output value. There is no feedback for the open-loop control as in closed-loop control. So with the help of the feedback in a closed-loop control system is able to correct the changes in output that occur due to the disturbances. The feedback feature of a closed-loop system makes it an automatic control system. In this system, the output is checked all the time so that it can be compared with the desired input and if it is not close to the desired input then there would be an error signal. So by checking the error signal the control elements in the system will do the required actions and thus the required output can be achieved.

What are the advantages and disadvantages of a closed loop control system?


  • High bandwidth range
  • Accurate
  • This is very accurate even in the presence of non-linearity
  • Stability is increased by decreasing the sensitivity
  • The system is not affected by noise


  • Costlier
  • Design is complicated
  • More maintenance is needed
  • Due to the feedback, the gain is reduced
  • Less stable

What is a feedback and feed-forward control?

The feedback control takes the system output to the controller and the controller would compare this output to the required value. The feed-forward control would detect the disturbances directly and it would take proper actions to remove the effect of this disturbance from the output.

What are the advantages and disadvantages of a feedback control?


  • It would measure the controlled variable
  • It would take proper actions regardless of the disturbance source
  • It would decrease the sensitivity of the controlled variable to the disturbances and also to the change in process


  • Corrective action will only take place after the disturbance
  • The response is not stable

What are the advantages and disadvantages of a feed-forward control?


  • Disturbance variable
  • It would correct the disturbance before it makes any changes in the process


  • It is not really sensitive so sometimes it can’t measure the disturbance
  • There won’t be any corrective action for the unmeasured disturbances

What are the advantages of the automatic control system?

  • It can reduce the consumption of energy
  • Production labor will be decreased
  • There won’t be any human errors
  • It can also maintain the operational constraints
  • Protection of the equipment
  • Smooth plant operation
  • Profitable

What are the applications of automatic control system?

• Automobile
• Refrigeration
• Air conditioning
• It is used in transportation systems such as railways, planes, etc.
• It is used in many process industries such as chemical, steel, power, flow rate, etc,

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