What is an Open Loop Control System & Its Working

The first control system was invented by “James Watt’s Flyball governor” in the year 17. The main intention of this device is to maintain the engine speed constant by changing the steam supply to the engine. At present, the control system plays an essential role in modern technology because these systems will affect our daily lifeless or more. The best examples of control systems are automobiles, air conditioners, refrigerators, geezer, etc. These systems are used in different products of industries for quality control, transport systems, robotics, weapon systems, space technology, etc and also these are used in engineering/non-engineering fields. This article discusses an overview of what is a control system and one of its type namely the open-loop control system.

What is a Control System?

Definition: The Control system can be defined as, the output of a system that can be controlled by changing its input. So the system behavior can be expressed with the help of differential equations. So the desired output can be achieved in a control system through managing, directing, or commanding the behavior of the system. Control systems are classified into two types namely the open-loop control systems and closed-loop control systems.

What is Open-Loop Control System?

The open-loop control system block diagram is shown below. In the following diagram, the input can be given to the control system so that the required output can be obtained. However, this obtained output cannot be considered using this system for additional reference input.

In the following system, it includes two blocks like controller as well as the controlled process. Generally, the input is given to the system mainly depends on the required output. Based on the input, the control signal can be generated through the controller. This signal can be given to the processing unit. Therefore, based on the control signal, appropriate processing can be performed so that output can be attained.

Open Loop Control System
Open Loop Control System

In the open-loop control system, there is no feedback path. So, this is the reason the input in the open-loop control system is independent of the output. It is notable here that this usually generates a fault within the system because there is no chance of changing the input once the output illustrates the difference from the estimated value.

Open-loop control system examples include the following.

  • Automatic washing machine
  • Coffee or Tea making machine
  • Volume on the stereo system
  • Electric hand drier
  • Bread toaster
  • Inkjet printers
  • Servo motor/Servo motor
  • Electric bulb
  • Clothes drier based on a timer
  • Light switch
  • TV remote control
  • Water faucet
  • Door lock system

Control System Features

The features of this system include the following.

  • The control system features mainly include, the mathematic relationship of any control system that must be clear in between input as well as the output of the system.
  • For a linear control system, the relationship between input as well as output can be specified through a linear proportionality.
  • For a non-linear control system, the relationship between input & output can be signified through a linear proportionality.

For a good control system, the following factors are necessary.

  • Accuracy
  • Oscillation
  • Sensitivity
  • Speed
  • Noise
  • Bandwidth
  • Stability


The characteristics of the open-loop control system are,

  • There is no contrast between real and preferred values.
  • It has no control act on the value of output.
  • Every input setting decides a set operating location for the controller.
  • The changes within external conditions will affect to change the output directly.

Example of Open-Loop Control System

We can observe a traffic light controller at different road crossings. The signals which are generated through the control system are time-dependent. At the designing time of the controller, an internal timing can be given to the controller.
Thus, once the controller of a traffic signal is fixed at the crossing after that every signal can be displayed through the controller.

Here the control system has nothing to perform using the produced output because it cannot change its input based on the traffic there at any side. After some fixed time gap, based on the primarily generated input, the control system generates the output.

Here in the control system, the timing sequence can be provided by the relays used.

So it indicates clearly that the input will stay independent for the generated output.

Consider the control system shown below.

Transfer Function
Transfer Function

The transfer function of a control system can be derived by using the following equation.

G(S) = Output/Input

When the above transfer function is considered separately for every block then it is given like the following.

For the first block G1(S), the transfer function is G1(S) = Y1/Yi

For G2(S) = Y2/Y1

For G3(S) = Y0/Y2

So, the total transfer function can be calculated as

G1 x G2 x G3 = Y1/Yi * Y2/Y1 * Y0/Y2

So the gain of open-loop can be calculated as G = Yo/Yi

So, the use of the open-loop control system specifies that the system operator is ready to consider the least difference within the output from the estimated value.


The advantages of the open-loop control system include the following.

  • Very simple & easy to design these types of control systems.
  • Low cost as compared with other systems
  • Less maintenance
  • The output is stable
  • Very suitable to use
  • Convenient operation


The disadvantages of the open-loop control system include the following.

  • The bandwidth is less.
  • Inaccurate
  • The non-feedback system is not dependable when their output is influenced through some outside disturbances,
  • The output differences cannot correct automatically.
  • It needs timely recalibration.
  • These control systems are more horizontal to errors.
  • The changes within the preferred output can be the effect of disturbances.
  • The change in output can be done automatically


The applications of the open-loop control system include the following.

  • It is used in the controlling system of traffic light
  • Immersion rod
  • TV remote control,
  • Automatic washing machines,
  • Heaters in rooms
  • Door opening & closing systems automatically.

Thus, this is all about an overview of the open-loop control system. In this kind of control system, there is no influence on the control of the input signal. These are commonly known as nonfeedback systems because it doesn’t include any feedback to decide if its necessary output was attained. Here is a question for you, what is a closed-loop control system?