The collection of subsystems that controls the input signal to get the desired output is known as a system. The main function of any electronic system is regulating the output and keep that within systems desired input i.e when the input of the system changes, the output of the system should respond and change according to the changed input value. In another case, if there is no change in input but the output of the system is getting disturbed then the output should respond by coming back to its previous value. To carry out a specific objective the Control systems direct the operation. In olden days, these control systems were controlled manually which is known as the open-loop control system. Refrigerator, TV, Fan, Satellite all these systems need controlling to get proper output, thus control systems are needed to get specific output.
What is a Control System?
Definition: Coming to the definition, a control system in which the system’s output is depending on the input, but the input is not dependent on the output of the system is an Open-loop control system. This system is also called as non -feedback systems as it doesn’t have any feedback loop. In this non-feedback system, the output is not measured and even it’s not given as feedback to input for further considerations.
Open Loop Control System Block Diagram
The block diagram of this control system is shown below. In the following diagram, we can see two blocks, one is a controller block and another one is a controlled process block. Basing on the output requirement, the input is given to the controller of the system. The controller receives the input signal and generates the control signal and it is forwarded to the processing unit block, this block receives the control signal and process it properly and finally gives the output signal.
As this is also the non feedback system, due to no feedback path in the system, input can’t do anything though the output received at the end is desired or not. This is the reason to say the input is independent of output in the control unit system. The error is produced in the system because there is no chance of adjusting input as there is no feedback signal in this control system.
Examples of Open-Loop Control System
In many applications which we are using in our day to day life, this control system is used. Now we will see different systems that are designed based on the open-loop control system concept.
- Electric bulb
- TV remote control
- Washing Machine
- Volume on the stereo system
- Clothes drier
- Servo motor or stepper motor
- Door lock systems
- Coffee or tea making machine
- Inkjet printers
We can see the working of some real-time applications of this open-loop control system.
This is also an open-loop control system. When the information is entered through a keypad, then the other blocks like hardware components in the control system will process the information and displays it on LCD. When typing the peripheral is stopped by the operator then no input is given to the system so nothing will be displayed on LED. So word processor became an example of this control system.
Electrical Clothes Drier
The electrical clothes drier is a perfect example of the open-loop control system as it doesn’t consider clothes conditions before stooping of its work. There are 3 blocks in electrical drier system timer, heating elements, and cloths
When we set a timer for a specified time for the drying of clothes, this timer control, and heating elements together work to give the output of dry clothes. As it is a non-feedback system, the feedback about clothes is not given in the open-loop control system.
So the system stops working after the pre-set time without considering the state of clothes. The clothes may be dry or not dry, the system will switch off after the given time. This is because output only depends on the input signal and no other control action is given by input as it is not having any feedback signal.
If we are setting the timer for 15 minutes in clothes drier, it will stop working after the completion of 15 mins and it will not consider whether clothes are dried or not because it is working based on the given input signal of a timer and there is no control action given by input as there is no feedback loop.
The main advantages of the open-loop control system are
- These systems are very much suitable for use
- The design of this system is very simple.
- The maintenance aspect of this system is simple.
- The stability is good for some extent of time in this control system
- The convenience in usage is very good
- The cost is low when compared to other systems.
- The output produced is stable
The disadvantages of the open-loop control system are
- The automatic correction of output deviations cannot be done in this control system
- Inaccuracy exists in these systems
- There exists less bandwidth
- Timely recalibration is required in this control system
- As it is a non-feedback system, the automation of the process will not be initiated
- The disturbances from outside also show the impact on the required output
Open Loop Control System Applications
The applications of the open-loop control system are
Automatic Washing Machine
We use a washing machine to wash and dry clothes. This machine runs on the timer and not depends on the condition of clothes
Electric Hand Drier
The hands drier works on the electric power supply. When the hand is kept in front of it, hot air will be blown from it for some time for making the hand dry, it will not consider how much our hand is dried it will only consider the time
The Volume of the Audio System
he adjustment of the volume of the audio system is done manually
he bread toaster will toast the bread according to the given time and it will not consider the bread state into account.
Please refer to this link to know more about Control System MCQs
This is an overview of the open-loop control system. In this control system, there is no feedback path so there is no control over the input signal. We have also seen the applications of this system. Here is a question to answer, What are closed-loop control systems and its real-time applications?