Open loop and Closed loop system
Table of Contents
Difference Between Open loop and Closed loop system
The desired output in an open loop system is independent of the control action, which is one of the key differences between it and a closed loop system. While in a closed loop system, the desired output is determined by the system’s control action. Below, in the comparison chart, are the other distinctions between the open loop and closed loop system.
|Basis For Comparison
|Open Loop System
|Closed Loop System
|The term “open loop control system” refers to a system whose control action is independent of the output.
|In a closed loop, the output is based on how the system is being controlled.
|Controller and Controlled Process.
|Amplifier, Controller, Controlled Process, Feedback.
|Depends on calibration
|Accurate because of feedback.
|Traffic light, automatic washing machine, immersion rod, TV remote etc.
|Air conditioner, temperature control system, speed and pressure control system, refrigerator, toaster.
Open Loop Control System
The output in an open loop control system has no bearing on how the system controls itself. In other words, an open loop control system is one whose operation is time dependent. The feedback is absent from the open loop system. Let us use a few examples to help you understand this.
Example 1: Consider a dryer that requires manual operation from the operator. Assume the operator set the timer for 30 minutes, depending on how wet the clothing was. Even after the clothes are wet, the timer will stop after 30 minutes.
Even if the desired output is not obtained, the dryer stops operating. This demonstrates the lack of feedback in the system. The timer serves as the system’s controller in this example of an open loop system involving a clothes dryer.
Example 2: The open loop system is demonstrated by the automatic washer. The machine’s running time is manually set by the operator. Even though the desired level of clothing cleanliness is not achieved, the machine stops working after the predetermined time. This occurs because the machine lacks a feedback system that would alert the system to change its behavior in order to produce the desired results.
The open loop system is straightforward and requires less upkeep. Additionally, it operates quickly and is very cost-effective. But the system’s reliability and accuracy are declining.
Closed Loop Control System
The output of the system depends on their input because it is a closed-loop control system. One or more feedback loops connect the system’s input and output. By comparing the desired output with the actual input, closed-loop systems are built so that they automatically produce the desired output. The error signal, which is the difference between the input and output, is produced by the closed-loop system.
Example 1: Assume that in the closed dryer example from above, we are using a transducer to detect how dry the clothes are and send a feedback signal to the controller about their dryness. The system’s output in this case is dryness. The sensor serves as the system’s feedback. The dryer produces the desired result by receiving the signal from the sensor and sending it to the machine’s controller.
Example 2: A closed-loop system is exemplified by an air conditioner. By comparing the temperature to that of the surrounding air, the air conditioner controls the temperature. With the aid of the thermostat, temperature comparisons are made. The thermostats switch on or off the compressor when the air conditioner sends out an error signal, which is the difference between the temperature outside and inside the room.
Key Differences between Open Loop and Closed Loop System
- The open loop system is called the non-feedback system while the closed loop is the feedback system.
- An open loop system means that its output is independent of its input. The desired output in a closed-loop system is dependent on the input.
- Systems can be built quickly because they only use a few components. The closed-loop system’s construction is quite challenging.
- The open loop system consists of two parts: control and controlled process. Certain elements, such as an amplifier, controller, controlled process, feedback system, etc., are needed for the closed loop.
- The accuracy of the system is less as compared to the closed-loop system.
- The open loop system is not reliable whereas the closed-loop system is reliable.
- In comparison to a closed loop system, an open loop system is more stable. The word “stable” in this context refers to the system’s output remaining constant despite disturbances.
- The open loop system gives the fast response, whereas the closed loop system gives the slow response.
- While the closed-loop system is optimized, the open loop system is not.
- The calibration of open loop system is difficult as compared to the closed-loop system.
- In contrast to the input control system, which has linear responses, the output control system exhibits non-linear behavior.
- In an open loop system, the disturbance affected the output, whereas in a closed loop system the output is not much affected by the disturbances.
- Examples of an output system include a traffic light and an automatic washing machine, whereas examples of a closed-loop system include a temperature controller and a toaster.
There are two different kinds of control systems: open loop and closed loop. While the closed loop system is complex and its output is dependent on the input, the open loop system operates on input and is easier to build.