Instruments: [Weekly Question] Week 39 of 2011: What are open-loop and closed-loop control systems?

This post was last edited by denghl on 2012-12-12 at 20:58. An open-loop control system is one in which the output of the system has no effect on the control action of the system; in other words, there is no closed loop in terms of the signal relationship between the control device and the controlled object. A closed-loop control system, also known as a feedback control system, feeds the signal representing the change in the variable being controlled back to the input of the control device, which serves as the basis for the control device to exert its regulatory action.

This post was last edited by denghl on 2012-12-12 at 20:59. Reply to 1# Baghdad: Open-loop control refers to a control system that does not take feedback into account; it only controls the output without considering the consequences. Closed-loop control refers to a feedback control system, which is a regulating system that receives signals output by the regulator after they have been altered by the control variable. The only difference between open-loop control and closed-loop control is whether there is feedback or not. Open-loop control lacks feedback, while closed-loop control has it. By feedback, it is meant the effects resulting from certain actions or behaviors

This post was last edited by denghl on 2012-12-12 at 20:58. A system in which the output signal of the control signal (the controlled variable) is not fed back to the input side of the system, and thus has no impact on the control action. It is called an open-loop control system. Open-loop control lacks a feedback mechanism; as a result, the system’s stability is not high, its response time is relatively long, and its accuracy is low. It is used in simple systems where high requirements regarding system stability and accuracy are not necessary. The output of the system (the controlled variable) is sent back to the system’s input side through a measurement and transmission mechanism, where it is compared with the setpoint signal. The resulting difference is then fed into the regulator, which uses this information to control the system. In this way, a closed feedback loop is formed, and such a control system is known as a closed-loop control system. Closed-loop control includes a feedback mechanism; through this feedback system, the accuracy of the system is improved and the response time is reduced, making it suitable for systems that require high responsiveness and stability.

This post was last edited by denghl on 2012-12-12 at 20:59. A control system that detects the output, calculates the error, and uses it to correct the error has its output transformed in some way and fed back to the input side; this is a closed-loop control system. Conversely, a control system that does not perform detection and feedback on the output, and thus no feedback loop is formed between the output and the input, is an open-loop control system. Missile launch is a closed-loop control system. The missile control system corrects deviations based on the error relative to the target, in an effort to hit it. Cannon firing is an open-loop control system. There is aiming control before firing, but once the shell leaves the barrel, no further control is applied.

This post was last edited by denghl on 2012-12-12 at 20:59. If the output of a control system has no effect on controlling the system, such a system is called an open-loop control system. A closed-loop control system detects the output value, converts it into a physical quantity, and feeds it back to the input side for comparison with the input value. Using the resulting deviation signal, a controller (regulator) is used to control the controlled object, thereby suppressing the impact of internal or external disturbances on the output value and reducing errors in the output.

This post was last edited by denghl on 2012-12-12 at 20:59. Reply 1#: Baghdad A control system that detects the output, calculates the error in the regulator, and uses this information to correct the error; its output is transformed by detection elements and fed back to the input side – this is a closed-loop control system. Conversely, a control system that does not perform detection and feedback on the output, and thus no feedback loop is formed between the output and the input, is an open-loop control system. Missile launch is a closed-loop control system. The missile control system corrects deviations based on the error relative to the target, in an effort to hit it. Cannon firing is an open-loop control system. There is aiming control before firing, but once the shell leaves the barrel, no further control is applied.

This post was last edited by denghl on 2012-12-12 at 20:59. An open-loop control system is one in which the output of the system has no influence on its control mechanism; in other words, there is no closed loop in terms of the signal relationship between the control device and the controlled element. A closed-loop control system, also known as a feedback control system, involves the feedback of signals representing changes in the quantity being controlled to the input of the control device, which serves as the basis for the control device to take action.

This post was last edited by denghl on 2012-12-12 at 20:59. An automatic control system that consists of a signal forward path and a feedback path to form a closed loop is also known as a feedback control system. Therefore, a feedback control system is also known as a closed-loop control system. Conversely, a control system that does not perform detection and feedback on the output, and thus no feedback loop is formed between the output and the input, is an open-loop control system.

This post was last edited by denghl on 2012-12-12 21:00. Open-loop system: A control system in which the input signal of a system is not affected by the output signal. In other words, it is a system that does not feed back the results of control to influence the current control. Closed-loop system: A system in which the output is fed back to the input, directly or indirectly, to form a closed loop that participates in control is called a closed-loop control system.

This post was last edited by denghl on 2012-12-12 at 21:00. A control system that detects the output, calculates the error, and uses it to correct the error has its output transformed in some way and fed back to the input side; this is what is known as a closed-loop control system. Conversely, a control system that does not perform detection and feedback on the output, and thus no feedback loop is formed between the output and the input, is an open-loop control system. Reply 1# Baghdad