These are also called as non-feedback control systems. Open Loop Control SystemsĬontrol action is independent of the desired output.Ĭontrol action is dependent of the desired output. The differences between the open loop and the closed loop control systems are mentioned in the following table. Traffic lights control system having sensor at the input is an example of a closed loop control system. Hence, the closed loop control systems are also called the automatic control systems. In this combination, the output of the control system is adjusted automatically till we get the desired response. So, the controller produces an actuating signal which controls the plant. Instead of the direct input, the error signal is applied as an input to a controller.
This feedback signal is obtained from the block (feedback elements) by considering the output of the overall system as an input to this block. The error detector produces an error signal, which is the difference between the input and the feedback signal. The following figure shows the block diagram of negative feedback closed loop control system. So, the control action is dependent on the desired output. In closed loop control systems, output is fed back to the input. The traffic lights control system which we discussed earlier is an example of an open loop control system. So, the plant produces an output, which is controlled. This signal is given as an input to a plant or process which is to be controlled. Here, an input is applied to a controller and it produces an actuating signal or controlling signal. The following figure shows the block diagram of the open loop control system. So, the control action is independent of the desired output. In open loop control systems, output is not fed-back to the input. Open Loop and Closed Loop Control SystemsĬontrol Systems can be classified as open loop control systems and closed loop control systems based on the feedback path. Whereas, MIMO (Multiple Inputs and Multiple Outputs) control systems have more than one input and more than one output. SISO (Single Input and Single Output) control systems have one input and one output. But, in discrete time control systems, there exists one or more discrete time signals.Ĭontrol Systems can be classified as SISO control systems and MIMO control systems based on the number of inputs and outputs present. In continuous time control systems, all the signals are continuous in time. Continuous time and Discrete-time Control SystemsĬontrol Systems can be classified as continuous time control systems and discrete time control systems based on the type of the signal used.
Classification of Control Systemsīased on some parameters, we can classify the control systems into the following ways. So, the traffic lights control system operates on time basis. Accordingly, the input signal controls the output. Based on the traffic study at a particular junction, the on and off times of the lights can be determined. During this time, the other two lights will be off. Here, a sequence of input signal is applied to this control system and the output is one of the three lights that will be on for some duration of time. Traffic lights control system is an example of control system.
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In the next section on open loop and closed loop control systems, we will study in detail about the blocks inside the control system and how to vary this input in order to get the desired response.Įxamples − Traffic lights control system, washing machine
We will vary this input with some mechanism. Since, the output is controlled by varying input, the control system got this name. Here, the control system is represented by a single block. The following figure shows the simple block diagram of a control system.