Control systems

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These can be described as follows: 1 The value of the controlled quantity is varied by a motor this word being used in a generalized sense , which draws its power from a local source rather than from an incoming signal. Thus there is available a large amount of power to effect necessary variations of the controlled quantity and to ensure that the operations of varying the controlled quantity do not load and distort the signals on which the accuracy of the control depends.

Thus, for example, in the case of a thermostatic heating system, the supply of fuel to the furnace is determined by whether the actual temperature is higher or lower than the desired temperature. A control system possessing these fundamental characteristics is called a closed-loop control system, or a servomechanism see Figure. Open-loop control systems are feedforward systems. The stability of a control system is determined to a large extent by its response to a suddenly applied signal, or transient. If such a signal causes the system to overcorrect itself, a phenomenon called hunting may occur in which the system first overcorrects itself in one direction and then overcorrects itself in the opposite direction.

Because hunting is undesirable, measures are usually taken to correct it. The most common corrective measure is the addition of damping somewhere in the system. Damping slows down system response and avoids excessive overshoots or overcorrections.

Control Systems are Ubiquitous | IEEE Control Systems Society

Damping can be in the form of electrical resistance in an electronic circuit, the application of a brake in a mechanical circuit, or forcing oil through a small orifice as in shock-absorber damping. Another method of ascertaining the stability of a control system is to determine its frequency response — i.

The output of the control system is then compared to the input with respect to amplitude and to phase— i. Frequency response can be either determined experimentally—especially in electrical systems—or calculated mathematically if the constants of the system are known. Mathematical calculations are particularly useful for systems that can be described by ordinary linear differential equations. Graphic shortcuts also help greatly in the study of system responses.

Several other techniques enter into the design of advanced control systems. Adaptive control is the capability of the system to modify its own operation to achieve the best possible mode of operation. A general definition of adaptive control implies that an adaptive system must be capable of performing the following functions: providing continuous information about the present state of the system or identifying the process; comparing present system performance to the desired or optimum performance and making a decision to change the system to achieve the defined optimum performance; and initiating a proper modification to drive the control system to the optimum.

These three principles—identification, decision, and modification—are inherent in any adaptive system. Dynamic-optimizing control requires the control system to operate in such a way that a specific performance criterion is satisfied. This criterion is usually formulated in such terms that the controlled system must move from the original to a new position in the minimum possible time or at minimum total cost. Learning control implies that the control system contains sufficient computational ability so that it can develop representations of the mathematical model of the system being controlled and can modify its own operation to take advantage of this newly developed knowledge.

Thus, the learning control system is a further development of the adaptive controller. Multivariable-noninteracting control involves large systems in which the size of internal variables is dependent upon the values of other related variables of the process. Thus the single-loop techniques of classical control theory will not suffice. More sophisticated techniques must be used to develop appropriate control systems for such processes.

Control system. Article Media. During this time, the other two lights will be off.


  1. Context Aware Human-Robot and Human-Agent Interaction.
  2. Distributed Control Systems.
  3. Primary Cilia.
  4. Closed loop control system;

Based on the traffic study at a particular junction, the on and off times of the lights can be determined. Accordingly, the input signal controls the output.

Types of control systems

So, the traffic lights control system operates on time basis. Control Systems can be classified as continuous time control systems and discrete time control systems based on the type of the signal used. In continuous time control systems, all the signals are continuous in time. But, in discrete time control systems, there exists one or more discrete time signals. Control Systems can be classified as open loop control systems and closed loop control systems based on the feedback path. In open loop control systems , output is not fed-back to the input. So, the control action is independent of the desired output.

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Here, an input is applied to a controller and it produces an actuating signal or controlling signal. This signal is given as an input to a plant or process which is to be controlled. So, the plant produces an output, which is controlled. The traffic lights control system which we discussed earlier is an example of an open loop control system.

In closed loop control systems , output is fed back to the input.

So, the control action is dependent on the desired output. The error detector produces an error signal, which is the difference between the input and the feedback signal. This feedback signal is obtained from the block feedback elements by considering the output of the overall system as an input to this block.

Control Systems in Practice, Part 1: What Control Systems Engineers Do