Closed feedback control system

Figure 13.2 Block diagram of a closed feedback control system.

With this technology it is now possible to achieve extremely accurate speed control of the order of 0.01 % to 0.001 %. To achieve such high accuracy in speed control, closed-loop feedback control systems and microprocessor-based control logistics can be introduced into the inverter control scheme to sense, monitor and control the variable parameters of the motor to very precise limits. 

Very accurate controls through microprocessor-based closed-loop feedback control systems... 

Any system in which the output quantity is monitored and compared with the input, any difference being used to actuate the system until the output equals the input is called a closed-loop or feedback control system. 

Fig. 4.1 Block diagram of a closed-loop control system. R s) = Laplace transform of reference input r(t) C(s) = Laplace transform of controlled output c(t) B s) = Primary feedback signal, of value H(s)C(s) E s) = Actuating or error signal, of value R s) - B s), G s) = Product of all transfer functions along the forward path H s) = Product of all transfer functions along the feedback path G s)H s) = Open-loop transfer function = summing point symbol, used to denote algebraic summation = Signal take-off point Direction of information flow.

The closed-loop transfer function for any feedback control system may be written in the factored form given in equation (5.41)... 

Fig. 8.10 Closed-loop control system with full-order observer state feedback.

Figure 3 Feedback in a Closed-Loop Control System. 3...

Feedback is information in a closed-loop control system about the condition of a process variable. This variable is compared with a desired condition to produce the proper control action on the process. Information is continually "fed back" to the control circuit in response to control action. In the previous example, the actual storage tank water level, sensed by the level transmitter, is feedback to the level controller. This feedback is compared with a desired level to produce the required control action that will position the level control as needed to maintain the desired level. Figure 3 shows this relationship. 

Feedback is information in a closed-loop control system about the condition of a process variable. 

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We have chosen the steady state with Yfa = 0.872 and FCD = 1.0 giving a dense phase reactor temperature of Yrd = 1.5627 (Figure 7.14(b) and (c)) and a dense-phase gasoline yield of x-id = 0.387 (Figure 7.14(a)). This is the steady state around which we will concentrate most of our dynamic analysis for both the open-loop and closed-loop control system. We first discuss the effect of numerical sensitivity on the results. Then we address the problem of stabilizing the middle (desirable, but unstable) steady state using a switching policy, as well as a simple proportional feedback control. 

Positioning systems can use either an open-loop or a closed-loop control system. In closed-loop motion control, such as the optimized positioning of solar collectors based on measuring their shadows, the positions of both the collector and the shadow are continuously detected. Based on this feedback, the position and velocity of the collector can both be controlled. The reported position is continuously compared to the desired one, and the collector is moved to reduce the error between the two. This is called servo control (Figure 3.154). 

There are adaptive PCs. They are control system that changes the settings in response to changes in machine performance to bring the product back into its preset requirements or specification. The shift is maintained so that the control has adapted to changing conditions. It is a technique typically used to modify a closed loop control system. The process control comparator is the portion of the control elements that determines the feedback error on which a controller acts. 

Then one can state the following criterion for the stability of a closed-loop system A feedback control system is stable if all the roots of its characteristic equation have negative real parts (i.e., are to the left of the imaginary axis). If any root of the characteristic equation has a real positive part (i.e., is on or to the right of the imaginary axis), the feedback system is unstable. 

Control systems may be classified from their signal flow diagrams as either open-loop systems or closed-loop systems depending on whether the output of the primary control circuit is fed back to the controlling component. As Fig. 2 suggests, the typical control circuit consists of sequential arrays of components deployed about the process under control. If the controller is not apprised of the behavior of the controlled variable, the control system is an open-loop one. Conversely, if the measuring means on the controlled variable sends its signals back to the controller so that the behavior of the controlled variable is always under the scrutiny of the controller, the system is a closed-loop or feedback control system. 

Typically, for human disease, the systems one encounters are much too large and far too complex for the modeler to derive simple closed-form solutions and/or to perform simple steady-state analyses. As just noted, these systems usually include significant nonlinear dynamics, feedback controller systems, and time dependencies that are not easily modeled with pencil and paper. However, one can, by applying numerical differential equation solvers, still attack the problem by numerically estimating, under a variety of conditions, a set of systemwide solutions. Numerically solving the equations that make up a model of human disease and projecting these solutions forward in time is termed predictive biosimulation [9,10]. 

The system in Figure 13.1a is known as open loop, in contrast to the feedback-controlled system of Figure 13.1b, which is called closed loop. Also, when the value of d or m changes, the response of the first is called open-loop response while that of the second is the closed-loop response. The origin of the term closed-loop is evident from Figure 13.1b. 

In Figure 1.2 we see such a control action to keep T = Ts when T, or Fi changes. A thermocouple measures the temperature T of the liquid in the tank. Then T is compared with the desired value T yielding a deviation e = Ts - T. The value of the deviation e is sent to a control mechanism which decides what must be done in order for the temperature T to return back to the desired value Ts. If e > 0, which implies that T < Ts, the controller opens the steam valve so that more heat can be supplied. On the contrary, the controller closes the steam valve when c < 0 or T > Ts. It is clear that when T = Ts (i.e., e = 0), the controller does nothing. This control system, which measures the variable of direct importance (T in this case) after a disturbance had its effect on it, is called the feedback control system. The desired value Ts is called the set point and is supplied externally by the person in charge of production. 

A similar configuration can be used if we want to keep the volume V, or equivalently the liquid level h, at its set point hs when F, changes. In this case we measure the level of the liquid in the tank and we open or close the valve that affects the effluent flow rate F, or inlet flow rate F, (see Figure 1.3). It is clear that the control systems shown in Figure 1.3 are also feedback control systems. All feedback systems shown in Figures 1.2 and 1.3 act post facto (after the fact), that is, after the effect of the disturbances has been felt by the process. 

While designing a feedback control system (i.e., selecting its components and tuning its controller), we are seriously concerned about its stability characteristics. Therefore, before we proceed with the particular details of designing a feedback control loop, we will study the notion of stability and analyze the stability characteristics of closed-loop systems. 

Consider the generalized feedback control system shown in Figure 14.1. The closed-loop response for such system is given by eq. (14.5) ... 

Consider two different feedback control systems producing the two closed-loop responses shown in Figure 16.2. Response A has reached the desired level of operation faster than response B. If our criterion for the design of the controller had been... 

Figure 12.4 illustrates the principle of a feedback control system. The control system compares the value of the controlled variable (y) with the desired one (r). The control error is used to calculate the manipulated variable u that will bring the controlled variable y as close as possible to the setpoint r. The action of controller can be characterised by the transfer function K, so that the controller output / plant input is ... 

Suppose the design of the engine conld be snbstantially improved snch that k conld be reduced to say 0.1 (approaching a valne for a typical closed-loop feedback controlled system). Table 2.5 shows comparable results to those given in Table 2.4. 

Hence the closed-loop control system for steady state conditions may be described by the forward transfer function of (2.52), using the positive root, and the feedback transfer function of... 

The management system model can also be characterized as a feedback or closed-loop control system. In this version, the management team is the controller (who), the process is the system being controlled (what), and the instrumentation (how) monitors the system states and feeds these back to the controller so that deviations between the actual and the desired states can be nulled. The interfaces between each of the elements also represent the management process. Between the what and the how elements is the measurement-to-data interface. Between the how and who elements is the information portrayal/information perception interface. And between the who and the what elements is the decision-to-action interface. Viewed from the perspective of this model, the management of a function would entail ... 

Servo-controlled robots are run in a "closed loop . A feedback control system is used to drive the robot to certain sequenced desired points. Normally the robots are run with a limited accuracy therefore the final position is determined by an error signal. The error signal is created by the difierence between the manipulator s momentary position and the position the manipulator is to be directed. The closed-loop servo system continuously minimizes the error signal and drives the manipulator to keep the positioning error as small as possible. 

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