Open control loop

After definition of the optimum operation policies, different strategies can be used for actual implementation at the polymerization plant. The simplest strategy is the implementation of u°P at the plant, without using any sort of feedback signal for x and/or y, for evaluation of the operation performance. In mathematical terms, one might define the implementation of open-loop control strategies in the form  

However, control variables are usually manipulated indirectly. For instance, one has to change the valve position to increase the flow rate through the reactor jacket. Similarly, one has to reduce the electrical resistance of the heating bath in order to increase the inlet temperature of the cooling fluid. For this reason, one may also define the open-loop control problem as 

Open-loop control strategies were developed and implemented to allow for reduction of transition times during grade transitions in continuous high-impact styrene polymerizations [61]. Similar strategies were also used to control the MWDs in emulsion homopolymerizations and to control the copolymer composition and the MWDs simultaneously in non-hnear emulsion polymerizations [36,37,182]. 

3 FUNDAMENTALS OF SINGLE INPUT-SINGLE OUTPUT SYSTEMS 

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In open-loop control applications wdiere best static acciiracv is needed. 

The PI controller, even when optimally tuned, is also unable to prevent surge. Furthermore, it is unable to stop surge once it occurs. In the above situation, the operator would correctly identify the problem as instability of the closed-loop PI controller. The only viable action would be to open the closed control loop by placing the controller in manual, thereby freezing the valve open. In this scenario, open-loop control will stop surge. 

A similar type of open-loop control response is combined with closed-loop control in a patented method of surge protection. In this control method an open-loop control response is added before surge occurs. 

Breaker Trip Triggers Open-loop Control... 

An open-loop control system is one in which the control action is independent of the output. An example of an open-loop control system is a chemical addition pump with a variable speed control (Figure 1). The feed rate of chemicals that maintain proper chemistry of a system is determined by an operator, who is not part of the control system. If the chemistry of the system changes, the pump cannot respond by adjusting its feed rate (speed)... 

An open-loop control system is one in which the control action is independent of the output. 

Several methods have been investigated to find correlations between physical properties of fuel gas mixtures and the excess air ratio to optimize the combustion procedure. In spite of the varying composition of natural gas it is said to be possible to control a heater system by measurements of the dynamic viscosity of the gas [7]. One explanation could be the correlation between Wobbe number and viscosity With increasing Wobbe numbers the viscosity decreases, and if the Wobbe number of a gas is known, the excess air ratio can be adjusted, resulting in an open loop control. 

Open hollow fiber membranes, 16 2, 3 Open-loop control systems, 9 56-57 Open-loop dynamics, 20 694... 

OPEN-LOOP CONTROL OF SWIRL-STABILIZED SPRAY FLAMES... 

A periodically forced system may be considered as an open-loop control system. The intermediate and high amplitude forced responses can be used in model discrimination procedures (Bennett, 1981 Cutlip etal., 1983). Alternate choices of the forcing variable and observations of the relations and lags between various oscillating components of the response will yield information regarding intermediate steps in a reaction mechanism. Even some unstable phase plane components of the unforced system will become apparent through their role in observable effects (such as the codimension two bifurcations described above where they collide and annihilate stable, observable responses). 

Forcing function is a term given to any disturbance which is externally applied to a system. A number of simple functions are of considerable use in both the theoretical and experimental analysis of control systems and their components. Note that the response to a forcing function of a system or component without feedback is called the open-loop response. This should not be confused with the term open-loop control which is frequently used to describe feed-forward control. The response of a system incorporating feedback is referred to as the closed-loop response. Only three of the more useful forcing functions will be described here. 

Most automatic control strategies are a combination of feedback (closed-loop) and feedforward (open-loop) control components. Feedback control maintains a desired process condition by measuring and comparing it to a set point and initiating corrective action based on the difference between the desired and the actual conditions. Feedforward control provides fast compensation to disturbances if its "model" is accurate. The main limitation of feedforward is our inability to prepare perfect process models or to make perfectly accurate measurements. 

As presented in the earlier chapters, the operating policy for a batch distillation column can be determined in terms of reflux ratio, product recoveries and vapour boilup rate as a function of time (open-loop control). Under nominal conditions, the optimal operating policy may be specified equivalently in terms of a set-point trajectory for controllers manipulating these inputs. In the presence of uncertainty, these specifications for the optimal operating policy are no longer equivalent and it is important to evaluate and compare their performance. 

To date, similar experiments on dissociative ionization of molecules by adaptively shaped ultrashort laser pulses have been reported, where specific ion ratios were targeted during iterative control using GA and SA [14,15]. However, less detailed comparisons between adaptive control and open-loop control experiments regarding the laser pulse width, pulse train, and peak intensity exist. Moore et al. claimed that not only accelerated specific bondbreaking, but even new bond formation, can specified by adaptive pulse shape control [14]. Because ethanol molecules have a relatively simple main struc-... 

A simple example of an open-loop control system would be a steam-jacketed resin kettle very much like that in Fig. 1 except that the steam pressure is regulated automatically by the behavior of the measured jacket pressure but not by the actual temperature of the resin batch in the kettle. In the corresponding closed-loop system the steam pressure is regulated by the temperature of the resin batch as in Figs. 1 and 2. The only way open-loop control can be precise is through a close calibration between steam pressure and batch temperature. Since this close calibration can be maintained inexpensively only in the absence of load changes of any kind, it is obvious that the field of application of open-loop control is limited. In the example of Fig. 1, load changes would result... 

An elaboration of open-loop control which sometimes can be competitive with closed-loop control is feed-forward control, in which the controller is apprised of factors which affect the key process variable to be controlled, but is not directly apprised of the behavior of this variable. Thus for the kettle of Fig. 1, it would be possible to measure the flow rate and temperature of the feed and have a simple computer analyze the information and on the basis of this information set the steam pressure to be maintained by the controller. So long as the computer considered all pertinent factors, the control would be satisfactory, but an unaccounted factor, such as a change in agitator speed, might make the control ineffectual. 

Closed-loop control is often considerably more simple than open-loop control. The programmer usually must send a command, perhaps over a serial port, telling the motor controller what movement to make. The probe motion and data acquisition must be synchronized. The programmer is advised to not rely on simply computing the probe position based on the requested motion, but instead to acquire the position information directly from the controller. One must beware of latencies between the reported position and the actual position during scanning. 

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