Control algorithms

Some of the inherent advantages of the feedback control strategy are as follows regardless of the source or nature of the disturbance, the manipulated variable(s) adjusts to correct for the deviation from the setpoint when the deviation is detected the proper values of the manipulated variables are continually sought to balance the system by a trial-and-error approach no mathematical model of the process is required and the most often used feedback control algorithm (some form of proportional—integral—derivative control) is both robust and versatile. 

Classical Feedback Control. The majority of controllers ia a continuous process plant is of the linear feedback controller type. These controllers utilize one or more of three basic modes of control proportional (P), iategral (I), and derivative (D) action (1,2,6,7). In the days of pneumatic or electrical analogue controllers, these modes were implemented ia the controller by hardware devices. These controllers implemented all or parts of the foUowiag control algorithm ... 

Tj = integral time constant and = derivative time constant. Upon the advent of digital control devices, this basic control algorithm was implemented as a digital approximation ... 

C. R. Cutier and B. L. Ramaker, "Dynamic Matrix Control A Computer Control Algorithm," Proceedings of Joint Auto. Control Conference, Paper... 

The second area, the implementation of a modem process monitoring and control system, is the most dramatic current appHcation of CAD/CAM technology to the chemical process industry. The state of the art is the use of computer graphics to display the process flow diagram for sections of the process, current operating conditions, and controUer-set points. The process operator can interact directly with the control algorithms through the... 

In order to improve the performance of time-delay systems, special control algorithms have been developed to provide time-delay com-... 

One important class of nonlinear programming techniques is called quadratic programming (QP), where the objective function is quadratic and the constraints are hnear. While the solution is iterative, it can be obtained qmckly as in linear programming. This is the basis for the newest type of constrained multivariable control algorithms called model predic tive control. The dominant method used in the refining industiy utilizes the solution of a QP and is called dynamic matrix con-... 

The ISA symbology provides different symbols for different types of actuators. Furthermore, variations for the controller symbol distinguish control algorithms implemented in DCS technology from panel-mounted single-loop controllers. 

Presently, fieldbus controllers are single-loop controllers with 8- and 16-bit microprocessors and are options to digital field-control devices. These controllers support the basic PID control algorithm... 

The main shortcomings of the pneumatic controller is its lack of flexibility when compared to modern electronic controller designs. Increased range of adjustability, choice of alternate control algorithms, the communication link to the control system, and other features and services provided by the electronic controller make it a superior choice in most of todays applications. 

A further substantial improvement in control response was achieved by including the expander inlet pressure into the control algorithm. With this change, the regenerator pressure falls by only 5 mbar, thereafter rising by 9 mbar, representing a fluctuation that is substantially below the contractual agreement. 

The essence of surge protection is determining when and how much to open or close the recycle valve. In the simple application of Figure 6-45, the antisurge controller (UIC) will position the recycle valve using a control algorithm based on AP, AP, and data on the location of the surge limit. 

This is a control algorithm that attempts to eliminate the offset (caused by proportional control) between the measurement and the setpoint of the controlled process variable. This control mode remembers how long the measurement has been off the setpoint. 

This author developed a reboiled absorber alternate from the Smith-Brinkley generalized equation, and friends have developed plant fractionator control algorithms using Smith-Brinkley. 

Figure 7.25 shows that the continuous and discrete responses are identical, both with ( = 0.5. The control algorithm can be implemented as a difference equation... 

Proportional control A control algorithm in which the final control element moves to a position proportional to the deviation of the value of the controlled variable from the set point. 

Proportional integral (PI) control A control algorithm that combines the proportional response and integral response control algorithms. 

Proportional integral derivative (PID) control A control algorithm that enhances the PI control algorithm by adding a component that is proportional to the rate of change of the deviation of the controlled variables. 

The complexity and reduced time constants of modern processes imply the adoption of high performance programmable controllers. This requires not only higher processing speed but also more advanced control algorithms that can optimize the process operation in real time. 

It should have sufficient flexibility to allow development of complex control algorithms without software customization. 

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