1. SELF TUNING OF CONTROLLERS What is a Controller Controller is an active element or device that receives the information from the measurements and takes appropriate corrective action to adjust the values of manipulated variables of a process. Different Types of Controllers Proportional controller Proportional Integral Controller Proportional Derivative Controller Proportional Integral Derivative Controller Tuning of a Controller Tuning of a controller may be defined as process of identifying ideal set of values to a selected controller for a specific process control We need to obtain the values of K c, T I and T D for optimizing the process output.

2. Ziegler-Nichols Tuning (Ultimate Cycle method) Unlike process reaction curve method which uses data from the open loop response of a system, this technique is a closed loop procedure. It goes through following steps 1. Bring the system to desired operation level 2. Using proportional control only & with the feedback loop closed, introduce a set point change and vary proportional gain until the system oscillates continuously. The frequency at continuous oscillation is known as cross over frequency ω co. Let M be the Amplitude Ratio of system response at ω co 3. Compute the following quantities Ultimate Gain K u = 1/M Ultimate period of sustained cycling P u = 2 π / ω co min/cycle

3. 4. Using the values of Ku and M. Ziegler-Nichols have recommended the following settings for the feedback controls The settings above reveal the following 1. For Proportional control alone use of gain margin is equal to 2 2. For PI control use lower K c because the presence of Integral control mode introduces additional phase lag at all frequencies with destabilizing effects on the system. Therefore lower or approximately same is the value of K c a 3. The presence of Derivative control introduces phase lead with strong stabilizing effects in the closed loop response. Thus K c can be increased without threatening the stability of the system KcŤIŤI ŤDŤD ProportionalK u /2 --- P IK u /2.2P u /1.2 --- P I DK u /1.7P u /2P u /8

4. Definition of a Self Tuning controller A Self tuning controller may be defined as a system capable of readjusting the controller tuning settings automatically to provide an optimal process output Blocks of a Self Tuning Controller System Identifier: This Item estimates the parameters of the process Controller Synthesizer: This element synthesizes or calculates the controller parameters specified by control objective function Controller Implementation Block: This is the controller whose parameters are updated at periodical intervals by the controller parameter calculator r: set point; c: controlled output; m: manipulated variable

5. BLOCK DIAGRAM OF SELF TUNING CONTROLLER DESIGN CRITERION IMPLEMENTATION BLOCK Set Point ( r ) m c + - b = c Fig: The Main components of Self Tuning Regulator CONTROL SYNTHESIS SYSTEM IDENTIFIER CONTROLLER PROCESS

6. Most self tuning controllers will self tune -During Startup -Retune on request -Retune on naturally occurring upsets -Continuously when excitation introduced into the process by controller Advantages of Self Tuning Controllers 1.Facilitates controlling critical processes of systems; 2.Approaches optimum operation regimes; 3.Facilitates design unification of control systems; 4.Shortens the lead times of system testing and tuning; 5.Lowers the criticality of technological requirements on control systems by making the systems more robust; 6.Saves personnel time for system tuning.

7. Video on functioning of a Self Tuning Control (Real Time Application)

8. THANK YOU Presentation by Ravi Shankar 1 / 2 MTech (Industrial Process Instrumentation) AUCE