tuning of pid gains by trial and error

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Feedback Control Systems -IE361

PRACTICAL NO.03 Object To Tune PID Gains by Trial and Error Method.

Theory Control System A Control System is a device, or a collection of devices that manage the behaviour of other devices. Some devices are not controllable. A control system is an interconnection of components connected or related in such a manner as to command, direct, or regulate itself or another system.

Feedback control system In feedback control, the variable being controlled is measured and compared with a target value. This difference between the actual and desired value is called the error. Feedback control manipulates an input to the system to minimize this error. The error in the system would be the Output - Desired Output. Feedback control reacts to the system and works to minimize this error. The desired output is generally entered into the system through a user interface. The output of the system is measured (by a flow meter, thermometer or similar instrument) and the difference is calculated. This difference is used to control the system inputs to reduce the error in the system.

PID controller A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems – a PID is the most commonly used feedback controller. A PID controller calculates an "error" value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs. The PID controller calculation (algorithm) involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted P, I, and D. Heuristically, these values can be interpreted in terms of time: P depends on the present error, I on the accumulation of past errors,

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Feedback Control Systems -IE361

and D is a prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve, or the power supplied to a heating element.

Simulink Block Diagram

MATLAB screen shots SET 1

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SET 2

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Feedback Control Systems -IE361

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Feedback Control Systems -IE361

SET 4

Results and Conclusion We studied the significance of PID controller in a closed loop system and adjusted its gains by trial and error method and we observed that:   

Proportional gain is used to decrease the rise time. Differential gain is used to reduce the overshoot and rise time. Integral gain is used to eliminate the steady-state-error.