MATERIALS The tuning rules of PID, Cohen-Coon and

MATERIALS AND METHODS:2.1 PID Structures:         The Proportional, Integral and Derivative types are arranged into  different controller structure, which are also known as controller algorithms. They are:-Interactive -Non-interactive -Parallel -Series In the controller software these different controller algorithms are given as configuration option by many controller manufacturers.2.1.1 Interactive controller Algorithm:           The interactive algorithm of PID is referred as real and used for direct field control. The mean of direct field control is that either both of its input or output is directly connected to the field or process equipment. It is designed in such a way that it can easily cope with any electrical noise induced in its circuit.The controller output of interactive algorithm is given as: 2.1.2 Non-Interactive Controller Algorithm:                        The non-interactive algorithm of PID is referred as ideal and is classical teaching method. The tuning rules of PID, Cohen-Coon and lambda were designed for this algorithm.So from the above figure for non-Interactive algorithm, the controller output can be given as:   An ideal process variable is a noise-free, refined and optimized variable. They are a result of computer optimization, process modeling, statistical filtering and value prediction algorithms. These types of ideal process variables don’t come from field sensors. In these cases, it’s of great benefit that the actual formula of the Ideal PID algorithm is simple.             If the derivative term is removed by putting Td=0 then the Interactive and non-Interactive algorithm becomes same.2.1.3 Parallel Controller Algorithm:The controller gain of PID algorithm is not only multiplied with error in parallel controller algorithm as the interactive and derivative form are independent of controller gain, so it makes the use of parallel controller algorithm difficult.                 The controller output of the parallel controller algorithm is given as, as from the above figure: 2.2 Difference between different PID algorithms:   The biggest difference between the controller algorithms of PID is that interactive and non interactive algorithm have Controller gain (Kc) while the parallel algorithm has a true proportional gain (Kp). Controller gain has its affect on all three modes (Proportional, Integral and Derivative) of the series and ideal controller, while only proportional mode of the parallel controller is affected by Proportional gain.2.3  Effects on different parameters of PID:Parameters Rise time Over shoot Setting time Steady state errorKp Decrease Increase Small change Decrease Ki Decrease Increase Increase Significantly decrease Kd Minor decrease Minor decrease Minor decrease No effect2.3.1 Effect of Kp:     The effect of add Kp while Ki and Kd held constant is shown below:2.3.2 Effect of Ki:        The effect of add Ki while Kp and Kd held constant is shown next:2.3.3 Effect of Kd:            The effect of add Kd while Ki and Kp held constant is shown below:2.2 Design Method:         The design method of PID controllers are also referred as tuning rules. Some of the popular tuning rules are:- Ziegler-Nichols- Cohen-Coon- Lambda