This article is going to provide a brief description about the structure and working of PID controller. Let us know what is PID controller.

PID stands for Proportional Integral Derivative and is used mostly in industrial automation sector. Most of the operations that uses this controller is closed loop. The 3 controllers together form a control signal.

It provides the desired levels of the control output and acts as a feedback controller. Before the invention of micro-processors, PID controllers were in action by the analog electronic components.

Now a days PID microprocessors process the PID controllers. If you consider the Programmable Logic Controllers they have an inbuilt PID controller instructions. Process control application traditionally use the PID controllers because of its reliability and flexibility.

How does PID controller works?

The work of an On-Off controller is in a binary pattern either fully off or fully on and it is a simple and cost effective but it’s frequent oscillation is unwelcoming and therefore it is replaced with PID controllers.

With the help of PID controller there is no error in the process until the desired output. There are 3 basic use of PID controllers and they are explained below:

P- Controller:

As the name says Proportional controller, its output depends proportionally to the current error e(t). There is a comparison process between set point with actual value or feedback process value. For getting the output the proportional constant is multiplied by the resulting error and if the controller value is zero then the controller output is zero. There is a need for manual reset as it never reaches the steady state condition but there is a steady state maintenance of error. Proportional constant Kc increases when the speed of the response is increased.

I-Controller:

As there is a drawback in p-controller where there is an offset between the set point and process variable, I controller is required and it takes the action to remove the steady state error. This state is achieved by the I controller by frequent integration of the error values. When negative error takes place, integral control reduces the output and thereby the speed of the response is reduced and affects the stability of the system. Integral gain Ki is reduced for increasing the speed of response. The I controller drawback is its output is restricted to some range for overcoming integral wind up conditions and in this condition the error state value goes on increasing due to non linear plants.

D-Controller:

I-controller has a restriction because it cannot anticipate the future of the error. When the set point is changed it reacts normally and therefore in such cases D controller over comes this drawback by predicting the future reaction with respect to the error. Rate of change of error is the basis for the outputs with respect to time multiplied by derivative constant. For increasing the system response the kick start for the output is given from here. Increasing the derivative gain increases the response speed.

PID CONTROLLER DETAIL

This manipulates the process variables like pressure, temperature, flow, and speed. There are some cascade networks where two or more PIDs are used in some applications for achieving this control. The PID block present in the device gives its output to the process block. Actuators, Control devices, Control valves are used for controlling processes on industry or plant. Feedback signals from the process plant is compared to reference signal and error signal and is given as input into the PID algorithm. After getting combined response from the controller it is applied to various appliances in the plant.

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