What is PID Controller used for Industrial Automation

Introduction to PID Controller :

PID Controller is a most common control algorithm used in industrial automation and applications and more than 95% of the industrial controllers are of PID type. PID controllers are used for more precise and accurate control of various parameters.

Most often these are used for the regulation of temperature, pressure, speed, flow and other process variables. Due to robust performance and functional simplicity, these have been accepted by enormous industrial applications where a more precise control is the foremost requirement.

What is PID Controller?
A combination of proportional, integral and derivative actions is more commonly referred as PID action and hence the name, PID (Proportional-Integral-Derivative) controller. These three basic coefficients are varied in each PID controller for specific application in order to get optimal response.

It gets the input parameter from the sensor which is referred as actual process variable. It also accepts the desired actuator output, which is referred as set variable, and then it calculates and combines the proportional, integral and derivative responses to compute the output for the actuator.

In a control loop an error is calculated by taking difference between the desired value and the obtained value. It is called as error. If correction is applied proportional to the error, then the controller is called as Proportional Controller. If correction is applied based on the integral value of the error signal then the controller is called as Integral Controller. Similarly if correction is based on the derivative of the error signal it is called as Derivative Controller. If correction is based on all the above correction factor then the controller is called as PID controller (Proportional – Integral – Derivative). In the same way PI and PD controllers are obtained.

PID controller digram — PID controller diagram

Each controllers have different effects on the system and the selection of controller depends on the application.

PID controller is a common Industrial controller. It gives robust performance in wide range of operating condition. There are three coefficients viz Proportional, Derivative, and Integral, controlling these values optimum response is obtained.

P Controller
It provides stable operation but always maintains the steady state error. Speed of the response is increased when the proportional constant increases.

I Controller
It limits the speed of response and affects stability of the system. Speed of the response is increased by decreasing integral gain

D Controller
I-controller doesn’t have the capability to predict the future behavior of error. So it reacts normally once the set point is changed. D-controller overcomes this problem by anticipating future behavior of the error. Its output depends on rate of change of error with respect to time, multiplied by derivative constant. It gives the kick start for the output thereby increasing system response.

Advantages Of PID Controller :

PID is one of the many control techniques used in industry. Its advantages are as follows:

Even if you do not wish to waste any time in creating a mathematical model of a system, you can still use a PID controller with it by tuning it with trial and error.
PID is not heavy on hardware, therefore it can be implemented on cheap hardware also. For e.g. arduino Uno can run a couple of PID loops very efficiently
PID controller once designed, then its further tuning doesn’t require a skilled personnel

Application Of PID Controller :

PID controllers have wide variety of applications manufacturing industry. Some of them are listed as follows.

PID control is used in automatic car steering when it is integrated with Fuzzy Logic
In movement detection system of modern seismometer
In water/oil level monitoring in tanks
Head positioning of a disk drive
Automated inspection and quality control
Manufacturing process control: CNC machine tools
Chemical process control: flow control, temperature control
Automatic control of material handling equipments
Automatic packaging and dispatch
To ensure safety during manufacturing operations