What is a PID control? How does it work?

Today we will learn about PID control. Especially, what it is and when we use this with automation and PLCs. So what is a PID controller? It is an acronym that stands for proportional, integral, and derivative. If we need to retain something or some variable constant, like a temperature, then this is the approach to do it. Basically, it uses a control feedback loop to ensure the output required is what we will get. Simply, put a set in the controller and it will keep the output constant based on feedback from some input, typically some kind of sensor. Something we possibly come across every day that is basically PID control is your cruise control in your automobile. First, you get to the speed that you want to be going. Then you set your cruise control. The intelligent control sends the signals to the main actuator to regulate the speed. A speed sensor delivers the control loop feedback to communicate the cruise if the automobile should speed up or slow down, or how much more or less control to deliver to the actuator. A simple objective type control that we use in manufacturing and industry is a temperature controller PID. These controllers are pretty simple to use and set up, hold less space, and do a great job at controlling the temperatures of a variety of equipment.Image Credit: Google

that controls the temperature of heat tracing on process piping. First, we need to enter a set point, let’s say 200 degrees Fahrenheit is just for example. Now the controller will give a signal to the output to start heating up the heat tracing. The control loop feedback is in the form of a thermocouple to read the temperature at any spot and to tell the controller how much more or less value is required when compared to the set value. For our example, the PID controller can work as on-off control for heat tracing. We will set the controller at a couple of degrees above and below 200 as well along with the set point of 200 degrees. Let’s say the above value is 104 degrees and the below value is 196 degrees. When the thermocouple read out some above the set value like 204 degrees it will turn the heating off. When it reads some below the set value 196 it will turn it back on. This is the common and very simplest form of PID control. We can also set up a PID controller with a PLC. As a replacement for of the standalone unit, we can use the input and output modules already on our PLC. The process variable, or control loop feedback, is to be connected to the input module and programmed into the PID. The output is controlled is wired to our output module. The PID in the PLC can do the entire math and make the decisions based on the variables and set points. A PID is an excellent choice for an automated process no matter which way we decide to set it up. Let's look back at today's information. A PID controller is a proportional integral derivative controller that can keep an automated process like temperature, Pressure, or flow, constant automatically. PIDs use a control loop feedback to monitor where the output should be. These are typically available in the form of sensors and meters. PIDs are available in many different forms including individual units and PLC programming. We can use input and output cards along with programming software to make a PID for any automated purpose. They are a very convenient tool to use. 

We hope this really helped you get a grasp of how to use a PID. So don't forget to comment and subscribe so you never miss another topic! 

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