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# What is a PID Controller?

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• Written By: Jessica Reed
• Edited By: Heather Bailey
2003-2018
Conjecture Corporation
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A proportional-integral-derivative controller, known as a PID controller for short, is a type of device often used in control systems. These systems control other devices or systems and the PID controller helps regulate important variables within the control system. It may affect only one device or many at the same time. Typically, is it used in the industrial and manufacturing fields.

To understand what the PID controller does and why it is such an advantage, an example from everyday life can be used. When a homeowner is cold, she sets the thermostat for the heating unit in her home to the desired temperature. The temperature the house is currently at is known as the process variable. A variable is simply a factor, like the temperature of the house, that can change over time.

The ideal temperature that the homeowner has set her thermostat to is known as the setpoint. The process variable and the setpoint can be the same at a given time. If the current temperature of the home is at the desired temperature, they would be the same. Unlike the setpoint, however, the process variable can change. This happens when the house gets too hot or too cold.

These two terms, the process variable and the setpoint, are the same terms used to express how a PID controller works. The controller is set to control a variable, whether it's temperature or a different aspect of the system it has control over. The controller tries to find the best solution for keeping this variable at the desired setpoint.

Differences occur between the PID controller and normal controllers in the way they work. The PID controller uses an advanced formula to try and prevent any errors from occurring. This ensures the devices or systems being controlled perform as flawlessly as possible.

This formula type is known as an algorithm. An algorithm directs actions based on what is happening. The algorithm would have specific directions on how to react to certain changes. It is similar to a magazine quiz that asks questions and then uses arrows to direct the reader to the next question based on her answer to the previous question. In this way, an algorithm is a series of different procedures that can be followed or altered based on what the device receiving the orders is doing.

Finally, the PID controller participates in a feedback loop. Information is sent out by the controller, received by the devices, and information from the devices is sent back to the controller. The controller then makes a decision on how to proceed based on the information it receives and sends it out, creating a continuous loop.

One main advantage stands out above the rest when using a PID controller. It can control various systems or devices with little human interaction. Not only does this allow the workers to concentrate on other tasks, but it also allows many processes to run at once. The drawback to this method comes from the fact that the controller must be tuned, meaning the instructions that tell it what to do must be tweaked, to keep it functioning properly. To do this, advanced knowledge for setting up this type of controller is required to avoid error.