How do PID controllers work? What are they used for?

In a general sense, there are 2 ways you can control a process - use a feedback controller or use a feed forward controller. Feed forward controllers use a model of the process you want to control and can give you the best possible control. For example, if you had a good model of the car and the road (assumed traffic free) then you could build a cruise control system that would work perfectly and keep the speed constant whether the road was flat or sloping. Obviously, developing such a model is both hard and expensive and hence feed forward control is impractical for many applications.

Feedback control, alternatively, may be understood as "correcting for error". In the cruise control example, you permit the automobile run and have a look at its velocity. If it goes up, you reduce the throttle and vice versa. This method that the speed may also deviate now and again (eg when the automobile is going up a slope) but it will get corrected through remarks manipulate. If the control is good, the car will run close to the set speed at some stage in the trip. Feedback control is less difficult and inexpensive compared to feed forward manage.

The maximum commonplace algorithm used for feedback manage is the PID set of rules. They are the workhorses for process manipulate and extensively used in lots of exclusive manage packages. Some commonplace examples are cruise control in a automobile, temperature manage in an oven and waft manage in a water plant. All but the handiest of chemical flowers use those controllers. They have been around for decades, are clean to recognize, layout and implement. Behavior and design of these controllers has been studied in amazing detail.

The PID controller looks at the error and takes different forms of motion to carry it down. The P (proportional) part operates the technique in proportion to the mistake, however isn't always enough to deliver the mistake all of the way right down to 0. That is the process of the I (vital) element which corrects for the error remaining after the proportional motion. PI controllers are sufficient for most approaches. The D (by-product) element gives additional manage movement relying on whether the mistake goes up or down.