PID control stands for proportional, integral, and derivative control. This type of process management is used to maintain set parameters, and works well for temperature or motion. All three portions of this control setup manage whatever parameter you desire in different manners.
Proportional control controls how far the measured parameter is from the set parameter. In terms of temperature it will tell you how far off from ideal the process is running; i.e. +1.85 °F or -.07°F. Managing the process with proportional controls alone will work, but the systems will swing between over- and under- correcting.
Integral controls are added onto proportional controls to factor in timing into the setup. By measuring the time between measurements of the parameter the system can determine the speed at which the motion or temperature are changing; i.e. -.1 °F/second. By knowing this measurement the system can then account for this with more precision, cutting down the amount of over-correcting. Still this combination will need one final layer to appropriately maintain the parameter dynamically.
Derivative control measures the acceleration of the parameter, in effect the speed at which the speed is changing. With this level of control, the parameter changes can be dampened and returned to the set point reliably. In terms of motion parameters, with a properly installed PID control system a ball bearing can be kept from rolling off a glass plate even when pushed by people.
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