What Are Digital PID Controllers?

Andrew Kirmayer

A proportional-integral-derivative (PID) controller is a device often used to control electronic devices and systems. Mathematical principles are typically applied by the device to process a signal and trigger a response in the electronics it is connected to. Digital PID controllers often function similar to analog ones, but can include microprocessors, programmable logic controls, as well as specialized software. The device controlled is sometimes referred to as a plant, which can be an industrial motor, actuator, and other machinery, as well as a home thermostat.

Man with a drill
Man with a drill

Digital PID controllers are sometimes used to manage single devices, but can also be included in an entire system. They are typically used to accurately adjust the output signals in systems such as temperature controllers, based on some level of feedback. The devices generally use mathematical calculations called algorithms, which can allow them to activate when programmed thresholds are reached. Conditions can also be monitored consistently at specific times; this function is often called the sample rate.

Error signals typically help drive the function of digital PID controllers. The proportional term usually refers to the mathematical reduction of the error, while the integral function typically aims to make the error as small as possible. When the output signal changes too fast, the derivative function sometimes limits the actions of the other two so the correction is not overdone. The three elements of proportional-integral-derivative controllers are often designed by experts in mathematical theory as well as by software programmers. A control interface, usually a computer program, can help people manage digital PID controllers without advanced expertise.

Sometimes software code is needed to tune a digital PID controller, while debugging may be needed to adjust the variables managed by the device. In the case of home temperature control, the device is often designed to respond to set point temperatures and the deviation from those. Digital PID controllers can also learn the times needed to heat up a room or cool it down. They are usually able to keep the temperatures steady in a room as well.

Most digital PID controllers operate by using fixed values. The process is typically ignored by the controllers; just the parameters of operation are usually tracked. Different PID controllers can be connected to manage the performance of a large system, however, or even adapt them to various uses in an overall application. Another benefit of digital PID controllers is that the sampling time can be a small fraction of how long it takes for a parameter to be adjusted, so accuracy and effectiveness are typically maximized.

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