Examining The Fundamentals Of Pid Control

Examining the Fundamentals of PID Control 1 of 5 http://www.controleng.com/archives/1996/02/issues/na/02c152.htm Examining the Fundamentals of PID Control Algorithms take the simple feedback controller one step further Vance J. VanDoren, CONTROL ENGINEERING This tutorial presents an overview of how and why PID controllers work. It is the first in a four part series on the fundamental concepts of modern control theory. A feedback controller is designed to generate an "output" that causes some corrective effort to be applied to a "process" so as to drive a measurable "process variable" towards a desired value known as the "setpoint." Figure 1 shows a typical feedback control loop, with blocks representing the dynamic elements of the system and arrows representing the flow of information, generally in the form of electrical signals. PROCESS CONTROL TUTORIAL Process control and instrumentation PID (proportional/integral/derivative) Process controllers Open architecture Programmable logic controllers (PLCs) Virtually all feedback controllers determine their output by observing the "error" between the setpoint and the actual process variable measurement. A home thermostat, for example, uses the air conditioning system to correct the temperature in a process comprised of a room and the air inside. It sends an electrical signal (an output) to turn on the air conditioner when the error between the actual temperature (the process variable) and the desired temperature (the setpoint) is too high. A look at PID control A proportional-integral-derivative or PID controller performs much the same function as the thermostat, but with a more elaborate algorithm for determining its output. It looks at the current value of the error, the integral of the error over a recent time interval, and the current derivative of the error signal to determine not only