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. Shown is 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. Virtually all feedback controllers determine their output by observing the error between the setpoint and the actual process variable measurement. PID control A proportional-integral-derivative or ‘PID’ controller 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 how much of a correction to apply, but for how long.
Controllers that juggle multiple process variables are neither simple nor common, but they can handle some of the most complex control problems.
Control Engineering classic: In this article, the consequences of performing feedback control with sampled rather than continuous data are examined.
Arguably the trickiest problem to overcome with a feedback controller is process deadtime -- the delay between the application of a control effort and its first effect on the process variable. During that interval, the process does not respond to the controller's activity at all, and any attempt to manipulate the process variable before the deadtime has elapsed inevitably fails. This classic article is among the most-read on the Control Engineering site. (See diagrams.)
KEY WORDSMotors, drives, & motion controlAC variable-speed drivesAC induction motorsAdaptive controlControversial right from their name, "sensorless" ac drives actually use current and voltage sensors to achieve motor control. Even beyond terminology, it's not obvious what sensorless ac drives can or can't do, and where they fit into the big picture.
KEYWORDS Process and advanced control Neural networks Multivariable sensors Sensing/measurement Analyzers What do the FBI (Federal Bureau of Investigation) and your mother have in common? Both use real measurements to reach an inferred outcome; are you telling the truth? Think about it, your mother would do a subtle interrogation all the while observing your body language—pupil dilation,...
Milwaukee, Wis.— To better reflect its business focus, Rockwell International Corp. announced Feb. 19 that it will assume the name of its primary remaining subsidiary, Rockwell Automation, after it spins off its avionics business, Rockwell Collins (Cedar Rapids, Ia.), as a separate, publicly traded company in June 2001.
KEY WORDS PC-based control Machine control Software for control Flowchart programming Simulation Imagine a product design, completed in software, and rendered in 3-D graphics. This rendering allows designers to strip away layers to view and work on components underneath. Next, manufacturing engineers can design the machines, fixtures, and processes required to produce components and completed ...
To help developers build devices with embedded networking and Internet connectivity, Lantronix Inc. (Irvine, Calif.) unveiled April 9 what it reports is the first fully integrated semiconductor with the hardware components needed to enable those capabilities. The Device Server Technology Network Interface (DSTni) chip is scheduled to be available in fall 2001.
Control Engineering editors— in the 14th annual process—highlighted the best products of the year, based on technological advancement, impact on the market, and service to industry.Editors selected from among thousands of products mentioned in Control Engineering and Control Engineering Online during year 2000, in nine product categories: Control components; Human-machine interface...