BUS OF THE MONTH: Profibus-DP
Smart Distributed System
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.)
Driven by manufacturing's desire to connect the factory floor with the rest of the enterprise, web-enabled PLCs and Ethernet are giving users new ways to view and control factory data using embedded web servers. When selecting a web-enabled automation device, users can choose from three distinct system architectures.
Chicago, Ill.—Wherever two or more gathered during National Manufacturing Week 2001, March 5-8, their discussion involved patents. As reported in Control Engineering, Feb. '01, p. 32, Schneider Electric Automation (North Andover, Mass.) followed news about its minority investment in Entivity by announcing an open auction on the web for its patent, "Device for Communicating Real-time Dat...
Chicago, Ill.— Hundreds of exhibitors showed thousands of innovative products and services at the National Industrial Automation Show during National Manufacturing Week 2001 at McCormick Place. For more coverage, including streaming video clips, click on "NMW 2001" at www.controleng.com. Advantech Automation (Cincinnati, O.