DCS, SCADA, Controllers
BUS OF THE MONTH: LonWorks
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.)
Trends in Process Variable Transmitters Diagnostic capabilities Digital protocols Faster communication ONLINE See this product focus at www.controleng.com for additional information. Process variable transmitters (PVTs) perform a type of dance that goes on between various processes and the transmitter moving information to the end-user.
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.
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...
Applied Data Systems (Columbia, Md.) and Synergetic Micro Systems (Downers Grove, Ill.) announced March 5 at NMW a collaborative design effort to produce a new 32-bit StrongARM computer incorporating Synergetic's EmbeddedComm/EC-1 universal fieldbus chip. The two partners report their new product suite will be sold to OEMs and equipment suppliers, and expect the suite to offer price and perform...
Foxboro, Mass.— The Foxboro Company, a unit of Invensys Process Automation, announced March 19 that it has been awarded a $15 million SCADA system contract for the Shanxi Wanjiazhai Yellow River Diversion Project in China. This important project, funded by the World Bank, diverts floodwaters from the Yellow River to communities in Shanxi province, thereby mitigating life-threatening flood...