Popular terms integrate control components

Control components help integrate control, automation, and instrumentation systems. Similarly, the terms we use—and sometimes take for granted—tie together our understanding.

By Control Engineering Staff January 8, 2004

Control components help integrate control, automation, and instrumentation systems. Similarly, the terms we use—and sometimes take for granted—tie together our understanding. I recall my first visit to an automation trade show, more than a few years ago, when I asked a number of people what the term “I/O” meant. I was looking for the acronym, input/out. I even remember one person saying that he didn’t know what it stood for, but it was the stuff that connected everything to everything else. (At Control Engineering , we typically use I/O as an adjective with a noun afterward, as in I/O devices.)

Here’s some output from us; input to you. Some of the leading search terms at Control Engineering Online are provided below, along with simple definitions, and some links for more information.

CAN bus —CAN stands for Controller Area Network; CAN bus is a serial bus (network) system especially suited to interconnect smart devices to build smart systems or sub-systems. CAN in Automation (CiA) is the international users’ and manufacturers’ organization that develops and supports CAN-based higher-layer protocols.

CANopen— CANopen is considered open and vendor independent, and standardized in EN50325-4. CANopen is a CAN-based higher layer protocol originally developed for industrial control systems. The family of specifications also includes different device profiles as well as frameworks for specific applications. CAN stands for Controller Area Network. For more see CAN in Automation.

control valves—”Control valves are devices with movable, variable, and controlled internal elements for modulating fluid flow in a conduit. The valve restricts flow in response to the command signal from a process measurement control system. Basically, a control valve consists of a pressure containment enclosure body and various internal elements—fixed and movable—commonly called the valve trim,” according to Control Engineering ‘s ” Control Valves: Sizing, Design, Characteristics .”

controller area network—Controller area network, CAN, is its own network protocol and is the basis for several other device-level industrial protocols. The CAN chip provides reliable communications at a low cost. Expensive, complex wire harnesses, used in traditional two-wire field I/O, are replaced with a single twisted pair of wires. For more, search on CAN at www.controleng.com or go to the CAN organization URL .

DeviceNet—DeviceNet is a low-cost communications link to connect industrial services (limit switches, photoelectric sensors, valve manifolds, motor starters, process sensors) to a network. DeviceNet eliminates expensive hardwiring and has important device-level diagnostics not easily accessible or available through hardwired I/O interfaces. The DeviceNet communication protocol is based on a broadcast-oriented, communications chip—the Controller Area Network (CAN) chip. DeviceNet is among networks considered “open” because an organization, rather than single vendor, oversees the protocol. For more, search DeviceNet at www.controleng.com or go to ODVA, Open DeviceNet Vendor Association . ODVA is said to support “network technologies built on the Common Industrial Protocol (CIP)—DeviceNet, EtherNet/IP, CIP Sync, and CIP Safety.”

DCS—DCS stands for distributed control system and consists of microprocessors inside industrial controllers and operator terminals, connected over a network with sensors and actuators through I/O connections. Process automation system, PAS, is a wider term—control systems most frequently applied in process applications and traditionally referred to as distributed control systems (DCS), hybrid control systems, and/or open control systems.

fieldbus—”Fieldbus architecture—Control architecture that uses digital, serial, multidrop, two-way communications between and among intelligent field devices and control/monitoring systems,” according to Control Engineering previous coverage. Fieldbus with a capital “F” often refers to the ISA organization standard ISA-S50, which includes multiple protocols. A fieldbus, or industrial network, allows different manufacturers’ field instruments, controllers, and remote I/O systems to work with each other as if they were a part of a single control system. Foundation Fieldbus refers to those network protocols under guidance of the Fieldbus Foundation (FF) network organization based in Austin, TX. For more from FF, see ” Fieldbus Facts “.

HMI—Human-machine interface is a method of displaying machine status, alarms, messages, and diagnostics, often graphical display on a personal computer, providing operator feedback,” according to key definitions at ” Back to Basics: Top 20 ‘must-know’ terms in control & automation .”

OPC—OPC has come to refer to a collection of standards from the OPC Foundation. The original double acronym stands for: “OLE for process control (OPC). Object linking and embedding (OLE) treats data as collections of objects to be shared by applications supporting OLE specifications. OPC provides extensions to OLE to support process control data sharing,” according to previous Control Engineering coverage.

P&ID—P&ID stands for piping and instrumentation diagrams. Being able to understand instrumentation symbols appearing on diagrams means understanding ANSI/ISA’s S5.1-1984 (R 1992) Instrumentation symbols and identification standard, according to Control Engineering ‘s ” How to read P&IDs “

PID—PID stands for proportional-integral-derivative. “A 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,” according to Control Engineering ‘s ” PID—The Basic Technique for Feedback Control .”

PID control—PID (proportional-integral-derivative) control: “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. The controller uses an actuator to affect the process and a sensor to measure the results. Virtually all feedback controllers determine their output by observing the error between the setpoint and a measurement of the process variable. Errors occur when an operator changes the setpoint intentionally or when a disturbance or a load on the process changes the process variable accidentally. The controller’s mission is to eliminate the error automatically,” according to Control Engineering ‘s ” Understanding PID Control .”

PID tuning—PID tuning refers to corrections made to a proportional-integral-derivative (PID) controller, which tracks the error between the process variable and the setpoint, the integral of recent errors, and the rate by which the error has been changing. The controller computes its next corrective action from a weighted sum of those three terms (or modes), then outputs the results to the process and awaits the next measurement, according to Control Engineering ‘s ” Loop Tuning Fundamentals .”

PLC—PLC stands for programmable logic controller: “A solid-state control system with user-programmable memory for storage of instructions to implement specific control and automation functions,” according to previous Control Engineering coverage.

Profibus—Profibus refers to a collection of fieldbus and network protocols, in the U.S. represented by Profibus Trade Organization and globally by Profibus International (PI), the parent organization of all Regional Profibus Associations (RPA) worldwide. For more from Profibus, see Profibus e-news .

SCADA—SCADA stands for supervisory control and data acquisition, which provides data display, alarming, trending, reporting, and control for devices and equipment in another location (via network, modem, wireless technologies, or Internet), according to previous Control Engineering coverage.

Safety—safety in automation, instrumentation, and control can be referred to in many contexts including, but not limited to, machine safety, intrinsic safety, safety integrated level (SIL), safety area classifications, safety networks.

For more on the topic from Control Engineering see:

  • ” Intrinsic safety protects your plant against explosions “

  • ” Reach for Machine Safety “

  • ” Back to Basics: ‘Division’ or ‘zone’ by any other name is still hazardous “

  • ” Understanding Safety Integrity Levels “

  • ” Safety Networks Begin to Emerge “

—Mark Hoske, Editor-in-Chief, Control Engineering, MHoske@cfemedia.com