Glossary

actuator The first component in the control system which generates physical movement, typically a motor. The actuator gets its instructions directly from the controller. Another name for the actuator is the final control element

analog control system A control system where the controller is based on analog electronic circuits, that is, linear amplifi­ers.

batch process A process that has a beginning and an end and is usually preformed over and over

closed-loop control system A control system that uses feedback. A sensor continually monitors the output of the system and sends a signal to the controller, which makes adjustments to keep the output within specification

comparator Part of the control system that subtracts the feedback signal (as reported by the sensor) from the set point, to determine the error.

computer-aided design (CAD) A computer system that makes engineering drawings

computer-aided manufacturing (CAM) A computer system that allows CAD drawings to be converted for use by a nu­merical control (NC) machine tool

computer-integrated manufacturing (CIM) A computer system that oversees every step in the manufacturing process, from customer order to delivery of finished parts

continuous process A process wherein there is a continuous flow of product—for example, a steam boiler where water is continuously pumped in and steam continuously comes out

controlled variable The ultimate output of the process; the actual parameter of the process that is being controlled

controller The machine intelligence of the control system

control strategy The set of rules that the controller follows to determine its output to the actuator

control system A system that may include electronic and mechanical components, where some type of machine intelligence controls a physical process

digital control system A control system where the controller is a digital circuit, typically a computer

direct digital control (DDC) An approach to process control where all controllers in a large process are simulated by a sin­gle computer

distributed computer control (DCC) An approach to process control where each process has its own local controller, but all individual controllers are connected to a single computer for programming and monitoring

error In a control system, the difference between where the system is supposed to be (set point) and where it really is

event control system A control system that cycles through a predetermined series of steps

event-driven operation In a sequentially controlled system, an action that is allowed to start or continue based on some pa­rameter changes. This is an example of closed-loop control

feedback The signal from the sensor, which is fed back to the controller, follow-up system A control system where the output follows a specified path

forward path The signal-flow direction of the controller to the actuator

iteration See scan

motion control A term that refers to an electromechanical system wherein things move

numerical control (NC) A digital control system that directs machine tools, such as a lathe, to automatically machine a part

open-loop control system A control system that does not use feedback. The controller sends a measured signal to the ac­tuator, which specifies the desired action. This type of system is not self-correcting.

pick-and-place robot A simple robot that does a repetitive task of picking up and placing an object somewhere else

programmable logic controller (PLC) A small, self-contained microprocessor-based controller used primarily to replace relay logic controllers

process The physical process that is being controlled

process control A control system that maintains a uniform, correct output for some industrial process

regulator system A control system that maintains an output at a constant value

robot A servomechanism type control system in the form of a machine with a movable arm

scan One cycle through the program loop of a computer-based controller

sensor Part of the control system that monitors the system output, the sensor converts the physical output action of the sys­tem into an electric signal, which is fed back to the controller

sequentially controlled system A control system that performs a series of actions in sequence, an example being a wash­ing machine

servomechanism An electromechanical feedback control system where the output is linear or rotational movement of a me­chanical part

set point The input signal to the control system, specifying the desired system output

time-driven operation In a sequentially controlled system, an action that is allowed to happen for a specified period of time. This is an example of open-loop control