JAOMAD Glossary D:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Intro
D—Derivative (rate) action in modulating process control in which rate of change (speed) of correcting force is proportional to error signal; also: Thermocouple type for Tungsten 3% Rhenium vs. Tungsten 25% Rhenium; also: formerly meant "Density"(Mass), or Specific Gravity when used in first alpha character position of ISA instrument function tag, still means "Differential" in modifier position [see ANSI/ISA S5.1-1984 (R1992)]; also: d (lowercase) in math is abbreviation "deci-" for 10-1 (=0.1).
D/A—Digital to Analog conversion of signal; also: Dynamometer.
DAB—Designated Audit Body.
DAC—Digital to Analog Converter; electronic device that converts digital signal, often from a computer, into proportional analog voltage or current; also: Digital Audio Compression; also: Data Acquisition & Control, see definition, DAS, DAHS, DAQ.
Daemon— Disk And Execution MONitor; computing process which waits in the background and runs when a request is made on the port that it is watching; normally works out of sight of the user, performing specified operation at predefined times or in response to certain events; UNIX® term now used with other operating systems; comes from Greek mythology where dæmons were guardian spirits.
DAHS—Data Acquisition & Handling System.
DAIS—Database Access Integration Services; profile for uniform access to computer data.
Daisy Chain—To connect one device to another in sequence; method of propagating signals along a bus, often used in applications in which devices are connected in series, sometimes in order of priority.
DAL—Data Access Language; in computers, database access standard which provides transparent connection among variety of databases and any applications depending on them.
DALI—Digitally Addressable Lighting Interface; see definition.
DAQ—Data Acquisition; gathering of discrete and analog parameters from process sensors, switches, transducers, often implies conversion of these signals to digital for use in computing devices; sometimes incorrectly called SCADA; see SCADA.
Dark Current—Thermally induced current that exists in photodiode in absence of incident optical power (total darkness).
DAS—Data Acquisition System, see definition; also: Direct Attached Storage, see definition.
Dashpot (DP)—Fluid filled cylinder containing loose fitting piston that is used to damp vibratory motion or to change effect of sharp change in load from instantaneous change in position to more gradual change; see Snubber.
DAT—Duration Adjusting Type process control output (time proportioning); also: Digital Audio Tape.
Data—In computers and transmission, Information represented in digital form, including voice, text, facsimile, and video; also: character in Star Trek-TNG. J
Data Abstraction—In Object Oriented Programming (OOP), reduction of an object description to unique and general characteristics which define a class.
Data Acquisition System—Any instrument or computer system designed to gather data from many sensors through amplifiers, multiplexors, etc. usually for presentation at some central location.
Data Acquisition & Control—A Data Acquisition System that additionally provides control signals from a workstation (usually a PC) out to controllers to operate end elements in a plant; communication network is not designed for the complexities of long distances as in traditional SCADA systems, but since the mid 1990s some suppliers have been calling these SCADA systems; see SCADA.
Data Averaging—Optional mode of operation for an automatic data logger which allows readings from two or more data acquisition channels to be averaged in each scan or, alternatively, readings from each of several channels to be averaged over some preselected number of successive scans.
Data Base—In computer systems, those store of data placed into system by user, and in DCS, by the process being monitored; usually consolidates many records into common pool of data records which serves as single central file.
Data Base Manager—System that provides meaningful information from data included in some database; computer program that allows users to manipulate data in every conceivable way except the absolutely essential way they conceive on the day after entering 20 megabytes of raw data. J
Data Encryption Standard—In digital communications; NIST-standard secret key cryptography method that uses 56-bit key based on IBM algorithm which was further developed by U.S. National Security Agency; employs block cipher method which breaks text into 64-bit blocks before encrypting them; most popular of several encryption modes, exclusive ORs each plaintext block with previous encrypted block; DES decryption is very fast and widely used: secret key may be kept a total secret and used over again, or key can be randomly generated for each session, in which case new key is transmitted to recipient using public key cryptography method such as RSA; enhancement with considerably more security is Triple DES of which there are several methods: EEE3 uses 3 keys and encrypts 3 times, EDE3 uses 3 keys to encrypt, decrypt and encrypt again, EEE2 and EDE2 are similar to EEE3 and EDE3, except that only 2 keys are used where first and third operations use same key.
Data File—Portion of computer memory allocated to specific set of organized data, including codes that identify file name and sometimes file type.
Data Flow—View of system as set of independent asynchronous processes, each communicating with each other via I/O streams; by Tom DeMarco, Yourdon Press.
Data Highway—Popular term used for communication network of distributed control systems, cable physically connecting various hardware items (devices) distributed along that control system over which transfer of data is communicated; usually proprietary to individual vendors because of need to work with real-time data in very dynamic process, requiring data transmission much faster than available on LANs designed for business computers.
Data Integrity—Performance measure based on rate of undetected errors.
Data Link—Any serial data communications transmission path, generally between two adjacent nodes or devices and without intermediate switching nodes; data link includes physical transmission medium, protocol, and associated devices and programs, so it is both physical and logical link.
Data Link Layer—In digital communication, second layer in the OSI model; the network processing entity that establishes, maintains, and releases datalink connections between (adjacent) elements in network; controls access to physical medium (layer one); also: in FOUNDATION Fieldbus technology, controls transmission of messages onto fieldbus, and manages access to fieldbus through Link Active Scheduler (LAS); defined in IEC 61158 and ISA S50; includes Publisher/Subscriber, Client/Server and Source/Sink services.
Data Mining—Process of discovering meaningful new correlations, patterns, and trends by sifting through large amounts of data stored in repositories, using pattern recognition technologies, statistical, and mathematical technologies; typically used in Enterprise Resource Planning systems to develop an optimum business plan; currently moving well beyond the field's original focus on highly structured, relational databases, such as "text data mining,"or extracting unexpected relationships from huge collections of free-form text documents, and "video mining,"or using a combination of speech recognition, image understanding and natural-language processing techniques to open up the world's vast video archives to efficient computer searching.
Data Processing—Automatic or semiautomatic organization of numerical data in desired manner; any system that can receive, store, or transmit data, as well as perform operations upon data and present results.
Data Rate—Average number of bits, characters, or blocks of information per unit of time being transmitted, such as bits per second, and which may or may not be equal to signal rate or baud rate; see Baud.
Data Space—Where data reside within device or system.
Data Streaming—Capability to deliver time-based digital data as it’s requested, much like audio or video cassette, rather than to require downloading all the information before it can be used (or played).
Data Table—Organized form on which data are held in computer.
Data Warehouse—Repository of extremely large amounts of data generated both inside and outside of enterprise (corporation), generally for purposes of developing some business plan to cope with complex operations to make them profitable.
Datagram—Packet delivery service between nodes in network, that is, provided by ISO layer 2 interface; has no acknowledge, no ordering, no retransmission.
DATC— Design Automation Technical Committee of IEEE.
Daytona—Version 3.5 of Windows™NT (not NT 94), much faster, leaner, more applications.
dB—DeciBel, logarithmic unit of ratio; ratio can express power, voltage or current difference between two signals; in signal to noise measurements, dB usually signifies voltage difference between desired signal and root mean square (RMS) value of noise...the higher the ratio, the less noise that is present in the signal; also: measurement developed to approximate response of human senses, which are logarithmic in response, that is, doubling of signal power, voltage, or current does not double volume of perceived sound or brightness of perceived light.
dBm—Measured signal power compared with standard signal power of 0.001 Watt into 600 Ohms.
DBMS—Data Base Management System; collection of hardware and software that organizes and provides access to data base, simplifying management of additions and rearrangement.
dBmV—Measured signal voltage compared with 0.001 Volts into 75 Ohms.
DC—Direct Current; electric current flowing in one direction only and generally constant in value; also: Device Control, in data communications, category of control characters intended to turn other (usually subordinate) equipment ON or OFF; also: Distribution Center.
DCC—Digital Compact Cassette, uses digital audio compression method (PSSC) for quality similar to CD but with less "data;" also: Duty Cycle Control.
DCCS—Distributed Computer Control System; another term used by a few for DCS (Distributed Control System).
DCD—Data Carrier Detect(ed); modem interface control signal (typically EIA RS232/422) indicating device is connected from DCE; is also called Received Line Signal Detector (RLSD).
DCE—Data Communications Equipment; sits between end devices and network (such as modem) establishing, maintaining, and terminating connection in data conversation data between two digital devices; also: Data Circuit-terminating Equipment; also: Distributed Computing Environment, software technology licensed by Open Software Foundation (OSF) that provides services for distributed computing; includes technologies for threads, remote procedure calls, directory service, security, time service, distributed file system, personal computer integration, and management.
DCN— Distributed Communications Network; see definition.
DCOM—Distributed Common Object Model; highly optimized protocol which extends Common Object Model for network communication of independent, interoperable software objects (remote objects).
DCPDP—Direct Current Plasma Display Panel; see definition.
DCS—Distributed Control System; see definition; also: Digital Control System (same definition); also: in system network architecture, Digital Cross-connect Systems.
DCT—Discrete Cosine Transform; data compression technique; also: Device-supported Time Code.
DCTV—Digital Composite TeleVision.
DCU—Digital Communication Unit
DCX—Intel® file format for saving multiple PCX graphics in electronic memory, used for exchanging data between computers.
DD—Device Description, in FOUNDATION Fieldbus & HART context, definition and description of function blocks and their parameters; see definition.
DD-IDE—Device Description Integrated Development Environment; supports efficient development, testing and maintenance of enhanced DDs.
DDAC—Digitally Directed Analog Control, otherwise called Supervisory Control.
DDAS—Diagnostic Data Acquisition System.
D/DBP—Disinfectants and Disinfection By-Products rule; nationwide U.S. study designed to control allowable levels of contamination in public water supplies due to these factors.
DDC—Direct Digital Control; controlling action on process by digital device (generally central computer) which establishes signal sent directly to final controlling element.
DDCMP—Digital Data Communications Message Protocol; character-oriented protocol developed by DEC® for transmission of data between stations in point-to-point or multipoint data communications system where physical method of transfer may be parallel, serial, synchronous, or serial asynchronous.
DDD—Direct Distance Dialing; telephone service in North America which permits subscriber to call other subscriber in different areas without operator assistance, permitting computers to do the same.
DDE—Dynamic Data Exchange; de facto dstandard convention for information exchange among various Windows software packages; Microsoft® developed inter-application communications protocol where data from one program automatically updates another; originally to move data from spreadsheet to word processor; is baseline protocol for OLE 1.0, but not for OLE 2.0 (is supported there, however, to maintain upward compatibility); has become more complex with advent of Windows™ and WindowsNT™ in industrial applications, causing wags to refer to it as "Different Dynamics to Everyone." J
DDES—Digital Data Exchange Specifications.
DDL—Data Definition Language, used in DBMSs; also: Device Description Language from InterOperable Systems Project and HART, & now called VDS; also: Dynamic Data Link.
DDMC—Distributed Discrete Manufacturing Control.
DDP—Distributed Data Processing; network of geographically dispersed, logically connected processors which share common resources.
DDR—Digital Data Repeating; scheme on single radio frequency which allows peer-to-peer communication between RTUs to share workload, compare output to inputs, monitor remote I/O, and relay data back and forth; also: Digital Disk Recorders, stand-alone devices that connect to host computer via Ethernet or SCSI interface to share files for video image processing and animation effects.
DDS—Dataphone® Digital Service; AT&T® communication service in which data is transmitted in digital rather than analog form, thus eliminating need for modems; also: Digital Data Storage; also: Digital Data Service by DEC®.
DDSN—Demand-Driven Supply Network.
DE—Digitally Enhanced; proprietary digital multi-drop instrument protocol by Honeywell.
Dead Volume—Volume of pressure port of transducer at room temperature and ambient barometric pressure.
Deadband—Increment through which input signal to device or system is varied before action is detected; expressed as percentage of input span; also: quite dull group of musicians. J
Debug—To find and correct mistakes in software or hardware; compare: Bug.
DEC—Do Expect Cuts J.
Decibel—(dB) Dimensionless unit used to express ratio of two powers, voltages, currents, or sound levels; ten times common logarithm of power ratio: n=10log10(Output/Input); dBm = decibel referenced to milliwatt; dBµ = decibel referenced to microwatt.
Decimation—In digital signal processing (DSP), process by which sampled data rate of signal is reduced by some factor (usually an integer); its purpose is to reduce number of samples that must be processed by circuitry that follows.
DECNET™—Digital Equipment Corporation NETwork; proprietary architecture to communicate among all of that company's equipment using peer-to-peer technique.
DED—Dark Emitting Diode; converse to LED (think about it), no doubt used to show output state of WOM; see WOM. J
Deduplication—Method of reducing digital storage needs by eliminating redundant data from a device; sometimes known as "intelligent compression" or "single-instance storage."
De Facto Standard—Standard that is widely adopted by marketplace but has no official legal status; compare De Jure Standard.
Default—Value(s) or option(s) that are assumed when not particularly specified; usually important in very flexible systems with so many selections to make by user, that most decisions can be extremely confusing, time consuming, or just unnecessary; user is free to concentrate on only those selections appropriate for the use at hand.
Default Directory—In computers, black hole into which all files that you need disappear.J
Degrees Of Freedom (DOF)—In control theory, number of independent variables available to be controlled in a process; such as in process of travel, one degree of freedom would be speed (as with a train), two would be speed and direction to left or right (as with a ship), three would be speed, direction left or right, and direction up or down (as with an airplane); any effort to control more variables than the number of degrees of freedom, the process loops will fight each other.
De Jure Standard—Standard that has recognition extended among various organizations, agreed upon by consensus (substantial agreement, although not necessarily unanimous); usually administered by official organizations, such as ISO/IEC,ANSI, ITU, IEEE, etc.; compare De Facto Standard.
DEK—(Dansk Elektroteknisk Komite); the Danish member of IEC.
Delay Distortion—In Communications, distortion resulting from non-uniform speed of transmission of various frequency components of signal through transmission medium.
Delay ON Release—Mode of operation where delay timing period begins when control switch is opened.
Delayed Contacts—Output contacts that transfer when timer times out.
Delimiter—In digital communication, character that separates and organizes elements of data.
DEMKO—(Danmark Elektriske Materiellkontroll); Danish certification and testing laboratory for testing equipment of different vendors to some common standard.
Demodulation—Process of retrieving original signal from modulated carrier wave; this technique is used in data sets to make communications signals compatible with computer signals.
Density—Mass per unit volume of substance (specific weight of fluid); often expressed in grams/cm3 or pounds/ft3.
Derivative Action—(Rate) Process control response that speeds correction based upon deviation rate of change from set point, thereby eliminating overshoot in system.
DES—Data Encryption Standard, data security scheme approved by NIST and specified by FIPS, see definition; also: Distribution Execution System, software packages for such functions as marketing and sales; also: Discrimination Expert System; also: Discrete Event Simulation, see definition.
Descender—In typography, that part of lower case letter extending below main body, as in characters "p" & "g."
Design, Operate, and Maintain (DOM)—Interoperability strategies of a company to leverage their vast amounts of Plant Lifecycle Information for better plant performance, faster response to market shifts, and therefore more profitable operations; ARC Advisory Group’s names for the three key interdependent factors that determine Plant Performance are Design –Having the right set of assets to satisfy customer needs; Operate –Optimizing use of these assets during each production run; Maintain –Ensuring that assets always have maximum production availability.
Destination Field—In digital communication, field in message header that contains address of station to which message is being directed.
Detail View—In process control room video screen views, depiction of all the parameters of a control loop such as alarm settings, gain, reset, and rate (PID), all connected inputs and outputs as well as all the “faceplate” values used in Group View; view is used for adjusting that loop; sometimes called Point View.
Detector—Optoelectronic transducer used in fiber optics for converting optical power to electric current; In fiber optics, usually a photodiode.
Deterministic Communication—In Networks, predicable schedule of communication based upon protocol characteristics and especially network access techniques, such as some token passing methods.
Deterministic Control—When controller can ensure that processing happens within a fixed range of time; can be influenced by processor, operating system, bus, memory, interfaces, the process itself, applications, and other factors.
Deterministic Model—Mathematical model which upon given set of input data, will produce single output or single set of output (will act in only one very predictable way).
Deviation—Difference between the set point (SP; desired value) and process variable (PV; actual, measured value at present) being controlled.
Deviation Amplitude—Total variation from desired setpoint of system; sometimes called closeness in control, expressed as "closeness of control is ±2°C" or system bandwidth of 4°C.
Devicebus Architecture—Control architecture that uses digital, serial, multidrop, two-way communications between and among intelligent field devices and control/monitoring systems; there are several different “competing” types; generally considered communicating intermediate sized, “byte level” messages of medium function among modestly sophisticated devices at medium to high speeds over short distances, as defined by Automation Research Corporation (ARC), see also Sensorbus, Fieldbus.
Device Driver—Software program that controls how computer interacts with devices such as printer, mouse, monitor, etc.; enables use of devices with computer.
Device Description (DD)—In FOUNDATION Fieldbus & HART context, definition and description of function blocks and their parameters, providing extended description of each object in Virtual Field Device (VFD), and includes information needed for control system or host to understand meaning of data in the VFD.
DeviceNet™—"Open"(non-proprietary) device level networking protocol on top of CANbus created by Allen Bradley based on Bosch’s CAN chips, now owned and operated by Open DeviceNet Vendors Association.
Dew Point (DP)—Temperature, referred to a specific pressure, at which water vapors condense, defined as that temperature at which condensation of moisture from vapor phase begins.
DFA—Digital Fault Analysis; also: Design For Assembly, discipline to synchronize and optimize fabrication and assembly techniques.
DFM—Design For Manufacturing; discipline to synchronize and optimize fabrication and assembly techniques.
DFS—Distributed File System; network version of UNIX® which provides transparent file transfer capability by allowing files and other resources attached to one system on network to be used by other systems, as though they were local resources; also: Design For Service; design of equipment which economically allows for easy access and repair.
DFT—Design for Test.
DGIS—Direct Graphics Interchange Standard proposed and created by Graphics Software Systems, Inc. (GSS).
DHCP—Dynamic Host Configuration Program; network protocol that allows workstation to be assigned IP address dynamically from centrally managed configuration server, used in Windows™NT Advanced Server; is supported in most networking devices and software--from ISDN routers to firewalls to every mainstream operating system on the market--and networks of all sizes are using DHCP to help manage their infrastructure equipment.
DHMO—Dihydrogen monoxide, see definition.
DHS—(Department of Homeland Security), [USA].
DHW—Data HighWay for digital communication, see Data Highway.
DI/O, DIO—Discrete Input/Output.
Diagnostics—Messages to user automatically presented by system which pinpoint failures in that system.
Dialog Box—Video screen pop-up window within selected view which carries an appropriate message for actions involved, and usually into which response can be made.
Diaphragm—Flat or convoluted plate which deforms to provide displacement in response to applied pressure
DIAT—Direction Impulse Adjusting Type process control output (pulsed signal).
DIB—Device Independent Bitmap format for saving graphics in electronic memory, used for exchanging data between computers; also: directory Information Base, for directory services.
DIBIT—Group of two bits providing four possible states: 00, 01, 10, 11.
Dichroic Filter—Optical filter that transmits light selectively according to wavelength.
DIF—Data Interchange Format; method of saving data to electronic memory expressly for exchanging data between computers.
Differential—For an ON/OFF controller, refers to difference between point where controller is triggered OFF and point where it is triggered back ON; control deadband or neutral zone; if too narrow, it can cause "chatter" causing high wear of components; if too wide, it causes poor control; with proportional control, the differential effect is usually averaged out and is of little consequence.
Differential Input—Analog input signals consisting of voltage difference between two terminals, both of which are different from device ground.
Differential Pressure (DP)—Difference in static pressure between two identical pressure taps at same elevation located in two different locations in a device.
Diffuser—Device that attenuates any fluid flowing through it, gas, liquid, light, or even electric power.
Digital—Referring to communications procedures, techniques, and equipment by which information is encoded as either binary "1" or "0;" the representation of information in discrete binary form, discontinuous in time.
Digital Backup—Alternative method of digital process control initiated by use of special purpose digital logic in event of failure in computer system.
Digital Control—Automatic process control loops performed by digital control devices, such as computer, microcomputer, microprocessor; compare: Analog Control.
Digital Light Processing (DLP)—A 3D printing technique; see Additive Manufacturing.
Digital Rights Management (DRM)—Technique which allows Internet content-owners to see who is passing content to whom, allowing varying degrees of protection to intellectual properties; usually an encryption scheme with a built-in e-business cash register; content is encoded and to get the key a user needs to do something - typically pay, but perhaps providing an e-mail address.
Digital Scrubbing—In video development, usually refers to audio scrubbing, reading back and forth over small portion of audio to locate precise edit point.
Digital Zoom—Ability to simulate range of focal lengths in digital video imaging device using dithering and other software techniques. See Optical Zoom.
Digitalization—Process of transforming analog (video) signal into digital information.
Digitally Addressable Lighting Interface (DALI)—Electrical interface and bus protocol mainly used to control lightning systems defined in the standard IEC 60929/EN 60929 Section E.4 & NEMA standard NS-243(-2004).
Digitized Typesetting—In typographic imaging, the creation of typographic characters and symbols by the arrangement of pixels.
Digitizer Tablet—Graphics drawing tablet used for sketching new images or tracing old ones for workstaion views of process or engineering schemes; user makes contact with tablet using pen or puck (mistakenly called a mouse) that is either wireless or connected to tablet by a wire; when sketching, user draws with pen or puck and screen cursor "draws" corresponding image.
Dihydrogen monoxide (DHMO)—Scientific name for water that is relatively unknown to most of the public, used in hoaxes that illustrate how the lack of scientific knowledge and an exaggerated analysis can lead to misplaced fears. "Di" meaning two, and "Mono" meaning single, describes how water is made up of two hydrogen atoms and one oxygen atom (H2O). L
DIIK—Darned If I Know. J
DIL—Dual In-Line (packaging); see DIP.
Dilberted—To be exploited and oppressed by your boss; derived from the experiences of Dilbert comic strip character: “I've been dilberted again. The old man revised the specs for the fourth time this week.” J
DILTDD41—Do It Like Th’ Darn Drawing For Once! J
DIMM—Dual In-line Memory Module; printed circuit board holding memory chips; plugs into DIMM socket on motherboard.
DIN—(Deutsches Industrie Norms, Deutsches Institut für Normung e.V.); German industrial standards often used internationally.
Dingbat—In typographical composition of screen displays and printing, ornamental character used to enhance or draw attention to text, which is not part of the standard alphanumerical set; also: TV’s Archie Bunker's pet name for his wife. J
Diode—Any electronic device that has only two electrodes and voltage characteristic which allows ac current to pass only in forward direction (as in flow check valve).
DIP—(sometimes DIL) Dual In-line Packaging, type of microprocessor chip housed in a rectangular casing with two rows of connecting pins on either side; standard package for integrated circuits ranging in size from 8 to 48 pins; compare SIP, and PGA.
DIP Switches—Miniature circuit switches in a DIP configuration for mounting on circuit boards.
Direct Attached Storage (DAS)—Computer storage that is directly attached to one computer or server and is not, without special support, directly accessible to other ones.
Direct Current Plasma Display Panel (DCPDP)—Type of Liquid Crystal Display (LCD) which relies upon emission of photons from gas that has been ionized by electric charge where electrodes are exposed to working gas; have lower driving voltages than ACPDPs, but luminescence diminishes over time because of electrode deterioration; compare with Alternating Current Plasma Display Panel.
Direct Digital Control—Process or manufacturing control performed by digital device (such as computer, microcomputer, microprocessor), which determines signal to final control element.
Direct Metal Laser Sintering (DMLS)—A 3D printing technique; sometimes also referred to by the terms Selective Laser Sintering (SLS) or Selective Laser Melting (SLM); see Additive Manufacturing.
Direct Port—Direct physical connection, such as a serial port on a computer, as opposed electrically isolated, or remote connection through a network.
Directory—Computer software structure for organizing files into convenient groups; used to locate files.
DIS—Draft International Standard (ISO standard status which has been registered and numbered but not yet given final approval).
Disc—In computer based devices, moving optical surface memory in disk shape to provide faster recall access than magnetic tape reels, and much more memory capacity than magnetic disks; high-intensity light sources such as lasers burn information into the disc surface; (Disks that employ magnetism are spelled with a "k" at the end; discs that use optics typically end with a "c").
Discrete—Separate and distinct, such as a signal toggled ON or toggled OFF.
Discrete Event Simulation—Technique often used by engineers in design and modification of production systems, whereby models output statistical estimates of performance, using graphic animation to help create a greater understanding of system dynamics.
Discrete Manufacturing—Production line for assembly of specific hardware, such as typically found in automobile and electronic industries.
Discrete Part Manufacturing—Manufacturing process that produces discrete parts in comparatively small lots or batches of one to perhaps 50,000.
Discrete Value— Variable with only two states: ‘1’ (true, ON) or ‘0’ (False, OFF).
Discriminator—Circuit that selects signals with particular range of amplitude or frequency and rejects all others; also: circuit that converts frequency-modulated or phase-modulated signal into amplitude-modulated signal.
Disk—In computer based devices, moving magnetic surface memory in disk shape to provide faster recall access than magnetic tape reels; (Disks that employ magnetism are spelled with a "k" at the end; discs that use optics typically end with a "c").
DiskOnKey—Flash memory based storage device that works on any USB-equipped PC without special drivers.
Disk Mirroring—In computer based devices, data protection by duplication on disk drives.
Disk Operating System (DOS)—Set of programs which instruct disk-based computing system to operate equipment through applications programs, and manage its resources such as tracking, saving, retrieving files, allocating storage space, etc.
Disk Server—Mass storage device that can be accessed by several computers, providing common sharing of stored data.
DISOSS—DIStribution Office Support System; server portion of client/server facility for handling E-mail.
Dispersion—General term for those phenomena that cause broadening or spreading of light as it propagates through optical fiber; the three types are modal, material, and waveguide.
Display—In industrial applications, typically the dynamic representation of data and plant information in visible form through CRT (video), LCD (flat panel), etc. methods.
Display Station—Location of video screen and keyboard, etc. from which plant, portion of plant, or process can be monitored and perhaps operated.
Dissipation Constant—Ratio for thermistor which relates change in internal power dissipation to resultant change of body temperature.
Dissolve—In video development, any of several transitions that involve the gradual decrease or increase in opacity of clip relative to another clip, graphic or matte.
Distance—In ultrasonic, radar & similar technologies for level measurement, distance from sensor to surface of contents; contrast with Level.
Distance Learning—Term encompassing all learning that takes place at locations remote from the point of instruction; may take the form of instructor-led course delivered via satellite to multiple remote locations; may also be training applications delivered via computer networks to students at any network node; Web-based training is one distance learning method in that the training application resides on a Web server while students may use the training from any location that can access that server.
Distortion—Extent to which system or component fails to reproduce accurately at its output the characteristics of the input; also: in video displays called pincushioning, manifests itself at sides of screen image by inward or outward bowing of vertical lines, such as those in spreadsheets and tables, can vary after switch of resolution and tends to worsen as monitor ages.
Distributed Communications Network (DCN)—Communications link among various (hardware) components in distributed control system; see also: Data Highway.
Distributed Computing Environment (DCE)—Software technology licensed by Open Software Foundation (OSF) that provides services for distributed computing; includes technologies for threads, remote procedure calls, directory service, security, time service, distributed file system, personal computer integration, and management.
Distributed Control System (DCS)—Real-time, fault tolerant system for continuous and complex batch process applications which evolved from central computer control of the 1960's and were developed initially for continuous flow processes which required loop, analog and limited discrete control; system which, while being functionally integrated, consists of subsystems which may be physically separate and remotely located from one another.
Distributed Network Protocol—See DNP3.
Distributed Management Environment (DME)—Part of Distributed Computing Environment (DCE) that unifies system and network management of stand-alone and distributed systems in heterogeneous computing environment; consists of graphical user interface and application services for software installation, software distribution, software licensing, printer services, and user group administration.
Distributed Control—Use of multiple microprocessors to distribute functions of DDC (central, or host computer) for performing process control, thereby distributing risk from component failure; later techniques to minimize ground loops permitted physical distribution around a plant, placing microprocessors at various points in process.
Distributed Processing—In computing, sharing application (sometimes operating system load as well) load among multiple processors within a device, or along some network of devices.
Distributed System—Group of connected computers sharing software, information, and/or load.
Dithering—Electronic graphic technique of filling gap between two pixels with another pixel having average value of those two to minimize difference, to add detail to smooth resulting line, or intermingling dots of various colors to create color not in palette which supports display being presented.
DLC—Data Link Control; rules (protocol) used by two devices on communication network to perform orderly exchange of information; also: Distributed Line Carrier, see PLC.
DLL—Dynamic Link Library; see definition; also: In FOUNDATION Fieldbus technology, Data Link Layer; see definition.
DLP—Digital Light Projector, Digital Light Processing; high definition projection using thousands of tiny Digital Micromirror Devices which reflect light source (divided into red, green, and blue beams with a prism) either on or away from screen driven by digital signals from computer memory rather than using vulnerable conventional film or video tape; compete with LCD and LCOS technologies for use in projectors; see DMD, LCD, & LCOS.
DLP—Digital Light Processing; a 3D printing technique; see Additive Manufacturing.
DLT—Digital Linear Technology; contains compressed digital data, generally for creation of commercial CDs.
DMA—Direct Memory Access; method of moving data from storage device to RAM without need for CPU intervention.
DMAC—Direct Memory Access Control.
DMACS—Distributed Manufacturing Automation and Control System.
DMC—Distributed Measurement & Control system.
DMD—Digital Micromirror Device; uses digital information from dynamic graphics & pictures (such as cinematography) that is stored in computer memory which switch thousands of tiny micromirrors to direct colored, high intensity light beams towards or away from lense to cause projection of moving images onto very large screens; see DLP.
DME—Distributed Management Environment; part of Distributed Computing Environment (DCE) that unifies system and network management of stand-alone and distributed systems in heterogeneous computing environment; consists of graphical user interface and application services for software installation, software distribution, software licensing, printer services, and user group administration.
DML—Data Manipulation Language for DBMSs.
DMLS—Direct Metal Laser Sintering; a 3D printing technique; see Additive Manufacturing.DMM—Digital MultiMeter; multiple electrical signal tester, which shows values in digital display.
DMOS—Double-diffused Metal Oxide Semiconductor.
DMS—Dynamic Mapping System; also: Distribution Management Systems; provide electric utilities with products and services to monitor, control, and automate their distribution networks; also: Dynamic Mechanical Spectroscopy; also: Document Management System; see definition; also: Desktop Management Suite; collection of software administration and backup programs for Windows from Seagate Software; also: Digital Multiplex System; digital switch from Nortel Networks that is used in telephone company central office.
DMT—Dead Man Timer; time-out device built into equipment to prevent continued operation if equipment operates too long for the intended function (indicating problem or malfunction).
DMT (BvS)—(Deutsche Montan Technologie); German certification and testing laboratory for testing equipment of different vendors to some common standard.
DMZ—DeMilitarized Zone; In computer networks, middle ground between an organization's trusted internal network and untrusted, external network such as the Internet; subnetwork (subnet) that may sit between firewalls or off one leg of a firewall; ISPs typically place their Web, mail and authentication servers in the DMZ; also: military term that refers to the area between two enemies (see the connection?).
DNA—Digital Network Architecture; Digital Equipment Corporation's layered data communication protocol; also: Microsoft Windows’ Distributed interNet Applications architecture standard.
DNC—Distributed Numeric Control; also: Direct Numerical Control.
DNP3—Distributed Network Protocol; from Westronics®, now Harris Controls Division, transferred to user's group of utilities & vendors formed in 1993; industry standard SCADA communications protocol based on drafts of the IEC870-5 SCADA protocol standards (now known as IEC 60870-5); DNP3 is touted to be a light protocol that can survive on a communication channel with inherent instability; currently used in many industries worldwide.
DNS—Distributed Name Service; also: Domain Name System, Domain Name Service, and Domain Name Server; database system that translates an IP address on the Internet into a digital domain name; a static, hierarchical name service which uses TCP/IP hosts, and is housed on a number of servers on the Internet; basically, it maintains this database for figuring out and finding (or resolving) host names and IP addresses, allowing users to specify remote computers by host names rather than numerical IP addresses.
DNV—(Det Norske Veritas); Norwegians standards group.
Document—In computers, some unit of printer output which must be printed contiguously, that is, no other output must be interspersed within; software application must define start and end of each document.
Document Management—Capture and management of documents within an organization; usually implies management of documents after they were scanned into computer, but has become an umbrella under which document imaging, workflow, text retrieval and multimedia are considered.
Document Management System—Computer software that manages storage, retrieval, and manipulation of documents for electronic publishing; generally supporting large variety of document formats and provides extensive access control and searching capabilities across LANs and WANs; may support multiple versions of a document, and be able to combine text fragments written by different authors; often includes workflow component that routes documents to appropriate users.
Document Object Model (DOM)—Platform and language-neutral application programming interface that will allow computer programs and scripts to dynamically access and update the content, structure and style of documents; that document can be further processed and the results of that processing can be incorporated back into the presented page.
DOD—Dissolved Oxygen Demand; also: (Department of Defense), in US.
DOE—(Department Of Energy); U.S. agency responsible for research and development of energy technology; also: Design of Experiments.
DOF—Degrees Of Freedom; see definition.
Dongle—Security hardware key that usually connects to PC parallel ports, and its software checks hardwired code on it to operate correctly; it passes signals through for printer or other hardware with no loss of functionality.
DOM— Document Object Model, see definition; also: Design, Operate, and Maintain, see definition
Domain Name—Unique name which defines Internet site, such as “(company).com”; always has two or more parts, separated by periods (part to left is more specific, to the right is more general); an organization called InterNIC registers domain names for a small fee and keeps people from registering the same name; see DNS.
Dopelar Effect—Tendency of stupid ideas to seem smarter when you come upon them rapidly J.
DOS—Disk Operating System; see definition; also: Defunct Operating System J.
DoS—Denial of Service; implemented by crackers (not hackers, see definitions) who break into business website to disrupt or destroy service to users & customers of that business by denying access to their site.
Dot—Individual element of halftone; can be as small as pixel in screen displays.
Dot Generator—Test generator used with video receiver to adjust convergence of picture tube.
Dowatchados—Vendor named category of control system specifications written by users & system consultants which are typified by sections such as "cabinets shall be metal," followed by six pages of paint specifications contributed by their paint expert; see also Druthers, Expectifications, Gotchas, Ropushers, Smokescreens, Stickits, Stonecutters, Wannagirls. J
Downloading—Process of sending configuration parameters, operating software, or related data to remote stations or devices from (usually central) configuration station; transferring file, or data, from one electronic device to another.
Downtime—Period during which manufacturing system, process, plant, computer system, control system, etc. is unavailable to users because of failure.
DP—Differential Pressure; see definition; also: Dew Point; see definition; also: Dash Pot; see definition; also: Draft Proposal (ISO standard status).
DPDT—Double Pole Double Throw; electrical switch action on pair of wires which can be used to select one of two paths for the pair, or be used to reverse direction of single polarized pair; relay output contact form C.
DPI—Dots Per Inch; measure of screen image or printed page.
DPM—Digital Panel Meter; also: Dynamic Performance Measures, see definition.
DPMCS—Distributed Process Measurement and Control Systems.
DPMI—DOS Protected Mode Interface; multi-tasking DOS extender, replaces VCPI.
DPS—Distributed Processor System; term created by Sam Herb in 1994 to identify the newer architectures being developed for Distributed Control Systems in light of connectivity to MES/ERP systems, emerging fieldbus capabilities, "smart" transmitters, "smart" valves," etc. as well as the blurring of distinction between process controllers and programmable logic controllers; see DCS.
DPSK—Differential Phase shift Keying; modulation technique used in Bell 201 modem & common form of phase modulation used in modems; does not require complex demodulation circuitry and is not susceptible to random phase changes in the transmitted wavefor; see FSK and QPSK.
DPST—Double Pole Single Throw; electrical switch action used to interrupt flow through pair of wires.
DPU—Distributed Processing Unit; also: Differential Pressure Unit.
DQDB—Distributed Queue Dual Bus; implementation of reservation strategy Metropolitan Area Network in which each station on 150Mbs twin bus records and maintains reservations in local queue.
Drag & Drop—In programming computers, ability to execute some function graphically without typing any command; for example, in some applications one can copy or move a file by “dragging” it across the screen from one folder and “droping” it into another.
DRAM—[pronounced: dee-ram] Dynamic Random Access Memory is inexpensive, high-density, and high speed, but must be refreshed regularly, reducing performance; see RAM, SRAM, MRAM.
DRC—Design Rule Checking.
Drift—Variation over time of any electrical property or signal value of circuit or apparatus, usually due to change in ambient temperature, time, line voltage, etc.; an advantage of values held in digital memory is that there is no drift in value.
Drill Press—Tall upright machine useful for suddenly snatching flat metal bar stock out of your hands so that it smacks you in the chest and flings your soda pop across the room, splattering it against that freshly-stained heirloom piece you were drying. J
Drive—In computers, used as noun for disk drive mechanism; often identified with alphabetical letter (A-Z) followed by colon (:) to indicate logical disk drive.
Driver—Hardware: circuit or device that provides input for another circuit, or controls operation of that circuit; also: Software: series of instructions to reformat data to transfer from one computing device to another; often electrical, mechanical, and software requirements of various devices in system are quite different when they each come from different vendors, and driver packages are needed to allow them to interconnect; open systems considerably reduce, and even eliminate this need.
DRM—Digital Rights Management; see definition; also: Drawing Requirements Manual..
Droop—Common occurrence in time-proportional controllers, it refers to difference in output requested by setpoint and where system actually stabilizes due to time-proportioning action of the controller.
Drop Cap—In typographical composition of screen displays and printing, an enlarged, initial capital letter of paragraph set into first several lines of that paragraph.
Drop-in—Character that appears erroneously (on display screen, printer, file, etc.) because disk or tape drive misstored or misread one or more bits.
Drop-out—Character that vanishes (from display, printout, or file) because disk or tape drive misstored or misread one or more bits; in data transmission, momentary loss in signal, usually due to effect of noise or system malfunction.
Dropping Resistors―Precision resistors for 4-20mA transmitters that are typically 250 ohms ±0.25 ohms with a temperature coefficient of not more than 0.01%/8C, used to convert 4-20mA signals to 1-5Vdc signals; also called Range Resistors.
DRP—Distribution Resource Planning.
Druthers—Vendor named category of control system specifications written by users & system consultants which appear to assemble one best feature from 10 different vendors into impossible single specification for same one system; see also Dowatchados, Expectifications, Gotchas, Ropushers, Smokescreens, Stickits, Stonecutters, Wannagirls. J
DS—(Dansk Standardiseringsråd); standards group in Denmark; also: Double-Sided.
DSA—Directory Service Agent, for directory services; also: Digital Signature Algorithm; in cryptography, popular public-key technique, though it can only be used only for signatures, not encryption.
DSC—Differential Scanning Calorimetry.
DSL—Digital Subscriber Line; technology using special modems to send digital signals, rather than analog waveforms, over existing twisted pair copper phone lines; see also ADSL and SDSL.
DSM—Demand Side Management; electric power industry term.
DSP—Digital Signal Processor(ing); RISC microprocessor optimized to execute digital signal processing algorithms; algorithm process by which sampled and digitized data stream is modified in order to extract relevant information.
DSR—Data Set Ready; modem interface control signal (typically EIA RS232/422) which indicates that the terminal is ready for transmission from DCE.
DSS—Decision Support System; form of computer-based data warehousing and management using DBMS techniques to focus retrieval of information for specific needs.
DSSS—Direct Sequence Spread Spectrum; used for wireless communication systems.
DST—Daylight Saving Time (called Summer Time in many countries); gets more out of summer days by advancing clocks by one hour during the summer; sun then appears to rise one hour later in morning when people are usually asleep anyway, at benefit of one hour longer evenings when awake
DSVD—Digital Simultaneous Voice Data; telephone connections to permit simultaneous transfer of voice and data similar to ISDN.
DTD—Document Type Definition; language that describes contents of SGML document; is also used with XML, and definitions may be embedded within an XML document or in a separate file.
DTE—Data Terminal Equipment; end point of communication link such as device acting as data source, data sink, or both (workstation, repeater, fileserver, etc.); usually producing data in human-readable form, as with printer or video screen.
DTM—Device type Manager; in context of FDT use in process control fieldbuses, software driver developed by device manufacturer for each of his devices or group of devices which encapsulates all device-specific data, functions and management rules such as device functions, its communication capabilities, internal data structure and dependencies as well as user interface elements; provides functions for accessing device parameters, configuring and operating the devices, calibrating, and diagnosing problems; can range from a simple user interface for setting device parameters to a highly sophisticated application; may perform complex calculations for diagnosis and maintenance purposes or display results in the form of curves, trends and other graphical elements. See FDT.
DTMF—Dual Tone Multiple Frequency; audio signaling frequency on touchtone, pushbutton telephones.
DTP—Distributed Transaction Processing; also: Desk Top Publishing; also: Diameter True Position.
DTR—Data Terminal Ready; modem interface control signal (typically EIA RS232/422) which indicates that the terminal is ready for transmission to DCE.
DTV—DeskTop Video; combines animation, image metamorphosis, photography, etc. within common data manager.
DUA—Directory User Agent, for directory services.
Dub—In video development, copy of master tape, usually at lower resolution, for off-line editing.
Dumb Terminal—ASCII asynchronous terminals that do not use data transmission protocol and usually send data one character at time, such as printer or VDT.
Duplex Cable—In fiber optics, two fiber cable suitable for duplex transmission; with copper wire, pair of wires insulated from each other and with an outer jacket of insulation around the inner insulated pair.
Duplex Transmission—Transmission in both directions, either one direction at a time (half duplex) or both directions simultaneously (full duplex).
DUT—Device Under Test.
Duty—Statement of operating conditions and their durations to which device or equipment is subjected, including rest and de-energized periods.
Duty Cycle—In digital transmission, ratio of high levels to low levels; in electrical apparatus, the pulse width times the frequency; in process control equipment, group of variations of load with time, as with repetitious operation (such as 2 sec. ON, 6 sec. OFF), often expressed as the energized percentage of total time cycle; the total time to complete one ON/OFF cycle.
DV, DVCAM—Digital Videocassette CAMera video format; potential emerging video production standard promoted by SONY®. [DVCPRO = version by Panasonic®; Digital-S = version by JVC®].
DVB—Digital Video Broadcasting; international digital broadcast standard for TV, audio and data; can be broadcast via satellite, cable or terrestrial systems; initially used in Europe and Far East.
DVD—Digital Versatile Disc; also incorrectly called Digital Video Disc; “versatile” because it can be used for audio, video, and computer data; concept to bring worldwide (consumer) electronics industry into one standard for both computer [extensive memory for archiving historical information from process] and entertainment industries [large CD-ROM, movie playback platform, game platform, large computer data drive and erasable memory]; 5 inch disk fits 3.7GB of data on single side using size of pits and spacing between pit tracks, and read using red laser beam rather than current infrared beam; a variation provides up to 7.4GB on single side using two layers, semi-reflective layer above fully reflective one; another variation provides 5GB on each side of two sided disc; later format for agreed upon standard among audio, video, and computer industries exceeds 17 GB, see MMCD, SD, and HDCD.
DVD+RW—Digital Versatile (not Video) Disc +Read Write; rewritable DVD disc technology endorsed by Sony, HP and Philips; using phase change technology, the first DVD+RW discs hold 3GB per side instead of the 2.6GB of DVD-RAM. DVD+RW discs can be rewritten 100,000 times and do not require the use of a caddy as do DVD-RAM discs; DVD+RW drives are also expected to write CD-R discs. See DVD-R/W.
DVD-R/W—Digital Versatile (not Video) Disc-Write; rewritable DVD disc from Pioneer using phase change technology; holds 3.95GB per side and can be rewritten up to 100,000 times; unlike DVD-RAM and DVD+RW discs, DVD-R/W discs can be read in current-day DVD-ROM drives, making DVD-R/W technology suitable for developing content that can be read in more existing machines.
DVD-RAM—Digital Versatile (not Video) Disc-Random Access Memory; rewritable DVD disc endorsed by Panasonic, Hitachi and Toshiba; uses phase change technology and expected to have significant impact on VHS tape market after Y2000, since they provide erasable, high-capacity optical disc that should become widely accepted; first DVD-RAM drives with a capacity of 2.6GB (single sided) or 5.2GB (double sided) became available in the spring of 1998.
DVD-R—Digital Versatile (not Video) Disc-Recordable; Write-once optical disc introduced by Pioneer, used to master DVD-Video and DVD-ROM discs; not expected to compete with DVD-RAM, which is rewritable DVD; DVD-Rs are DVD counterpart to CD-Rs and use same dye-layer recording technology to "burn" the disc.
DVD-ROM—Digital Versatile (not Video) Disc-Read Only Memory; used for storing data, interactive sequences as well as audio and video; provides 4.7 gigabytes of memory, roughly 7 times more than the 650 megabytes held by CD-ROMs; expected to become the CD-ROM of 21st century, they run in DVD-ROM or DVD-RAM drives, not DVD-Video players connected to TVs and home theaters; most, however, will play DVD-Video movies.
DVD-Video—Read-only Digital Versatile (not Video) Disc used for full-length movies; hold approximately 133 minutes of full-motion video per side using MPEG-2 compression; first DVD-Video players became available at the end of 1996.
DVI—Digital Visual Interface; digital flat panel interface from the Digital Display Working Group which was formed to create universal standard for attaching flat panel monitor, and expected to become widely used; based on TMDS signaling, the final draft of DVI was introduced in early 1999; also: Digital Video Interactive; brand name of Intel® for variety of product families having to do with earlier digital compression technique for data, audio, and full-motion video; provided up to 72 minutes of full-screen video on a CD-ROM with up to 100:1 compression ratio; Intel acquired DVI™ in 1988 from RCA's Sarnoff Research labs in Princeton, New Jersey, but DVI never caught on.
DVMRP—Distance Vector Multicast Routing Protocol; first popular routing protocol to support multicast; stemming from RIP and used in the Internet's Mbone (multicast backbone), DVMRP allows for tunneling multicast messages within unicast packets; supports rate limiting and distribution control based on destination address.
DVP—Digital Valve Positioner.
DVR—Dynamic Voltage Restorer; turns distorted waveform, including voltage dips, into required waveform by interjecting precise amount of voltage using series-connected transformer into distribution feeder between power supply side and load side; also: Digital Video Recorder, see definition.
DVST—Direct View Storage Tube; early graphics screen that maintained image without refreshing; entire screen had to be redrawn for any change.
DWDM—Dense Wavelength Division Multiplexing; optical transmission technique by which separate channels, distinguished by wavelength, are multiplexed through a transmission media.
DXF—Drawing File format by AutoCAD® adopted by others.
Dynamic Analysis—Study of data under changing internal and/or external conditions; can include static analysis, linear or nonlinear.
Dynamic Calibration—Calibration in which input varies over specific length of time and output is recorded against time.
Dynamic Data Exchange (DDE)—Microsoft® developed inter-application communications protocol where data from one program (application) automatically updates another; originally to move data from spreadsheet to word processor; is baseline protocol for OLE 1.0, but not for OLE 2.0 (is supported there, however, to maintain upward compatibility); has become more complex with advent of Windows™ and WindowsNT™; in industrial applications, causing wags to refer to it as "Different Dynamics to Everyone." J
Dynamic Dispatching—In real time (as it occurs), reporting to MES system all status changes such as work completed, operational problem, priority changes, updates entire plant floor, and automatically rescheduling all operations for all released jobs to reflect those changes.
Dynamic Link Library—unlike static libraries in DOS, code for all functions of program is not copied into executable file at link time, but rather linking occurs at run time when library code is joined with program code; this allows single DDL file to be shared by multiple applications w/o increasing memory or hard disk, there is standard interface independent of languages, compilers, and applications software, and updating DDL does not require all applications to be re-linked or rebuilt
Dynamic Memory—Solid state memory in which stored information decays over period of time, depending on nature of device and its physical environment; the memory must be refreshed often enough to maintain integrity; MOS random access memory and CCD memory are both dynamic.
Dynamic Performance Measures—Real-time econometrics of plant performance, linking production costs with automation system.
Dynamic Pressure—Difference in pressure levels from static pressure to stagnation pressure caused by an increase in velocity; increases by the square of the velocity.
Dynamic Range—Range over which active device can produce suitable output signal in response to input signal; often determined as difference in decibels between noise level of system and level at which output is saturated (overload level).
Dynamometer—Electrical instrument in which current, voltage or power is measured by determining force between fixed coil & moving coil; also: special type of rotating machine used to measure output or driving torque of rotating equipment.
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