JAOMAD Glossary L:
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
L—Means "Level" when used in first alpha character position of ISA instrument function tag, means "Light"(pilot) in succeeding position, "Low" when used as modifier [see ANSI/ISA S5.1-1984 (R1992)].
l—(lambda) Closed loop time constant which specifies closed loop performance in process control.
L-Glass—In construction of glass bulb type pH sensors, this is used for membranes of electrodes for processes where measurements are to be made in alkaline media with high process temperatures; see E-, G-, S-Glass.
La—In context of intrinsic safety, maximum allowed inductance from barrier protecting a hazardous area in an intrinsically safe installation; see Intrinsically Safe.
LA—Latin America; usually used in reference to markets that include South & Central America plus Mexico.
LAD—Local Area Disk; access by Digital Equipment Corporation to virtual disks via Ethernet.
Ladder Logic—Traditional language of programmable controllers which originated with electricians and electrical maintenance of electromechanical relay panels; symbolic representation which schematically illustrates functions of control circuit where power lines form sides of ladder-like structure, with program elements arranged to form rungs; one of five languages accepted under IEC 1131 standard for PLCs; see Function Block Diagram, Instruction List, Structured Text, and SFC; see also State Logic; also: training program for firemen. J
Lag—In instrumentation, time delay between output of signal and response of equipment to which signal is sent, usually caused by conditions such as capacitance, inertia, resistance, and dead time, either separately or in combination; also: in communications, time relationship between two waveforms where fixed reference point on one wave occurs after same point of reference wave.
Laminar Flow—Streamlined flow of fluid where viscous forces are more significant than inertial forces, generally below Reynolds number of 2000.
LAN—Local Area Network; data communications network within given area, such as control room, office, specific workspace, building, building cluster, etc.; up to 6 miles (10 kilometers), but not using common carrier.
Land Ban—Under Resource Conservation and Recovery Act (U.S.), prohibits land disposal of certain hazardous wastes unless they meet applicable treatment standards.
LAP—Line Access Procedure; CCITT specified data link protocol.
Laptop—Portable Professional Computer.
LAPB—Link Access Procedure, Balanced.
LAPI—Layered Application Programming Interface.
LAPUT—Light Activated Programmable Unijunction Transistor.
LAS—Link Active Scheduler; see definition.
LASCR—Light Activated Silicon Controlled Rectifier.
LASER—Light Amplification by Stimulated Emission of Radiation; intense light beam with very narrow bandwidth, which can produce images by electronic impulses from digital data.
Laser Disk—Optical medium capable of holding 30 minutes of moving video footage or up to 54,000 individual frames of still video per side; individual segments of frames can be accessed by computer.
LAT, (LAST)—Local Area Transport, (Local Area System Transport); protocol unique to Digital Equipment Corporation products for virtual terminal access across an Ethernet network.
Latency—Time interval between when network station seeks access to transmission channel and when access is granted or received; equivalent to waiting time.
Latent Heat—Amount of heat needed (absorbed) to convert pound of boiling water to pound of steam, expressed in BTU per pound.
Lateral Displacement Loss—Loss of power that results from lateral displacement from optimum alignment between two optical fibers or between a fiber and an active device.
Layer—Element of digital communication stack; one level of hierarchy of functions or segments of protocol which perform specialized roles (physical, data link, application, user); in OSI reference model, one of seven basic layers, referring to collection of related network processing functions.
LBS—Location-Based Services; feature set for ability to pinpoint the location of a mobile caller or vehicle in transit.
LC—Liquid Chromatography.
LCCA—Life Cycle Cost Analysis; orderly selection/elimination method which includes all cost factors (fixed & variable) of project, product, or an endeavor, see Life Cycle Costs.
LCCC—Leadless Ceramic Chip Carrier.
LCD—Liquid Crystal Display; see definition.
LCE—Life Cycle Economics, see definition.
LCH—Luminance, Chroma, Hue; model for color correction software for digital scanning, output devices, and displays.
LCI—Load Commutated Inverter.
LCIE—French certification and testing laboratory for testing equipment of different vendors to some common standard.
LCOS—Liquid Crystal On Silicon; reflective LCD technology that is small and inexpensive; competitive with DLP & LCD technologies; see DLP & LCD.
LCP—Liquid Crystal Polymer; material frequently used to make electronic connectors.
LD—Ladder Diagram; type programming for programmable logic controllers, see Ladder Logic; also: Laser Disk, see definition.
LDA—Logic Design Automation.
LDES—Linear Discrimination Expert System.
LD-RAM—Laser Disk Random Access Memory.
LD-ROM—Laser Disk Read Only Memory.
LD-V—Laser Disk Video.
LDAP—Lightweight Directory Access Protocol; standard Internet access protocol embraced by many software vendors.
LDAR—Leak Detection And Repair; programs maintained by EPA to assure extremely low valve stem leakage.
LDP—Laser Disk Player.
LDR—Land Disposal Restrictions, which are EPA promulgated rules implementing the land ban.
LDT—Linear Displacement Transducer; detects physical changes in position; used in factory automation, level measurement; etc.
Leaders—In typographical composition of screen displays and printing, rows of dashes or dots to guide user’s eye across screen or page; used in tabular work, programs, tables of contents, etc.
Leading—[pronounced: ledding]; in typographical composition of screen displays and printing, the distance between lines of type measured in points.
Leakage Rate—Maximum rate at which fluid is permitted or determined to leak through (pipe, valve, vessel, etc.) seal; type of fluid, differential pressure across seal, direction of leakage, and location of seal must be specified.
Leased Line—Telephone line reserved for exclusive use of leasing customers, without inter-exchange switching arrangements; also called private line; used for connecting to or more locations (such as company plants) on private WAN.
Least Squares Line—Straight line for which sum of squares of deviations is minimized.
LEC—Local Exchange Carrier, responsible for telephone service to final user, compare IXC.
LED—Light-Emitting Diode; see definition
Legacy Systems—Software and/or hardware systems which have existed for some time and yet are still viable, are often proprietary in nature, are not practical to remove from operation, perhaps because of the volume of use or popularity, but usually need some interface to operate with more current systems.
LEL—Lower Explosive Limit.
LEP—Light Emitting Polymer; organic polymer that glows (emits photons) when excited by electricity; LEP screens are used to make organic LED (OLED) displays and are expected to compete with LCD screens in the future. See OLED.
LER—Label Edge Router, see discussion of MultiProtocol Label Switching.
LES—Logistics Execution System.
Letterspacing—In typographical composition of screen displays and printing, the placing of extra space between each letter of a word.
Level—In ultrasonic, radar & similar technologies for level measurement, level of contents from bottom of vessel; contrast with Distance.
LF—Line Feed.
LGA—Lang Grid Array.
Li—In context of intrinsic safety, maximum unprotected inductance permitted in a hazardous area in an intrinsically safe installation; see Intrinsically Safe.
LIC—Linear Integrated Circuit.
LIF—Low Insertion Force.
Life—A whim of several billion cells to be you for a while. J.
Life Cycle—In instrumentation, minimum number of pressure cycles transducer can endure and still remain within specified tolerance.
Life Cycle Costs—Price of control system + project engineering + installation + net present value of on-going annual costs.
Life Cycle Cost Analysis—Orderly selection/elimination method which includes all cost factors (fixed & variable) over entire lifetime of project, product, or an endeavor.
Life Cycle Economics—Model showing benefits of equipment over their lifecycle less the costs over that same period.
LIFO—Last In, First Out.
Lift-off Voltage—Defined by some instrument vendors as minimum voltage that must appear across transmitter for it to function properly; some others may refer to this as " Compliant Voltage."
Light-Emitting Diode (LED)—Device that accepts electrical signals and converts the energy to light signal; semiconductor diode, junction of which emits light when passing current in forward (junction ON) direction; often light source for fiber optic transmission and also used as annunciator lamps in red, amber, green, and blue.
LILO—Last In, Last Out.
LIM EMS—Lotus®/Intel®/Microsoft® Expanded Memory System.
Limit Switch—Electromechanical device positioned to be actuated when certain motion limit is reached, thereby deactivating actuator causing that motion.
Limits of Error—Tolerance band for thermoelectric response of thermocouple wire expressed in degrees or percentage defined by ANSI specification mc-96.1 (1975).
LIMS—Laboratory Information Management System; used to integrate analytical data from process control laboratory with the plant wide process control, manufacturing, and inventory systems for more rapid contribution to quality control, process optimizing and operational costs.
Link(s)—In context of Internet, emphasized (with underlines, color, etc.) words in Hypertext document that act as pointers to more information on that specific subject; “mouse click” on them can transport user to another Web site.
Line Driver—Signal converter that conditions digital signal to ensure reliable transmission over an extended distance; also: baseball player who regularly hits the ball so it travels close to the ground. J
Line Power—Main power source supplied by power company or central generator of self-sufficient site; U.S. equivalent to what in U.K. is called Mains.
Line Regulation—In power supplies, change in value of dc output voltage resulting from change in ac input over specified range from low line to high line; normally specified as plus or minus change of nominal ac input voltage.
Line Spacing, Line Depth, Line Feed—In typographical composition of screen displays and printing, the distance from baseline to baseline between two lines of type.
Line Turnaround—In digital communication, reversing of transmission direction from sender to receiver or vice versa when half-duplex circuit is used.
Linear—Motion, action of device (typically a sensor), or value of signal where effect is exactly in proportion to its cause; also: in video development, editing limitation that requires edits to be performed from beginning to end of production piece in sequential order, changes cannot be made to previous edit decisions without loss of quality or starting over (compare with non-linear).
Linear Editing—In video development, central to old paradigm of using tape, editing from data stored on media that is not instantly accessible because of the continuous and linear layout of the data and therefore slower than nonlinear editing.
Linear Power Supply—Also known as series pass power supply, this style is most commonly used power supply design, consisting of transformer, rectifiers and filter capacitors, followed by pass element that varies voltage drop to maintain constant output voltage; provides best performance in regulation, ripple, transient response, output impedance and cost, but is larger, heavier, and has lower efficiency.
Linear Programming—Technique applied to problems in which linear function of several variables is subject to number of constraints in form of linear inequalities.
Linear Variable Differential Transducer (LVDT) —Electromechanical device that produces output proportional to displacement operating on principal of magnetic coupling between a primary and two secondary windings; offers many distinct advantages over other displacement measurement devices including: frictionless movement, infinite resolution, null repeatability, temperature stability, and environmental ruggedness; can measure displacements from a few microns to several feet in a wide variety of environments; one version is Linear Velocity Differential Transformer; sensor to measure rotational movement as linear displacement.
Linearity—Closeness of instrument calibration curve to specified straight line; expressed as maximum deviation of any calibration point on specified straight line during any one calibration cycle; linearity error is usually expressed as a percent of full scale output.
Link—Any specified relationship between two nodes in some network; communications path between two nodes; in FOUNDATION Fieldbus technology, logical medium by which H1 Fieldbus devices are interconnected; composed of one or more physical segments interconnected by bus Repeaters or Couplers; all devices on a link share common schedule which is administered by that link's current LAS.
Link Active Scheduler (LAS)—In FOUNDATION Fieldbus technology, deterministic, centralized bus scheduler that maintains list of transmission times for all data buffers in all devices that need to be cyclically transmitted; only one Link Master (LM) device on an H1 fieldbus Link can be functioning as that link's LAS.
Link Layer—Layer two of OSI reference model; see Data Link Layer.
Link Master (LM)—In FOUNDATION Fieldbus technology, any device containing Link Active Scheduler (LAS) functionality that can control communications on an H1 fieldbus Link; must be at least one LM on an H1 Link, one of those LM devices will be elected to serve as LAS.
Link Objects—In FOUNDATION Fieldbus technology, contains information to link Function Block (FB) Input/Output (I/O) parameters in same device and between different devices; links directly to Virtual Communications Relationship (VCR).
Link Segment—In data communications, electronically continuous piece of bus consisting of same cable with only two devices in point-to-point configuration, also called Inter-Repeater Link.
Linux—[pronounced: lee-nucks] Freely-distributable implementation of UNIX that runs on a number of hardware platforms, including Intel and Motorola microprocessors; developed mainly by Linus Torvalds, computer science student in Finland in 1991; because it's free and NOT Microsoft, and because it runs on many platforms, including PCs, Macintoshes and Amigas, Linux has become extremely popular over the last couple years; another popular, free version of UNIX that runs on Intel microprocessors is FreeBSD; see GNU.
Liquid Crystal Display (LCD)—Reflective visual readout of alphanumeric characters, generally of two types: Passive-Matrix Displays (PMLCDs) and Active-Matrix Displays (AMLCDs), which refer to how pixels in display are controlled; competes with DLP technology for projectors; see Organic Light Emitting Diode, DLP.
LIS—Logistics Information System, computer database of sales, purchasing, production, plant maintenance, and quality control used in EIS.
LISP—LISt Processing; computer language created by John McCarthy using data type list as its basic element; many artificial intelligence applications are written in LISP; some have also defined this as Logical Instruction Set Processing.
Live Object— In context of Internet, term by Netscape® for “plug-ins” that enable browser to play image, cinema, and sound files as inline part of Web page.
LIW—Loss In Weight; generally measured in processes which create change in density of product or volume of product in some vessel during operations on product.
LLC—Link Layer Control; also called Logical Link Control, Link Level Control; protocol developed by IEEE 802 committee for data-link level transmission control; LLC addresses distinguish different applications within the same station; includes end system addressing, error checking.
LLSAP—Link Layer Service Access Point (ISO model for digital communication); different for particular applications in specific stations.
LM—Link Master; see definition.
LMC—Least Material Condition.
LNA—Low Noise Amplifier.
Load—Electrical demand of process expressed as power (Watts), current (Amps), or resistance (Ohms).
Load Cell—Transducer for measurement of force or weight; action is based on strain gauges mounted within cell on force beam.
Load Impedance—Impedance presented to output terminals of some device by associated external circuitry.
Load Regulation—In power supplies, change in value of dc output voltage due to change in load resistance from open circuit to some value that yields maximum rated output current, or from full load to open.
Load Sharing—In communication systems, distribution of given load among several computers on network.
Loaded Line—Communications line for analog signals, such as telephone, equipped with loading cells to add inductance to minimize amplitude distortion.
LOC—Lines of Code; Lines of executable computer programming.
Local—In instrumentation, location of instrument that is neither in nor on panel or console, nor is it mounted in control room; local instruments are commonly in vicinity of primary element or final control element; use is often synonymous with "field," or "field mounted."
Local Panel—Panel that is not central or main panel; local panels are commonly in vicinity of plant subsystems or sub-areas; local panel should not be confused with "local instrument."
Logarithm—Exponent that indicates power to which a number is raised.
Logical Address—Digital number that uniquely identifies each device in a system.
Logical Circuit—see Virtual Circuit.
Logical Link Control—Protocol developed by IEEE 802 committee for data-link level transmission control; LLC addresses distinguish different applications within the same station; includes end system addressing, error checking; also called Link Layer Control.
Logical Port—Port specifically defined by a name (such as COM1, COM2, etc.) without a strictly defined physical port.
LOM—Laser Object Manufacturing, form of Rapid Prototyping, see RP; also: Spanish certification and testing laboratory for testing equipment of different vendors to some common standard.
LON—Local Operating Network, by Echlon, Inc., used as an inexpensive, unsophisticated communication bus.
LonMark—LON interoperability testing program.
LonTalk—LON protocol.
LonWorks—LON hardware including neuron chip licensed to Toshiba® & Motorola®.
Loop—In process control, the combination of process, sensor, controller, and final control element.
Loop Approval—Intrinsically safe concept that specifies the exact part number and products that can be used in the loop; no deviation from the specified units is allowed; see Intrinsically Safe.
Loop Resistance—Total resistance of complete electrical circuit.
Loopback—Type of diagnostic test in which transmitted signal is returned to sending device after passing through all or part of data communications link or network so that returned signal can be compared with transmitted signal.
LOSC—(Londonderry Occupational Safety Centre); British certification and testing laboratory for testing equipment of different vendors to some common standard.
Loss—Reduction in signal strength, expressed in decibels; also: attenuation, opposite of gain.
Lossless—Digital data technique that reduces size of file without sacrificing any of original data; this tool allows expanded of restored file to be exact replica of original file before compression.
Lossy compression—Digital data compression technique in which some data is deliberately discarded to achieve massive reductions in size of compressed file.
Low Pass Filter—In digital signal processing (DSP), filter that passes low frequencies and attenuates high frequencies.
Low Voltage Directive (LVD)—Establishes safety guidelines for electronic products that operate at 50 volts or above to ensure customers can handle such products safely (no exposed voltages or other hazards that can cause injury; part of regulations set in January, 1997 for companies selling electronic systems within European Economic Area, comprising of European Union and European Free Trade Association.
Lower Case—In typographical composition of screen displays and printing, the small letters in type, as distinguished from capital letters.
Lower Range Value—Lowest value of the measured variable that a device is adjusted to measure.
LP—Linear Programming, computation technique for finding optimum combination of process variables where there may be no single best one.
LPISM—Liquid Photo-Imageable Solder Mask.
LPM—Liters Per Minute.
LPT—Line PrinTer.
LPTTL—Low Power Transistor-Transistor Logic.
LRC—Longitudinal Redundancy Check; error detecting scheme consisting of bits calculated from odd and even parity for all characters in block.
LRDCT—Linear Rotary Differential Capacitive Transducer; measures rotational movement more precisely than linear differential transformers.
LRU—Least Recently Used; also: Lowest Replaceable Unit.
LRV—Lower Range Value; see definition.
LSB—Least Significant Bit; refers to smallest increment of resolution in an A/D or D/A conversion.
LSC—Least significant Character
LSD—Least Significant Digit; digit representing smallest value.
LSI—Large Scale Integration; multifunction semiconductor, such as microprocessor, with high density electronic circuitry on single silicon chip (as high as 1000 equivalent gates); integrated circuit.
LSL—Lower Sensor Limit (of a transmitter).
LSP—Local Set Point; of process control loop, typically entered by control room operator.
LSR—Label Switch Router, see discussion of MultiProtocol Label Switching.
LTCC—Low Temperature Co-fired Ceramic.
LU—Logical Unit; in systems network architecture, set of protocols that provides peer-to-peer communication between applications.
LU 6.2—In Systems Network Architecture, set of protocols providing peer-to-peer communication between applications.
Lugs, Landing Lugs—Used to terminate electrical cable conductors on termination facilities.
Lug, Range-Taking—Lug designed to accept more than one size electrical cable within a specified range.
Lug Landing—See Bus Stubs.
Lullabuoy—Idea that keeps floating into your head and prevents you from drifting off to sleep J.
Luminance - also brightness; in video displays, greatest light monitor can emit without losing focus; measured in units called footlamberts.
LUT—Look Up Tables; in digital data handling, method of comparing data which can often be used to simplify data communication, classify and analyze data for storage or retrieval, linearize digitalized analog signals, etc.
LV-ROM—Laser Video Read Only Memory; also: LaserVision™ ROM by Pioneer®.
LVD—Low Voltage Directive; see definition.
LVDT—Linear Velocity Differential Transformer; sensor to measure rotational movement as linear displacement a variation of Linear Variable Differential Transformer; also: Linear Variable Differential Transformer, see definition.
LVHC—Low Volume, High Concentration, usually in reference to pollutant measurement for EPA (U.S.) regulations.
LVIT—Linear Variable Inductance Transducer; linear measurement sensor based upon chemically etched planar coil technology.
Lw—In context of intrinsic safety, inductance of interconnecting wiring running through a hazardous area requiring intrinsic safety; see Intrinsically Safe.
LWT—Listen while Talk; sometimes used to identify the CSMA/CD protocol access technique.
L-Z Algorithm—Lossless data compression technique developed by two researchers named Lempel and Ziv.
LZH—Lempel-Ziv-Huffman; method of data compression which can reconstruct data exactly like original with no loss.
LZSS—Refinement of L-Z algorithm for data compression which can reconstruct data exactly like original with no loss.
LZW—Lempel-Ziv & Welch; patented by Unisys®, another refinement of L-Z algorithm for data compression which can reconstruct data exactly like original with no loss.
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