JAOMAD Glossary P:
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
P—Proportion (gain) action in modulating process control which responds to deviation from set point within proportional band (corrective action is proportional to amount of error); also: means "Pressure"(or Vacuum) when used in first alpha character position of ISA instrument function tag, means "Point"(test connection) in succeeding position [see ANSI/ISA S5.1-1984 (R1992)]; also: P(uppercase) in math is abbreviation "peta-" for 1015; also: p(lowercase) in math is abbreviation "pico-" for 10-12, once called micromicro (µµ) [also called: mickeymikes].
DP—Pressure drop (psig) across a restriction; inlet pressure minus outlet pressure.
P&IA Packaging and Interconnecting Assembly.
P&ID—Piping and Instrumentation Diagram; also: Process & Interlocking Diagram; also: Plant & Instrument Diagram.
P&IS Packaging and Interconnecting Structure.
P-I-N—Positive - Intrinsic - Negative (semiconductor).
P-I-N Diode—Typically used for photodiode, this semiconductor contains depletion layer within region of almost intrinsic (i-type) semiconductive material between its p-type and n-type regions.
P-P—Peak to Peak (between amplitudes of a signal).
P2P—Peer-to-Peer Computing, see definition.
PaaS—Platform as a Service; see definition.
PAC—Programmable Automation Controller; began as “politically correct” term for PLC, after a supplier chose to claim a copywrite on that term, now called by some as cross between PC & PLC for control, see definition, see PLC; also: Process Automation Controller; a term used by some who come from the process control realm rather than the factory automation arena; also: Precision Air Control; also: Packet Access Connection; also: Password Access Code; also: Personality Adapter Card; also: Platform Adapter Component; also: Platform Applicable Clients; also: PoCket Access; also: Programmable Analog Chips; (also over 100 additional definitions).
Packet—In digital communications, group of bits, including data and call control signals, transmitted as whole on packet-switching network; usually smaller than transmission block.
Packet Filter—In computer based networks, security protection system designed to prevent unauthorized access through firewall technology which looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules; this filtering is fairly effective and transparent to users, but is difficult to configure and susceptible to IP spoofing; see Firewall Technology, IP Spoofing.
Packet Switching—Data transmission technique whereby physical resources on path are switched on per packet basis, using control information in header of each packet (channel is occupied only for duration of transmission of packet); in some data communication networks, data may be formatted into a packet, or divided and then formatted into number of packets for multiplexing the transmission; see also Circuit Switching, and Message Switching.
PACS—Picture Archiving and Communication System; digital storage, retrieval, and presentation of input from video sensors.
PACT—President's Advisory Committee on future Technologies; IEC term.
PAD—Packet Access Device; interface between terminal or computer and packet switching network.
Page Mode Memory—type of Dynamic RAM that allows faster access to data in same row or page; called FPMRAM, works by eliminating need for row address if data is located in row previously accessed.
PAL—Programmable Array Logic; trade name by AMD®, see definition, see also GAL and PEEL; also: Phase Alternation Line, in which subcarrier derived from color burst is inverted in phase from one line to next in order to minimize hue errors that may occur in transmission, and has become a color video scan standard for Europe and other countries with 625 lines, 50 Hz, 220 Volts, first introduced in Europe in 1960's (UK on July 1, 1967, Germany on August 21,1967, Netherlands on September 21,1967), often referred to as "Peace At Last" J ; see also NTSC, SECAM, PAL-M.
PAL-M—Brazilian version of "Phase Alternation Line," used only in Brazil, 525 lines, 50 Hz, 220 Volts, often remembered as "Pay A Little More." J
PALC—Plasma Addressed Liquid Crystal; technology in which gas-plasma channels perform much similar pixel-triggering duties as do thin-film transistors in active-matrix LCD panels, with standard LCD-style backlighting provides illumination.
Palette—Collection of colors or shades available to computer graphic system or program within workstation.
PalmOS—Operating system engineered specifically for Palm Pilot hand-held devices.
Palm-size PC—Personal computers which were originally called “PalmPCs,” until that term was contested by 3Com, maker of the popular PalmPilot; name was altered to “palm-size PCs,” although H/PC seems to be gaining ground as the lead term. See H/PC.
PAM—Physical (or Plant) Asset Management, see definition under Physical Asset Management; also: Pulse Amplitude Modulation; in digital communication on control inputs, the process (or results of the process) in which series of pulses is generated having amplitudes proportional to measured signal samples.
PAM/FM—Frequency Modulation of a carrier by pulse amplitude modulated (PAM) information.
PAM/FM/FM—Frequency Modulation of a carrier by subcarriers that are Frequency Modulated by pulse amplitude modulated (PAM) information.
PAN— Personal Area Network; transmission technology that lets people transfer information by touch; For example, unit worn on the wrist could transmit a user's ID to all variety of check-in or check-out machines at security checkpoints, control rooms, consoles, etc.); miniscule amount of current used is thousand times less than electricity generated by combing your hair and is easily conducted through the body; also: in computer graphics, to move (while viewing) to different part of image without changing magnification.
Panel—Structure that has group of instruments mounted on it to function as the operator interface to the process; panel may consist of one or more sections, cubicles, consoles, or desks.
Panel Mounted—Term for instrument that is mounted on panel or console and is accessible for normal operator's use; a function that is normally accessible to an operator in a shared display (video screen) system is equivalent of discrete panel mounted device.
PANS—Process Analytical Systems.
PAR—Program Aid Routine.
Paradigms—Sets of rules and regulations, written or unwritten, which establish or define boundaries, and govern how to behave inside those boundaries to be successful; also: four nickels. J
Parallax—Optical illusion which occurs when viewing eye is not in same plane (perpendicular) as device being used; most noticed when a glass separates target, such as reading a meter or using a touchscreen.
Parallel Processing—Concurrent or simultaneous execution of two or more processes or programs, within same processor, as contrasted with serial or sequential processing.
Parallel Transmission—Transmission mode that sends number of bits simultaneously over separate lines, such as 16 bits over 16 lines; usually unidirectional.
Parameter—Arbitrary constant; variable in algebraic expression that temporarily assumes properties of a constant; also: In Plant Simulation, constants in plant model that quantify plant's physical characteristics; also: in object oriented software, information often included in a message call, needed by the method being called; see method.
Parametrics—Geometry dynamically linked to list of specific parameters, where changes to them result in changes to overall system (such as drawing in CAD system).
Parasang(es)—See Farsang.
Pareto Chart—SQC diagram for correlating data that is used to help uncover causes of quality variations
Pareto's Analysis—Technique of arranging data according to priority or importance and tying it to a problem solving framework.
Pareto's Law—The 80/20 rule: 80% of problems arise from 20% of sources.
PARISC—Precision Architecture Reduced Instruction Set Computing; see RISC.
Parity Bit—Bit that is set at "0" or "1" in character to ensure that total number of 1 bits in data field is even or odd within digital communication between devices or components.
Parity Check—Addition of information bits that make up transmission block to ensure number of 1s is always either even (even parity) or odd (odd parity); used to detect digital transmission errors; also: satirical Czechoslovakian imitator. J
PAS—Publicly Available Standards; also: Process Automation Systems; represents emergence of two-layer industrial automation model that consists of open business systems (OBS) and open control systems (OCS).
PASC—Precision Adaptive Sub-band Coding; coding method to create Digital Compact Cassette, averaging 4 bits/sample as compared with 16 bits used with compact discs; also: Pacific Area Standards Congress.
Pascal—Computer language named after 17th century mathematician Blaise Pascal; designed by Niklaus Wirth to teach students programming, it produces structured programs simple to follow and maintain.
Pass Band—In digital signal processing (DSP), frequency band in filters which is attenuated less than some certain amount (usually 3 dB in analog filters); see Stop Band.
Pass Through—Ability to gain access to one network element through another.
Passive Device—Any device, component, or circuit that does not introduce gain or does not have directional function; in practice only pure resistance, capacitance, inductance, or combination of these three is passive; in current loop applications, device not capable of supplying current for the loop, but must draw its current from connected equipment.
Passive-Matrix Displays (PMLCDs)—Liquid Crystal Display (LCD) technique where pixels on screen are controlled by voltage signals applied in rows and columns, and crystals respond by reorienting along field lines to transmit or block light to create image, and return to original orientation when voltage drains away; compare with Active-Matrix Displays.
Passive-Matrix Organic Light Emitting Diode—Relates to the way OLED display is controlled (or driven); display uses a simple control scheme in which each row (or line) in the display is controlled sequentially (one at a time); PMOLED electronics do not contain a storage capacitor and so the pixels in each line are actually off most of the time but needs to use more voltage to make them brighter to compensate.
Password—Entry with user’s identification (ID) to gain access to computer-based systems, is only known by owner of the User ID; proves to system that person using User ID is the correct owner of that ID.
PAT—Position Adjusting Type control output; uses direct feedback to controller algorithm from actual end element physical position (Not just positioner, nor simple feedback control from process sensor); also: Process Analytical Technology; initiative by the FDA (US) for foundation for new risk-based regulatory framework grounded in scientific & engineering principles in response to several manufacturing “sins” in pharmaceutical industry, see definition; also: Process Action Team; also: PATch (File Name Extension); also: Performance Acceleration Technology; also: Performance Analysis (Appraisal, Assessment) Team; also: Plasma Arc Technology ; also: Preliminary Acceptance Test (Trial); also: Process Analysis Technique; also: Product (Production) Acceptance (Assurance) Test; also: Portable Appliance Testing.
Path—In computer programs, hierarchy of files through which control passes to find particular file; designates one or more disk drives and/or directory paths to be searched sequentially for specific program or batch file.
Pathname—In computer programs, description of location of directory or file within some system; usually includes drive letter, colon (:), followed by directory and subdirectory names, followed by file name, with each name separated from previous by backslash (\).
Pathworks—DEC® replacement term for PCSA.
PB—Proportional Band; over which proportioning (gain) action occurs in modulating control.
PBGA—Plastic Ball Grid Array.
PBP—Picture By Picture; split screen video display, with simultaneous adjacent views or channels.
PBX—Private Branch Exchange; user owned telephone exchange.
PC—Printed Circuit; also: Programmable Chip; also: Pareto Chart; also: PerCent/age; also: Phase Control; also: Photo-Conductive; also: Pocket Calculator; also: Pocket Computer; also: Point of Curvature; also: Polycarbonate; also: Power Carrier; also: Power Converter; also: Primary Conveyor; also: Primary Plant Control (including coolant pump power control and identification); also: Prime Contract; also: Principal Consultant; also: Probable Cause; also: Process Control(ler); also: Processor Cache; also: Production Contractor; also: Program Coordinator; also: Program Counter; also: Project Control; also: Project Coordinator; also: Proximate Cause; also: Psychometric Chart; also: Pulsating Current; also: Pulse Compression; also: Punched Card; also: Programmable (logic) Controller [see comments under PLC]; also: Proportional Control; also: Professional Computer; also: Personal Computer (In reference to IBM® computer: Intel 8088/16-bit internal, 8-bit data bus, no internal memory protection); the processing speeds and memory capacity have been continually increasing; since 2000 term used interchangeably with laptop, workstation, and computer; see H/PC, Auto-PC, Palm-size PC; aren’t you glad I didn’t list ALL 240 definitions of this acronym?
PC Card—Another name for PCMCIA; also: Printed Circuit Card; also: politically correct humorist. J
PC-Control—Software-configured control strategy using standard personal computer hardware and software.
PC-DOS—DOS operating system originally developed by Microsoft and supplied by IBM on its PCs before Windows 95 became the norm; up until DOS 6, PC-DOS was almost identical to Microsoft's MS-DOS for non-IBM PCs, and both versions are called DOS.
PC-MOS/386—Personal Computer MultiLink Operating System for 80386 microprocessor.
PC/AT—Personal Computer/Advanced Technology; PC with Intel 80286/16-bit data bus, supports multiple displays.
PC/RT—Personal Computer/Risk Technology; using RISK with UNIX® System V as native operating system.
PC/XT—Personal Computer eXTended architecture; PC with Intel/16-bit internal, 8- bit data bus, no memory protection, hard disk, no cassette support.
PCA—Printed Circuit Assembly.
PCB—Printed Circuit Board; electronic subassembly consisting of an insulating board or card and circuit components such as diodes and integrated circuits; also: PolyChlorinated Biphenyl, a consideration in EPA (U.S.) regulations, colorless liquid used as insulating fluid in electrical equipment, a pathogenic and teratogenic.
PCD—Plasma Display Panel.
PCEbus—Personal Computer Eurocard bus; "open standard" architecture based on ISA electrical standard providing PC software compatibility on EU Eurocard format.
PCI—Peripheral Component Interconnect; CPU bus architecture by Intel® increases physical capacity for high speed data transfer in graphically intensive applications such as HMIs and video systems on Personal Computers.
PCI-DSS—Payment Card Industry Data Security Standard; worldwide, multifaceted security standard that includes requirements for security management, policies, procedures assembled by the Payment Card Industry Security Standards Council (PCI SSC); created to help organizations that process card payments prevent credit card fraud, hacking and various other security vulnerabilities and threats.
PCI-ISA—Peripheral Component Interconnect - Industry Standard Architecture; defines CPU card and backplane arrangement which allows PCI modules built for personal computers to operate in more modular and rugged systems offered by passive plane ISA vendors.
PCL—Printer Control Language; used for Hewlwtt Packard and compatible laser printers in communicating with Windows or DOS operating systems in computers.
PCM—Pulse Coded Modulation; technique in which an analog signal, such as process sensor signal or voice, is converted into digital signal by sampling signal's amplitude (slicing) and expressing different amplitudes as binary numbers; sampling rate must be twice the highest frequency in the signal; also: Plug Compatible Manufacturer; provides interchangeable components for systems which can be built from products designed by many different venders.
PCMCIA—(Personal Computer Memory Card International Association); not-for-profit trade association of more than 300 companies established in 1989 chartered with establishing, marketing, and maintaining series of hardware & software standards for credit-card-sized integrated-circuit PC cards; not always consistent standard for memory cards, sometimes called Personal Computer Memory Card Interface Access; also called PC Card; emerging uses go beyond memory to include communication capabilities and I/O ports; available in three versions: Type I, Type II, Type III, all with same 68-pin edge connector; Type I is 3.3mm thick, typically for memory enhancements such as RAM, OTP, EEPROM and flash memory; Type II is 5.0mm thick, most common, also for memory, increasingly as modems, sound cards, networking, I/O ports, and SCSI; Type III is 10.5mm thick, for additional memory and I/O features needing larger size such as hard disk drives, radio communication devices, etc.; also: referred to by some wags as "Pretty Confusing, May Cause Intense Anxiety"J; some others as "People Can't Memorize Computer Industry Acronyms."J
PCN—Personal Communication Network; envisioned combination of MANs and wireless networks; also: Process Control Network.
PCR—Phase-Change Rewritable optical disk system; developed by Panasonic® to operate with quadruple-speed CD-ROM drive, providing ability to write to optical media as well as read from it.
PCS—Plastic Clad Silica; optical fiber having glass core and plastic cladding; also: Process Control System; responsible for manufacturing of product, as compared to MIS, context being used by vendors of PLC systems (and some market research firms) as equivalent to DCS; also: Personal Communications Services; wireless communicators such as cellular telephones.
PCSA—Personal Computer System Architecture; by DEC®.
PCSF—(Process Control Systems Forum); an open, collaborative, voluntary forum that leverages combined experience, capabilities, & contributions of control systems stakeholders to develop & adopt common architectures, protocols, standards, best practices, & to define common requirements; is sponsored by Department of Homeland Security (DHS) National Cyber Security Division (NCSD) Control Systems Security Program (CSSP).
PCTE—Portable Common Tool Environment.
PCX—PiCture eXchange; Intel® bitmap file format for saving graphics in electronic memory, used for exchanging data between computers.
PD—Means "Pressure Differential" when used in first two alpha character positions of ISA instrument function tag [see ANSI/ISA S5.1-1984 (R1992)]; also: Positive Displacement; also: Plasma Display; also: Panasonic Drive, developed by Panasonic® as quadruple-speed CD-ROM with phase-change re-writable (PCR) optical disk system.
PDA—Personal Digital Assistant; small hand sized computer which acts as appointment diary, To Do list, phone list, and other functions; also: Power Distribution Assembly; also: Process and Data Automation.
PDAS—Process Data Acquisition System.
PDC—Primary Domain Controller, see definition; also: Personal Digital Communications, see definition.
PDCA—Plant-Do-Check-Act; continuous cycle of performance to assure quality production called “Deming Cycle” (Deming called it “Shewart’s Cycle”).
PDC(S)—Plant Data Collection (System).
PDES—Product Definition Exchange Standard; ANSI standard for engineering data representation; recently changed formally to mean “Product Definition Exchange using STEP” from “Product Data Exchange…”
PDF—Portable Document Format; file format for saving literature layout with graphics in electronic memory, used for exchanging data between computers, even eliminating requirement that target machine contain same fonts; modeled after the PostScript language that is both device and resolution independent.
PDIF—Product Definition Interchange Format; formerly Product Data Interchange Format.
PDL—Page Description Language.
PDLI—Physically Distributed/Logically Integrated; engineering design team efforts through data management computer networking.
PDM—Positive Displacement Meter; generally used to measure flow; also: Product Data Management; system that tracks product data creation, revision, and movement for management control of engineering design information; also: PreDictive Maintenance, see definition.
PDN/VAN—Public Data Network/Value Added Network; such as X.25.
PDP—Programmable Data Processor; also: Plasma Display Panel, see definition.
PDR—Preliminary Design Review; used to identify issues in design practicality; compare: CDR.
PDT—Portable Display Terminal.
PDU—Protocol Data Unit; ISO term referring to packet of information exchanged between two network layer entities.
PDXI—Process Data eXchange Institute; non-profit, sponsored research initiative under the American Institute of Chemical Engineers (AIChE) for leveraged, cooperative effort by process industry companies and its suppliers to create, maintain, and use industry-wide standards for automating the exchange of process engineering technical data using data models that formally describe and define process engineering technical data in sufficient detail to permit automated data exchange.
Peak Value—Maximum value of impulse voltage, current, or any alternating signal; can be positive or negative value of any alternating quantity during\given time interval, positive and negative components are not necessarily equal in value.
PECL—Positive Emitter Coupled Logic; reference to 5V.
PEEL—Programmable Electrically Erasable Logic; same as Programmable Array Logic device, but AMD® made "PAL" a tradename; another term is GAL.
Peer-to-Peer—Digital communication directly between two autonomous devices on same network without any intervening devices to “store & forward” messages.
Peer-to-Peer Architecture—Type of computer network in which each station has equivalent capabilities and responsibilities; differs from client/server architectures, in which some computers are dedicated to serving the others; these networks are generally simpler and less expensive, but they usually do not offer same performance as client/server architectures under heavy loads.
Peer-to-Peer (P2P) Computing—Computer communication which allows sharing of files and processing over internet among different computers in several (many) locations; in this way several computers, working together, can solve problems that would previously take a massive main-frame or super-computer.
Peer-to-Peer Communication—Computer communication directly between devices that operate on same communications level on network, without intervention of any intermediary devices such as host or server; peer-to-peer communication method (or protocol) defines only basic mechanisms used to transfer data; it need not specify when or why peer application programs or nodes interact or how communication between such applications or nodes should be organized in a distributed environment; the latter problems fall into domain of peer-to-peer operating system (see peer-to-peer network below).
Peer-to-Peer Network—Network consisting of nodes (computers) which all have both client and server capabilities and on which communication and data sharing is carried on directly between nodes, rather than being arbitrated by an intermediary node; on a peer-to-peer network all nodes run same peer-to-peer operating system, which gives them both client and server capabilities.
Peltier Effect—When current flows through thermocouple junction, heat will either be absorbed or evolved, depending upon direction of current flow.
PEM—Plastic Electronic Module.
Percentage Timer—Time cycle of this type timer is fixed with percentage ON time adjustable; the cycle repeats.
Percussive Maintenance— Fine art of whacking an electronic device to get it to work again. J
Performance Qualification—In process validation, documented verification that the process and/or the total process related system performs as intended throughout all anticipated operating ranges.
Peripheral—Device external to CPU and main memory, such as printer, modem, terminal, etc. which are still connected into system.
PERL—Practical Extraction Report Language; High-level, general-purpose, interpreted, dynamic computer programming language that combines syntax from several UNIX® utilities and languages; introduced in 1987, designed to handle variety of system administrator functions and provides comprehensive string handling functions to make report processing easier and since has undergone many changes and revisions and become widely popular among programmers; widely used to write Web server programs for such tasks as automatically updating user accounts and newsgroup postings, processing removal requests, synchronizing databases and generating reports; has also been adapted to non-UNIX® platforms; compare with PURL.
Permanent Split Capacitor Motor—Low cost ac motor designed for low starting torque; startup and running windings stay ON during operation.
Persistence—Ability to continue to exist, often refers to use of nonvolatile memory to retain information through power outage or maintenance shutdown; also: refers to retention of screen images on CRT due to phosphorus, and images on retina within human eyeball permitting sense of smooth motion of rapidly changing views.
Personal Area Network (PAN)—IBM transmission technology that lets individuals exchange data with a simple touch or grasp (such as a handshake).
Personal Communications Services (PCS)—Refers to wireless services that emerged after the U.S. Government (FCC) auctioned commercial licenses in 1994 and 1995; radio spectrum works over CDMA in the 1.8-2GHz range is typically used for digital cellular transmission that competes with analog and digital services in the 800Mhz and 900MHz bands.
Personal Conferencing Specification (PCS)—Videoconferencing technology that uses Intel's Indeo compression method. It is endorsed by the Intel-backed Personal Conferencing Working Group (PCWG). Initially competing against H.320, Intel subsequently announced its videoconferencing products will also be H.320 compliant.
Personal Digital Communications (PDC)—Digital cellular phone system widely used in Japan, based on TDMA.
PES—Programmable Electronic System; system based upon one or more computers connected to sensors and/or actuators in a process plant for purposes of control, protection, or monitoring; also: Process Electrochemistry Systems.
PET—Process Engineering Tools; see definition.
Petaflop—Thousand trillion floating point operations per second; a measure of performance for the fastest computers in the world.
PEX—Protocol which is the PHIGS EXtension to the X-window system.
PFD—Process Flow Diagram; also: Probability of Failure on Demand; chances of failure in energized mode.
PFU—Programmable Function Unit; standard building block of Field-Programmable Gate Arrays (FPGA).
PG—Protective Ground; such as shield or frame.
PGA—Professional Graphics Adapter (Array); for PC/AT & PC/XT high resolution graphics; see CGA, EGA SVGA, UXGA, VGA, XGA; also: Pin Grid Array, type of microprocessor chip package in which connecting pins are located on bottom in concentric squares; particularly good for chips that have many pins, compare with DIP and SIP; also: Programmable Gain Amplifier; Signal amplifier that can be programmed to apply different signal gain depending on input voltage, effectively increasing dynamic range and sensitivity of A/D converter.
pH—Indication of acidity or alkalinity of solution; units range from 0 (most acidic) to 14 (most alkaline), with 7 as neutral; the term is used to describe hydrogen ion activity (aH+) of a system, so is equal to -log(H+) [negative log of hydrogen concentration in moles per liter].
PHA—Process Hazard Analysis; used to identify hazards and determine protective and mitigating measures to be applied as appropriate to protect employees, the community, and the environment to meet regulations, such as PSM & RMP.
Phase—Time based relationship between periodic function and reference; in electricity, it is expressed in angular degrees to describe voltage or current relationship of two alternating waveforms.
Phase Coherent—Single channel communication signaling method which uses frequency shifts of signal to encode data; frequencies are directly related to the data represented and proportional to data rate, changes between frequencies occur at 0 crossings.
Phase Difference—Time expressed in degrees between same reference point on two periodic waveforms.
Phase Linearity—In digital signal processing (DSP), property of filters, meaning that all signals are delayed the same amount of time, regardless of their frequency; this becomes series of straight lines when plotting phase vs. frequency.
Phase Modulation—One of three ways of modifying sine wave signal to make it "carry" information; the sine wave or "carrier" has its phase changed in accordance with information to be transmitted.
Phase Proportioning—Form of control, usually for electric heating, where power supplied to process is controlled by limiting phase angle of line voltage.
Phase Shift—In digital signal processing (DSP), angular measure of shift between two signals.
Phillips Screwdriver—Normally used to stab the vacuum seals under lids and for opening old-style paper-and-tin oil cans and splashing oil on your shirt; but can also be used, as the name implies, to strip out Phillips screw heads. J
PHIGS—Programmer's Hierarchical Interactive Graphics System.
Phonemes—Smallest individual component of speech; necessary in developing speech recognition and “talking control rooms;” see visemes.
Photodetector—Optoelectric transducer, such as p-i-n photodiode or avalanche photodiode.
Photodiode—Semiconductor diode that produces current in response to incident optical power and used as detector in fiber optics.
Photon—Quantum of electromagnetic energy; small "particle" of light.
Physical Asset Management (PAM)—Defined by some as management of the tangible assets used to produce/process some product, or to deliver a company’s services; generally involves all phases of asset management from determining the organization's needs, through design/selection/procurement, placing into service, operation and maintenance, and final disposal, including management issues in areas of project management, maintenance management, fleet management, and facilities management; sometimes called Plant Asset Management; see more terms: Enterprise Asset Management, Asset Management.
Physical Layer—Within OSI model of digital communication, lowest layer (layer one) of network processing, below link layer; concerned with electrical, mechanical, and handshaking procedures over interface that connects a device to transmission medium; referring to an electrical interface, such as RS232C; also: in FOUNDATION Fieldbus technology, receives messages from Communications Stack and converts messages into physical signals on fieldbus transmission medium, and vice-versa.
Physical Port—Port specifically defined by address that can take on almost any logical port name, for example, address 2F8H may normally be called COM2, but could be called COM1 if system "finds" only this COM port and initializes it first.
P/I—Pressure to Current conversion.
PI—Process Information (system); also: Proportional-Integral (2-mode) modulating control.
Pi Characters—In typographical composition of screen displays and printing, characters not usually found in a typical font, such as reference marks, mathematical signs, accents, and symbols.
PI/O, PIO—Parallel Input/Output.
PIA—Peripheral Interface Adapter.
PIB—(Physikalisch-Technische Bundesanstalt); German national intrinsic safety testing and certifying agency and mark associated with the agency; also: Process Instrument Building; environmentally controlled structure in a process area used to hold I/O modules and occasionally controllers & emergency/maintenance workstations.
PIC—Programmable Interrupt Controller.
Pica—In typographical composition of screen displays and printing, a printer's unit of measurement, equals 12 points, approx. 1/6 inch.
PICMG™—(PCI Industrial Computer Manufacturers Group); founded in May, 1994 as consortium of four, now over 122 computer products vendors to develop interconnection standards to peripherals.
PICSA—Protocol Implementation Conformance Statement; from MMS.
PICT—PICTure vector & bit mapped format by Apple® in Macintosh™ for saving graphics in electronic memory, used for exchanging data between computers.
PID—Proportional-Integral-Derivative; (3-mode) modulating control which combines effects of error signal with its integral and derivative to provide more responsive control system; also: Process IDentifier; temporary number assigned by the operating system to a process or service; also: Packet IDentifier; also: Parameter IDentification; also: Primary Input Device; also: Programmable Interupt Device; also: Protocol Identifier Data; also: Photo-Imageable Dielectric; check P&ID.
Piezoresistance—Resistance that changes with (physical) stress, such as pressure in a sensor.
Pilcrow – The paragraph sign (¶).
Pilot Light—Light that indicates which of a number of normal conditions of a system or device exists; it is unlike alarm light, which indicates abnormal condition; also: called Monitor Light.
Pilot Plant—Smaller version of projected industrial plant, used to gain experience and data for design and operation of final plant.
PIM—Personal Information Manager; also: Process Information Manager; also: Plant Information Management; also: Parallel Inference Machine which contains many independent processors working simultaneously on pieces of the same overall problem for supercomputing capability.
PIMS—Process Information Management System.
PIN—Plant Information Network; see also: P-I-N.
PIN Diode—More correctly see P-I-N Diode.
PING—Packet InterNet Groper; a utility to determine whether a specific IP address is accessible; important when making plant network available to other plant sites.
Pinout—List or diagram showing location/definition of individual wires in cable or connector.
PIN Photodiode—Photodiode having large intrinsic layer sandwiched between p-type and n-type layers; called P-I-N Diode.
PIP—Picture In Picture; video screen with more than one simultaneous view or channel, usually one or more insets within larger view; also: Process Industry Practices consortium of major oil and chemical companies which have adopted ISA S84 as the criteria (specification) document for safety systems; also: Partner Interface Process.
Pipe Schedule System—Graduated differences in weight (wall thickness) are designated by "schedule number;" lower numbers are lightest weight grade (thinnest walls), and graduated weight schedules become thicker toward the inside, maintaining a consistent outside diameter in each of the nominal sizes involved.
Pirated Software—Illegal copy of copyrighted software.
PIRS—Process InfraRed Systems.
PIT—Programmable Interval Timer, see definition.
PIXEL—PIcture ELement; smallest unit on video display screen that can be stored, displayed, or addressed; a computed picture is typically composed of an array of 450x300, 720x560, etc.; in color video, contains red, green, and blue values, and the color depth refers to number of bits of data used to define the pixels' color (8 bits = 256 colors, 16b = 65,535 colors, 24b = 16.7 million colors).
PIXEL Tags—See Clear GIF.
PKNMiJ—(Polski Komitet Normalizacji); standards group in Poland.
PL/1—Thirty year old computer language by IBM® intended to replace COBOL and FORTRAN without much success; is not an acronym for Programming Language 1.
PLA—Programmable Logic Array; see definition.
Planimeter—Drafting instrument used to measure area of graphically represented planar region; region being measured may have any irregular shape, making this instrument remarkably versatile in interpreting instrument chart records; with use of CAD and digital images, this tool may bee outmoded, but they are still being manufactured.
Plant Asset Management (PAM)—See definition under Physical Asset Management as well as other terms: Enterprise Asset management, Asset Management.
Plant Inputs—In Plant Simulation, anything that control system does to influence activities of the plant; see Plant Model, Plant Outputs.
Plant Model—In Plant Simulation, set of mathematical or logical relationships that quantify behavior of the plant; see Plant Inputs, Plant Outputs.
Plant Outputs—In Plant Simulation, measurable results of a control system's efforts; see Plant Model, Plant Inputs.
Plasma Display Panel (PDP)—Type of Liquid Crystal Display (LCD) which relies upon emission of photons from gas that has been ionized by electric charge; offered in two versions: Direct Current (DCPDPs) and Alternating Current (ACPDPs).
Platform—In computers, a microprocessor and operating system.
Platform-as-a-Service (PaaS)—Cloud computing model of service delivery where computing platform is from an outside provider as on-demand service on which applications can be developed & deployed; main purpose is to reduce the cost & complexity of buying, housing, and managing underlying hardware & software components of platform, including any needed program & database development tools; cloud consumer has control over applications & application environment settings of platform; security provisions are split between cloud provider & cloud consumer; compare: Infrastructure-as-a-Service, Software-as-a-Service.
Platinel®—Nonstandard, high temperature platinum thermocouple alloy whose thermoelectric voltage nearly matches type K thermocouple; trademark of Engelhard Industries.
PLC—Programmable Logic Controller (originally called PC, but IBM usurped the term so this one was taken from Allen-Bradley… now this term is claimed to be under copy write so a new term PAC is being used by some); a controller, usually with multiple inputs and outputs, that contains an alterable program, generally to perform high speed repeatable tasks; see definition & PLD; also: Power Line Carrier, see DLC; also: PROWAY Link Control.
PLCC—Plastic Leaded Chip Carrier.
PLCopen—Vendor- and product- independent international association founded in June 1992 to advance IEC 1131-3 open software development standard for programmable controllers.
PLD—Programmable Logic Device; see definition.
PLED Polymer (Polymeric) Light-Emitting Diode; see definition.
Plenum-rated Cable—Cable which has flammability and smoke characteristics (& NEC rating) to allow routing between walls, under structural floors (plenums), and above drop ceilings without being enclosed in a conduit; does not give off toxic fumes when it burns; usually this is only fiber optic as metallic wire is for electrical energy which have additional safety code restrictions.
Pleslochronous—In multiplexing, method used when not all data flows have same bit rates and are adjusted by inserting or deleting bits.
Pliers—Tool used to round off bolt heads; sometimes used in the creation of blood-blisters. J
PLL—Phase Locked Loop.
PLM—Product Life-cycle Management; see definition.
Plug-and-Play (PnP)—Ability for circuit boards from any vendor to be inserted into the same backplane, to be fully configured without setting DIP switches, jumpers, and other configuration elements; usually relates to boards built to PC ISA specifications; technology developed by Microsoft and Intel; since introduction of NuBus, Apple Macintosh has been a plug-and-play computer.
PLV—Production Level Video; video encoding using oldest digital compression scheme, by Intel/IBM.
PM—Phase Modulation; method of transmission whereby angle of phase of carrier wave is varied in accordance with signal, see PM & FSK; also: Permanent Magnet; also: Project Manager; also: Preventive Maintenance, see definition.
PMC – PCI Mezzanine Card; peripheral Component Interface to PCs which allows low profile PCI attachment to larger format buses such as VME and MULTIBUS.
PM&C—Process Management & Control.
PMD—Programmable Message Display.
PMLCD—Passive-Matrix Display; see definition.
PMG—Permanent Magnet Generator.
PMOLED—Passive-Matrix Organic Light Emitting Diode, see definition.
PMOS—P-channel Metal Oxide Semiconductor.
PMP® (Project Management Professional) certification - Offered by PMI (Project Management Institute), the PMP® demonstrates advanced knowledge of and experience with Project Management concepts.
PMS—Process Messaging Service; intended companion standard to MMS for process control.
PMSM—Permanent Magnet Synchronous Motor.
PNO—(PROFIBUS NutzerOrganisation); charter European group formed in 1987 to standardize work of Joint Fieldbus Project, and embracing German national standard for fieldbus protocol.
PnP—Plug-aNd-Play; see definition; also: Plug ‘n Pay, Plug ‘n Pray J.
PNP—Positive-Negative-Positive (Transistor); also: Pulse Narrowband Processor.
PoC—Proof-of-Concept; evidence that demonstrates an idea or business model is feasible.
PoE—Power over Ethernet; specification IEEE 802.3af, which is still in its infancy, Ethernet provides no power so installers normally need to supply additional wires.
Point—In typographical composition of screen displays and printing, a printer's unit of measurement used originally for designating type sizes (from top of ascender to bottom of descender); there are 12 points to a pica, approximately 72 points to an inch; also: an electrical power outlet (U.K.); also: In Power Industry SCADA software, data record comprising a real-time value plus quality codes (and sometimes including in the concept metadata such as scale, offset and description).
Point-to-Point (Link)—Connection between two, and only two, pieces of equipment.
Poke—In computer programming, instruction used to place value (poke) into specific location in computer’s storage.
Polarity—Any condition in which two opposing magnetic fields, voltage levels, or charges such as positive and negative.
Polish Notation—Logical programming notation for series arithmetic operations in which no grouping symbol is used, for example, a*(b+c) is *a+bc; see RPN, Postfix; developed by Polish logician, Jan Lukasiewicz in 1929.
Polling—In digital communication, media access method (ISO data link layer 2) of controlling devices on bus (multipoint, multidrop) or ring (loop) communication network through single network "master", sometimes called "traffic director;" process of inviting another station or node to transmit data, compared to selecting.
Polymer (Polymeric) Light-Emitting Diode (PLED) Thin film displays created by sandwiching an undoped conjugated polymer between two proper electrodes designed so polymer emits light when exposed to electricity; little power emits substantial light; enables full-spectrum color displays & relatively inexpensive compared to other display technologies such as LCD or OLED.
Polymorphism—In Object Oriented Programming (OOP), different objects respond differently to same command, but each appropriately to their function.
POMS—Process Operations Management System; IBM® software aimed at providing integration at manufacturing execution level, of third party applications for quality, process engineering, and plant operations around distributed relational database.
POP—Picture Outside Picture; simultaneous multiple view video screen, but without insets; also: Points Of Presence, term used by Internet providers to indicate number or geographical locations of their access to Internet.
Port—Point of access into computer, network, or other electronic device; physical or electrical interface through which one gains access; interface between process and communications or transmission facility; if digital, may be for serial or parallel transmission (for a mouse, modem, printer, etc.).
Portable—Handles were added. J
Portability—In computing, ability to use and migrate software across different platforms.
Portal—Type of e-commerce internet site which is gateway to the internet, which may be search engine or directory web page; typically a starting point for web surfing for certain interest groups; most have links to variety of interesting sites, and some kind of search engine or Web directory; additionally a combination possibility for different e-business solutions; commercial examples of traditional portals are Infoseek, Excite, Yahoo, Lycos, AOL.
POS—Point Of Sale.
Positioner—( see Valve Positioner).
Positive Temperature Coefficient—Increase in resistance due to an increase in temperature.
POSIX—Portable Operating System Interface eXchange; originated for computer environments as means of standardizing critical interfaces for the many divergent variations of UNIX® operating system; living under auspices of both IEEE and ISO, it has evolved into an entire family of standard interface definitions, no longer limited to UNIX®; specifies how software applications and operating system software should be implemented so that applications can be ported to other POSIX compliant environments.
Postfix—Programming notation system in which operator follows operands, for example, addition of x and y is xy+; see RPN.
Postprocessing—Program that formats graphical or other data after it is processed on a system, so that data can be used elsewhere.
PostScript™—Output protocol by Adobe Systems Inc. originally to be used by DEC® with X-windows; sophisticated page description language used for printing high-quality text and graphics on laser printers and other high-resolution printing devices; page description generally includes position, scale, & orientation of text, graphic figures, and digitalized images.
Potential Energy—Energy related to position from, or height above, the place to which fluid could flow or an object could relocate.
POTS—Plain Old Telephone System.
POTW—Publicly Owned Treatment Works; municipal wastewater treatment facility.
Power Circuit—Conductors and components of supply, branch, and feeder circuits, supplying main line power to loads such as heaters, motors, lighting, receptacles, power transformers, and appliances
Power Down—To shut down (or turn off) system power supply.
Power Isolated Transmitters―Type 4 analog (4-20mA) transmitters used in an ungrounded circuit.
ppb, p/b—Parts per Billion (usually lower case).
PPI—Plan-Position Indicator; also: Programmable Peripheral Interface.
PPM—Pulse Position Modulation, see definition.: Project Portfolio Management, see definition.
ppm, p/m—Parts per Million (usually lower case).
PPP—Point-to-Point Protocol; enables TCP/IP over asynchronous (regular telephone) lines (and modem), important to UNIX® and Internet communities; gradually replacing SLIP for this purpose.
PPO—Polyphenylene Oxide.
PPS—Polyphenylene Sulfide (Plastic).
PPTP—Point-to-Point Tunneling Protocol; software digital communications protocol developed by Microsoft for secure communications over Internet by encapsulating other protocols for transmission over an IP network; for example, it can be used to send NetWare IPX packets over the Internet; due to its RSA encryption, PPTP is also used to create a private network (VPN) within the public Internet; remote users can access their corporate networks via any ISP that supports PPTP on its servers.
PQS—Process Query System: see definition.
PRACL—Page-Replacement Algorithm & Control Logic.
PRAM—Parameter Random Access Memory; stores time and date settings, as well as other information about the computer in which it is used; typically battery-powered for use upon start-up.
Precedence—In computer programming, rules that state which program operators should be executed first within an expression.
Precision—In measurement, the finest degree of resolution expressible, see also accuracy and resolution.
Predetermined Counter—Counter that accumulates pulses and compares total to preset value to determine when to initiate control action.
Predictive Maintenance (PDM)—To operate process or system until predetermined condition indicates that controlled shutdown is appropriate, then make necessary repairs; usually least expensive method in the long run because shutdown occurs only when needed, but before damage is done; does require planning, thought, and proper monitoring; compare: Corrective Maintenance, Preventative Maintenance.
Preemptive Multitasking—Ability to assign higher priority to certain tasks running on computer so safety conditions are covered first, control actions second, advanced control third, reporting later, “bells & whistles” last.
Preprocessor—Program that performs conversion, formatting, condensing, or other functions on input data prior to further processing.
Presentation Layer—In digital communication, layer six of ISO reference model; provides standards for restructuring data into required format, character set, or language.
Pressure Loss/Drop—Reduction occurring in pressure from start to finish of processing operation.
Pressure Transducers—Three types are used to measure: Absolute (total pressure at a point, including atmospheric), Gauge (difference between actual and atmospheric), and Differential (difference between two points); about 60% of differential types are used to measure flow, 30% to measure level.
Preventative Maintenance (PM)—To operate process or system with time-based shutdown schedule, then make necessary repairs; usually prevents loss and is therefore less expensive than Corrective Maintenance; compare: Corrective Maintenance, Predictive Maintenance.
Primary Element, Primary Device—In process control, actual sensing device which detects measured parameter in the process, such as thermocouple junction, differential pressure capsule, etc.; also called Sensor.
Primary Domain Controller (PDC)—Windows NT service that manages security for its local domain; every domain has one PDC, which contains database of usernames, passwords and permissions; See BDC.
Primary Standard—Standard reference units and physical constants maintained by National Institute of Science and Technology (NIST) upon which all measurement units in United States are based.
Primary Station—In communications system, station which at any given instant has right to select and transmit information to secondary station, and responsibility to insure information transfer; station which has control of data link at given instant; assignment of primary status may be temporary and governed by standardized control procedures.
Primitives—Basic units of machine instruction; also: fundamental graphic entity called entities, these can also be design elements at lowest stage of complexity, such as lines or arcs, which are joined to make symbols or groups.
Print Server—Intelligent device used to transfer information to series of printers.
Printer—Electromechnical paper shredding device created as joke in poor taste consisting of three main parts: the case, the jammed paper tray, and the blinking red light.J
Private Network—Broadband service needed usually for video signals such as in conferencing, using leased, dedicated phone lines to avoid the switching done in normal phone service.
PRML—Partial-Response Maximum-Likelihood read channel technology, as used in hard disk drives.
Procedural Programming Language—Computer programming language used to express sequence of operations to be performed by a computer, such as FORTRAN; see Non-procedural Programming Language.
Process—Continuous and regular industrial production executed in definite, uninterrupted manner; any operation or sequence of operations involving continuous change of energy, state, composition, dimension, or other properties that may be defined with respect to fixed point of reference; art of making “stuff;” also: in computer technology, executing program, to perform some useful operations on data.
Process Analytical Technology (PAT)—A system for designing, analyzing and controlling manufacturing through timely measurements (i.e., during processing) of critical quality and performance attributes of raw and in-process materials and processes with the goal of ensuring final product quality.
Process Colors—In printing, the subtractive primaries: yellow, magenta, and cyan, plus black in 4-color process printing.
Process Control—Automatic monitoring and control of process by instrument, computer, or system of both designed to respond appropriately to signals returning from that process.
Process Control Loop—All components in controlling portion of process: sensor, transducer, transmitter, controller, final element, and process itself.
Process Engineering Tools (PET)—Consists of plant design software, process simulation software used for design purposes, and off-line process optimization applications.
Process Query System (PQS)—Evolving algorithmic and software framework in a system to make sense of the huge volume of data collected each day from computer network monitors, video surveillance cameras, financial transaction records, databases of e-mail exchanges, etc., closing the gap between gathering a tremendous amount of valuable data and figuring out what the data means; most interesting application of PQS to date is in network security monitoring
Process Simulation—Use of mathematical model by computer programmed to envision process design scenarios with real-time visual and numerical feedback; used for optimization and prediction of potential problems; three of the approaches include on-line steady-state optimization, dynamic model-based optimization, and real-time optimization.
Process Simulation & Optimization (PSO)—Integrated tools that allow users to progress from concept & design engineering through checkout & commissioning and onto optimized operations, while utilizing data, tools, and modeling from each previous phase of the project; provides plants with ability to respond more quickly to customers' needs.
Process Variable (PV)—Any variable property of process other than instrument signals; usually the measured variable in process control, often converted by a transmitter for delivery to a meter or controller.
Producer/Distributor/Consumer Model—In digital communications, method of data exchange over fieldbus from any variable producing device (producer), controlled by bus arbiter (distributor) and consumed by subscriber (consumer).
Product Lifecycle Management (PLM)—Business approach defined for solving problem of managing complete set of product definition information—creating that information, managing it through its life, and disseminating and using it throughout the design/build/support/maintain progression of product lifecycle from concept to obsolescence.
Production Capacity Planning—Determining levels of activity needed to be sustained in future with respect to sales forecast and availability of personnel, equipment, materials, and money.
Production Control—Systematic planning, coordination, and direction of all production activities to ensure that products are made on time, of appropriate quality, and at reasonable cost.
Productivity—Measure of effectiveness based on efficiency and utilization; production output per unit of input, such as units per labor man-hour.
PROFIBUS—PROcess FIeld BUS; German national field bus standard (DIN 19245), operational since 1989 and used world-wide to link sensors, actuators, and controllers in an automation system; based OSI 7497.
PROFIBUS-DP—PROFIBUS Decentral Periphery.
PROFIBUS-PA—PROFIBUS Process Automation.
Profit Velocity—Profit per hour per part.
Program—List of instructions which computer follows to perform task; repeatable sequence of actions that defines status of outputs as fixed relationship to set of inputs.
Programmable Array Logic (PAL)—Family of devices consisting of a small PROM (programmable read-only memory) core and additional output logic used to implement particular desired logic functions with few components; these are "field-programmable" but each PAL device was "one-time programmable" (OTP), meaning that it could not be updated and reused after its initial programming.
Programmable Automation Controller (PAC)—Term created by Automation Research Corporation (ARC) about 2004, used to describe new generation of industrial controllers that combine functionality of PLC & PC, blending logic, motion and process control on a common development platform; the PAC acronym is being used both by traditional PLC vendors to describe their high end systems and by PC control companies to describe their industrial control platforms; PACs can accommodate small process applications, but typically cannot tackle the large bursts of continuous data that move through big batch environments.
Programmable Interval Timer (PIT) —One that just counts down from some value to zero, then sends an interrupt to a processor indicating that it has finished counting; often used in thermostats, which periodically test the temperature around them to see if they need to turn the air conditioner on, the heater on; can be one-shot or periodic: one-shot timers interrupt only once, and then stop counting; periodic timers interrupt every time they reach a specific value.
Programmable Logic Array (PLA)—Device used to implement set of programmable AND gate planes, which link to a set of programmable OR gate planes, which can then be conditionally complemented to produce an output; layout allows for a large number of logic functions to be synthesized in the sum of products (and sometimes product of sums); not necessarily filed programmable; those that can be are called FPLA (Field-programmable PLA).
Programmable Logic Controller (PLC)—Originally solid state replacement for “relay boxes;” designed in 1968 to eliminate large cost of replacing complicated relay-based machine control systems; Bedford Associates proposed a MODular Digital CONtroller (MODICON), which as second model 184 became first commercial product; current devices have been microprocessor-based, perform wide variety of control functions, but still are used predominantly for discrete manufacturing production; see MODICON, Cyclelog.
Programmable Logic Device (PLD)—Variety of logic chips that are programmable at the customer's site using either fusible links, which are "blown" to open the lines or Actel's Antifuse technology to fuse them together; wide variety of PLD techniques exist; most PLDs are of PLA (Programmable Logic Array) or PAL (Programmable Array Logic) variety, which provide different configurations of AND & OR gates; unlike gate arrays, which require final masking fabrication process, PLDs are easily programmable in field; PLDs are always used for logical functions, but programmable storage chips such as PROMs and EPROMs may also be considered as PLDs if they contain program code rather than just data.
Programmers—Computer avengers; once members of that group of high school nerds who wore tape on their glasses, played Dungeons and Dragons, and memorized Star Trek episodes; now millionaires who create "user-friendly" software to get revenge on whoever gave them noogies. J
Programming Language—Artificial language that enables people to instruct machines; computer commands that form procedure by which software programmers design and implement computer software programs.
Project Hub—Internet/intranet/extranet online platform for temporary Research & Development projects or project business (information exchange, project management). Objective is the optimization of internal operations and communication activities as well as the reduction of necessary time and costs.
Project Portfolio Management (PPM)—Centralized management of processes, methods, and technologies used by project managers and project management offices (PMOs) to analyze and collectively manage a group of current or proposed projects based on numerous key characteristics; objectives are to determine the optimal resource mix for delivery and to schedule activities to best achieve an organization’s operational and financial goals, while honoring constraints imposed by customers, strategic objectives, or external real-world factors.
PROLOG—PROgramming LOGic; computer language created at University of Marseilles, France; used largely for artificial intelligence applications as a logic oriented language which arrives at problem solutions by "reasoning" to the answer; it is declarative rather than procedural, solutions are based upon rules put in by programmer.
PROM—Programmable Read Only Memory; storage device in which data are accessed on demand, but not changed; also: event generally associated with final high school dances. J
Proof-of-Concept (PoC)—Evidence that demonstrates an idea or business model is feasible.
Proof Pressure—Specified pressure which may be applied to sensing element without causing permanent change in output characteristics.
Propagation Delay—Time it takes signal (of electromagnetic energy) to travel from one point to another over transmission channel.
Proportional Action (or Control)—Control response proportional to deviation from set point within proportional band, also called "gain"; also: performance of proportional band on stage (see next entry). J
Proportional Band—Range of values above and below set point, where control action is full ON below the band, full OFF above the band, and proportional in between; also: group of musicians who can play fast, slow, and in between. J
Proprietary System—System (or devices), which operates only to the methods, standards, and protocols of manufacturer, and not able to be interchanged with, or to communicate with devices or systems made by other manufacturers.
PROSUMER—PROsfessional conSUMER.
Protocol—Formal set of conventions governing the formatting, timing, sequencing, and/or error checking of message exchange between two digital communicating systems; it can exist on many levels within a network to establish, maintain, and control communications.
Protocol Analyzer—Device or software application that enables user to analyze performance of network data to insure that the network and its associated hardware/software are operating within network specifications.
PROWAY—PROcess data highWAY; local area network standard for industrial process control systems developed through International Purdue Workshop on Industrial Computer Systems, compatible with but more restrictive standard than IEEE 802.2 and 802.4, ISA S72.01; specified as part of MAP, layer 2.
Proximity Switch—Device that senses presence of an object without physical contact in response closes or opens circuit contacts.
Proxy Server—In computer based networks, server that sits between a client application, such as a Web browser, and a real server, intercepting all requests to real server to see if it can fulfill requests itself, and if not, forwards request to real server; can be used to improve performance, and to provide security to networks; role as security protection system it prevents unauthorized access through firewall technology which intercepts all messages entering and leaving the network; server effectively hides true network addresses; see Firewall Technology.
PRP—Potentially Responsible Party; under Comprehensive Environmental Response, Compensation and Liability Act, individual, group, or organization legally liable in U.S. for cleaning up National Priorities List sites.
PRT—Platinum Resistance Thermometer; also: Planar Resistor Technology.
PRV—Pressure Regulating Valve; Pressure Reducing Valve.
Pry Bar—Tool used to crumple the metal surrounding that clip or bracket you needed to remove in order to replace a 50 cent part. J
PS—Power Supply; also: PostScript™; see definition.
P/S—Power Supply; also: Publisher/Subscriber communication model; see definition.
PS/2®—Personal System/2®; family of IBM® second generation of personal computers (PCs) which along with OS/2® to provide higher level performance, capacity, and software consistency than earlier IBM® PCs.
PSD—Position Sensing Diode; also: Process Shut Down.
Pseudo A/B Role—In video development, editing between two sources where edited result shows one source visibly in motion against a constant image (usually the last frame of preceding clip or scene).
PSIA—Pounds per Square Inch Absolute; pressure referenced to vacuum, sum of atmospheric and gauge pressure.
PSID—Pounds per Square inch Differential; pressure difference between two points.
PSIG—Pounds per Square inch Gauge; pressure referenced to ambient air pressure.
PSIS—Pounds per Square inch Standard; pressure referenced to standard atmosphere.
PSK—PreShared Keys; use of secret passwords or encryption keys that are entered into both sides of message exchange ahead of time; typed into the clients and servers (authentication servers, access points, etc.) or entered via floppy, CD-ROM or smart card. Contrast with "server-based keys," in which one side generates a key and sends it to the other side during the authentication session.
PSM—Process Safety and Management; OSHA standard covering more than 130 specific toxic, reactive and hazardous chemicals in various threshold quantities.
PSO—Process Simulation & Optimization; see definition.
PSSE—Polarization-Sensitive Scattering Element; provides a means for recapturing light energy which would otherwise be lost in display devices, while reducing degradation and heat build-up due to light absorption.
PSTN—Public Switched Telephone Network; which refers to the international telephone system based on copper wires carrying analog voice data; contrasted to newer telephone networks base on digital technologies, such as ISDN and FDDI.
PSU—Power Supply Unit.
Psychrometer—Wet-dry bulb type hygrometer for determining relative humidity.
PTB—(Physikalisch-Technische Bundesanstalt) German certification and testing laboratory for testing equipment of different vendors to some common standard.
PTC—Positive Temperature Coefficient; such as in PTC resistor (thermistor) which will make large, abrupt change in resistance when an overcurrent or high temperature heats it above a specific point, thereby effectively "switching OFF," or in reality, acting like solid state fuse.
PTFE—PolyTetraFluoroEthylene (Teflon®); used in packing of valves to control emissions to below EPA standard.
PTH—Plated Through Holes on circuit boards.
PTO—(PROFIBUS Trade Organization); North American sister group of PNO, dedicated to promote German standard (DIN 19245) as worldwide protocol for industrial automation.
PTP—Profitable-to-Promise.
PU—Power Unit.
Public Network—Network operated by common carriers or telecommunications administrations for the provision of circuit switched, packet switched, and leased line circuits to the public.
Publisher/Subscriber Model—In data communications, method for sharing data on bus network in which any station in network containing particular item of information maintains “subscriber's list” of all other stations needing that information, so when that information changes by some specified amount, it is “published” to all those subscribers, so they are then automatically updated with this new data.
Pull Box—Enclosure used for pulling electrical power, or communication signal cables through conduit.
Pull Manufacturing—Operations (Flow manufacturing style) where production is based upon actual demand (orders); compare: Push Manufacturing.
Pull Section—Compartment within equipment where power or signal conductors are terminated (with room to pull them through conduit).
Pulse Position Modulation—Digital communication method of modulating data by encoding its value as position of pulse within time interval.
Pulse Spreading—Dispersion of an optical signal with time as it propagates through an optical fiber.
Pulse Width Modulation—Output in form of duty cycle, which varies as function of applied measurand.
PURL—Persistent URL; one that points to another URL; used when document pages are expected to be moved to different locations from time to time; maintained as the official URL for that resource, and when that PURL is requested, a PURL server redirects browser to actual current URL; compare with PERL.
Push—In video development, transition where new scene moves into frame from a particular direction, for example "push right."
Pushbutton Timer—This type has momentary start switch to begin timing action.
Push Manufacturing—Operations (MRP style) where production is based upon forecast demand; compare: Pull Manufacturing.
PUT—Programmable Unijunction Transistor.
PV—Process Variable; usually the measured variable in process control, often conveted by a transmitter for delivery to a meter or controller.
PVC—PolyVinyl Chloride; frequently used for cable covering and instrument enclosures; good high temperature resistance w/ high impact strength, good overall chemical resistance, can be adversely affected by ultraviolet and cold temperature impact; appropriate for indoor, light duty applications; produces, however, toxic fumes when it burns, compare with Plenum-rated; also: Permanent Virtual Circuit; in digital communication, point-to-point connection that is established ahead of time; group of PVCs defined at time of subscription to a particular service is known as a virtual private network (VPN), contrast with SVC.
PVDF—PolyVinyliDene Fluoride (Kynar®); material used in place of stainless steel to reduce leaching contamination in some conditions..
PVGA—Paradise Video Graphics Adapter.
PVI—Peak Inverse Voltage.
PVR— Personal Video Recorder; device that digitizes broadcast TV onto a hard disk and plays it back immediately, allowing viewer to pause at any time and return later; also called Digital Video Recorder.
PWA—Printed Wiring Assembly.
PWB—Printed Wiring Board; electronic subassembly consisting of insulating board or card and conductive circuit pathways, (often “printed wiring”); sometimes term is used interchangeably with printed circuit board (PCB), which additionally includes circuit components such as diodes and integrated circuits.
PWM—Pulse Width Modulation; also: Pulse Width Modulated type of variable frequency drive, see VFD.
PWR—Pressurized Water Reactor.
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