| Packet Switching The method used to move data around on the Internet. In packet switching,all the data coming out of a machine is broken up into chunks, each chunk has the address of where it came from and where it is going. This enables chunks of data from many different sources to co-mingle on the same lines, and be sorted and directed along different routes by special machines along the way. This way many people can use the same lines at the same time.
You might think of several caravans of trucks all using the same road system. to carry materials.
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| Packet Switching: A method of transmitting units of data (called packets) through a mesh network. There is no physical circuit established between end points; instead, each packet is individually relayed from one switching node to the next, and individual packets may take different routes through the switching node.
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| Packet: The unit of data sent across a packet switching network. The term is used loosely.
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| PAL : Acronym for phase alternation by line. A television signal standard (625 lines, 50 Hz, 220 V primary power) used in the United Kingdom, much of the rest of western Europe, several South American countries, some Middle East and Asian countries, several African countries.
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| Palette The magnitude of colors that a display is capable of producing.
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| Palette : The magnitude of colors that a display is capable of producing.
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| Parallax: An optical illusion which occurs in analog meters and causes reading errors. It occurs when the viewing eye is not in the same plane, perpendicular to the meter face, as the indicating needle.
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| Parallel Processing: An efficient form of information processing that emphasizes the exploitation of concurrent events in the computing process. Concurrency implies parallelism, simultaneity and pipelining. Parallel events may occur in multiple resources during the same time instant; pipelined events are attainable in a computer system at various processing levels. Parallel processing demands concurrent execution of many programs in the computer as a cost-effective means to improve system performance.
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| Parallel Transmission: Sending all data bits simultaneously. Commonly used for communications between computers and printer devices.
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| Paramagnetism: Property of a material that, when placed in a magnetic field, is magnetized parallel to the field to an extent proportional to the field; this does not apply at very low temperatures or in extremely large magnetic fields.
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| Parity Error: The effort that occurs in a DTE when the received data has the wrong parity.
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| Parity: A technique for testing transmitting data. Typically, a binary digit is added to the data to make the sum of all the digits of the binary data either always even (even parity) or always odd (odd parity).
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| Particle: A subatomic object with a definite mass and charge. |
| Passivation: The changing of the chemically active surface of a metal to a much less reactive state. Contrast with activation. |
| Passive Filter : A filter circuit containing resistors, inductors and capacitors that are passive.
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| Password A code used to gain access (login) to a locked system. Good passwords contain letters and non-letters and are not simple combinations such as virtue7. A good password might be:
5%df(29)
But don?t use that one! |
| PC Card : A computer device packaged in a small card approximately the size of a credit card and conforming to the PCMCIA standard. |
| PCMCIA : Portable Computer Memory Card International Association |
| Peak Hold: Output of the maximum temperature measurement indicated by an instrument during the time duration for which this display mode has been active. |
| Peltier Effect: When a current flows through a thermocouple junction, heat will either be absorbed or evolved depending on the direction of current flow. This effect is independent of joule I2 R heating.
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| Peripheral: A device that is external to the CPU and main memory, i.e., printer, modem or terminal, but is connected by the appropriate electrical connections.
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| Peritectic : An isothermal reversible reaction in metals where a liquid phase reacts with a solid phase to produce a single (and different) solid phase upon cooling. |
| Permeability : 1) passage or diffusion of a gas, vapor, liquid, or solid through a material without physically or chemically affecting it; (2) term used to express various relationships between magnetic induction and magnetizing force; either absolute permeability or specific (relative) permeability.
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| pH Junctions: The Junction of a reference electrode or combination electrode is a permeable membrane through which the fill solution escapes (called the liquid junction).
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| pH(S) (Standard pH Scale): The conventional standard pH scale established on the basis that an individual ionic activity coefficient can be calculated from the Debye-H?ckel law for primary buffers.
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| Phase Difference: The time expressed in degrees between the same reference point on two periodic waveforms. |
| Phase Locked Loop: A circuit containing a voltage-controlled oscillator whose phase or frequency can be "steered" to keep it in sync with a reference source. A PLL circuit is generally used to lock onto and "up-convert" the frequency of a stable source.
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| Phase Proportioning: A form of temperature control where the power supplied to the process is controlled by limiting the phase angle of the line voltage.
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| Phase Shift: The phase angle between the output signal and the applied acceleration.
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| Phase Transformation: Changes that can occur within a given material system; how one or more phases in an alloy change into a new phase or mixture of phases; transformation occurs because the initial state of the alloy is unstable relative to the final state; at constant temperature and pressure the relative stability of a system is determined by its Gibbs free energy.
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| Phase-Locked Loop (PLL): An electronic circuit that consists of a phase detector, low pass filter and voltage-controlled oscillator. A PLL can be used as an FSK demodulator or to synchronize a terminal?s internal clock to the received bit stream.
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| Phase: A time based relationship between a periodic function and a reference. In electricity, it is expressed in angular degrees to describe the voltage or current relationship of two alternating waveforms.
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| Photon: The carrier particle of electromagnetic interactions |
| Photondetector or Quantum Detector: A type of detector in which the photons or quanta of energy interact directly with the detector to generate a signal.
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| PID: Proportional, integral, derivative. A three mode control action where the controller has time proportioning, integral (auto reset) and derivative rate action.
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| Piezoelectric Accelerometer: A transducer that produces an electrical charge in direct proportion to the vibratory acceleration.
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| Piezoelectric Transducer: Transducer with a sensing element that generates an electrical charge when mechanically loaded.
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| Piezoelectricity: Elastic strain caused when an electrical current is applied to a piezoelectric material and conversely, an electric current produced when pressure is applied to a piezoelectric material. |
| Piezoresistance: Resistance that changes with stress.
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| Piezoresistive Transducer: Transducer with a semiconductor bridge as the sensing element. The measuring bridge must be electrically excited to produce an output signal.
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| PIN Diode : A semiconductor device which is capable of converting, in a receiver, optical signals to electrical signals.
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| Pion: The least massive type of meson, pions can have electric charges of +1, -1, or 0. |
| Pitot Tube: A device used to measure the total pressure of a fluid stream that is essentially a tube attached to a manometer at one end and pointed upstream at the other.
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| Pixel: Picture element. Definable locations on a display screen that are used to form images on the screen. For graphic displays, screens with more pixels provide higher resolution.
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| Plane Separation: Of a balancing machine, is the operation of reducing the correction plane interference ratio for a particular rotor.
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| Plastic Deformation: The permanent (inelastic) distortion of a material under an applied stress that strains the material beyond its elastic limit; the ability of a material to be permanently deformed without fracture.
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| Platinel: A non-standard, high temperature platinum thermocouple alloy whose thermoelectric voltage nearly matches a Type K thermocouple (Trademark of Englehard Industries).
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| Platinum 10% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type S thermocouple. |
| Platinum 13% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type R thermocouple.
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| Platinum 30% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with platinum 6% rhodium to form a Type B thermocouple.
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| Platinum 6% Rhodium: The platinum-rhodium alloy used as the negative wire in conjunction with platinum-30% rhodium to form a Type B thermocouple.
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| Platinum: A noble metal which in its pure form is the negative wire of Type R and Type S thermocouples.
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| PLC: Programmable Logic Controller. |
| Plenum Chamber Used in air amplifier and gas booster assemblies to dampen pulsatiuon between stages. |
| Plutonium: A highly toxic, heavy, radioactive metallic element. There are 15 isotopes of plutonium, of which only five are produced in significant quantities: plutonium-238, -239, -240, -241, and -242. Plutonium-239 is the most important plutonium isotope as it is fissile and is used in nuclear weapons and some reactors. One the other hand, plutonium-240 is unsuitable for use in nuclear weapons and reactor fuel. Thus, in a reactor whose main purpose is plutonium production, the rate at which plutonium-240 is formed controls the length of time fuel is allowed to remain under irradiation. Plutonium is categorized according to plutonium-240 content, as follows: super-grade has 2-3% Pu-240; weapons-grade has less than 7% Pu-240; fuel-grade has 7-18 (or sometimes given as 7-19) % Pu-240; and reactor-grade has 18 or greater (or 19 or greater) % Pu-240. (Note: Despite what the name implies, "reactor-grade" plutonium has been used successfully to make a nuclear bomb.)
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| Poissons Ratio : The ratio of the transverse contracting strain to the longitudinal elongational strain when a tensile stress is applied to a material.
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| Polarity: In electricity, the quality of having two oppositely charged poles, one positive one negative.
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| Polarization : Of an electromagnetic wave, the property that describes the orientation, i.e., time-varying direction and amplitude, of the electric field vector.
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| Polarization: The inability of an electrode to reproduce a reading after a small electrical current has been passed through the membrane. Glass pH electrodes are especially prone to polarization errors caused by small currents flowing from the pH meter input circuit and from static electrical charges built up as the electrodes are removed from the sample solution, or when the electrodes are wiped.
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| Polling: A control message sent from a master terminal to a slave terminal as an invitation for the slave to transmit.
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| Polymorphism: Different crystal structures at different temperatures or pressures for a single compound.
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| POP -- (Point of Presence, also Post Off Two commonly used meanings:
Point of Presence and Post Office Protocol.
A Point of Presence usually means a city or location where a network can be connected to, often with dial up phone lines. So if an Internet company says they will soon have a POP in Belgrade, it means that they will soon have a local phone number in Belgrade and/or a place where leased lines can connect to their network.
A second meaning, Post Office Protocol refers to a way that e-mail client software such as Eudora gets mail from a mail server. When you obtain an account from an Internet Service Provider (ISP) you almost always get a POP account with it, and it is this POP account that you tell your e-mail software to use to get your mail. Another protocol called IMAP is replacing POP for email.
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| Port 3 meanings. First and most generally, a place where information goes into or out of a computer, or both. E.g. the serial port on a personal computer is where a modem would be connected.
On the Internet port often refers to a number that is part of a URL, appearing after a colon (:) right after the domain name. Every service on an Internet server listens on a particular port number on that server. Most services have standard port numbers, e.g. Web servers normally listen on port 80. Services can also listen on non-standard ports, in which case the port number must be specified in a URL when accessing the server, so you might see a URL of the form:
gopher://peg.cwis.uci.edu:7000/
This shows a gopher server running on a non-standard port (the standard gopher port is 70).
Finally, port also refers to translating a piece of software to bring it from one type of computer system to another, e.g. to translate a Windows program so that is will run on a Macintosh.
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| Port: A signal input (access) or output point on a computer.
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| Portal Usually used as a marketing term to described a Web site that is or is intended to be the first place people see when using the Web. Typically a "Portal site" has a catalog of web sites, a search engine, or both. A Portal site may also offer email and other service to entice people to use that site as their main "point of entry" (hence "portal") to the Web.
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| Positive Temperature Coefficient: An increase in resistance due to an increase in temperature.
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| Positron (e+) : The antiparticle of the electron. |
| Positron: An elementary particle with a positive electric charge, but in other respects identical with an electron.
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| Posting A single message entered into a network communications system.
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| Potential Energy: Energy related to the position or height above a place to which fluid could possibly flow. |
| Power Supply: A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.
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| PPM: Abbreviation for "parts per million," sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%.
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| PPP -- (Point to Point Protocol) The most common protocol used to connect home computers to the Internet over regular phone lines.
Most well known as a protocol that allows a computer to use a regular telephone line and a modem to make TCP/IPconnections and thus be really and truly on the Internet.
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| Precipitation Hardening: Increase the hardness of a supersaturated solid solution by heat treating it to cause a second phase to precipitate out; coherency of the precipitate/matrix interface and how well the two lattices match up greatly influence the effect of precipitate.
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| Precision : Precision is reproducibility. Saying "These measurements are precise" is the same as saying, "The same measurement was repeated several times, and the measurements were all very close to one another". Don?t confuse precision with accuracy. |
| Pressure Limit or Proof Pressure (Overpr The maximum allowable pressure difference between the rated pressure and the over pressure, without affecting in subsequent operation, the performance requirements over the rated pressure range.
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| Pressure Range (Rated Pressure): The algebraic difference between the maximum pressure and the minimum pressure over which the device is calibrated.
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| Pressure Reference (Operational Pressure The reference pressure against which the input pressure is measured in-
Vented Gauge: ambient atmospheric pressure.
Sealed Gauge: internal sealed atmospheric reference pressure.
Absolute: internal sealed vacuum.
Differential Gauge: difference of two (unknown) pressures.
Residual Unbalance or Zero Balance The electrical output at the rated electrical excitation at zero pressure applied at room temperature.
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| PRI: See Primary Rate Interface.
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| Primary Axis: The axis along which the transducer is designed to be loaded; normally its geometric centerline. |
| Primary Standard (NBS): The standard reference units and physical constants maintained by the National Bureau of Standards upon which all measurement units in the United States are based.
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| Primary Standards: Aqueous pH buffer solutions established by the National Bureau of Standards within the 2.5 to 11.5 pH range of ionic strength less than 0.1 and which provide stable liquid junction potential and uniformity of electrode sensitivity.
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| Principal Axes: The axes of maximum and minimum normal stress. |
| Probe: A generic term that is used to describe many types of temperature sensors.
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| Process Meter: A panel meter with sizeable zero and span adjustment capabilities, which can be scaled for readout in engineering units for signals such as 4-20 mA, 10-50 mA and 1-5 V. |
| PROFIBUS: German Token Ring Bus Standard Developed By Siemans.
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| Program: A list of instructions that a computer follows to perform a task. |
| PROM: Programmable Read Only Memory. A semiconductor memory whose contents cannot be changed by the computer after it has been programmed.
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| Proof Pressure: The specified pressure which may be applied to the sensing element of a transducer without causing a permanent change in the output characteristics.
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| Propagate: To spread from one place to another. |
| Proportioning Band: A temperature band expressed in degrees within which a temperature controller?s time proportioning function is active. |
| Proportioning Control Mode: A time proportioning controller where the amount of time that the relay is energized is dependent upon the system?s temperature.
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| Proportioning Control plus Derivative Fu A time proportioning controller with a derivative function. The derivative function senses the rate at which a system?s temperature is either increasing or decreasing and adjusts the cycle time of the controller to minimize overshoot or undershoot.
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| Proportioning Control plus Integral: A two-mode controller with time proportioning and integral (auto reset) action. The integral function automatically adjusts the temperature at which a system has stabilized back to the setpoint temperature, thereby eliminating droop in the system.
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| Protection Head: An enclosure usually made out of metal at the end of a heater or probe where connections are made.
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| Protection Tube: A metal or ceramic tube, closed at one end into which a temperature sensor is inserted. The tube protects the sensor from the medium into which it is inserted.
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| Protocol: A formal definition that describes how data is to be exchanged.
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| Proton (p): The most common hadron, a baryon with electric charge +1 equal and opposite to that of the electron. Protons have a basic structure of two up quarks and one down quark (bound together by gluons). The nucleus of a hydrogen atom is a proton. A nucleus with electric charge Z contains Z protons; therefore the number of protons is what distinguishes the different chemical elements. |
| Proton: An elementary particle with a positive electric charge and a mass that is given the value 1 on the scale of atomic weights.
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| Proximity Sensor: Ultrasonic sensor designed to measure the distance from the sensor face to a target.
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| PSI: Pounds per square inch.
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| PSIA: Pounds per square inch absolute. Pressure referenced to a vacuum. |
| PSID: Pounds per square inch differential. Pressure difference between two points.
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| PSIG: Pounds per square inch gage. Pressure referenced to ambient air pressure.
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| PSIS: Pounds per square inch standard. Pressure referenced to a standard atmosphere.
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| PSTN -- (Public Switched Telephone Netwo The regular old-fashioned telephone system.
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| Pull Plate: Load cell attachment which allows tension or compression force to be directed at the center line of a load cell through a threaded center hole.
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| Pulse Code Modulation: A method of quantizing audio-range analog signals into a digital form for transmission in digital communications systems, or for processing in DSP. Effectively the same as analog-to-digital conversion. |
| Pulse Width Modulation: An output in the form of duty cycle which varies as a function of the applied measurand. |
| Pumping Section, Haskel liquid pumps The section containing the hydraulic body, plunger/piston, seal package and check valves. All parts of this section are exposed to the pumped fluid. Therefore, all materials used must be compatible with the pumped fluid. |
| Pyroelectric Detector: Thermal detector that has a signal generated by means of the pyroelectric effect wherein changes in temperature of the detector generates an electrical signal.
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| Pyrometer: A broad class of temperature measuring devices, originally designed to measure high temperature, but some are now used in any temperature range. Includes radiation pyrometers, thermocouples, resistance pyrometers, and thermistors. |
Additions/Suggestions/Assistance
