الجزءالخامس عشر من معجم الاجهزة O

object 1. An entity that has

O state, behavior, and identity. [ISA-TR50.02, Part 9-2000] 2. In object-oriented program­ming (OOP), a single struc­ture that comprises a data structure definition and its defined procedures.

object code 1. The machine code that can be directly executed by the computer. It is pro­duced as a result of the translation of the source code. 2. A relocatable machine-lan­guage code.

object dictionary An object dictionary (00) contains all the function block (FB), resource block (RB), and transducer block (TB) param­eters used in a device. Through these param­eters, the blocks may be accessed over the field bus network.

objective variable A quantity or condition that is not measured directly for the purpose of controlling it but is rather controlled through its relation to another, controlled variable.

object language A language that is the out­put of an automatic coding routine. Usually, object language and machine language are the same. However, a series of steps in an automatic coding system may involve the object language of one step serving as a source language for the next step and so forth.

object linking and embedding (OLE) In computers, a database feature of the Microsoft Windows and Windows NT envi­ronments that treats data as a collection of objects to be shared by applications that sup­port the OLE specification. OLE enables sev­eral application, to be linked to accomplish a given task. It also allows the user to keep information current across several software applications simply by changing the infor­mation in one of them.

object machine The computer on which the object program is to be executed. Same as tar­get co I1lp II ter.

object module The primary output of an assembler or compiler. It can be linked with other object modules and loaded into mem­ory as a program. The object module is com­posed of the relocatable machine-language code, the relocation information, and the cor­responding symbol table that defines how symbols are used within the module.

object-oriented drawing An approach in drawing and layout programs that treats dig­ital graphics as line-and-arc segments (boxes, ellipses, etc.) rather than as individual dots.

Also called "vector-oriented drawing." See vector-oriented drawing.

object-oriented programming (OOP) A pro­gramming technique whose central feature is the object. The concepts of "procedures" and "data" are replaced by "objects" and "mes­sages." See object.

object-oriented system A system in which both data and procedures combine in soft­ware objects, message passing is used to communicate digitally. with and between objects, similar objects are grouped into class structures, and both data and procedures are inherited through the Class structure to spe­cific instances (copies) of objects.

object program' A fuHy compiled or assem­bled program that is ready to be loaded into the computer. See also target program.

object time system The collection of modules that is called by the compiled code to per­form various utility or .supervisory opera­tions. For example, an object time system usually includes I/O and trap-handling rou­tines.

object type A software element that specifies the common attributes that are shared by all instances of an object. [ISA-TR50.02, Part 9­2000] .

observer A linear system that estimates a plant's state from the plant inputs and mea­surements.

obsolescent Off something that is lower in physical or functional value as a result of changes in technology rather than of deterio­ration.

obsolete No longer suitable for its intended Iuse because of changes in technology or requirements.

octal Pertaining to eight. Usually describes a number system of base or radix eight. For example, in octal notation, octal 214 is 2 times 64, plus 1 times 8, plus 4 times 1, and equals decimal 140.

octal digit The symbols 0, I, 2, 3, 4, 5, 6, or 7 when used as a digit in the system of nota­tion for which 8 is the base or radix. Clarified by definition for /lumber system.

octal number A number that consists of one or more figures and that represents a sum in which the quantity represented by~ach fig­ure is based on a radix of eight. THe figures used as octal numbers are 0, I, 2,3,4,5,6, and 7. Clarified by octal.

octave 1. Any gro~p or series of eight. [ISA­26-1968].2. The interval between two fre­quencies that have a ratio of 2:1.

octave-band analyzer A portable sound ana­lyzer that amplifies a microphone Signal,

345

octave-band filter / offset voltage drift

feeds it into one of several band-pass filters that are selected by a switch, and indicates the signal amplitude on a logarithmic scale. With the exception of the highest and lowest band, each band spans an octave in fre­quency.

octave-band filter A band-pass filter in which the upper and lower cutoff frequen­cies are in a fixed ratio of 2:1.

octet A group of eight bits that are treated as a unit. See byte.

OCX· OLE custom controls (extension). Object-oriented software building blocks that considerably reduce programming time in the creation of applications. Theoretically, they can readily be plugged into Visual Basic, Visual C++, databases, spreadsheets, and word processors.

odd-even check Same as parity check. odograph An instrument that is mounted in a

vehicle in order to automatically plot the vehicle's course and distance traveled on a map.

odometer An instrument for measuring and indicating distance traveled.

OEM Original equipment manufacturer. An organization that provides the final systems made from the assemblies and subassemblies of other manufacturers.

Oersted The CGS unit for magnetic field strength. The SI unit, ampere-tum per meter, is preferred.

off Referring to the nonoperating state of a device or circuit.

off-axis mirrors Mirrors whose mechanical center does not correspond to the axis of the mirror's optical figure.

Off delay A timer that begins when the power is removed completely from the unit.

off hook The condition in which a receiver or handset is removed from the hook.

off-line [Comp] 1. Not being in continuous, direct communication with the computer. 2. Something that is done independently of the computer (as in off-line storage). 3. Describ­ing the state of a subsystem or piece of com­puter equipment that though operable is currently bypassed or disconnected from the main system. 4. Pertaining to a computer that is not actively monitoring or controlling a process or operation, or to a computer opera­tion that is performed while the computer is not monitoring or controlling a process or operation. [Eng] 5. Describing any lateral or angular deviation from the intended axis of a drilled or bored hole. [Safe] 6. A process, to which a safety instrumented system is con­

nected, that is shut down. [ANSI/ISA-84.01­1996]

off-line diagnostics 1. Describing the state of a control system, subsystem, or piece of com­puter equipment that is operable but is cur­rently not actively monitoring or controlling the process. 2. A program for checking out systems and subsystems and providing error codes if an error is detected. This diagnostic program is run while the system is off line.

off-line.equipment The peripheral equip­ment or devicesth"at are not in direct com­munication with the central processing unit of a computer.

off-line memory Any media capable of being stored remotely from the computer that the computer can read when the media is placed into a suitable reading device. Also see exter­nal storage.

off-line system A kind of system that requires human operations between the orig­inal recording functions and the ultimate data processing function. These operations include conversion as well as the necessary loading and unloading that are required in order to use point-to-point or data-gathering systems.

off load or offloading To relieve the data pro­cessing load on a CPU by performing an intensive application's calculations in a dedi­cated or specialized processor.

offset [Cont] 1. A sustained deviation of the controlled variable from set point. This char­acteristic is inherent in proportional control­lers that do not incorporate reset action. 2. The steady-state deviation when the set point is fixed. Note: The offset that results from a no-load to a full-load change (or other specified limits) is often called "droop" of load regulation. See also deviation, steady­state. [ANSI/ISA-51.1-1979 (R1993)]. 3. The count value output from an AID converter that results from a zero input analog voltage. Offset is used to convert subsequent nonzero measurements. 4. A short distance that is measured perpendicular to a principal line of measurement in order to locate a point with respect to that line. 5. A printing process in which ink is transferred from;~the printing plate or master to a rubber-cfvered roller, which in turn transfers the ±hK to the paper. [Comp] 6.The difference between a base loca­tion and the location of an element that is related to the base location. The number of locations relative to the base of an array, string, or block.

offset voltage drift Change in offset voltage with time or temperature.

346

OFHC I on delay

OFFSET

o I---------:!..~---­SET POINT W ...J ...JUJ _-----r---- ACTUAL VALUE O...J 0::<:01-«6i!:U;;

TIME __

Proportional Offset

OFHC Oxygen-free high-conductivity cop­per. An industry designation for pure copper used in a type T thermocouple.

ohm The metric unit for electrical resistance. An ohm is the resistance (or impedance) of a conductor such that an electrical potential of one volt exists across the ends of the conduc­tor when it carries a current of one ampere.

ohmmeter A device for measuring electrical resistance.

ohms per volt A standard rating of instru­ment sensitivity. It is determined by dividing the instrument's electrical resistance by its full-scale voltage.

oil Any of various viscous organic liquids that are soluble in certain organic solvents, such as naphtha or ether, but are not soluble in water. An oil may be of animal, vegetable, mineral, or synthetic origin.

oil bath 1. Oil in a container or chamber in which a part or mechanism is submerged or dips during operation or manufacture. 2. Oil that is poured on a cutting tool or in which it is submerged during a machining operation.

oil burner A burner for firing oil. oil cone The cone of finely atomized oil that

is discharged from an oil atomizer. oil gas A heating gas that is made by reacting

petroleum oil vapors and steam. oil heating and pumping set A group of

apparatuses that consist of a heater for rais­ing the temperature of the oil in order to pro­duce the desired viscosity and a pump for delivering the oil at the desired pressure.

oil-immersed equipment Equipment that is immersed in electrical insula ting oil for the purpose of preventing an ignitable gas or vapor from phYSically contacting the source of ignition. This type of protection is referred to by the International Electrotechnical Com­mission (IEC) as "Ex 0." Note: This type of equipment may also serve the purpose of preventing a particular corrosive gas or vapor from contacting the electrical compo­nents, provided that consideration is given to

the solubility of the corrosive atmosphere in the oil. [ANSI/ISA-12.01.01-1999]

oil-immersion A type of protection in which the electrical apparatus, or parts of it, are immersed in a protective liquid in such a way that any explosive atmosphere above the liquid or outside the enclosure cannot be ignited. This type of protection is referred to as "0." [ISA-12.01.01-1999; ANSI/ISA­12.26.01-1998 (IEC 6Q079-6 Mod)]

OLE Object linking an.d ~mbedding. In computers, an application integration feature of the Microsoft Windows and WindowsNT environments that treats data as a collection of objects to be shared by applications that support the OLE specification. OLE enables several different applications to be linked so as to accomplish a given task. It allows the user to keep information current across sev­eral different software applications simply by changing information in one of them. With the arrival of the Internet, Microsoft now prefers to use the term"ActiveX."

olemeter 1. A device for measuring the spe­cific gravity of oil. 2. A device for measuring the proportion of oil in a mixture.

oleophillic Oil receptive. oleophobic Oil repellent. Olsen ductility test A method for determin­

ing the relative formability of metal sheet. A sheet metal sample is deformed at the center by a steel ball until it fractures. The heighth of the cup at the moment of fracture indicates the relative ease with which deep-drawn or stamped parts can be formed.

ombroscope An instrument for indicating Iwhen precipitation occurs. A heated water-sensitive surface is exposed to the weather. When it rains or snows, an electrical or mechanical output trips an alarm or records the occurrence on a time chart.

omnidirectional (antenna) An antenna that has equal gains in all directions.

omnigraph An automatic acetylene flame-cutting device that cuts several blanks simultaneously, duplicating the pattern traced by a mechanical pointer.

on Referring to the operating state of a device or circuit. ,

on-condition maintenance Mainten*",ce done when equipment needs it. Critical com­ponents are inspected, safety is regarded as raramount, defects are repaired, but if the equipment works, don't fix it.

on delay A timer that starts when power is applied and output contacts transfer at the end of the timing period. This type of timer resets during power failure.

347

one-piece element clamp / open loop

I •II! I, i

one-piece element clamp Also known as a "pinch valve." A valve that consists of a one-piece flexible element or liner that is installed in a body such that the element or liner extends over the flange faces and act as gaskets between the valve and connecting piping. [ANSI!ISA-75.08-1999] The dimen­sions of "long style" one-piece element clamps are the same as those for flanged-end control valves in ANSI 816.10 and ANSI! ISA-S75.03-1985, except for the 6-inch size. "Short-style" dimensions are the same as those for flanged-end gate valves in ANSI 816.10 and MSS SP-72, except for the 6-inch and the 8-inch sizes. [ANSI!ISA-75.08-1999]

ones complement The radix-minus-one com­plement in binary notation. The ones com­plement of an octal 3516 is 4261. See also complement.

online [Comp] 1. The state of a subsystem or piece of computer equipment that is operable and currently connected to the main system. The opposite of off-line. 2. Pertaining to a computer that is actively monitoring or con­trolling a process or operation or a computer operation that is performed while the com­puter is monitoring or controlling a process or operation. 3. Directly controlled by, or in continuous communication with, the com­puter (e.g., on-line storage). 4. Done in real time. [Eng] 5. Describing the coincidence of the axis of a drilled or bored hole with its intended axis, without measurable lateral or angular deviation. [Safe] 6. A process, to which a safety instrumented system is con­nected, that is operating. [ANSI!ISA-84.01­1996]

online computer system A computer system that is characterized by real-time response to a user's inquiries and commands.

online data reduction Of a computing sys­tem, the processing of information as rapidly as information is received or as rapidly as it is genera ted by the source.

online debugging The act of debugging a program while-time sharing its execution with an online process program.

online diagnostics 1. Referring to a state of a control system, subsystem, or piece of com­puter equipment that is operable and actively monitoring or controlling the pro­cess. 2. A program to checking systems and subsystems and then providing error codes and alarms if errors are detected. This diag­nostic program runs in the backgr~und while the control system is in the operating mode.

online equipment Of a computer system, the peripheral equipment or devices whose

operation is controlled by the central pro­cessing unit and in which information that reflects current activity is introduced into the data processing system as soon as it occurs. Thus, online equipment is directly in line with the main flow of transaction processing. Clarified by online.

online memory Any media that the com­puter system can directly access. Also see internal storage.

online processi~~.. Same as online. online system ...1: Synonymous with online. 2.

A system in which the input data enters the computer directly from the point of origin and/or in which output data is transmitted directly to the location where iris used. Com­pare offlinc.

C :1.-off control A simple form of control whereby the control variable is switched fully ON or fully OFF in response when the process variable rises above or falls below the set point, respectively. Cycling always occurs with this form of control.

on-off controller See controller, on-off. OOP Object-oriented programming.

Programming that is based on objects that talk by passing messages. An "object" is a package of information and descriptions of procedures that make it possible to manipu­late that information.

opacity The reciprocal of optical transmissiv­ity.

MOUNTING FLANGE & BOLTS

THERMAL INSULATION

LIGHT SOURCE If LIGHT DETECTOR

LOW VOLTAGE GAS SENSOR WIRING

FLOW

AIR PURGE LINE (TYPICAL)

Opacity Monitor

opcode The pattern of bits in an instruction that indicates the addressing mode.

open circuit 1. An interrupti9n in an electri­calor hydraulic circuit, ustrilly because of a failure or disconnection, t~t'renders the cir­cuit inoperable. 2. A nonrecirculating (once-through) system or process.

open loop Pertaining to a control system in which there is no self-correcting action for misses of the desired operational condition, as there is in a closed-loop system. See feed­forward control action.

348

l I

open position I operating influence

open position A position that is 100 percent and safety of the public are designed to open. [ANSI/ISA-5.2-1976(R1992)]

open seal An impulse line that is filled with a seal fluid that is open to the process.

open system 1. A system that complies with the requirements of the Open System Inter­connection (OSI) reference model in its com­munication with other open systems. 2. A h<lrdware / software design in which a degree of interchangeability and connectivity pro­

I• vides the user with choices, that is, the ability f

I . to select multiple products from multiple • vendors and to integrate them seamlessly on

powerful networks. Open systems make every resource on a network available to any authorized user who needs it. See Open Sys­tem Interconnection (OSl).

Open System Interconnection (051) A con­nection between one communication system and another using a standard protocol.

open-end protecting tube A tube that extends from a physical boundary into the body of a medium in order to surround and protect a thermocouple yet that allows direct contact between the thermocouple's measur­ing junction and the medium.

open-flow nozzle See Kennison nozzle. opening pressure The static inlet pressure

that initiates a discharge. open-loop control 1. A control system that

does not take any account of the error between the desired and actual values of the controlled variables. 2. An operation in which computer-evaluated control action is applied by an operator. See open loop and closed loop. 3. A system in which no compari­son is made between the actual value and the desired value of a process variable.

open-loop numerical control A type of numerical control system in which the drive motor provides both actuation and measure­ment with no feedback to the control console.

openness of scale With respect to measuring instruments, the amount of change in a mea­sured quantity that causes the pointer to move 1 mm (or in some instances, 1 in.) on the instrument scale.

operand The address of an instruction that is to be executed by the processor.

operating basis earthquake (aBE) That earthquake which, according to ISA standard ISA-67.03-1982 "could reasonably be expected to affect the plant site during the operating life of the plant; it is that earth­quake which produces the vibratory ground motion for which those features of the nuclear power plant necessary for continued operation without undue risk to the health

349

remain functional." [ISA-67.03-1982] operating conditions The conditions to

which a device is subjected, not including the variable it measures. Examples of operating conditions include ambient pressure, ambi­ent temperature, electromagnetic fields, gravitational force, inclination, power-sup­ply variation (voltage, frequency, harmon­ics), radiation, shqck, and vibration. Both static and dynamic variations in these condi­tions should be co~sidered. [ANSI/ISA-51.1­1979 (R1993)] See also environmental condi­tions. .

operating conditions, normal The range of operating conditions within which a device is designed to operate and for which operat­ing influences are stated. [ANSI/ISA-51.1­1979 (R1993); ANSI/ISA-71.03-1985]

operating conditions, reference 1. The range of operating conditions of a device within which operating influences are negligible. Note 1: The range is usually narrow. Note 2: Reference operating conditions are the con­ditions under which reference performance is stated and the base from which the values of operating influences is determined. [ANSI/ISA-51.1-1979 (R1993)] 2. The condi­tions to which a device is subjected, not including the variable it measures. See also environmental conditions.

operating control A control to start and stop a burner. It must be in addition to the high limi t control.

operating influence The change in a perfor­mance characteristic that is caused by a change in a specified operating condition from reference operating condition. It is assumed that all other conditions are held within the limits of reference operating con­ditions. Note 1: The specified operating con­ditions are usually the limits of the normal opera ting condi tions. Opera ting influence may be stated in either of two ways: (a) as the total change in performance characteris­tics from the reference operating condition to another specified operating cond ition and (b) as a coefficient that expresses the change in a performance characteristics that correspond to a unit change of the operating ~ndition,

from the reference operating con4,ition to another specified operating condition. Note 2: If the rebtion between operating influence and change in operating condition is linear, one coefficient will suffice. If it is nonlinear, it may be desirable to state more than one coef­ficient, such as 0.05% per volt from 120 to 125

operating level/operator

V to and 0.15% from 125 to 130 v. [ANSI/ ISA-51.1-1979 (RI993)]

operating level The nominal position or out­put at which a system or process operates. Typical examples are the water level in a boiler, the production rate of a manufactur­ing process, or the acoustical output (vol­ume) of a loudspeaker system.

operating pressure 1. The nominal pressure or pressure limits at which a system or pro­cess operates. 2. In a pneumatic or hydraulic system, the high and low values (range) of pressure that will produce the full-range operation of an output device such as a motor operator, positioning relay, or data transmission device. See pressure, operating.

operating rod (spindle) A component of cir­cular cross-section that is used for transmit­ting control movements that may be rotary or linear or a combination of both. [ANSI! ISA-12.22.01-1998 (IEC 79-1 Mod)]

operating specifications The operating­range environmental conditions over which equipment or a system will operate and maintain its specified performance without any degradation. See extreme (operating) con­ditions, storage, and specifications.

operating system 1. An integrated collection of service routines for supervising the sequencing of programs by a computer. Syn­onymous with monitor system and executive systenl. An operating system may perform the functions of input/ output control, resource scheduling, and data management. It pro­vides application programs with the funda­mental commands for controlling the computer. 2. A group of programming sys­tems that operate under the control of a data processing monitor program.

operating temperature range The range in extremes of ambient temperature within which the transducer must perform to the requirements of the temperature error or temperature error band. [ISA-37.12-1982 (RI995); ISA-37.6-1982 (RI995)]

operating time That part of available time during which the hardware is operating and assumed to be yielding correct results. It includes development time, production time, and makeup time. Contrast with idle time.

operation 1. A procedural element that defines an independent processing activity that consists of the algorithm necessary for the initiation, organization, and control of phases. [ANSI! ISA-88.01-1995]2. A well­defined action that, when applied to any per­missible combination of known entities, pro­duces a new entity. [ISA-TR50.02, Part 9­

2000] 3. A set of tasks or processes, usually performed at one location.

operational Referring to a state of readiness for immediate use, as of equipment or vehi­cles.

operational maintenance Any maintenance activity, other than corrective maintenance, that the operator is intended to perform and that is required if the equipment is to serve its intended purpose. Such activities typi­

. ~alty iflclude .the correcting of "zero" on a panel instrument, changing charts, making records, adding ink, or the like. [ANSI/ISA­12.12.01-2000]. Operational maintenance activities are expected to be performed by staff unfamiliar with the risks of electrical shock, likelihood of fire, or personal injury.

operational qualification In process valida­tion, documented verification that an equip­ment-related system or subsystem performs as intended throughout its represented or anticipated operating ranges.

operational test See test. operation analysis An evaluation process in

industrial engineering that assesses deSign, materials, equipme!!t, tools, working condi­tions, methods, and inspection standards. The purpose of operation analysis is usually to improve production output or decreasing cost.

operation code The part of a computer instruction word that specifies, in coded form, the operation to be performed.

operations analysis See operations research. operations research The use of analytic

methods adopted from mathematics to solve operational problems. The objective of such research is to provide management with a more logical basis for making sound predic­tions and decisions. Among the common sci­entific techniques used in operations research are linear programming, probability theory, information theory, game theory, the Monte Carlo method, and queuing theory.

operative limits The range of operating con­ditions to which a device may be subjected without permanently impairing its operating characteristics. Notes: 1. In general, perfor­mance characteristics are not stated for the region between the limits of ~rmal operat­ing conditions and the opera~e limits. 2. When a device returns within the limits of normal operating conditions, adjustments may need to be made restore normal perfor­mance. [ANSI/ISA-51.1-1979 (RI993)]

operator [Mfg] 1. The person who operates equipment for its intended purpose. Note: The operator should have received training

350 ._.__ .~.·r' J j

operator command / optical flat

appropriate for this purpose. [ANSI/lSA­82.02.01-1999 (IEC 1010-1 Mod); lSA­12.02.01-1999] 2. The person who initiates and monitors the operation of a process. [Comp] 3. The person who initiates and monitors the operation of a computer. 4. The portion of an instruction that tells the machine what to do. [Sci] 5. A mathematical symbol that represents a mathematical pro­c~ss to be performed on an associated oper­and.

operator command A statement to the con­trol program, issued via a console device, that causes the control program to provide requested information, alter normal opera­tions, initiate new operations, or terminate existing operations.

operator control An operator-accessible con­trol, usually a knob, push button, lever, or the like, that is provided so the operator can cause the equipment to perform its intended function and serve its intended purpose.

operator interface The shared boundary between a computer system and its human operator. It typically consists of a graphical representation (on CRT or LCD) and an input device (keyboard, touch screen, mouse, trackball, or light pen).

operator's console A device that enables the operator to communicate with the computer. It can be used to enter information into the computer, to request and display stored data, to actuate various preprogrammed com­mand routines, and so on. See also process engineer's console and programmer's console.

operator station The operator interface from which a process or plant is run.

opisometer An instrument that incorporates a tracing wheel for measuring the length of curved lines, such as those on a map.

optical ammeter An electrothermic instru­ment that typically employs a photoelectric cell and indica ting device for the purpose of determining the magnitude of electric cur­rent. It does this by measuring the light that is emitted by a lamp filament carrying the current. The instrument is calibrated by determining the amount of light that is emit­ted when known currents are carried by the same filament.

optical amplifier A type of amplifier in which an electric input signal is converted into light, amplified as light, and then con­verted back into an electric output signal.

optical attenuation meter A device that mea­sures the loss or attenuation of an optical fiber, fiber-optic cable, or fiber-optic system. Measurements are usually made in decibels.

optical bench A rigid horizontal bar or track for holding and supporting optical devices in fixed positions while allowing these posi­tions to be changed or adjusted quickly and easily.

optical character reader A scanning device that can recognize some typewritten charac­ters.

optical comparator 1. Any comparator in which the moveplent of a measuring plunger tilts a small rhirror, w!)ich in turn reflects light in an optical syst~m. 2. A type of com­parator in which the sil!:ouette of a part is projected onto a graduated screen, and the dimensions or contour are evaluated from that projected image.

optical density A measurement of transmis­sion that is equal to the base 10 logarithm of the reciprocal of transmittance. An object that has optical density of zero is transpar­ent; an optical density of one corresponds to 10 percent transmission.

optical disk A large electronic storage device that uses laser beam patterns to read and write digital information (it comes in read­only and write-once types). Unlike magnetic media, an optical disk is not inadvertently changed or erased by EMI/RFl fields.

optical emission spectrometry The measure­ment of the wavelength(s) and intensities of the visible light that is emitted by a sub­stance after it is stimulated.

optical encoder tachometer A type of instru­ment that combines a sensor (optical encoder) with a microprocessor for the pur­pose of converting sensor impulses into a measurement of rotational velocity.

optical fiber Any filament or fiber that is made of dielectric materials and consists of both a core for carrying a light signal and surrounding cladding that reflects the signal back into the core. A thin glass thread is most commonly used, but plastic fiber can also be chosen.

optical filter A semitransparent device that selectively passes rays of light that have pre­determined wavelengths.

optical flat A transparent disk, usually made of fused quartz, that has precisely P¥allel faces. One face is polished for cleari~tsion and the other face is ground optica1fy flat. When the optical flat is placed on a surface and illuminated under proper conditions, interference bands can be observed. These bands can be used to either assess surface contour (relative flatness) or determine dif­ferences between a reference gauge or gauge

351

optical fluid flow measurement / optimization

block and a highly accurate part or inspec­tion gauge.

optical fluid flow measurement Any method for measuring the density of a fluid in motion that involves measuring the refrac­tion and phase shift among different rays of light as they pass through a flow field of varying density.

optical gauge A gauge that measures the image of an object without touching the object itself.

optical glass Glass that is fre~ of such imper­fections as bubbles, chemical inhomogene­ity, or unmelted particles, which degrade its ability to transmit light.

optical grating 1. A diffraction grating that is usually employed with other appropriate optics to fabricate a monochromator. These gratings consist of a series of parallel grooves that are carefully and uniformly shaped in an optical surface that is either flat or concave, depending upon the application. The num­ber of grooves formed and their shape (the grating's profile) determine in what region of the spectrum the optical grating is applica­ble. 2. Commonly referred to as a "Ronchi grating." 3. A highly accurate device that is used in precision dimensional measurement. It consists of a polished surface, commonly an aluminum coating on a glass substrate, onto which close, equidistant, and parallel

II grooves have been ruled. The distribution of

grooves range from several hundred to many thousands of grooves per inch. Gratings are used in conjunction with monochromatic light to produce interference patterns that are sometimes referreJ to as moire patterns. Optical gratings are used in optical testing as well as in generating the dot matrix for reproducing pictures from a photographic negative.

optical indicator An instrument that plots pressure variations as a function of time by using magnification in an optical system cou­pled with photographic recording.

optical isolation Two networks that are con­nected only through an LED transmitter and photoelectric receiver, with no electrical con­tinuity between them.

optical mark reader A device that uses light sensing to read marks made on special forms.

optical material Any material that is trans­parent to visible light or to X-ray, ultraviolet, or infrared radiation.

optical plastic Any plastics material that is transparent to light and can be used in opti­cal devices and instruments to take advan­

tage of the lower cost of the plastics material or of such physical or mechanical properties as the plastics material's superiority to glass.

optical pressure transducer Any of several devices that use optical methods to accu­rately measure the position of the sensitive element of the pressure transducer.

optical pyrometer An instrument that deter­mines the temperature of an object by com­paring its incandescent brightness with that of ~nelectrically.}1e,ftedwire. The current through the'v.vire is adjusted until the visual image of the wire blends into the image of the hot surface. The temperature is read directly from a calibrated dial attached to the current a0j~rstment.

'----===-~If; EYE

lAM' CURRENT

optical rangefinder An optical instrument for measuring distance, usually from the instrument's location to a target some dis­tance away, by measuring the angle between rays of light from the target to separate win­dows on the rangefinder body.

optical recording Making a record of an instrument reading by focusing a tiny beam of light on photosensitive paper. The position of the light along one axis of the resulting orthogonal plot is directly related to the value of the quantity being measured.

optical rotation Rotating the plane of polar­ization about the axis of a beam of polarized light.

optical storage disk A computer storage medium that uses lasers to form surface pat­terns that represent data. CD-ROM (compact disk read-only memory) is an optical storage disk that stores data in digital form.

optical time domain reflectometer A device that sends a very short pulse of light down a fiber-optic communication system and mea­sures the time history of the pulse reflection. The reflection indicates any fwer dispersion and discontinuities in the fib'r path, such as breaks and connectors. The frille it takes for the light pulse to travel to and from the dis­continuity indicates how far it is from the test set.

optimization 1. The process of making a design, process, or system as nearly perfect in function or effectiveness as possible. 2. Using a structured decision-making tech­

352

optimize I orphan

nique to select the best way of achieving a defined goal from a set of alternatives.

optimize 1. To establish control parameters so as to make control as effective as possible. 2. To rearrange the instructions or data in storage so that the program can be run in minimum time.

optimizing control See control, optimize, steady-state optimization, and dynamic optimi­zation.

option module Any additional device that expands a computer's capability.

optoelectronic amplifier An amplifier whose input and output signals and method of amplification may be either optical or elec­tronic.

optoelectronics A technology that combines optics with solid-state electronics.

OR 1. A logic condition such that logic out­put 0 exists if, and only if, one or more of logic inputs A, B, and C exist. [ANSI/ISA­5.2-1976 (R1992)] 2. A logic operator that has the property that if P is an expression, Q is an expression, R is an expression ..., then the OR of P, Q, R ... is true if at least one expression is true, false if all expressions are false. P OR Q is often represented by P + Q, PVQ. OR is synonymous with "inclusive OR." Contrast with exclusive OR.

orders A unit of frequency fhaf is unique fo rotating machinery in which the first order is equal to rotational speed.

organic matter Compounds that contain car­bon, often derived from living organisms.

orient To place an instrument, particularly on€ for maki.ng optical measurements, so that i.ts physical. axis is aligned with a specific direction or reference line.

orientation The state of being aligned with a specific direction or reference line.

orifice 1. The opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged. 2. A cali­brated opening in a plate that is inserted in a gas stream to measure the velocity of flow.

orifice fitting A specially designed device for holding orifice plates.

orifice flange taps The 1/2 in. or 3/4 in. pipe taps in the edge of an orifice flange union.

orifice flange union Two unique flanges that are used to hold the primary element of an orifice plate, with specific design dimensions that are established by the American Gas Association.

orifice meter A general term for any record­ing differential-pressure measuring instru­ment.

Installed Orifice Meter

orifice mixer A piece of equipment for mix­ing two or more liquids by simultaneously directing them, under pressure, throuo-h a constriction in which the resulting turbu­lence blends them tog~ther.

orifice plate A disk or plate like member with a sharp-edged hole in it that is used in a pipe to measure flow or reduce static pres­sure.

or~fice run The differential pressure-produc­mg arrangement that consists of a selected pipe, orifice flange union, and orifice plate. An orifice run has rigid specifications that are defined by the' American Gas Associa­tion.

orifice-type variable-area flowmeter A now-measurement devjce that consjsts of a tube section containing an orifice and a guided conically tapered float that rides within the orifice. The flow of a fluid through the meter positions the float in relation to the I_ flow rate. The float's position is determined magnetically or by other indirect means.

o ring A toroidal sealing ring made of syn­thetic rubber or similar material. The cross section through the torus is usually round or oval, but it may be rectangular or some other shape.

orometer A barometer for measuring eleva­tion above sea level.

ORP "Oxidation-reduction potentiaL" Often called redox in the process industries, ORP is directly related to the oxidative streno-th of a biocidal agent such as chlorine. ORP is the ra tio of activities of the oxidized (1os~-of­electron) and reduced (gain-of-electron) forms of various substances in solu.!jon. Such activities gene~ate millivolt poten~~'l similar to pH, dependmg on the substance:

orphan In the typographical composition of screen displays and printing, a word or short line that ends a paragraph and is carried over ~o the top of the next column. Frowned upon in good typography. See widow.

353

orsat lout of round

I

t!III

IIII

III

II

I II

III

orsat A gas-analysis apparatus in which cer­tain gaseous constituents are measured by absorbing the gas in separate chemical solu­tions.

orthicon A camera tube that utilizes a low-velocity electron beam to scan an image that is stored electrically on a photoactive mosaic panel.

orthometric correction A systematic correc­tion that must be applied to a measured dif­ference in elevation to compensate for the fact that.level surfaces at different elevations are not exactly parallel.

oscillating piston flowmeter A flow mea­surement device that is similar to a nutating disk flowmeter. In contrast to the latter, the motion of the piston takes place in one plane only. The rotational speed of the piston is directly related to the volume of fluid pass­ing through the meter.

oscillation Fluctuation around the set point. oscillator A nonrotating device for produc­

ing alternating current. The output fre­quency is determined by the characteristics of the device. In some cases, the frequency is fixed, but in others it can be varied.

oscillator crystal A piezoelectric crystal device that is used chiefly to determine the frequency of an oscillator.

oscillatory circuit A circuit that produces a periodically reversing current when ener­gized by a direct current voltage. The circuit contains R, Land C elements, which may be varied to change the characteristics of the resultant AC output.

oscillogram The permanent record created by an oscillograph. Alternatively, a perma­nent record of the trace on an oscilloscope, such as might be recorded photographically.

oscillograph A device for determining wave­form by plotting instantaneous values of a quantity such as voltage as a function of time.

oscilloscope A CRT device that can display instantaneous values of AC voltages or cur­rents with respect to time or with respect to other AC voltages or currents. An oscillo­scope can also be used to display the instan­taneous values of other quantities that vary rapidly with time (not necessarily oscillatory values) and that can be converted into suit­able electrical signals by means of a trans­ducer. The display is a graphical representation of the electrical signals that are produced by varying the position of the focused spot where an electron beam strikes the fluorescent coating on the inside surface of the CRT face.

OSF Open Software Foundation. A not-for­profit coalition of DEC, IBM, Hewlett-Pack­ard, Apollo Computers, Groupe Bull, Nix­dorf Computer AG, and Siemens AG located in Cambridge Massachusetts. The OSF was founded in 1988 to develop and license core software technologies for the purpose of developing an alternative to UNIX after AT&T decided not to open UNIX for devel­opment.

OSHA Qccupati<;lpal Safety and He~lth . Administration', In 1970 the u.s. Congress passed the Occupational Safety and Health Act, which specified the requirements that employers must follow to guard against employee illness and injury. OSHA adminis­ters and enforces these requirements.

OSI reference model "Open System Inter­connection." A seven-layered model of com­munications networks defined by ISO (lnterna.tional Organization for Standardiza­tion). The seven layers are: Layer 7 (Ap~lica­tion)--provides the interface for the application to access the OSI environment; Layer 6 (PresentatioI1)--provides for data conversion to pres~rvethe meaning of the data; Layer 5 (Session)-provides user-to-user connections; Layer 4 (Trans­port)-- provides end-to-end reliability; Layer 3 ( etwork)--provides routing of data through the network; Layer 2 (Data Link)-­provides link access control and reliability; Layer 1 (Physical)-- provides an interface to the physical medium.

ounce A U.s. unit of weight. One ounce (avoirdupois) equals 1/16 pound, and is the metric used for most commercial products. One ounce (troy) equals 1/12 pound, and is the metric used for precious metals.

outage The decrease of fluid level in a tank or vessel.

outdoor area See area, outdoor. outdoor location A location where neither air

temperature nor humidity are controlled, and the equipment is exposed to outdoor atmospheric conditions such as direct sun­shine, wind, rain, hail, sleet, snow, and icing. [ISA-82.03-1988]

outgassing The release of adsqrbed or occluded gases and water va~or, usually du::-ing the evacuation or su1iSe"quent heating of an evacuated chamber.

out of round A dimensional condition in which diameters taken in different directions across a nominally circular object are unequal. The difference between them is the amount of "out of roundness."

354

output I overtlow

output 1. An output from the logic sequence. [ANSI/ISA-5.2-1976 (R1992)] 2. The electrical quantity produced by a transducer that is a function of the applied measurand. [ISA­37.1-1975 (R1982)] 3. The information that is transferred from the internal storage of a computer to secondary or external storage or to any device outside of the computer.

output, analog Nominally pertains to the output of data that takes the form of continu­ously variable physical quqntities as con­trasted with digital output. Most analog output subsystems utilize digital-to-analog converters (DAC), which provide a finite number of output levels and only approxi­mate a continuous variable. [ISA-RP55.1­1975 (R1983)]

output, contact A digital output that is gener­ated by operating a contact. [ISA-RP55.1­1975 (R1983)]

output, digital Pertaining to the output of data that takes the form of digits. Contrast with analog output. [ISA-RP55.1-1975 (R1983)]

output area An area of storage that is reserved for output.

output block 1. A block of computer words that are considered as a unit and are intended or destined to be transferred from an internal storage medium to an external destination. 2. A section of internal storage that is reserved for storing data that are to be transferred out of the computer. Synony­mous with output area. 3. A block that is used as an output buffer. See buffer.

output device The part of a machine that translates the electrical impulses represent­ing data processed by the machine into per­manent results such as printed forms, punched cards, and magnetic writing on tape or into control signals for a process.

output impedance Impedance that is mea­sured across the output terminals of a device as a result of circuitry within that device. In power supplies, the output of the equivalent dynamic series impedance of power supply. Output impedance is normally derived from the ratio of output voltage change to output current change as measured at output termi­

t nals. Load line effect and termination must

I.,

be considered to ascertain total impedance.

I output ind icator A device that is connected

to a radio receiver in order to indicate varia­tions in output signal without indicating a specific signal value. Output indicators are usually used for aligning or tuning.

output module An electrical!electronic/pro­grammable electronic system (E/E/PES) or subsystem that acts as an interface to exter­

nal devices and converts output signals into signals that can actuate external devices. [ANSI! ISA-84.01-1996]

output noise The rms, peak, or peak-to-peak (as specified) AC component of a trans­ducer's DC output in the absence of measur­and variations. Note: Unless otherwise specified, output impedance is measured at room conditions and with the excitation ter­minals open/circuited. However, nominal

.e;'\citation aud a m~asurand between 80 and 100 percent of span are applied when the transducer contains integral active out­put-conditioning circuitry. [ISA-37.1-1975 (R1982)]

output parameter A block parameter that has a data structure of value and status elements that are updated by the block algorithm. [ISA-TR50.02, Part 9-2000]

output rating The voltage and current-carry­ing capability of equipment's electrical out­put.

output regulation The change in output as a result of a change in excitation. Note: Unless otherwise specified, output regulation is measured at room conditions and with the measurand applied at its upper-range limit. [ISA-37.1-1975 (R1982)]

output signal A signal that is delivered by a device, element, or system. See also signal, output.

output variable A variable that is delivered by a control algorithm, for example, the sig­nal going to a stearn valve in a temperature control loop. See controlled variable.

outside caliper A caliper that is used to mea­sure distances across two external opposing surfaces.

outside diameter The outer dimension of a circular member such as a rod, pipe, or tube.

oval-shaped gear flowmeter A type of posi­tive displacement flowmeter. It operates by trapping a precise volume of fluid between an oval, toothed rotor and the meter housing as the rotor revolves in mesh with a second rotor. The volume flow of an incompressible fluid is indicated directly by determining rotor speed.

oven A heated enclosure for baking, heating, or drying, generally at temperatluts consid­erably lower than that a furnace. (",

oven dry In paper making, paper "from which all moisture has been removed by artificial evaporation using heat. See bone dry.

overdamped See damping. overflow The condition that arises when the

result of an arithmetic operation exceeds the capacity of the storage space allotted for it in

355

overtlow pIpe I overvoltage protection

i

II

I

TRAPPED liQUID

~ •A~

°B

~ TRAPPEC Ioo--.--:-----J

POSITION A POSITION B LIQUID POSITION C Oval-shaped Gear Flowmeter

a digital computer. Also, the digit arising from this condition if a mechanical or pro­grammed indicator is included. If it is not, the digit may be lost.

overflow pipe A pipe that has its open end protruding above the liquid level in a tank. It limits the height of liquid in the tank by car­rying away any liquid that enters the open end, usually to a drain or sewage system.

overfractionation The operation by which a distillation column produces a purer product than is required.

overhead In communications, all informa­tion, such as control, routing, and error­checking characters, that are used in addition to transmitted data. Overhead includes rout­ing information, operational instructions, and retransmissions of data that are received in error.

overheat To raise the temperature above a desired or safe limit. In metal heat treating, to reach a temperature that results in degraded mechanical or physical properties.

overlay The technique of repeatedly using the same blocks of internal storage during different stages of a problem. When one rou­tine is no longer needed in storage, another routine can replace all or part of it.

overload The maximum magnitude of a mea­surand that can be applied to a transducer without causing a change in performance beyond the specified tolerance. [ISA-37.1­1975 (R1982)]

overload capacity The force weight, power, pressure, or other capacity factor beyond which permanent damage occurs to a device or structure. Overload capacity is usually higher than the rated capacity.

overload protection The provision of protec­tion for equipment against excessive current, including short-circuit current. In power supplies, the protection circuitry is electronic with automatic recovery. The current charac­teristic is normally a foldback type.

overload recovery An effect caused by an analog signal input that is greater than the

~,

input for which the feedback capacity of an amplifier can compensate. The result is a loss of feedback control by the amplifier. This necessitates some recovery time after the overload is removed. [ISA-RP55.1-1975 (R1983)]

overrange In process instrumentation, any excess value of the input signal of a system or element above its upper-range value or below its lower-range value. [ANSI/ISA­51.1-1979 (R1993)] See also overload.

overrahgefimit· -The maximum input that can beappltedto a 'devi~e without causing dam­age or a permanent change in performance. [ANSI/ISA-51.1-1979 (R1993)] See also over­load.

override control 1. Generally, two control loops that are connected to a common final control element. One control loop is nor­mally in cpptrol, with the second loop being switched in by some logic element when an abnormal copdition occurs so that constant control is maintained. 2. A technique in. which more than one controller manipulates a final control element. The technique is used when constraint control is important.

AIR- TO-OPEN VALVE - - - - - - - -@"'-~SETPOINT

LOW SELECTOR

FUEL

OVERRIDE CONTROL

overshoot 1. The amount of output that is measured beyond the final steady output value in response to a step change in the measurand. Note: Overshoot is expressed in terms of percentage of the equivalent step change in output. [ISA-37.1-1975 (R1982)] 2. A transient response to a step change in an input signal that exceeds the normal or expected steady-state respons:l.· 3. The maxi­mum difference between the tdnsient response and the steady-state -re'sponse. See also transient overshoot.

overt faults Faults that are classified as announced, detected, revealed, and so on. [ANSI/ISA-84.01-1996]

overvoltage protection A protective device that interrupts power or reduces the voltage

356

overwriting / oxygen-sensing element

supplied to an operating device when the incoming voltage exceeds a preset value.

overwriting In data processing, the elimina­tion of data by writing new data over it.

Owen bridge A type of AC bridge circuit in which one leg contains a fixed capacitor, the opposite leg contains an unknO'vvn induc­tance and resistance, the third leg contains a fixed resistor, and the fourth leg contains a variable resistor and a variable capacitor. This type of bridge is especially useful for measuring wide ranges of inductances using reasonable ranges of standard capacitances. It can also be used to measure permeability or core loss.

oxidation 1. The loss of electrons by a constit­uent of a chemical reaction. [ISA-71.04-1985] 2. Chemical combination with oxygen.

oxide A chemical compound of an element, usually metal, with oxygen. [ISA-71.04-1985]

oxidizing atmosphere An atmosphere that tends to promote the oxidation of immersed materials.

oxygen attack Corrosion or pitting in a boiler that is caused by oxygen.

oxygen deficiency A significant reduction in the oxygen content of an atmosphere from that of the surrounding ambient air. [ANSI/ ISA-92.04.01-1996]

oxygen enrichment An increase in the oxy­gen content of an atmosphere from that of the surrounding ambient air. [ANSI/ISA­92.04.01-1996]

oxygen-monitoring instrument An assem­bly of electrical, mechanical, and chemical components that senses and reports the con­tent of oxygen in air. Note: For convenience, in the relevant ANSl/ISA standard, the term instrument is used as an abbreviation for "oxygen-monitoring instrument." [ANSl/ ISA-92.04.01-1996]

oxygen-sensing element The particular sub­assembly in the oxygen-monitoring instru­ment that, in the presence of oxygen, produces a corresponding electrical, chemi­cal, or physical characteristic. [ANSl/ISA­92.04.01-1996]

357

I