I Current or moment of

I inertia; iodine; integral (reset) action. In modulat­ing process control, the amount of change of a correcting force that is proportional to the error signal.

I&C Technician Instrumentation and control technician.

ice.bath The true freezing point of water; the temperature at which pure water freezes (O°C or 32°F). The temperature at which a mixture of air-s~turatedpure water and pure ice may exist in equilibrium at a pressure of 1 standard atmosphere. See ice point.

ice point See ice bath.• ICMP Internet Control Message Protocol. A

TCP lIP process that proviges a set of func­tions for the management and control of the networking layer.

I icon A graphic symbol that represents a func­tion or the functions to be performed by the system.

Ii I controller See controller, integral (reset) ([).

I 10 A unique IDentifier for batches, lots, oper­

ators, technicians, and raw materials. [ANSI/ISA-88.01-1995]

ideal elastic behavior A material characteris­tic under given conditions, when the strain is a unique straight-line function of stress andI is illdependent of previous stress history.

J ideal gas A hypothetical gas that obeys pre­cisely the equation for a perfect gas, PV = nRT.

idealized system See system, idealized. ideal transducer A hypothetical passive

transducer that produces the maximum pos­sible output for a given input.

ideal value See value, ideal. identification [Eng] 1. In engineering, the

sequence of letters, digits, or both, that are used to designate an individual instrument or loop. [ANSI/ISA 5.1-1984 (R1992)] Some­times called tag name. [Cant] 2. In control, procedures for deducing a system's transfer function, often from its response to a step­function input or to an impulse.

identification plate A less preferred term for nameplate. [ANSI/ISA-75.05.01-2000]

identified When applied to equipment, iden­tified means recognizable as being suitable for the specific purpose, function, use, envi­ronment, application, and the like, as described in a particular requirement (e.g., National Electrical Code). Note: The suitabil­ity of equipment for a specific purpose, envi­ronment, or application may be determined

by a qualified testing laboratory, inspection agency, or other organization concerned with product evaluation. Such identification may include labeling or listing. For additional information see labeled and listed. [ANSI/ISA-12.01.01-1999]

identifier 1. One or more characters that are used to identify or name a data element and possibly to indicate certain properties of that data element. [IS.A:TR50.02, Part 9-2000] 2. A ~mbol used in data processing whose pur­pose' is to identify; indicate, or name a body of data. '

idle characters Control charac·ters that are interchanged by a synchronized transmitter and receiver so as to maintain synChroniza­tion during nondata periods.

idlers Also "idler rdUers." Freely turning cyl­inders that are mounted on a frame to sup­port a conveyor belt. For a flat belt, the idlers may consist of one or more horizontal cylin­ders transverse to the direction of belt travel. For a troughed belt, the idlers may consist of one or more horizontal cvlinders as well as one or more additional cylinders placed at an angle that lifts the sides of the belt to form a trough. [ISA-RP74.01-1984]

idler spacing The center-to-center distance bdween a consecutive idler roller, as mea­sured parallel to the belt. [ISA-RI'74.01-1984]

idle time 1. That part of available time dur­ing which computer hardware is not being used. Contrast with operating tirne. 2. That part of uptime in which no job can run because all jobs are halted or are waiting for some external action such as I/O data trans­fer.

IDLH Immediately dangerous to life and health. The maximum concentration from which one could escape within 30 minutes after a respirator failure without a respirator and without experiencing irreversible health effects or effects that impair your ability to escape (e.g., severe eye irritation). An exam­ple of an IDLH condition is 300 ppm for hydrogen sulfide gas. [ISA-92.03,02-1999; ISA-92.06.01-1998]

10 synchronization A count that is contained in one word of a telemetry frame to indicate which subframe is being sampled1{t any given time."

10 synchronizer A method of PCM telemetry subframe recognition in which a specific word in the format activates a counter that identifies the number of the subframe word being received. See pulse code modulation (PC!v1).

I

253

ID (Time Code) / illuminance

10 (Time Code) A three-numeral identifica­tion that can be inserted into a time code manually in the place of the "day of the year" information.

IEEE 472 An electrical surge test standard. IEEE 488 A parallel transmission standard for

connecting instruments to a computer. An industry-standard byte serial, bit parallel sys­tem that handles 8-bit words. Originally developed by Hewlett-Packard for labora­tory instrumentation.

IEEE 488 bus A parallel instrument commu­nication bus that conforms to the IEEE 488 standard. Also called General-Purpose Inter­face Bus (GPIB).

IEEE 754 A mathematical floating-point stan­dard.

I IEEE 802.3 An Ethernet LAN standard

(except for the type f~eld [10 Mbps), physical­layer standard that uses the CSMA/CO access method on bus topology. See Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

IEEE 802.11 A radio and wireless LAN. IEEE-P1451 A draft standard for a smart

transducer interface for sensors and actua­tors.

IES integral error squared. A performance criterion that is based on error during tran­sient. IES is sometimes used to precisely tune automatic controllers and/ or adaptive con­trol strategies.

IF amplifier An intermediate-frequency stage in a typical superheterodyne radio receiver.

if and only if (IFF) A conditional statement that implies that an action is to be taken or that a result is true if, and only if, stated pre­requisite conditions are satisfied.

IFO Intelligent field device. A sensor, final element, or transmitter that uses a micropro­cessor(s).

IGES Initial Graphic Exchange Specification. A specification that is commonly used to translate data for other software.

I format Refers to a format in FORTRAN, such that lw indicates that w characters are to be converted as a decimal integer. For exam­ple, 17 yields -4680 as input, +24680 inter­nally, and -4680 as output.

if-then See inclusion. ignitable gas mixture A gas-air mixture that

is capable of being ignited by an open flame, arc or spark, or high temperature. [ANSI/ ISA 12.01.01-1999]

igniter A device for initiating an explosion or combustion in a fuel-air mixture.

ignition The initiation of combustion.

ignition (auto-ignition) temperature (AIT) The minimum temperature that is required to initiate or cause the self-sus­tained combustion of a solid, liquid, or gas independently of the heating or heating ele­ments. Note 1: For additional information, refer to NFPA 325. Note 2: A distinction is made between ignition temperature and flash point. See flash point. [ANSI/ISA­12.01.01-1999]

ignition capable 1. Equipment or wiring that in its normaloperating condition releases sufficient electrical or thermal energy to cause a spetific hazardous atmosphere or hazardous dust layer to ignite. 2. Apparatus or wiring that under normal conditions or under specified abnormal conditions can release sufficient electrical or thermal energy to cause a specific explosive atmosphere to ignite. [ANSI/ISA-12.01.01-1999]

ignition-capable equipment and wiring Equipment or wiring that under normal conditions may release sufficient electrical or thermal energy to cause a spe­cific ignitable atmosphere to ignite. [ANSI/ISA 12.01.01-1999]

ignition lag The time interval between spark discharge and fuel ignition in an internal combustion engine. Also known as "ignition delay."

ignition period See trial for ignition. ignition system That portion of the electrical

subsystems of an internal combustion engine that produces a spark for the purpose of igniting the fuel.

ignition temperature The lowest temperature of a fuel at which combustion becomes self-sustaining. The ignition temperature of an explosive gas atmosphere is the lowest temperature of a heated surface that, under conditions specified in IEC 60079-4, will ignite a flammable substance such as a gas or vapor mixture with air. [ISA-12.00.01-1999 (IEC 60079-0 Mod)]

igniter A flame or high-energy spark that is utilized to ignite the fuel at the main burner.

igniter intermittent An electric-ignited pilot that is automatically lighted each time there is a call for heat. It burns during the entire period that the main bumer:~ firing.

igniter interrupted An electric-ignited pilot that is automatically lighted each time there is a call for heat. The pilot fuel is cut off auto­matically at the end of the trial-for-ignition period of the main burner.

illuminance Luminous flux per unit area over a uniformly illuminated surface.

254

illuminants I impedance, input

illuminants Light oil or coal compounds that readily burn with a luminous flame such as ethylene, propylene, and benzene.

illuminated dial A transparent, semitrans­parent, or nontransparent circular scale that is artificially illuminated.

image converter camera A camera that con­verts images from one wavelength region into another, typically from the infrared to the visible.

image digitizer A device that measures light intensity'at each point in an image and gen­erates a corresponding digital signal, which indicates that intensity. It converts an analog image into a digital data set.

image impedances Of a transducer, the impedances that will-simultaneously pro­duce equal impedances in both directions at each of its inputs and outputs.

image intensifier A viewing' s)".stem that functions as a light amplifier, taking a faint image and amplifying it so it can be viewed more easily.

image inverter A fused fiber-optic bundle that is permanently twisted during manufac­ture so as to him the image it transmits upside down. The same can be done with conventional optics, but a fiber-optic image inverter can do it in a distance of less than an inch.

image maps In the context of the Internet, portions of images that are hypertext links. They allow the user to "mouse click" on dif­ferent parts of a mapped. image so as to acti­vate different hypertext links.

image orthicon A camera tube whose output is generated using a low-velocity electron beam. The beam scans the reverse side of a storage target. That target contains an image that was produced by focusing the electron image from a photo-emitting surface on it.

image processing Techniques for filtering, storing, and retrieving images and for pro­cessing pictorial information with a com­puter.

imagesetter In computer imaging, a device tha: outputs type, line art, and photos com­posed on line.

imbalance (or unbalance) Unequal weight distribution within a body that causes a peri­odic force (as measured at a stationary point) when the body is rotated.

IMC Instihlte of Measurement and Control; Internal Model-based Control. An alternative to the PID approach for self-regulating (non­integral type) processes.

immediate-access storage A device, usually consisting of an array of storage elements, in

which stored information can be read in one microsecond or less.

immediate address An address portion of a digital computer instruction in which is incorporated an operand instead of merely the address of an operand.

immediately dangerous to life and health (IDLH) The maximum level from which one could escape within 30 minutes without escape-impa!ring symptoms or any irrevers­ible effects.

immediate mode In'data'i)f(1Cessi~g,the abil­ity to interrupt a program sequence in order to perform another function.

immersion length Of a thermometer, the dis­tance along the thermometer body from the boundary of the medium whose temperature is being determined to the free end of the well, bulb, or element (if they are unpro­tected).

immunity An inherent or induced electro­chemical condition that enables a metal to IIresist attack by a corrosive solution.

impact idler A belt idler that incorporates resilient roll coverings so as to absorb large amounts of shock at the loading point. [ISA­RP74.01-1984]

impact pressure The pressure that a moving stream of fluid produces against a surface, which brings part of the moving stream abruptly to rest. It is approximately equal to the stagnation pressure for subsonic flow in the fluid medium.

impact strength The property of a material such that it resists breaking under extremely rapid loading. It is usually expressed as the energy absorbed during fracture.

impact temperature The temperature of a gas, after impact with a solid body. The impact converts some of the kinetic energy of the gas into heat and thus raises the gas tem­perature above ambient.

impact tube A small-diameter tube that is immersed in a fluid and oriented so that the fluid stream impinges normally on its open end.

impedance The complex ratio of electric volt­age to current, temperature to heat flow, or electric field strength to magnetic field strength, measured in ohms. Thefial part is resistance, and the imaginary part is reactance.

impedance, input 1. The impedance (pre­sented to the excitation source) measured across the excitation terminals of a trans­ducer. Note: Unless otherwise specified, input impedance is measured at room condi­tions, with no measurand applied, and with the output terminals open-circuited. [ISA­

255

II

impedance, load / inclinometer

37.1-1975 (R1982)] 2. Impedance that is pre­sented by a device to the source. [ANSl/ISA­51.1-1979 (R1993)] 3. The impedance pre­sented by a device or system output element to the input. [ISA-26-1968]

impedance, load Impedance that is pre­sented to the output of a device by the load. [ANSl/ISA-51.1-1979 (R1993)]

impedance, output 1. The impedance across the output terminals of a transducer that is presented by the transducer to the associated ex.ternal circuitry. [ISA-37.1-1975 (R1982)] 2. The impedance presented by a device to the load. [AN5l/ISA-51.1-1979 (R1993)] 3. The internal impedance of an output element, which limits that element's ability to deliver power. [ISA-26-l968]

impedance, source Impedance that is pre­sented to the input oba device by the source. [ANSl/ISA-51.1-1979 (R1993)]

impedance bridge A four-arm bridge circuit in which one or more of the arms have reac­tive components instead of purely resistive components. An impedance bridge must be excited by an AC signal in order to yield a complete analysis of the unknown bridge element.

impeller 1. As applied to pulverized coal burners, a round metal device that is located at the discharge of the coal nozzle in circular­type burners. Its purpose is to deflect the fuel and primary air into the secondary air stream. As applied to oil burners, an impeller is the same as a diffuser. 2. The driven por­tion of a centrifugal pump or blower.

impingement 1. The act of striking moving matter, such as the flow of steam, water, gas, or solids, against similar or other matter. 2. A method of removing entrained liquid drop­lets from a gas stream by allowing the stream to collide with a baffle plate.

impingement attack A form of accelerated corrosion in which a moving corrosive liquid erodes a protective surface layer, thus expos­ing the underlying metal to renewed attack.

implementation The development phase in which the hardware and software of a svs­tem become operational. [ISA-TR50.02, Part 9-2000]

implication See inclusion. important to safety Those structures, sys­

tems, and components that provide reason­able assurance that a facility can be operated without undue risk to the health and safety of the public. [ANSI/ISA-67.14.01-2000]

improvement maintenance Efforts that are aimed at reducing or eliminating the need for maintenance. Reliability engineering

efforts should emphasize eliminating failures that require maintenance. Improvement maintenance includes modification, retrofit, redesign, or change-order.

impulse excitation A method for producing oscillations in which the duration of a stimu­lus is relatively short in relation to the dura­tion of oscillation.

impulse line 1. Piping or tubing that con­nects the process to the sensor. [ISA 67.06­1984] 2. The conduit that transfers the pres­sure signal from the process to the measuring instrument.

impulse-type telemetering Employing inter­mittent electrical impulses in order to trans­mit instrument readings to remote locations.

inaccuracy See error. incandescence 1. The emission of light by an

object at an elevated temperahire. 2. Sponta­neous radiation of light energy from a hot object.

inches water gauge (w.g.) The usual term for expressing a measurement of relatively low pressures or differentials by means of a U-tube. "One inch w.g." equals 5.21b per sq ft or 0.036 lb per sq in.

incident wave A wave in a given medium that impinges on a discontinuity or on a medium of different propagation characteris­tics.

incipient cavitation The onset of cavitation, where only small vapor bubbles are formed in the flow stream. This level is represpnted by the incipient cavitation coefficient a i or l/x Fz . [ISA-RP75.23-1995]

incipient damage A cavitation level that is sufficient to begin minor, observable indica­tions of pitting damage. (Not to be confused with incipient cavitation.) [ISA-RP75.23-1995]

in-circuit emulation (ICE) A development aid for testing the software in computer hardware. It involves an umbilical link between a development system and the tar­get hardware that is being plugged into the microprocessor socket.

inclination error See error, inclination. inclined-tube manometer A glass-tube

manometer in vvhich one leg is inclined from ~he vertical so as to give moreflrecise read-Ings. ;to

inclinometer 1. An instrument for determin­ing the angle from the horizontal of the earth's magnetic field vector. 2. A device for finding the direction of the earth's magnetic field with respect to the horizon. 3. An instrument on a ship that indicates the angu­lar deviation of the ship's attitude to the true vertical.

256

inclusion / indexed addressing

inclusion A logic operator that has the prop­erty that if P is a statement and Q is a state­ment, then "P inclusion Q" is false if P is true and Q is false, true if P is false, and true if both statements are true. "P inclusion Q" is often represented by P>Q. Synonymous with "if-then" and "implication."

inclusive OR See OR. incoherent fiber optics A bundle of fibers in

which the fibers are randomly arranged at each end. The pattern may be truly random

.' so as to achieve uniform illumination, or the manufacturer may simply not bother to align individual fibers. In either case, the fiber bundle cannot transmit an image along its length.

incomplete combustion The partial oxida­tion of the combustible constituents of a fuel.

incompressible Referring,to liquids whose change in volume because of pressure is neg­ligible.

incompressible flow .Fluid flow under condi­tions of constant density.

Inconel A series of high-nickel, chromium, and iron alloys manufactured by Interna­tional Nickel Co. that are characterized by inertness to certain corrosive fluids.

increased safety A type of protection that is applied to electrical apparatuses that do not produce arcs or sparks in normal service and under specified abnormal condi tions. In this type of protection, additional measures are applied so as to provide increased security against the possibility of excessive tempera­tures and of arcs and sparks. This type of protection is referred to as "e." [ANSI/ISA­12.01.01-1999; ANSI/ISA-12.16.01-1998 (IEC 60079-7 Mod)]

increaser A pipe fitting that is identical to a reducer except that is specifically referred to for enlargements in the direction of flow.

increment The specific amount in which a variable is changed.

incremental See incremental representation. incremental backup A computer routine that

copies only those files that have not yet been backed up.

incremental compiler Computer software that compiles programs as they are entered into a computer rather than when they are completed.

incremental cost The cost of the next incre­ment of output from a process.

incremental encoder An electronic or electro­mechanical device that produces a coded digital output based on the amount of move­ment from an arbitrary starting position The

output for any given position with respect to a fixed point of reference is not unique.

incremental feedback In numerical control, the assignment of a value for any given posi­tion of a machine slide or actuating member based on its last previous stationary position.

incremental plotter A discrete X-Y plotter. See X-Yplotter.

incremental representation A method for repr.esenting a variable in which changes in the value of the. variables are represented rather than. the values themselves.

independent conformity See conformity, inde­pendent.

independent linearity See linearity, indepen­dent. ._

independent uncertainty Uncertainty com-'" ponents are independent of each other if their magnitudes or algebraic signs are not significantly c9rrelated. [ANSI/ISA­

•• ", RP67.04.02-2000] independent variable 1. A process or control II

system parameter that can change only as a result of external stimulus. 2. A parameter whose variations, intentional or uninten­tional, induce changes in other parameters according to predetermined relationships.

index [Comp]1. In computing, an ordered reference list of the contents of a computer file or document. It also includes the keys or reference notations for identifying or locat­ing those contents. 2. To prepare such a list. 3. A symbol or number that is used to identify a particular quantity in an array of similar quantities. An example would be the terms of an array represented by X(l), X(2), ... , 100, respectively. 4. Pertaining to an index regis­ter. 5. In engineering, to move a machine part to a predetermined position, or by a prede­termined amount, on a quantized scale.

index address modification (indexing) See address modification.

indexed address 1. An address in a computer instruction that indicates a location where the address of the reference operand is to be found. In some computers, the machine address indicated can itself be indirect. Such multiple levels of addressing are terminated either by prior control or by a termination symbol. Synonymous with "secoWi-Ievel address." 2. An address that is tobe modified or has been modified by an index register or similar device. Synonymous with "variable address."

indexed addressing A method for address­ing computer data in which the address is obtained by adding the instruction operand to the address in the index register.

257

indexed sequential files / indirect file

I

indexed sequential files A collection of related computer records stored on disks. The records are arranged in the same sequence as the key number, and an index or table is used to define the actual location of these records on the disk.

index graduations The heaviest or longest division marks on a graduated scale, oppo­site the scale numerals.

indexing A technique for modifying addresses that is often implemented by means of index registers. .

index-matching fluid A liquid with a refrac­tive index",that matches that of the core or cladding of an optical fiber. Index-matching fluid is used to couple light into or out of optical fibers and can help in suppressing reflections at glass stlrfaces.

index of refraction The ratio of the velocity of light in free space t~ the velocity of light in a given material.

index register A register that contains a quantity that may be used to modify addresses.

index word A computer storage position or register whose contents may be used to mod­ify automatically the effective address of any given instruction.

indicating extensions, direct A device that indicates flow rate by displaying the position of the extension of the metering float within a glass extension tube. [ISA-16.4-1960]

indicating extensions, magnetic A device that indicates flow rate by means of a mag­netic coupling between the extension of the metering float and an external indicator fol­lower that surrounds the extension tube. [ISA-16.4-1960]

indicating gauge Any measuring device whose output can be read visually but is not automatically transcribed on a chart or other permanent record.

indicating instrument See illstrul1lent, indicat­ing.

indicating measuring equipment Equipment that indicates the value of the measured quantity. [ISA-82.03­1988]

indicating scale On a recording instrument, a scale that allows a quantity to be observed as well as recorded.

indication In nondestructive testing, any vis­ible sign or instrument reading that must be interpreted to determine whether or not a flaw exists.

indicator 1. An instrument that graphically shows a value of a variable. 2. The pointer on a dial or scale that provides a visual readout

of a measurement. 3. An instrument for dia­gramming pressure-volume changes during the working cycle of a positive-displacement compressor, engine, or pump.

indicator card A chart on which an indicator diagram is produced by an instrument called an "engine indicator," which traces the real­performance cycle diagram as the machine is running.

indicatqr diagram A graphic representation of work ~one by or on the working fluid in a positive··displacement device such as a recip­rocating engine. "

indicator travel The length of the path that is described by the indicating means or by the tip of the pointer in moving from one end of the scale to the:other. Note 1: The path may be an arc or a straight line. Note 2: In the case of knife-edge pointers and other pointers that extend beyC?nd the scale division marks, the pointer ends at the outer end of the short­est scale division" marks. [ANSI/ISA-51.1­1979 (R1993)]

indicator tube An electron-beam tube in which useful information is conveyed by variations in beam cross section at a lumines­cent target.

indirect-acting recording instrument An instrument in which the output level of the primary detector is raised through interme­diate mechanical, electric, electronic, or pho­toelectric means in order to actuate the writing or marking device.

indirect address An address that specifies a computer storage location that contains either a direct address or another indirect address. Synonymous with "multilevel address."

indirect addressing A method of addressing computer data in which the operand of the instruction is a location address that contains the address of the data.

indirect commands In data processing, con1.­mands to the system from previously recorded inputs rather than from the opera­tor terminal. The operator can call a sequence of indirect commands by file name.

indirect entry A method for connecting an electrical apparatus to the electrical circuits by means of a terminal box o~ plug-and­socket connection that is external to the main enclosure. [ANSI/ISA-12.22.01-1998 (lEe 60079-1 Mod)]

indirect file In da ta processing, a file that contains commands that are processed sequentially, yet could have been entered interactively at a terminal.

258

indirect test I industrial hardened

indirect test A test that measures a quantity other than response time. The actual response time is determined by using this quantity and previous measurements of this quantity that have a known relationship to the actual response times. [ISA 67.06-1984]

indirectly controlled system See system, indi­rectly controlled.

indirectly controlled variable See variable, indirectly controlled.

indirectly heated cathode A cathode in a thermionic tube that is heated by an inde­pendent heating element.

induced draft ~Airflow through a device, such as a firebox or drying unit, that is produced by placing a fan or suction jets in the exit duct.

induced-draft fan 1. A fan that exhausts flue hot gases from the furna~e. [ANSI! ISA 77.41-1993] 2. A fan that exhausts hot gases from heat-absorbing equipment.

inductance 1. In an electrical circuit, the property that tends to oppose changes in cur­rent magnitude or direction. 2. In electro­magnetic devices, the process of generating electromotive force in a conductor by means of relative motion between the conductor and a magnetic field such that the conductor cuts magnetic lines of force.

inductance-type pressure transducer Any of several pressure sensor designs in which motion of the primary sensor element, such as a bourdon tube or diaphragm, is detected and measured by a variable-inductance ele­ment and measuring circuit.

induction heating Raising the temperature of an electrically conductive material by elec­tromagnetically inducing eddy currents in it.

induction instrument A type of meter whose indicated output is determined by the reac­tion between the magnetic fl ux in fixed windings and the flux in a moving coil. The two fluxes are induced by electric currents from different sources.

induction motor meter A type of meter resembling an induction motor, in which the rotor moves in direct relation to the reaction force between a magnetic field and currents induced in the rotor.

inductive Converting a change of measurand into a change of the self-inductance of a sin­gle coill. [ISA-37.1-1975 (R1982)]

inductive bridge position transducer A device for measuring linear position by means of the induction between a fixed member that is slightly longer than the limits of motion and a movable member approxi­mately half as long. This position is deter­

mined by selecting appropriate taps from the longer member, which are connected in a successive decade with external inductors to form a bridge circuit. The configuration that balances the bridge is then related with the actual position of the movable member. The chief advantage of this type of transducer is the relatively high output voltage that is developed for a relatively small change in position.

i-nductive coupling. Using common or mutual inducta.nce to cause signals in one circuit to vary in accordance with signals in another. '..' <

inductive load Electrical devices that are made of wound or coiled wire so that the current passing through the coil creates a magnetic field that in turn produces mechan­ical work.

inductive plate position transducer A device for measuring rotary position by means of the induction between a stationary and rotary plate, each of which have an etched winding that is projected onto a nonconduc­tive surface. The device may also be used to measure the linear motion by means of induction between a stator plate and a slid­ing member, each also having etched wind­ings. The advantages of this type of transducer include eliminating wear and backlash as well as providing good resolu­tion, often within 0.001 in. or less.

inductor A wire coil that will store energy in the form of a magnetic field.

industrial computer A computer that is used on line in various areas of manufacturing, including process industries (chemical, petroleum, etc.), numerical control, produc­tion lines, and the like. See process computer and numerical control.

industrial computer language A computer language for industrial computers. A lan­guage that is used for programming com­puter control applications and system development, for example, assembly lan­guage, FORTRAN, RTL, PROSPRO, BICEPS, and AUTRAN.

industrial controls A collective term for "control instrumentation," used in industry.

industrial engineering A branc~f engineer­ing that deals with the design arid operation of integrated systems of personnel, equip­ment, materials, and facilities.

industrial hardened Processing equipment that is installed to withstand the effects of the manufacturing environment, including dirt, heat shock, and vibration as well as insulat-

I

259

--

Industrial Technology Institute (lTI) / infrasonic frequency

I

ing equipment from poor-quality electrical power.

Industrial Technology Institute (ITO A non-profit organization founded by the Uni­versity of Michigan and dedicated to com­puter integrated manufacturing. III offers Manufacturing Automation Protocol (MAP) conformance testing and certification.

inelastic collision A collision between two or more bodies in which there is a net change in internal energy of at least one of tre partici­pating oodies and a net change in the sum of their kinetic energies.

INERIS Insti.tut National de L'Environne­ment Indust~ial et des Risques. The French certification and testing labora tory for test­ing the equipment ,of different vendors against some common standard.

inert gaseous constituent;; Incombustible gases such as nitrogen that may be present in a fuel. .

inertia The inherent resistance of a body to changes in its state of motion.

inertia-type timer Any of several types of relay devices that incorporate extra weights or flywheels to provide additional inertia in order to achieve a brief time delay in normal relay action. Delays are usually on the order of 80 to 120 milliseconds.

infallible component or assembly A compo­nent or assembly that is not likely to become defective, in service or in storage, in such a manner as to invalidate the type of protec­tion of the circuit. Note - Such a component or assembly is considered as not subject to fault when assessments or tests for the type of protection are made. [ISA-12.02.01-1999 (IEC 60079-11 Mod)]

infallible connections Connections, includ­ing joints and interconnecting wiring, that are not considered as becoming open-cir­cuited in service or storage. [ISA-12.02.01­1999 (IEC 60079-11 Mod)]

infallible separation and insulation Separation or insulation between electrically conductive parts that is not considered as becoming short-circuited in service or storage. [ISA-12.02.01-1999(IEC 60079-11 Mod)]

infiltration Casing molten metal that is to be drawn into void spaces in a powder-metal compact, foamed-metal shape, or fiber-metal layup.

infinite-capacity scheduling Loading a plant or work center without regard to its capacity. This technique is used to locate points of overload so that they can be corrected.

infinite loop In data processing, a routine that can be ended only by terminating the program. One of the most common errors committed by novice programmers.

influence The change in an instrument's indi­cated value when it is caused solely by a dif­ference between the value of a specified variable or condition and its reference value or condition, when all other variables are held constant.

influences Factors or effects that change the . damage rate 6~exteni of damage but do not

change the numerical value of cavitation coefficients. [ISA-RP75.23-1995]

information ProcE;ssing The organization and manipulation of data usually by a.com­puter. See data P,rocessing.

information theory The mathematical the­ory that is concerned with information rate, channels, channel width, noise, and other factors that affect information transmission. Initially developed for electrical communica­tions, infor;mation theory is now applied to business systems and other phenomena that deal with information units and the flow of information in networks.

infrared Any electromagnetic wave whose wavelength is 0.78 to 300 1m.

infrared absorption moisture detector An instrument for determining the moisture content of a material such as sheet paper. Moisture content can be read directly by determining the ratio of two beam intensi­ties. One intensity is at a wavelength within the resonant-absorption band for water and the other is at a wavelength just outside the band.

infrared-imaging device Any device that receives infrared rays from an object and dis­plays a visible image of the object.

infrared spectroscopy A technique for deter­mining the molecular species that are present in a material and then measuring their con­centrations. It involves detecting the charac­teristic wavelengths at which the material absorbs infrared energy and then measuring the relative drop in intensity associated with each absorption band.

infrared thermometer A thermometer that measures emitted infrared radii;\~on (heat) so as to determine the temperatur'i~ of an object that generally is not suitable for contact mea­surement. J

infrasonic frequency A sound-wave fre­quency that is lower than the audio-fre­quency range. f

260

r inherent damping Using mechanical hystere­

l sis of materials such as cork or rubber to I reduce vibrational amplitude.

inherent error The error in quantities that serve as initial conditions at the beginning of a step in a step-by-step set of operations. Thus, the error that is carried over from the previous operation from whatever source or cause.

irtheren.t flow characteristic The relationship between the flow rate through a valve and

". the travel of the closure member as the clo­sure member is moved from the closed posi­tion to rated travel, with constant pressure drop across the valve. [ANSI/ISA-75.11-1985 (R1997); ANSI/ISA-75.05.01-2000]

inherent rangeability. The ratio of the largest flow coefficient (Cv ) to the smallest flow coefficient (Cv ), within \Yhich the deviation from the specified inherent flow characteris­tic does not exceed the limits stated iI). Sec­tion 4 of the following standard: ANSIIISA-­75.11-1985 (R1997)

inherent regulation See self-regulation (inher­ent regulation).

inheritance A relationship between classes, wherein one class shares the structure or behavior defined in one or more other classes. [ISA-TR50.02, Part 9-2000]

inhibitor A substance that selectively retards a chemical action. For example, in using acid to remove scale in boiler work an inhibitor would be used to prevent the acid from attacking the boiler metals.

in-house maintenance 1. Maintenance that is performed by plant maintenance personnel. 2. Not contract maintenance.

initialization [Cont]1. In control, the begin­ning of an operation. Within the function blocks of cascaded PIO loops inside a micro­processor controller, initialization is the auto­matic balanCing of signals so that the transfer of a loop from manual, automatic, or com­puter mode to cascade mode will not disturb the process. [Comm]2. Within a token-pass­ing type data highway, initialization is the restarting of the token. This is usually done in order to revisit every potential address so any new station that may have been physi­cally added is found and included.

initialize In data processing, to send a rest command so as to clear all previous or extra­neous information, as when starting a new operating sequence.

initial set The start of a hardening reaction after water has been added to a powdery material such as plaster or portland cement.

inherent damping / innage

initial starting current IA The highest rms (root mean square) value of current that is absorbed by an AC motor when it is at rest or by an AC magnet whose armature is clamped in the position of maximum air gap, when that current is supplied at rated volt­age and rated frequency. [ANSI/ISA­12.16.01-1998 (IEC 60079-7 Mod)]

injection laser diode A semiconductor device in which lasing ttlkes place within the P-N junction. Light is emitted from the diode edge. . .

injector Any nozzle or nozzle-like device through which a fluid is 'forced into a cham­ber or passage.

ink A liquid or semisolid material that con­sists of a pigment or dye and a carrier. It used to produce a design or mark on a materia1 . such as paper or cloth, after which the carrier evaporates, leaving behind a colored residue of pigmen.t .ordye.

.~nk-jet printer····A printer that forms charac- I. ters by heating ink in the print head until bubbles form, "pop," and depOSit dots of ink on the page or sheet that is being printed.

ink-vapor recordin'~":A.type of electrome­chanical recording in\""hich the trace is pro­duced by depositing vaporized particles of ink directly on the chart paper.

inlet 1. The body end opening through which fluid enters the valve. [ANSI/ISA-75.05.01­2000] 2. A passage or opening where fluid enters a conduit or chamber.

inlet box An enclosure at or near the entrance to a chamber or duct system where a fan is attached to the system.

inlet valve A valve for admitting the work­ing fluid into the cylinder of a positive-dis­placement device such as a reciprocating pump or engine.

in line 1. Centered on an axis. 2. Having sev­eral features, components, or units that are aligned with each other. 3. In a motor-driven device, having the motor shaft parallel to the device's driven shaft and each approximately centered on the other.

inline graphic A digital graphic that can be displayed directly on an Internet Web page. See external graphic. .

in-line valve A valve that has a c$sure mem­ber that moves to seat axially in the direction of the flow path. In-line valves are normally operated by a fluid energy source but may be operated mechanically. [ANSI/ISA-75.05.01­2000]

innage Used to indicate the increase of fluid level in a tank or vessel.

261

in-plant system I input work queue

I

in-plant system 1. A system whose parts, including remote terminals, are all situated in one building or localized area. 2. The term is also used for communication systems that span several buildings and sometimes cover a large distance but in which no common carrier facilities are used.

in point In video development, the first frame of a clip.

in-process waiver-requests Requests for waivers on normal production procedures because of deviations in materials, equip­ment, or quality metrics on which normal product specifications are maintained. [ANSI!ISA-95.00.01-2000]

input 1. An input into the logic sequence. [ANSI!ISA-5.2-1976 (R1992)]2. The data to be processed. [ISA-RP55.1-1975 (R1983)]3. The state or sequence of states that occurs on a specified input channel. [ISA-RP55.1-1975 (R1983)]4. The device or collective set of devices that are used to bring data into another device. [ISA-RP55.1-1975 (R1983)]5. A channel for impressing a state on a device or logic element. [ISA-RP55.1-1975 (R1983)] 6. The process of transferring data from an external storage to an internal storage. [ISA­RP55.1-1975 (R1983)]7. Signals accepted by an input interface as indicators of the condi­tion of the process being controlled. 8. Data that are keyed into a computer or computer peripherals. See excitation or measurand.

input, analog Information or data in analog form that is transferred or to be transferred from an external device into the computer system. [ISA-RP55.1-1975 (R1983)]

input, contact A digital input that is gener­ated by operating an external contact. [ISA­RP55.1-1975 (R1983)]

input, digital Information or data in digital form that is transferred or to be transferred from an external device into the computer system. [ISA-RP55.1-1975 (R1983)]

input area An area of computer storage that is reserved for input. Synonymous with "input block."

input block See input area. input channel A channel for impressing a

state on a device or logic element. See chan­nel, input.

input counter See counter, input. input device In data processing, the device or

collective set of devices that is used to con­vey data into another device.

input impedance Impedance that is mea­sured across the input terminals of a device as a result of circuitry within that device.

input interface Any device that connects computer hardware or other equipment for the purpose of inputting data.

input module Electrical, electronic, or pro­grammable electronic systems (E/E/PES) or subsystems that act as an interface to exter­nal devices and convert input signals into signals that the E/E/PES can utilize. [ANSI! ISA-84.01-1996]

input/output OIq) subsystem interface An input/o~tpuf(I!O)s.ubsystem interface is a device that is use<:i to-connect other types of communications protocols to a fieldbus seg­ment or segments.

input-output (110) software That portion of the operational software that organizes the efficient flow ofdata and messages to and from external equipment.

input-output (110) statement A statement that controls the transmission of information between the computer and the input/output units.

input-output (1/0) A general term for the equipment that is used to communicate with a computer as well as the data involved in the communications. Synonymous with I/O.

input-output control system (laCS) A set of flexible routines that supervise the input and output operations of a computer at the detailed machine-language level.

input-output limited Pertaining to a com­puter system or condition in which the time for input and output operation exceeds that of other operations.

input-output, data processing 1. A general term for the equipment that is used to com­municate with a computer. [ISA-RP55.1-1975 (R1983)]2. The data involved in such com­munication. [ISA-RP55.1-1975 (R1983)] 3. The media that carries the data for input-out­put operations on data. [ISA-RP55.1-1975 (R1983)]

input parameter A block parameter that has a data structure of value and status elements that may be updated through a link to an output parameter. [ISA-TR50.02, Part 9-2000]

input ports In computer hardware, terminals for making connections in external devices that input data into the computer.

input resistance See resistancei~put. input signal A signal that is applied to a

device, element, or system. See signal, input. input state The state that occurs on a speci­

fied computer input channel. input strobe (INSTRB) A signal that enters

setup data into registers. input work queue A list of the summary

information of job-control statements that is

262 ---_-_....... J

inquiry I Institute of Measurement and Control (IMC)

maintained by the job scheduler, from which it selects the jobs and job steps to be pro­cessed.

inquiry A technique in which the interroga­tion of the contents of a computer's storage may be initiated at a keyboard.

insensitive time See dead time. insert 1. Any design feature of a cast or

molded component that is made separately and placed in the mold cavity prior to the casting or molding step. 2. A removable part of a die, mold, or cutting tool.

insertion gain The ratio of the power that is delivered to the portion of a transmission system following a transducer to the power that is delivered to the same portion when the transducer is not in place.

insertion loss Loss of power when a compo­nent such as a connector br splice is con­nected into some previously continuous electrical path.

insertion point In computer screens, the place where text will be inserted when typ­ing. It is usually identified with a flashing vertical line (cursor), which appears to the left of the insertion point and is pushed to the right as text is entered.

inside caliper A caliper that has outward­turned feet on each leg for measuring inside dimensions.

inside diameter The maximum dimension across a cylindrical or spherical cavity. Ide­ally, this is a line that passes through the exact center of the cavity and is perpendicu­lar to the cavity's inner surface.

inside gauge 1. A fixed-dimension device for checking inside diameters. 2. The inside diameter of a bit, measured between oppos­ing cutting points.

inside micrometer A micrometer caliper that is designed for measuring inside diameters and similar inside dimensions between opposing surfaces.

in situ In the natural or original position. In process control applications, in situ generally refers to cleaning, treating, or disposal meth­ods that do not require the removal of vessels or contaminated material.

inspection A deliberate critical examination to determine whether or not an item meets established standards. Inspection may involve measuring dimensions, observing visible characteristics, or determining the inherent properties of an object. However, it usually does not involve determining operat­ing characteristics, which is more properly termed testing.

inspection, in process A periodic check to verify schedule conformance or quality con­trol. When an inspection is prearranged, it may also permit a visual inspection or a spe­cial test of items that cannot be checked or inspected when the system is completely assembled.

inspection, visual (static) A check made without power or continuity equipment. It is normally intended to verify: (a) dimensions, (b)"layout.arrangement, (c) nameplate inscriptions, (d) general adherence to specifi­cations, (e) quality of workmanship, and (f) accessibili ty. .

inspection door A small door in the outer enclosure so that certain parts of the interior of the apparatus may be observed.

instability See stability. installation Putting equipment or software in

place prior to commencing operation. installation category'For overvoltage catego­

ries, an installation category is the classifica­tion of parts of installation systems or circuits by using standardized limits for tran­sient overvoltages (dependent on the nomi­nalline voltage to earth). [ANSI/ISA­82.02.01-1999 (lEe 61010-1 Mod)]

installation qualification In process valida­tion, documented verification that all key aspects of hardware installation adhere to appropriate codes and approved design intentions and that the recommendations of the manufacturer have been suitably consid­ered.

installed flow The true performance of a valve or flowmeter when it forms part of an actual processing line.

installed flow characteristic The relationship between the flow rate and the closure mem­ber travel as it is moved from the closed posi­tion to rated travel as the pressure drop across the valve is influenced by the varying process conditions. [ANSI/ISA-75.05.01­2000]

instance In object-oriented programming (OOP), the definition of a specific object according to its class and individual charac­teristics.

instantaneous contacts Output coIfFcts that transfer when a timer begins timir!g.

instantaneous frequency In an angle-modu­lated wave, the derivative of the angle with respect to time.

instantaneous sampling Taking a series of readings of the instantaneous values of one or more wave parameters.

Institute of Measurement and Control (lMC) A British professional organization.

263

I

instruction / instrumentation

instruction In data processing, a statement that specifies an operation and the values or locations of its operands. In this context, the term instruction is preferable to the terms command or order, which are sometimes used synonymously with it. The term command should be reserved for electronic signals, and order should be reserved for sequence, inter­polation, and related usage.

instruction address An instruction's com­puter memory address. An asterisk is fre­quently used to designate this address.

instruction area 1. A part of computer stor­age that is allocated for receiving and storing the group of instructions to be executed. 2. The storage locations that are used to store the program.

instruction buffer An eight-bit byte buffer in the computer processor that is used to con­tain bytes of the instruction that is currently being decoded and to prefetch instructions in the instruction system.

instruction code See operation code. instruction counter A counter that indicates

the location of the next computer instruction to be interpreted.

instruction format The bits or characters of a computer instruction that are allocated to specific functions.

instruction list A low-level language of programmable controllers that is similar to assembler language in which only one opera­tion, such as storing a value in a register, is allowed per line. It is useful for smaller applications or for optimizing parts of an application. One of five languages accepted under the IEC 61131 standard for PLCs. See function block diagram, ladder logic, structured text, and sequential function chart (SFC).

instruction register In data processing, a storage register that contains the address of the instruction.

instruction repertory 1. The set of instruc­tions that a computing or data processing system is capable of performing. 2. The set of instructions that an automatic coding system assembles.

instruction set In computer software, the particular set of instructions that are imple­mented on a microcomputer.

instruction time 1. The portion of an instruc­tion cycle during which the computer control unit is analyzing the instruction and prepar­ing to perform the indicated operation.

instrument 1. A device that is used directly or indirectly to measure and/or control a • variable. The term includes primary ele­ments, final control elements, computing

devices, and electrical devices such as annunciators, switches, and pushbuttons. The term does not apply to parts (e.g., a receiver bellows or a resistor) that are inter­nal components of an instrument. [ANSI/ ISA-5.1-1984 (R1992)]2. A device that per­forms some analysis of the sample fluid and for which a sample line is required and con­nected. Also referred to as analyzer or monitor. 3. A device for measuring the value of an o.bservable attribute. The device may merely

. indicate the obser'Ved value, or it may also record or control the value. 4. A measuring, recording, controlling, and similar appara­tus that requires the use of small to moderate amounts of electrical energy in normal oper­ation.

instrument, computing A device in which the output is related to the input or inputs by a mathematic·al.hmction such as addition, averaging, division, integration, lead/lag, signal limiting, squaring, square root extrac­tion, subtraction, and so one. [ANSI/ISA­51.1-1979 (R1993)]

instrument, indicating A measuring instru­ment in which only the present value of the measured variable is visually indicated. [ANSI/ISA-51.1-1979 (R1993)]

instrument, measuring A device for ascer­taining the magnitude of a quantity or condi­tion presented to it. [ANSI/ISA-51.1-1979 (R1993)]

instrument, recording A measuring instru­ment in which the values of the measured variable are recorded. Note: The record may be either analog or digital and mayor may not be visually indicated. [ANSI/ISA-51.1­1979 (R1993)]

instrument air (IA) Clean dry air that meets ANSI/ISA-7.0.01-1996.

instrumental analysis Any analytical proce­dure that uses an instrument to measure a value, detect the presence or absence of an attribute, or signal a change or end point in a process.

instrumentation 1. A collection of instru­ments used to observe, measure, or control (or any combination of these) or the applica­tion of those instruments. [ANSI/ISA-51.1­1979 (R1993); ANSI/ISA-5.1-~84 (R1992)]2. In a broader usage, the term may also include the equipment associated with these instruments as well as such additional pur­poses as signal transmission, signal conver­sion, and data storage. [ANSI/ISA-5.1-1984 (R1992)]

264

instrumentation amplifiers I instrument loop diagram

instrumentation amplifiers High-precision amplifiers that have high noise-rejection capabilities.

instrumentation tape Ungapped analog magnetic tape used for continuous data (as in PCM or FM telemetry).

instrument channel 1. A collection of instru­ment loops, including their sensing lines or sample lines, that may be treated or routed as a group while they are separated from instrument loops that are assigned to other redundant ~roups. [ANSI/ISA-67.02.01­1999] 2. An arrangement of components and modules (asreqpired) whose purpose is to generate a single protective action signal when required by a plant condition. A chan­nel that loses its identity when single protec­tive action signals are combined. (See IEEE Standard 60) [ANSI/ISA-6?04.01& .02-2000; ISA-67.06-1984]

instrument channel, response time The time interval between the time when the moni­tored variable exceeds its trip set point and the time when a protective action is initiated. [ISA-67.06-1984]

instrument correction A quantity that is added to, subtracted from, or multiplied into an instrument reading to compensate for the inherent inaccuracy or degradation of instru­ment function.

Instrument Engineer 1. A professional who applies standard engineering standards and practices to the specification, sizing, and functional design of instrumentation hard­ware or control systems. Involves a clear understanding of the manufacturing or sci­entific process to be controlled. Serves as the key person on the instrumentation design and operation team, often supervising and reviewing the team's efforts. 2. Under super­vision, participates in the design and plan­ning of control and instrument systems as required by the project assignment, includ­ing: (a) collecting background information, (b) preparing drawings and calculations, (c) designing or modifying systems, (d) assist­ing in the selection and procurement of equipment, (e) ensuring compliance with applicable standards and codes, (f) complet­ing assigned tasks on schedule, (g) assisting technicians and designers as needed, (h) pos­sibly specializing in a specific engineering discipline.

Instrument Engineering Technician Helps engineers design control and instrumenta­tion systems by providing semiprofessional technical assistance, including: (a) collecting background information, (b) performing cal­

culations, (c) transmitting information to project team members, (d) preparing design specifications, (e) checking design docu­ments to ensure that they comply with the applicable standards and codes, (f) preparing diagrams, (g) preparing requisitions, (h) exe­cuting the necessary tests, collecting data, and making analyses, (i) maintaining equip­ment, (j) performing miscellaneous adminis­trative work, (k) assisting in testing, field start-ups, an.d'training.

Instrument FielaEngin~er Provides field engineering services at installation and start-up sites, ensuring specification fulfill­ment and operating ability. Also defines any potential problems that may arise, including: (a) managing ih~tal1ationand initial servic­ing; (b) maintaining own technical abilities and awareness of new methodologies; (c) checking out operation of panels and instru­ments; (d) providing instruction in the main­tenance and repair of equipment to company service personnel; (e) consulting on service problems in the field.

Instrument Field Service Representative Fulfills customer service requirements on company-produced instru­ments and equipment, including: (a) analyz­ing and correcting instrument operating problems, (b) contacting the supervisor or field engineer for assistance when necessary, (c) promoting scheduled maintenance agree­ments and the sales of replacement or spare parts, (d) training new service personnel, (e) maintaining tools and equipment in good operating order, (f) reporting time, activities, and expenses in accordance with company requirements, (g) keeping up to date on new products and product applications.

instrument identification The sequence of letters, digits or both that are used to desig­nate an individual instrument or loop. [ANSI/ISA-S.1-1984 (R1992)]

instrument loop diagram 1. A loop diagram contains the information that is useful to engineering, construction, commissioning and start-up, and maintenance work. Loop diagrams are an extension of P&IDs. A loop diagram generally contains only one loop. The general layout of a loop diagrClih is divided into sections for the relatiY.e location of the devices. The symbols used are taken from ANSI/ISA-S.1-1984 (R1992), Instru­ment Symbols and Identification. 2. A loop diagram contains the information that is needed to understand the operation of the loop. It also shows all connections to facili­tate the start-up and maintenance of the

265

instrument maintenance technician / Instrument Technician

I

instruments. The loop diagram must show the components and accessories of the instru­ment loop, highlighting special safety and other requirements.

instrument maintenance technician Assembles, installs, maintains, troubleshoots, and repairs the components of measurement and control systems. A high school diploma or the equivalent is required, but with today's technology changing so rap­idly, vocational/technical school or commu­nity college training is also strongly recommended. Most employers also provide on-the-job .training.

instrument mechanic Installs, calibrates, inspects, tests, and repairs instruments and control system devices. Mechanics must be able to work well with their hands, be will­ing to improve their s~ills through training, and be interested in learning new technolo­gies. .••

instrument oil A special grade of lubricating oil for instruments and other delicate mecha­nisms. It is formulated to resist oxidation and gumming, to be compatible with electric insulation, and to inhibit metals from tar­nishing.

instrument-quality air Air, which is the working media for a number of devices, that has been treated to minimize liquid and par­ticulate matter. Note: Some individual devices may require that the air be further conditioned (e.g., filtration, dehumidifica­tion) to ensure reliable operation. [ANSI/ ISA-7.0.01-1996]

instrument range The region that lies between the limits within which a quantity is measured, received, or transmitted. It is expressed by stating the lower- and upper­range values. (See ANSI/ISA-51.1-1979 [R1993].) [ANSI/ISA-67.04.01-2000; ISA­RP67.04.02-2000]

instrument reading time The time lag between an actual change in an attribute and the stable indication of that change on a con­tinuous-reading instrument.

instruments Measuring, indicating, record­ing, computing, controlling, and similar apparatuses that require small to moderate amounts of electrical energy in their normal operation.

instrument service specialist Maintains and/or troubleshoots control and instrumen­tation equipment and calibrates instrument hardware. Typical duties include: (a) main­taining thorough knowledge of equipment, (b) possibly specializing in specific technol­ogy or complex equipment, (c) performing

analyses to ensure that instruments are func­tioning properly, (d) surveying available equipment, and (e) installing and repairing equipment.

instrument shutoff valve The valve or valve manifold that is nearest the instrument. [ANSI/ISA- 67.02.01-1999] Also referred to as "component isolation valve." [ANSI/ISA­67.01-1994]

instrument specification A detailed and . exact· statement of an instrument's particu­

lars, especially o'ne·rhat prescribes the perfor­mance, dimensiolis, construction, tolerances, bills of material, features, and operating con­ditions.

instrument supervisor Usually an experi­enced instrument technician who supervises the work of a team of instrument specialists. In addition to mechanical ability, the super­visor must understand the entire system or process operations for which the team is responsible. Leadership ability is also impor­tant.

instrument system See instrumentation. Instrument Technician Usually requires cer­

tification or graduation from a technical col­lege program. The technician works with theoretical and analytical problems, helping engineers find ways to improve the perfor­mance of an instrument or a system, as well as helping mechanics troubleshoot system components. An engineering technician is one who, in support of engineers or scien­tists, can responsibly carry out either proven techniques, known to those who are techni­cally expert in a particular technology of instrumentation and control systems, or those techniques especially prescribed by engineers. Engineering technicians must apply the principles, methods, and tech­niques prescribed by engineers and appro­priate to instrumentation and control systems technology. They must have a practi­cal knowledge of the construction, applica­tion, properties, operation, and limitations of engineering systems, processes, structures, machinery, devices, or materials. They must also have a practical knowledge, as required, of related manual crafts and instrumental, mathematical, or graphic skil~ Under pro­fessional direction, an engineering technician analyzes and solves technological problems; prepares formal reports on experiments, tests, and other projects; or performs draft­ing, surveying, designing, technical sales, technical writing, teaching, or training. The education of an instrument technician places great emphasis on mathematics and applied

266

instrument technologist / integral action time constant

physics and involves intensive laboratory work. Technicians differ from craftsmen in the extent of their knowledge of engineering theory and methods as well as in their more specialized technical background and skills.

instrument technologist The instrument technologist is qualified to practice engineer­ing technology because he or she has the knowledge and ability to apply well-estab­

• - lished principles and methods of mathemat­ics, physical science, engineering, and technological problem-solving. Will usually have earned a baccalaureate degree in engi­neering technology or gained considerable technical experience on the job. Is a member of the engineering team, which will normally include technicians and engineers and, for special projects, may include scientists, craftsmen, and other spe~ialists. Must have a thorough knowledge of the equipment, applications, and established state-of-the-art design and problemcsolving methods in instrumentation and control systems.

instrument torque The turning moment on an instrument's moving element. This move­ment is produced directly or indirectly by the quantity being measured.

f. instrument transformer A precision trans­former that is capable of reproducing a signal in a secondary circuit suitable for use in mea­suring, control, or protective devices.

insulating barrier Electrical insulating mate­rial lying between the groups of cells that subdivide the battery. [ANSl/ISA-12.16.01­1998 (IEC 60079-7 Mod)]

insulation 1. A material of low thermal con­ductivity that is used to reduce heat loss. 2. A ma terial of specific electrical properties tha t is used to cover wire and electrical cable.

insulation resistance The measured resis­tance between specified insulated portions of a device when a specified DC voltage is applied at reference operating conditions. [ISA-37.1-1975 (R1982)] Note: The (test) objective is to determine whether the leakage current would be excessive under operating conditions. [A Sl/ISA-51.1-1979 (R1993)]

insulation resistance test An insulation DC resistance test that is usually performed at a test voltage of 500 Vdc and a test time of one minute for a minimum acceptable resistance of one megaohm. Note 1: All wires to be tested must be disconnected from all elec­tronic instruments and ground connections. Note 2: This test is not recommended unless the installation of wiring is such that the wire insulation could be damaged.

267

insulation voltage breakdown The voltage at which a disruptive discharge takes place through or over the surface of the insulation. [ANSl/ISA-51.1-1979 (R1993)]

insulator 1. A material through which electri­cal current cannot flow. 2. A material that is a poor conductor of heat, sound, or electricity.

intake 1. An opening where a fluid enters a chamber or conduit; an inlet. 2. The amount of fluid that enters through the opening of a chamber or conduit. .

InTech Journalpublish"ed by ISA and previ­ously known as Ins(runientation Technology.

integer A negative or positive whole number and zero.

integer programming 1. In operations research, a class of procedures for locating the maximum or minimum of a function, subject to constraints. Some or all variables must have integer values. Contrast with con­vex programming, dynamic programming, linear programming (LP), mathematical programming. 2. Loosely, "discrete programming."

integral Control action will cause the output signal to change according to the summation of the input signal values sampled at regular intervals up to the present time, or their defi­nite integral over the same time period.

integral absolute error (IAE) A measure of controller error that is defined by the integral of the absolute value of a time-dependent error function. Used in tuning automatic controllers to respond properly to process transients. See also integral time absolute error (lTAE).

integral action limiter A device that limits the value of the output signal caused integral control action to a predetermined value. [ANSl/ISA-51.1-1979 (R1993)]

integral action rate (reset rate) 1. For propor­tional-pIus-integral or proportional-plus­integral-pIus-derivative control action devices, the ratio for a step input of the initial rate of change of output as a result of integral control action to the change in steady state output as a result of proportional control action. Note: Integral action rate is often expressed as the number of repeats per minute because it is equal to the nH'IDber of times per minute that the proporti~.:mal

response to a step input is repeated by the initial integral response. 2. For integral con­trol action devices, the ratio for a step input of the initial rate of change of output to the input change.

integral action time constant See time con­stant, integral action.

I

integral blower / Integrated Systems Digital Network (ISDN)

I

integral blower A blower that is built as an integral part of a device to which it supplies air.

integral-blower burner A burner of which the blower is an integral part.

integral control A form of control action that returns the value of the controlled variable to the set point when, vvithout this action, sus­tained offset OCC11rs. Also called "reset con­trol."

'integral control action An action in which the controller's output is proportional to the time integral of the error input. When used in combination with proportional action, it was formerly called "reset action." [ANSI/ ISA-77.44.01 & .02-1995]

PERCENT SIGNAL

At

TIME

Integral Control Response to Step Change

integral control action (reset) Control action in which the output is proportional to the time integral of the error input, that is, the rate of change of output is proportional to the error input. See control action, integral (reset) (I).

integral controller See controller, integral (reset) (I).

integral control mode A controller mode in which the controller output increases at a rate that is proportional to the controlled variable error. Thus, the controller output is the integral of the error overtime with a gain factor that is called the "integral gain."

integral flange A flange on a length of pipe, a nozzle, or a pressure vessel that is cast or forged \vith the item itself or is permanently attached to it by welding.

integral logic annunciator An annunciator that integrates visual displays and sequence logic circuits in one assembly. [ANSI/ISA­18.1-1979 (R1992)]

integral orifice A differential pressure mea­suring technique for small flow rates in which the fluid flows through a miniature orifice plate that is integral with a special flow fitting.

integral seat A flow control orifice and seat that is an integral part of the body. [ANSI/ ISA-75.05.01-2000]

integral square error A measure of svstem performance that is formed by integ;ating the square of the system error over a fixed interval of time. This performance measure and its generalizations are frequently used in linear optimal control and estimation theory.

integral stem A design in which the stem is either physically a part of the baIlor mechan­ically made part of the ball. Some integral stems are designed .to perform a turning and then a lifting action. [ANSI/ISA-75.05.01­2000] . 0·.0 ~:o

integral stem/shaft A design in which the sten1/shaft is an integral part of the closure member. [ANSI/ISA-75.05.01-2000]

integral time"absolute error (ITAE) A mea­sure of controller error that is defined by the integral of the product of time and the abso­lute value of a time-dependent error func­tion. Whereas the absolute value prevents opposite excursi0t:\s in the process variable from canceling. each-"other, the multiplication by time places a more severe penalty on sus­tained transients. See also integral absolute error (IAE).

integral windup The saturation of the inte­gral controller output in the presence of a continuous error. This saturation may cause an unacceptable response when returning the process to its set point within acceptable limits of time and overshoot. [ANSI/ISA­77.13.01-1999; ANSI/ISA-77.44.01, .02-1995]

integrate To bring separate parts together to make a whole.

integrated circuit (Ie) A complete electronic circuit. It contains active and passive ele­ments that are fabricated and assembled as a single unit. Usually, they are fabricated as a single piece of semiconducting material. This results in an assembly that cannot be disas­sembled without destroying it.

integrated circuit piezoelectric (ICP) A type of pressure-sensitive sensor that combi11es a piezoelectric element with an isolation amplifier and signal-conditioning microelec­tronics inside the sensor housing. This makes it possible to transmit the output signal over ordinary two-wire cable instead of special low-noise cable. ,

integrated software A compu'~ program that combines several functions for ease of use.

Integrated Systems Digital Network (ISDN) A suite of protocols that is being defined by CCITT to provide voice and data services over wide area netvvorks (WANs). See CCITT.

268

,.,

integrating Providing an output that is a time­integral function of the measurand. [ISA-37.1­1975 (R1982)]

integrating accelerometer A device that mea­sures the acceleration of an object and con­verts the measurement into an output signal that is proportional to speed or distance trav­eled.

integrating ADC A type of analog-to-digital converter in which the analog input is inte­grated over a specific time. Its advantages are high resolution, noise rejection, and lin­earity.

integrating extensions An integrator that derives its input from the motion of the float. It can be installed within the extension hous­ing.

integrating frequency meter A master fre­quency meter for an electric power system. It measures the actual number of cycles of alternating voltage so that result can be com­pared with the theoretical number of cycles for the same time at the prescribed fre­quency.

integrating meter 1. A totalizing meter, such as for measuring electric energy consumed. 2. An instrument whose output is propor­tional to the single (or higher-order) integral of the quantity measured.

integrating network A transducer circuit whose output waveform is a time integral of its input waveform.

integrating sphere A sphere used in optical measurements that is intended to integrate the input light over the output aperture in order to provide uniform illumination.

integration [Eng] 1. In engineering, the pro­cess of assembling multiple components or subsystems to form a system. [ANSI/ISA­84.01-1996] 2. A mathematical process of summing a function with respect to some variable, most commonly time. Integration converts acceleration into velocity, and veloc­ity into displacement. It can be considered as the inverse of differentiation.

integrator 1. A device that continually total­izes or adds up the value of a quantity for a given time. 2. A device whose output is pro­portional to the integral of the input variable with respect to time.

integrity In data processing, data that has not been corrupted.

intelligence In data processing, the process­ing capability of a computer.

intelligent terminal A computer terminal that has some local processing capability.

intensifying screen A sheet of material that is placed in contact with radiographic film. It

integrating / intercell connector

undergoes secondary fluorescence when it is struck with X-rays or gamma rays, thereby increasing the image density for a given exposure.

intensity 1. The lumination level (i.e., bright­ness) of the pixels of a video display unit (YDU). [ISA-5.5-1985] 2. The amount of light per unit area. For human viewing of visible light, the usual term is "illuminance." For electromagnetic radiation in general, the term is "raCiiArH'flux:"

intensity lEivel' J"he aniphtude of a sound wave, commonly measured in decibels.

interacting control Control action that is pro­duced by an algorithm whose various terms are interdependent.

interaction A phenomena that is characteris­tic of a multivariable process, in which the effect of a manipulative variable change in one control loop not only affects its own con­trolled variable. It also affects the controlled variable in another loop. In distillation, the primary consideration is interaction between the overhead composition control loop and the bottoms composition control loop.

interaction analysis A technique used to determine the pairing of manipulative and controlled variables in a control loop.

interactive In data processing, a technique for communication between a user and a sys­tem. The operating system immediately acknowledges and begins responding to a request entered by the user at a terminal. Compare with batch.

interactive computing See conversational mode.

interactive processing In data processing, interactive processing refers to time-dependent (real-time) data handling or communica­tions. The user enters data and then awaits a response from the destination before con­tinuing. Considered "conversational" rather than batch processing.

interactive video The fusion of video and computer technology. Running a video pro­gram and a computer program in tandem under the control of the user. With interactive video, the user's actions, choices, and deci­sions genuinely affect how the program unfolds. :.,fl

interblock gap The blank space oO';a com­puter storage medium between two adjacent blocks of data.

intercell connector An electrical conductor that is used to carry current between cells. [ANSI/ISA-12.16.01-1998 (lEC 60079-7 Mod)]

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269

intercept method / interferometer

intercept method A method for estimating the quantity of particles or the number of grains within a unit area of a microscopic image by counting the number intercepted by a series of straight lines through the image. This is one of the standard methods of determining the grain size of a polycrys­talline metal.

I

interchangeability The ability of two or more devices, regardless of their manufacturer, to work together in one or more distributed applications using the same communications protocol. The data and functionality of each device is so defined that should any device be replaced with a similar one by a different manufacturer, any distributed applications involving the replaced device will continue to operate as before the replacement, includ­ing identical dynamioresponses of the dis­tributed applications. Note: The parameters and functionality of interchangeable devices are sufficiently standardized to support the substitution of devices with those from other manufacturers. No redesign or reconfigura­tion of any associated distributed applica­tions is needed, nor does substitution cause changes to the dynamic responses of the dis­tributed applications.

interchangeability error A measurement error that can occur if two or more sensors are used to make the same measurement.

. This error is caused by a slight variation in the characteristics of those sensors.

interconnectability See interchangeability. intercooler A heat exchanger that is placed in

the path of fluid flow between stages of a compressor for the purpose of cooling the fluid and allowing it to be further com­pressed a t lower power demand.

interelectrode capacitance 1. The capacitance between the electrodes of a vacuum tube. 2. A capacitance that is determined by measur­ing the short-circuit transfer admittance between two electrodes.

interface 1. A common boundary between automatic data processing systems or parts of a single system. [ISA-RP55.1-1975 (R1983)] 2. A specific electronic circuit that is a bound­ary between other circuits or devices. 3. A shared boundary between two functional units. It is defined by functional characteris­tics, common phYSical interconnection char­acteristics, signal characteristics, and other characteristics, where relevant. [ISA-TR50.02, Part 9-2000] 4. The shared boundary through which information is conveyed. [ANSI/ISA­84.01-1996]

interference 1. The waveform that results from superimposing one wave train on another. 2. In signal transmission, spurious or extraneous signals that prevent the accu­rate reception of desired Signals. 3. A distur­bance in a useful signal that results from spurious or extraneous signals in the circuit or in the transmission system.

interference, common-mode A form of inter­ference that appears between measuring cir­

.cl,lit .terrv.inals and ground. [ANSI/ISA-51.1­19Jr9 (R1993)] .' ;.... . . ' ...

interference, differential mode See interfer­ence, normal-mode. [ANSI/ISA-51.1-1979 (R1993)]

interference, electromagnetic Any spurious effect that is produced in the circuits or ele­ments of a device by external electromag­netic fields. Note: A special-case ofinter­ference from radio transmitters is known as radio frequency intf!'rference (RFl). [ANSI/ISA­51.1-1979 (R1993)]

interference, electrostatic field See interfer­ence, electromagnetic.

interference, longitudinal See interference, common-mode.

interference, magnetic field See interference, electromagnetic.

interference, normal-mode A form of inter­ference that appears between measuring cir­cuit terminals. [ANSI/ISA-51.1-1979 (R1993)]

interference, transverse See interference, nor­mal-mode.

interference (electrical) Any spurious volt­age or current that rises from external sources and appears in the circuits of a device. See noise.

interference filter An optical filter that selec­tively transmits specific wavelengths of light because of the interference that results from dielectric coatings on the surface of the mate­rial. Multilayer interference coatings may include metallic layers.

interference fit Any combination of a pin or a shaft diameter and a mating hole diameter such that the tolerance envelope of the hole overlaps or is smaller than the tolerance envelope of the pin.

interference pattern The pattern of some characteristic of a stationary ~ve. It is pro­duced by superimposing onewave train on another. The pattern may be the distribution in space of energy density, energy flux, parti­cle velocity, pressure, or some other charac­teristic

interferometer 1. An instmment so designed that the variance of wavelengths and light­path lengths within it makes possible very

270

interferometric pressure transducer / intermittent duty

accurate measurement of distances. 2. A device that divides a single beam of light into two (or sometimes more) components. It then recombines them to produce interfer­ence. In general, the path lengths that light travels along the different arms will differ. The difference in distance is proportional to the wavelength of the light multiplied by the number of interference rings.

interferometric pressure transducer A type of pressure sensor that was developed to read pressure differentials on the order of 200 Pa (0.030 psi), with a resolution of 1 Pa (0.00015 psi) by using optical interferometry to detect very small deflections of a fragile diaphragm.

interlaced In video development, the alterna­tion of horizontal scan lines, such as in an NTSC signal, which deliv~rs 30 frames per second of 525 lines. The odd set of scan lines is displayed in the first 1/60th second, and the even set is displayed in the second 1/ 60th second in each frame.

interleave 1. In data communication, to send blocks of data alternately to two or more sta­tions on a multipoint system or to put bits or characters alternately into the time slots of a time division multiplexer. See time division multiplexer (TOM) 2. On a video screen, to alternate raster scan lines so as to transmit higher-resolution frames per second.

interleaving 1. The act of simultaneously accessing two or more bytes or streams of data from distinct computer memory banks. 2. The alternation of two or more operations or functions through the overlapped use of a computer facility.

interlock 1. To arrange the control of machines or devices so their operation is interdepen­dent in order to assure that they are coordi­nated properly. [ISA-RP55.1-1975 (R1983))2. A physical device, equipment, or software routine that prevents an operation from beginning or changing function until some condition or set of conditions is fulfilled. 3. A device, such as a switch, that prevents a piece of equipment from operating when a hazard exists. 4. To join two parts together in such a way that they remain rigidly attached to each other solely by physical interference. 5. A device used to prove the physical state of a required condition and to furnish that proof to the primary safety control circuit. 6. A device or group of devices (hardware or software) that are arranged to sense a limit or off-limit condition or an improper sequence of events. To avoid an undesirable condition, they then shut down the offending or related piece of

equipment or prevent it from proceeding in an improper sequence. [ANSI/ISA-77.44.01 & .02-1995)

interlock, motor start A connection that is made through contacts on the motor control­ler. The motor controller is wired in series with the safety circuit so that the motor must be energized before the system is allowed to proceed.

intermediate addressing A method for addressing the data stored in a computer memory. The in'&tructiop. operand is the data to be used with the instruction.

intermediate band A mode of recording and playback in which the frequency response at a given tape speed is "intermediate."

intermediate frequency In a superhetero­dyne receiver, the stage at which a d6wn­converted carrier is passed through a band­pass filter and amplifier.

intermediate means In an instrumentation or control system, all system elements that lie between the primary detector and the end device and that transmit or modify the out­put of the former to make it compatible with input requirements of the latter.

intermediate mode A method for operating a computer using interpretive languages such as BASIC, whereby an individual instruction or a small number of instructions that do not form part of a program are executed.

intermediate phase A distinct compound or solid solution in an alloy system whose com­position limits do not extend to any of the pure constituents.

intermediate (platen) superheater A heating surface that receives steam from the primary superheater located between the primary and secondary superheater. [ANSI/ISA­77.44.01 & .02-1995)

intermediate position A specified position that is greater than zero and less than 100 percent open.

intermediate zone See zone, intermediate. intermittency effect In photography or radi­

ography, a departure from the reciprocity law, which occurs when the emulsion is exposed in a series of discrete increments. This effect contrasts with the response when the emulsion is exposed continuotsly to the same total energy level. ..

intermittent blowdown The blowing down of boiler water at intervals.

intermittent duty An operating cycle that consists of alternating periods of use and idle time. For example, on and off, load and no-load, load and rest, or load, no-load, and rest. In most instances, successive periods of

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271

intermittent firing / International Standard (IS)

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use or idle time vary widely in length, although some intermittent-duty cycles fol­low well-defined patterns.

intermittent firing A method of firing by which fuel and air are introduced into and burned in a furnace for a short time, after which the flow is stopped. This succession repeats in a sequence of frequent cycles.

intermittent rating The rating that is applica­ble to a specified operation over a specified number of time intervals of specified dura­tion. The length of time between these "time intervals must also be specified. [ISA-37.1­1975 (RI982)]

intermodulation The modulation of the com­ponents of a complex wave by each other. This produces new. waves whose frequencies are equal to the sums and differences of inte­gral multiples of the cOJIlponent frequencies

,of the original complex wave. intermodulation distortion (1M D) 1. Distor­

tion that is caused by the interaction of two or more signals. 2. Defined as follows: 20 log (rms sum of the sum and difference distor­tion products)/(rms amplitUde of the funda­mental).

internal In PLC ladder programs, a coil or contact whose reference is a logical element in the program and is not directly concerned with I/O. Internal may also refer to the stor­age location that is used for the logical status of such an element.

internal combustion engine A mechanical prime mover that uses the exhaust gases that result from the burning of fuel within the engine as the thermodynamic working fluid.

internal communication Data exchange between the various devices within a given safety instrumented system. These include bus backplane connections, the local or remote I/O bus, and so on. [ANSI/ISA­84.01-1996]

internal energy The kinetic and potential energies of the constituent molecules of a system. The difference between the heat absorbed by a system and the work done is its change in internal energy, measured in joules.

internal furnace A furnace within a boiler that consists of a straight or corrugated flue, surrounded with water.

internal gear Any ring-type or annular gear whose teeth lie on the inner surface of the rim.

internally fired boiler A fire tube boiler that has an internal furnace. Examples include a Scotch, a locomotive firebox, a vertical tubu­

lar, and any other type that has a water­cooled plate-type furnace.

internal-mix oil burner A burner that has a mixing chamber in which high-velocity steam or air impinges on jets of incoming liq­uid fuel, which is then discharged in a com­pletely atomized form.

internal model-based control An alternative to the PID approach for self-regulating (non­integral type) processes.

internal oxidation A form of degradation of a material· that involves the absorption of oxygen at the surface and the diffusion of oxygen to the interior, where it forms subsur­face scale or oxide inclusions.

internal pressure See burst pressure, proofpres­sure, or referellce pressure.

internal standard In chemical analysis, espe­cially instrumental analysis, a material that is present in or is added to a sample in known amounts in order to serve as a reference in determining the composition of the sample.

internal storage Addressable storage that is directly controlled by the central processing unit (CPU) of a digital computer.

internal treatment The treatment of boiler water by introducing chemicals directly into it.

internal variable A variable that is used in or modified by one or more internal operations of a function block but is not visible to or modifiable through the communication net­work. [ISA-TR50.02, Part 9-2000]

internal wiring Wiring and electrical connec­tions that are made within an apparatus by the manufacturer. Within racks or panels, interconnections between separate pieces of apparatus made according to the manufac­turer's detailed instructions are also consid­ered to be internal wiring. [ANSI/ISA­12.01.01-1999; ISA-12.02.01-1999 (IEC 60079­11 Mod)]

International Electrotechnical Commission (lEC) An international standards develop­ment and certification group for electronics and electrical engineering.

International Federation for Information Pro­cessing (lFIP) An international group of technical societies. ,

International Standard (IS) Thttnhird (and highest) stage of the ISO standard process. Prospective ISO standards are balloted three times. The first stage is a Draft Proposal (DP). After a Draft Proposal has been in use for typically six months to a year, the standard is reballoted, frequently with corrections and changes, as a Draft International Standard (DIS). After the Draft International Standard

272

has been in use for typically one to two years it is reballoted as an International Standard (IS).

Internet An digital communications network that interconnects many other networks. Lit­erally, a "network of networks," the Internet is a global, wide-area hypermedia informa­tion retrieval initiative that aims to give uni­versal access to a large universe of documents. It uses hypertext as its means for interacting with commercial users.

interoperability 1. The ability to operate multiple devices, independent of manufac­turer, in the same system, without loss of functionality. [ISA-TR50.02, Part 9-2000] 2. The ability of two or more devices, regard­less of manufacturer, to work together in one or more distributed applications using the same application process fgr the user layer. The parameters and functionality of each device is so defined that, should any device be replaced with a similar one by a diffe.r~nt

manufacturer, then all distributed applica­tions involving the replaced device will con­tinue to operate as before the replacement. However, they may operate with different dynamic responses. Interoperability is achieved when both a field device and a sys­tem support the same combination of man­datory and optional parts of the same standard. Manufacturer-specific extensions may prevent interoperability between field devices and systems from different manufac­turers. Note: Interoperable devices support standard parameter formats and definitions as well as such functions of distributed user­layer applications as parameter status, block modes, the coordination of schedules for communications and device functions, and the standardized handling of event flows. The parameters and functionality of interop­erable devices are sufficiently standardized to support the substitution of devices with those from different manufacturers, without redesigning or reconfiguring the distributed applications. However, such substitutions may involve tuning changes so as to accom­modate the different dynamic responses of the distributed application with the substi ­tute device.

interpass temperature The lowest tempera­ture reached by weld metal before the next pass is deposited in a multiple-pass weld.

interpreter A system program that converts each instruction of a high-level language (user-written) program into machine code, then executes the machine code, before going on to the next instruction.

273

Internet I intranet

Inter-Range Instrumentation Group (IRIG) The telemetry working group of IRIG is responsible for specifying the indus­try-wide standards and practices of teleme­try.

inter-record gap (IRG) On magnetic tape, the blank gap between records. The tape can stop and start within this gap.

inter-repeater link In data communications, an electronically continuous piece of bus that consists of the same cabl~ in which only two devices are in }foint-ta-point configuration. Also called link segmenl. " ." .

interrupt, process Those interrupts that are available for connecting to the user-supplied equipment. Synonymous with external inter­rupt. [ISA-RP55.1-19?5 (R1983)]

interrupt (INT) [Comp] 1. In computers, the suspension of the execution of a routine as a result of a hardware or program-generated signal. [ISA-RP55.1-1975 (R1983)] 2. In data processing, a signal that, when activated, Icauses a transfer of control to a specific loca­tion in memory. This breaks the normal flow of control of the routine being executed. An interrupt is normally caused by an external event such as a "done" condition in a periph­eral. It is distinguished from a trap, which is caused by the execution of a processor instruction. [Eng] 3. In engineering, to stop a process in such a way that it can be resumed.

interrupt service routine In data processing, a unique address that points to two consecu­tive memory locations, which contain the start address of the interrupt service routine and the priority at which the interrupt is to be serviced.

interrupt vector In data processing, an address that is generated by an interrupt. It points to the start of the interrupt service routine. See interrupt service routine.

interrupt vector register In data processing, a register for storing the interrupt vector.

interval The number of word times that occur between successive repetitive samples of the same channel. See word time. Synony­mous with supercomnwtation and "strapping interval."

interval timer A device that provides an inter­rupt signal when a predetermined "!I pro­grammed time interval completes:$.ee timer. A timer whose output occurs during the tim­ing state.

interworkability See interoperability, inter­changeability, and interconnectability.

intranet A closed, internal network that uses TCP/IP. See TCP/IP (Transmission Control Pro­tocol/Internet Protocol).

intrinsically safe apparatus I inventory management

I

intrinsically safe apparatus An electrical apparatus in which all the circuits are intrin­sically safe circuits. [ISA-12.02.01-1999 (IEC 60079-11 Mod); ISA-12.01.01-1999]

intrinsically safe circuit A circuit in which any spark or thermal effect, whether it is pro­duced normally or in specified fault condi­tions, is incapable of igniting a given explosive atmosphere in the specified test conditions. [ANSI/ISA-12.01.01-1999; ISA­12.02.01-1999 (IEC 60079-11 Mod)]

intrinsically safe equipment and wiring Equipment and wiring that are incapable of releasing sufficient electrical or thermal energy, under either normal or abnormal conditions, to ignite a specific haz­ardolls atmospheric mixture in its most eas­ily ignited concentration. [ANSI/ISA-51.1­1979 (RI993)] )

intrinsically safe system An assembly of interconnected intrinsically safe apparatuses, associated apparatuses, other apparatuses, and interconnecting cables in which those parts of the system that may be used in haz­ardolls (classified) locations are intrinsically safe circuits. [ANSI/ISA-12.01.01-1999]

intrinsic barriers See intrinsic safety barrier. intrinsic joint loss A loss that is i~herent to

the fiber and that is caused by fiber parame­ter mismatches when two nonidentical fibers are joined.

intrinsic safety 1. A type of protection in which a portion of the electrical system con­tains only intrinsically safe apparatuses, cir­cuits, and wiring. These are, by definition, incapable of igniting in the surrounding atmosphere. No single device or wiring is intrinsically safe by itself (except for battery­operated, self-contained apparatuses such as portable pagers, transceivers, gas detectors, and the like. These are specifically designed to be intrinsically safe, self-contained devices). Devices and vviring can be intrinsi­cally safe only when they are employed in a properly designed intrinsically safe system. This type of protection is referred to as "i." Note: See also associated apparatus. [ANSI/ ISA-12.01.01-1999; ANSI/ISA-RPI2.6-1995] 2. A design methodology for a circuit or an assembly of circuits in which any spark or thermal effect produced under normal oper­ating and specified fault conditions is not capable of igniting a given explosive ahno­sphere under prescribed test conditions. Note: This definition is taken from EN 50 020 :1977 (Intrinsically safe electrical apparatus). [ANSI/ISA-50.02, Part 2-1992] 3. A method for providing safe operation of electric pro­

cess control instrumentation where hazard­ous atmospheres exist. The method keeps the available electrical energy so 10\'" that the hazardous atmosphere cannot ignite. 4. A protection technique that is based upon restricting the electrical energy within appa­ratuses and the interconnecting wiring in a potentially explosive atmosphere. They are restricted to a level below that which can cause ignition by either sparking or heating effects.. ~eGause of the method by which intrinsic safety is -achieved, it is necessary to ensure tha,t both the electrical apparatus exposed to the potentially explosive atmo- . sphere and other electrical apparatuses inter­connected with it are suitably constructed.

intrinsic safety barrier 1. A component that contains a network that is designed to limit the energy (voltage and current) available to the p.rotected circuit in tIle hazardous (classi­fied) location, under specified fault condi­tions. [ANSI/ISA-12.01.01-1999; ANSI/ISA­RPI2.6-1995] 2. A device that is inserted in the wire between process control instrumen­tation and the point where the wire passes into the hazardous area. It limits the voltage and current on the wire to safe levels.

1/8A 10 20 206

SAFE 01 02 HAZARDOUS AREA 30 V 30V AREA

2~-----4~----+------l4

intrinsic safety ground bus A grounding system that has a dedicated conductor sepa­rate from the power system. This prevents ground currents from flowing normally. This bllS is reliably connected to a ground elec­trode. Note: For fllrther information, refer to Article 504 of NEe, Section 10 of CSA C22.1, or ANSI/ISA-RP 12.6-1995. [ANSI/ISA­12.01.01-1999]

intrinsic safety ground system A grounding system that has a dedicated conductor, which is isolated from the pow~r system, except at one point. This prev~ts ground currents from flo\ving normally. This system is reliably connected to a grollnding elec­trode in accordance vvith Article 250 of the NEe or Section 10 of CEC Part I, CSA C22.1. [ANSI/ISA-RPI2.6-1995]

inventory management The systematic determination of items and qllantities to be ordered. The coordination of order release

274

inventory turnover / ionizing

and order due dates, changes in required ion exchange A chemical process for remov­quantities, and the rescheduling of planned ing unwanted dissolved ions from water by orders. inducing an ion-exchange reaction (either

inventory turnover The number of times that cation or anion) as the water passes through an inventory cycles during a year. a bed of special resin that contains the substi­

inverse response The dynamic characteristic tute ion. of a process, by which its output responds to ion-exchange resin A synthetic organic com­an input change by moving initially in one pound (resin) that can remove unwanted direction but finally in the other. ions from a dilute solution by combining

with them or by exchanging them for ions that prod.uce desirable or neutral effects.

ionic strength The effective strength of all ions in a solution. It is equal to the sum of one half of the product of the individual ion concentration and their ion valence or charge squared for dilute solutions.

ion implantation A process for enhancing the surface properties of a solid by bombard­ing it with a beam of high-energy ions, which are absorbed into the material's surface layer.

ionization The process of splitting a neutral TIME molecule into positive and negative ions or II

of detaching one or more electrons from a Inverse and Overshoot Response neutral atom.

to a Step Change ionization chamber A gas-filled enclosure that is ionized when radiation enters the

inversion temperature In a thermocouple, chamber. It contains two or more electrodes the temperature of the "hot" junction when that sustain an electric field and collect the the circuit's thermoelectric electromotive charge resulting from ionization. force is equal to zero. ionization constant A measure of the degree

inverter A NOT element. The output signal is of dissociation of a polar compound in dilute the reverse of the input signal. solution at equilibrium. It equals the product

invocation The process of initiating the exe­ of the concentrations of the dissociated com­cution of the sequence of operations that are pound (ions) divided by the concentration of specified in an algorithm. [ISA-TR50.02, Part. the undissociated compound. 9-2000] ionization gauge A pressure transducer that

I/O-bound A state of program execution in is tased on the conduction of electric current which all operations are dependent on the through the ionized gas of the system whose activity of an I/O device. For example, when pressure is to be measured. It is useful only a program is waiting for input from a termi­ for very low pressures (for example, below nal it is "I/O-bound." See also CPU-bound. 10-3 atm).

I/O hardware Computer hardware that is ionization time In a gas tube, the interval used to carry signals into and out of the pro­ between the time when conduction condi­cessing hardware. tions are established and when conduction

1 i' I/O isolation Usually refers to the electrical actually begins at some stated value of tube

separation of field circuits from a computer's potential. internal circuits. I/O isolation is accom­ ionization vacuum gauge An instrument for plished by opto-electronic devices. The term measuring very low pressures (high vacu­occasionally refers to the ability to have ums). It functions by using a current of posi­input or output field wiring on isolated cir­ tive ions, which are produced in ti\e gas by cuits, that is, with one return for each. electrons emitted from a hot cathode and

I/O limited See input-output limited. accelerated across a portion of the evacuated I/O module A basic set of I/O interfaces that space toward another electrode.

share a common computer unit housing. Can ionizing When used as a third modifier as be a set of discrete I/O or a smart control I/ stipulated by ISA-37.1-1975 (R1982), ionizing O. involves converting a change of measurand

ion A charged atom or radical that may be into a change in ionization current, such as positive or negative.

275

ionizing event / isolation

through a gas between two electrodes. [ISA­37.1-1975 (RI982)]

ionizing event Any interaction between an atom or molecule and an energy beam, parti ­cle, atom, or molecule that causes one or more ions to be generated.

ionizing radiation Any electromagnetic or particulate radiation that can produce ions, either directly or indirectly, when it interacts with matter.

ion laser A laser in which the active medium is an ionized gas, typically one of the rare gases argon or krypton, or a mixture of the two.

I

ionosphere That portion of the earth's atmo­sphere where ionization takes place as a result of the sun's ultraviolet radiation or from bombardment by hydrogen bursts from sunspots. The various~ayers,identified as B, e, D, E and F, have characteristics that reflect and refract radio waves according to their frequency, time of day, sunspot cycle, and earth's weather.

I/O page That portion of computer memory in which specific storage locations are associ­ated directly with I/O devices.

ion pair The combination of a positive ion and a negative ion that have the same magni­tude of charge. An ion pair is formed from a neutral molecule as a result of absorption of the energy in radiation.

I/O rack A chassis for mounting computer II o modules. It may be local or remote from the CPU I memory uni t.

IP Internet protocol. A protocol that is used in gateways that connect networks at the OSI network layer.

I/P converter A device that linearly converts electric current into gas pressure (for exam­ple, 4-20 mA into 3-15 psi).

IPDS Intelligent Printer Data Stream. A page description printer protocol that allows the complete page of text and graphics to be for­matted and stored in printer'S memory.

IP ratings Ingress Protection codes. IP ratings refer to IEC enclosure classes that are approxi­mately equivalent to NEMA ratings. The first digit (0-6) is protection from solid bodies, and the second digit (0-7) is protection from liquids. Higher digits mean greater protec­tion. For example, IPI0=NEMA 1 and IP67=NEMA 7.

ir Infrared; an area in the electromagnetic spectrum that extends beyond red light from 760 nanometers to 1,000 microns (106 nm). A form of radiation that is used to make non­contact temperature measurements. Infrared

is also the signal range for some fiber-optic communications systems.

irradiance The power per unit area that is incident upon a surface. Also called "radiant flux density."

irradiation 1. Exposing an object or person to penetrating ionizing radiation such as X-rays or gamma rays. 2. Exposing an object or per­son to ultraviolet, visible, or infrared energy.

ISA-The Instrumentation, Systems, and Automation Society A US-based society of instrument and controls professionals. Formerly, the Instrument Society of America (ISA). .

isentropic Proceeding at constant entropy. isentropic exponent A ratio that is defined

by the specific heat at constant pressure divided by the specific heat at constant vol­ume.

ISO 9000 International Standards Organiza­tion standards for quality systems.

isobaric Proceeding at constant pressure. isochronous Equally timed. In data

communications, timing information is transmitted on a channel along with data. Isochronous means sending asynchronous data by synchronous means. This method involves synchronously sending asynchro­nous characters between each pair of start and stop bits.

isochronous governor A device that main­tains the rotational speed of an engine con­stant, regardless of load.

isolated circuit A circuit in which the current to any other circuit or conductive part does not exceed the limit for leakage current, with the equipment at reference-test conditions. [ANSI/ISA-82.02-01-1999 (IEC 61010-1Mod)]

isolating element A movable membrane, usually made of metal, that physically sepa­rates the measured fluid from the sensing element. Usually, this membrane is consider­ably more flexible than the sensing element and is coupled to the sensing element using a transfer fluid. Its purpose is to provide mate­rial compatibility with the measured fluid while maintaining the performance integrity of the sensing element. [ISA-37.6-1982 (RI99S)]

isolation 1. The physical and e~ctrical arrangement of the parts of a Signal trans­mission system so as to prevent electrical interference currents within or between the parts. Note: This definition is taken from IEEE Standard 100-1984. [ANSI/ISA-SO.02, Part 2-1992] [Eng] 2. In vibration, isolation means diminishing the transfer of a vibration amplitude by the judicious selection of bar­

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rier materials and barrier configuration. One hundred percent isolation is not possible unless there is no physical contact and a per­fect vacuum surrounds the object to be iso­lated.

isolation valve The isolation valve that is nearest the instrument, the grab-sample point, or the in-line component and is avail­able to personnel during normal plant opera­tion. The root valve mayor may not perform the function of the isolation valve, depend­ing on its location. [ANSI/ISA-67.01-1994]

isometric view A drawing in which the hori­zontallines of an object are drawn at an angle to horizontal, and all verticals are pro­jected at an angle from the base.

isomorphic representation Representation in which there is a one-to-one correspondence between a scene and its representation.

isopotential point The point on the millivolt­versus-pH plot at 'which a change in temper­ature has no effect. It is at 7 pH and zero mil­livolts unless it is shifted by the standard­ization and meter zero adjustments or an electrode asymmetry potential.

isothermal At constant temperature. isotope Any of two or more nuclides that

have the same number of protons in their nuclei but different numbers of neutrons. Such atoms are of the same element, and thus cannot be separated from each other by chemical means. However, because they have different masses they can be separated by physical means.

isotope effect The effect of nuclear proper­ties, other than the number of protons, on the nonnuclear physical and chemical behavior of the nuclides.

italic In the typographical composition of screen displays and printing, the style of let­ters that slant as distinct from upright, or roman, letters. Generally used for emphasis within text.

ITB Intermediate block character. A digital transmission control character that termi­nates an intermediate block. A block check character usually follows it. Using ITBs allows error checking to be done on smaller transmission blocks.

iterate To repeatedly execute a loop or series of steps. For example, a loop in a routine iter­ates.

iterative Describing a procedure or process that repeatedly executes a series of opera­tions until some condition is satisfied. An iterative procedure can be implemented by a loop in a routine.

isolation valve I lTV

iterative testing A testing method that per­mits the characterization of the device under test by stepping through a series of tests until the device fails.

ITU-TSS International Telegraphic Union-­Telecommunications Standards Sector. The replacement organization for CCITT. See CCITT.

lTV Interactive television. Beyond video reception, 'ITVallows the viewer to respond to multichannel bmadcasts. This is made possible by the availability of broadband transmission media such-as fiber-optic cable. ITV has industrial implications that are simi­lar to those of videoconferencing.

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