. 21
( 42)


of interest to researchers in artificial intelligence
inductive microphone A microphone in which
sound waves vibrate a conductor or coil in a
strong magnetic field, producing a corresponding
alternating-current output by the resulting in-
Dielectric duction. Example: dynamic microphone.
induction neutralization Neutralization of a vac-
uum-tube radio-frequency power amplifier, via
negative feedback from the output to the input
Spirally wound
through coupling coils.
inductive reactance Symbol, X L. Unit, ohm. The
reactance exhibited by an ideal inductor, consid-
inductive capacitor
ered as a positive imaginary-number quantity; X L
= j6.28fL, where X L is in ohms, f is the frequency
inductive circuit 1. A circuit in which inductance in Hertz, L is the inductance in henrys, and j is
predominates. 2. A (theoretical) circuit containing the unit imaginary number (the square root of
inductance only. “1). Alternatively, f can be specified in megahertz,
inductive coupling The transfer of energy between and L in microhenries. In a pure inductive reac-
two inductors (or inductive devices) by a linking tance, current lags 90 degrees behind voltage.
electromagnetic field. Also see COEFFICIENT OF Also see INDUCTANCE, INDUCTION, INDUCTOR,
TUAL INDUCTANCE. inductive switching Switching operations in a cir-
inductive feedback See MAGNETIC FEEDBACK. cuit containing an inductor. Switching time is
inductive heater See INDUCTION HEATER. influenced by the INDUCTANCE-RESISTANCE
inductive heating See INDUCTION HEATING. TIME CONSTANT of the inductor; overall opera-
inductive kick See BACK VOLTAGE and KICK- tion is affected by the back voltage generated by
BACK. the inductor.
inductive load A load device that approaches a inductive transducer A transducer in which the
pure inductive reactance (e.g., loudspeaker and sensed phenomenon causes a change in induc-
electric motor). tance (or reluctance), which, in turn, causes a
inductive loading In an antenna, the addition of proportional change in output current, voltage,
inductance in series with the element(s). This re- frequency, or bridge balance. Compare CAPACI-
duces the resonant frequency for a radiator hav- TIVE TRANSDUCER, CRYSTAL TRANSDUCER,
ing a given physical length. It can also serve to MAGNETIC TRANSDUCER, and RESISTIVE
reduce the physical length required for a radiator TRANSDUCER.
inductive trimmer • inertial guidance

L = 100 µH inductors in parallel-series See PARALLEL-
inductors in series See SERIES INDUCTORS.
Reactance (ohms)

inductors in series-parallel See SERIES-PARAL-
4000 inductor substitution box An enclosed assort-
ment of common-value inductors that can be
switched, one at a time, to a pair of terminals. In
troubleshooting and circuit development, any of
several useful fixed inductances can be thus ob-
industrial data processing Abbreviation, IDP. The
application of digital computers and associated
0 2 4 6 8 10
equipment to industrial problems, through the
Frequency (MHz) classification, sorting, storing, and manipulation
of information.
industrial electronics The branch of electronics
f = 1 MHz concerned with manufacturing processes and
600 their control, and with the operation and safe-
guarding of factories.
Reactance (ohms)

industrial instrumentation 1. Supplementing an
industrial process with electrical and electronic
measuring instruments. 2. The instruments used
for the purpose defined in 1.
industrial television Abbreviation, ITV. A usually
200 closed-circuit television (CCTV) system, used as
an adjunct to a manufacturing process, or as a
means of communication or surveillance within
an industrial plant.
0 20 40 60 80 100 industrial robot A robotic device used in indus-
trial applications (e.g., mining, construction,
Inductance (µH)
manufacturing, or laboratory work).
industrial tube An (often heavy-duty) highly reli-
inductive reactance
able vacuum tube designed expressly for indus-
trial service, such as high-power radio or
inductive trimmer See TRIMMER INDUCTOR. television broadcasting.
inductive tuning Also called permeability tuning. ineffective time The period during which an oth-
In a radio receiver, transmitter or transceiver, the erwise operational computer is not being used ef-
adjustment of frequency by changing the induc- fectively because of delays or idle time.
tance of a coil having a movable core. inelastic collision A collision between charged
inductivity See DIELECTRIC CONSTANT. particles in which one gains energy and the other
inductometer An instrument for measuring in- loses energy.
ductance in terms of the resonant frequency of an inert gas A gas that does not readily react with
INDUCTANCE-CAPACITANCE (LC) circuit, in other elements. Inert gases include argon, helium,
which L is the unknown inductance and C is cal- krypton, neon, and xenon. Such gases are often
ibration capacitance. used in hermetically sealed devices to retard cor-
inductor A coil of wire wound according to various rosion.
designs, with or without a core of ferromagnetic inertance See ACOUSTIC INDUCTANCE.
material, to concentrate the magnetic flux result- inertia The tendency of a body at rest to remain at
ing from current flowing in the wire. The coiling of rest unless acted on by an outside force. Also, the
the wire and/or the addition of a ferromagnetic tendency for a body in motion to maintain that
core increases the self-inductance compared with motion unless acted on by an outside force. Com-
that of a straight wire having the same length. pare MOMENTUM.
Also see INDUCTANCE; INDUCTION, 1; and inertia in electric circuit The condition in a cir-
SELF-INDUCTANCE, 1. cuit containing inductance, in which a current
inductor alternator See ALTERNATOR. change lags behind a voltage change (analogous
inductor amplifier See MAGNETIC AMPLIFIER. to mechanical inertia; see INERTIA).
inductor decade See DECADE INDUCTOR. inertial guidance A system that automatically
inductor microphone See INDUCTIVE MICRO- guides missiles and satellites in a desired trajec-
PHONE. tory without the need for continuous control by
inductors in parallel See PARALLEL INDUCTORS. signals from a station.
364 inertia relay • information superhighway

infinity Symbol, ∞. A quantity that is unlimited in
inertia relay A time-delay relay whose operation is
slowed by the addition of weights or other attach- duration or dimension. A quantity that increases
ments. without limit is sometimes said to “approach in-
inertia switch A switch that can sense a distur- finity.”
bance of its inertia. infix notation A system of logical operation nota-
inference engine A circuit that gives instructions tion wherein operands are separated by opera-
to a computer or robot, by applying programmed tors, thus, A & B, where the ampersand means
rules to commands issued by a human operator. AND. Compare PREFIX NOTATION.
Comprises the functional portion of an EXPERT Infobahn See INFORMATION SUPERHIGHWAY.
SYSTEM. infobond On a printed circuit board, a form of
infinite Pertaining to a quantity or region that has wiring on the side opposite the components. The
no defined limits. wiring is used in place of the foil normally on
infinite baffle A loudspeaker baffle having no such a circuit board.
openings for the passage of sound from the front information 1. Collectively, data or communica-
to the back of the speaker cone. tions, excluding the symbols or signals used to
infinite-impedance detector A detector that of- describe, present, or store them. 2. The result of
fers the very high input impedance of a gate- data processing (i.e., that which is derived from
source circuit and the large-signal capabilities of the compilation, analysis, and distillation of
a diode detector. Audio-frequency output is taken data).
across the source resistor, which is bypassed for information bits In an encoded signal, data char-
radio-frequency signals. There is no drain resis- acters or digits that can be treated to give infor-
tor. Drain current increases with the input signal mation (excluding control characters).
from a very low value at zero signal level. information center A storage bank designed for
use by many different subscribers, via computer.
information channel A channel through which
data and associated signals are transmitted and
C3 R2 information feedback system In message trans-
mission, a control system in which intelligence
C1 received at a terminal is returned to the sending
unit for automatic verification.
R1 information gate A device or circuit that opens
and closes an information channel.
RF input L1
“information processor” species Anything that
uses data to derive conclusions, to produce other
data, or to take specific actions, and whose func-
tioning can be explained entirely on the basis of
’B AF data-processing operations. This includes com-
output puters and smart robots. Many (but not all) sci-
entists believe that animals are also included;
some believe that human beings qualify as well.
infinite-impedance detector
information retrieval In digital computer and
data-processing operations, the categorizing and
storage of information and the automatic recall of
specific file items. Also see ACCESS TIME.
infinite regress A reasoning pattern (either hu-
information separator An indicator that sepa-
man or machine-based) that is fallacious because
rates items of information or fields in a (usually
it defines or explains something in terms of itself.
variable-length) record.
infinite sample space In statistics, a sample
information storage In digital computer and data
space having no definite limits.
processing operations, holding information in
infinite series A mathematical series in which the
memory pending retrieval.
number of terms is limitless. For example, 1„6 = 0.1
information superhighway 1. General expression
+ 0.06 + 0.006 + 0.0006 + . . .
for a worldwide network consisting of computers
infinitesimal 1. A quantity, such as a differential,
(personal, educational, industrial, and govern-
that approaches zero as the limit. 2. Pertaining to
ment) interconnected by telephone lines. 2. See
a quantity whose magnitude is extremely small or
INTERNET. 3. A massive, evolving, somewhat
negligible. 3. Pertaining to an extremely small
controversial data communication network link-
change in a quantity or measured value.
ing computers, television, and telephone sys-
infinite transmission line A theoretical transmis-
tems. It uses high-speed, high-volume data links.
sion line with normal characteristics, but extend-
Communication technologies include fiberoptics,
ing away from the signal generator or receiver for
radio-frequency repeaters, microwaves, geosta-
a limitless distance.
information superhighway • inherited error

tionary satellites, and low-earth-orbit (LEO) satel- found. This band lies between the microwave ra-
lite systems. dio spectrum and the visible-light spectrum.
information word A character group representing infrared therapy The use of infrared rays by
stored information and managed, as a unit, by physicians and other practitioners to treat cer-
hardware or software. tain disorders.
infra- Prefix meaning below or lower than (e.g., IN- infrared waves Electromagnetic waves whose
FRARED). lengths are greater than those of visible light
infrablack region In a composite video signal, the waves, but less than those of microwaves.
blacker-than-black region (see BLACKER THAN infrared window Any portion of the infrared spec-
BLACK). trum in which energy is easily transmitted
infradyne receiver A superheterodyne receiver in through the lower atmosphere of the earth.
which the intermediate frequency is the sum of infrasonic Pertaining to acoustic disturbances
the signal and oscillator frequencies, rather than whose frequencies are below the range of human
their (usual) difference. hearing (less than about 20 Hz).
infrared Pertaining to electromagnetic energy in a infrasonic intrusion detector A system that de-
band whose wavelength is longer than that of vis- tects the presence of extremely low-frequency
ible light, but shorter than that of microwave en- acoustic disturbances, and sends a signal to an
ergy. alarm. Such INFRASONIC waves can be caused
infrared communication Communication by key- by various actions such as walking on a wooden
ing or modulating infrared rays. floor, opening or closing a door, etc.
infrared counter-countermeasure A military tac- infrasonics The branch of physics dealing with IN-
tic in which action is taken against an enemy in- FRASONIC phenomena.
frared countermeasure. infrasound Acoustic disturbances in the air,
infrared countermeasure A military tactic using whose frequencies are lower than about 20 Hz,
countermeasure methods to cripple enemy in- and whose wavelengths are longer than about 55
frared equipment. feet (17 meters).
infrared detector A device that senses the pres- inharmonic distortion Distortion in which the fre-
ence of infrared energy. Some such detectors are quencies of extraneous components are not har-
bolometers, radiometers, radiomicrometers, and monically related to the fundamental frequency.
photocells. It is sometimes experienced when a tone-burst
infrared-emitting diode Abbreviation, IRED. A signal is applied to a loudspeaker.
semiconductor diode, such as the gallium-
arsenide type, that emits infrared rays when a
current passes through the p-n junction in the Max.
forward direction.
infrared guidance A navigation and reconnais-
sance system using infrared rays. Fundamental
infrared homing The method whereby a guided
missile uses infrared rays to guide it to its target.

infrared light See INFRARED RAYS.
infrared motion detector See MOTION DETEC-
infrared photography Photography in which the
scene is illuminated with infrared light or emits
infrared rays, and the film is infrared sensitive.
infrared radiation See INFRARED RAYS.
infrared rays Radiation at frequencies in the IN-
FRARED region. Also (somewhat mistakenly)
called heat rays. 0 3
1 2
infrared remote control 1. The use of an infrared
link, usually over short line-of-sight distances, Frequency, kHz
for the purpose of controlling the operation of
electronic equipment. A common example is the inharmonic distortion
local remote control of a television receiver or
high-fidelity system. 2. A small box, containing
buttons, a transmitter and an infrared-emitting inherent component A (usually extraneous) prop-
diode (IRED), used for local remote control of de- erty possessed by a device because of its internal
vices, such as television receivers and high- peculiarities. Thus, an inductor has inherent ca-
fidelity sound systems. pacitance; a capacitor has inherent inductance.
infrared spectrum The region of the electromag- inherited error In an extended calculation, an er-
netic spectrum in which INFRARED radiation is ror carried through from one of the earlier steps.
366 inhibit • in-plant system

inhibit 1. In digital computer and logic operations, ink squeeze-out In the printing of matter for opti-
to prevent an action or block the input of data by cal character recognition, the squeezing of ink
means of a pulse. 2. To delay an action or pro- from a character™s center.
cess. ink-vapor recorder See INK-MIST RECORDER.
inhibit gate A pulse-actuated gate circuit that acts in-lb Abbreviation of INCH-POUND.
as an INHIBITOR. inlead The part of an electrode that passes through
inhibitor 1. A device or circuit that produces a the external shell or case of a component.
pulse or signal that prevents an action, or that inline procedure The main portion of a COBOL
blocks data input. 2. An additive, such as an or- computer program, responsible for the primary
ganic liquid, that delays the hardening of a mix- operations.
ture, such as an encapsulating compound. inline processing The action peculiar to a system
inhibit pulse In a computer, a drive pulse that pre- that processes data almost immediately upon re-
vents other pulses from changing the direction of ceipt (i.e., one that need not be capable of storing
magnetization in the cells of a magnetic core a lot of unprocessed data).
memory. inline readout In digital computer operations, a
inhibit signal In digital computer and logic opera- readout device that displays digits side-by-side
tions, the signal that causes an INHIBIT action. horizontally.
initial drain 1. The current supplied by a battery or inline subroutine A subroutine that must be writ-

cell at its rated voltage. 2. The current delivered ten each time it is needed, as compared with one
by a rechargeable battery or cell when it is put to that can be accessed by a program branch.

use immediately after receiving a full charge. inline tuning Tuning of all the stages of a channel,
initial failure The first failure occurring in the op- such as an intermediate-frequency amplifier, to
eration of a circuit or device. the same frequency.
initial instructions A resident computer routine inner conductor The inner wire or rod of a coaxial
used to aid program loading. Also called initial or- cable or coaxial tank. It generally carries the sig-
der. nal, and is isolated from the surrounding envi-
initial ionizing event In the operation of a ra- ronment by the grounded OUTER CONDUCTOR.
dioactivity counter, the first event that starts the inorganic Consisting of materials other than car-
chain of similar events constituting the count. bon compounds; therefore, it is not related to liv-

initialization A computer program instruction ing things.
that sets the value of a variable to zero. inorganic electrolyte Any electrolyte that is com-
initial permeability Permeability in the low mag- pletely inorganic: containing no compounds of
netization region of a material. carbon.
initial time delay Abbreviation, ITD. In acoustics, in phase The condition in which alternating or pul-
the elapsed time between the instant the direct sating waves or wave phenomena are in step with
sound wave is first heard, and the instant the each other at all points. Compare OUT-OF-PHASE.
first echoes (reflected sound waves) arrive.
initiate See TRIGGER.
injection 1. Introducing a signal into a circuit or
device. 2. Introducing charge carriers (electrons
or holes) into a semiconductor.
injector 1. An element or electrode for INJECTION.
2. A device or circuit that injects a signal into an-
other device or circuit.
injector electrode See INJECTOR, 1.
ink bleed In the printing of matter for optical char-
acter recognition, ink flow around the characters,
often making them unrecognizable to the reader. in phase
inkjet galvanometer A galvanometer whose move-
ment controls the pressure of a jet of ink for mak-
ing a recording on a paper chart. Also see in-phase carrier See I-PHASE CARRIER.
LIQUID-JET OSCILLOGRAPH. in-phase current Resistive current in an ac circuit
inkjet printer A printer commonly used with per- (i.e., current in phase with voltage). Compare
sonal computers, in which images are created by QUADRATURE CURRENT.
jets of ink sprayed directly onto the paper. Noted in-phase feedback Feedback in phase with a main
for low operating noise level, high image resolu- signal. Also called POSITIVE FEEDBACK and RE-
tion, and excellent color-reproduction capability. GENERATION.
ink-mist recorder A graphic recorder in which the in-phase voltage A voltage that is in phase with
line is traced by a mist of ink. another (reference) voltage.
ink recorder A graphic recorder using a pen-and- in-plant system An automatic data communica-
ink stylus. tions system within a specific building or complex.

input • input/output module

input 1. Energy or information delivered or trans- input guarding A method of eliminating stray cou-
ferred to a circuit or device. 2. The terminals of a pling among inputs in an integrated circuit. A
device or circuit to which energy or information is shield is provided at the input; it is driven to fol-
applied. 3. To deliver or transfer energy or infor- low along with the input voltage. This ensures low
mation to a circuit or device (as to input data loss and minimum errors resulting from un-
from a computer peripheral to memory). wanted coupling.
input admittance Symbol, Yi. The internal admit- input impedance Symbol, Z i. The internal im-
tance of a circuit or device, as “seen” from the in- pedance of a circuit or device, as “seen” from the
put terminals; the reciprocal of input impedance. input terminals. Compare OUTPUT IMPEDANCE.
Compare OUTPUT ADMITTANCE. input limited The processing time limitation im-
input area In a computer memory, an area set posed by an input unit on the speed of a program
aside for data input from a source other than a run.
program. input noise current At the input of an integrated
input bias current The input bias required by an circuit, the root-mean-square (rms) or peak-to-
operational amplifier. peak (pk-pk) noise current existing within a spec-
input capacitance Symbol, Ci. 1. The internal ca- ified range of frequencies.
pacitance of a circuit or device, as “seen” from the input noise current density The noise current,
input terminals. Compare OUTPUT CAPACI- usually expressed as a root-mean-square (rms)
TANCE. 2. The grid-cathode capacitance of a vac- value, in a band 1 Hz wide around a given fre-
uum tube. quency.
input capacitor 1. In a capacitance-coupled cir- input noise voltage At the input of an integrated
cuit, the input coupling capacitor. Compare OUT- circuit, the root-mean-square (rms) or peak-to-
PUT CAPACITOR. 2. The first capacitor in a peak (pk-pk) noise voltage existing within a spec-
capacitor-input filter (i.e., that capacitor electri- ified range of frequencies.
cally nearest the rectifier output electrode). input noise voltage density The noise voltage, usu-
input choke The first choke in a choke-input filter ally expressed as a root-mean-square (rms) value,
(i.e., that choke electrically nearest the rectifier in a band 1 Hz wide around a given frequency.
output electrode, when no preceding capacitor is input offset current In an operational amplifier,
used). the difference between the currents going to the
input circuit The circuit or subcircuit constituting input terminals when the output is zero.
the input section of a network or device. Compare input offset voltage In an operational amplifier,
OUTPUT CIRCUIT. the potential that has to be applied between the
input clamp current The current from an input input terminals for a zero output voltage.
when the input is in a state below ground poten- input/output Abbreviation, I/O. 1. Data transmit-
tial. A test for the input clamp diode. ted to, or received from, a computer. 2. A terminal
input conductance Symbol, Gi. The internal con- through which data is transmitted to, or received
ductance of a circuit or device, as “seen” from the from, a device.
input terminals; it is the reciprocal of INPUT RE- input/output bound A condition affecting a sys-
SISTANCE. Compare OUTPUT CONDUCTANCE. tem in which the time consumed by input and
input coupling capacitor See INPUT CAPACITOR, output operations is greater than that required
1. for other processes.
input coupling transformer See INPUT TRANS- input/output buffer A computer memory area
FORMER. specifically reserved for the receipt of data coming
input current Symbol, Ii. 1. The current delivered from or going to a peripheral.
to a circuit or device. 2. Current flowing in the in- input/output control The part of a computer sys-
put leg or electrode of a circuit or device. tem that coordinates activity between a central
input device 1. A device, such as an input trans- processor and peripherals.
former, that couples energy or information to a input/output equipment 1. In digital computer
circuit or device. Compare OUTPUT DEVICE. 2. A operations, devices for entering information into
device through which another device receives the computer or for reading information from it.
data. Examples: keyboard, mouse, display, and optical
input equipment Collectively, input devices used scanner. 2. In robotics and artificial intelligence,
with a computer. a data link between a controller and one or more
input error voltage In an operational amplifier, robots, and/or between or among two or more
the error voltage at the input terminals when a controllers.
feedback loop operates around the amplifier. input/output isolation Arrangement or operation
input extender A diode network that provides in- of a circuit or device so that there is no direct
creased fan-in for a logic circuit. Also see FAN-IN, path between input and output terminals around
1. the circuit or device. Also see ISOLATION.
input gap In a velocity-modulated tube, the gap in input/output module See INPUT/OUTPUT
which the electron stream is initially modulated. EQUIPMENT.
368 input/output routine • insect robot

input/output routine A routine for simplifying the Tank
programming of standard input/output equip- Output
ment operations.
input/output switching The allocation of more
than one channel to peripherals for communica- Input
tions with a central processor.
input/output voltage differential At a given load
current, the potential difference that is necessary
for an integrated circuit to operate according to
its output voltage specifications.
input power Symbol, P i. 1. The power presented to
the input terminals of a circuit or device. Also
called POWER INPUT. Compare OUTPUT
POWER. 2. The operating power of a circuit or de- input tank
vice (i.e., the power-supply requirement).
input protection In an integrated circuit, a
input terminals Terminals (usually a pair) associ-
means of preventing damage to the device from
ated with the input section of a circuit or device.
excessive voltage at the input, such as transient
spikes or the result of malfunctioning of some
input transformer The transformer that delivers
other circuit.
signal voltage or power to the input circuit of a
input record 1. A computer record of immediate
network or device. Compare OUTPUT TRANS-
interest that is ready for processing. 2. During a
computer program run, a record read into mem-
input uncertainty The combination of all parame-
ory from an input device.
ters that result in adverse behavior in an opera-
input recorder A device that makes a permanent
tional amplifier.
record of the signals or data input to a circuit or
input unit In a digital computer, the device or cir-
cuit that receives information from peripherals.
input register In a computer, a register that re-
input voltage 1. Symbol, E i or V i. The voltage pre-
ceives data from a peripheral relatively slowly and
sented to a circuit or device. Compare OUTPUT
then passes it on to a central processor at a faster
VOLTAGE, 1. 2. The voltage across the input leg
speed as a sequence of informational units. Also
or electrode of a circuit or device. Compare OUT-
input resistance Symbol, R i. The internal resis-
input-voltage drift For an integrated circuit (IC),
tance of a circuit or device, as “seen” from the in-
the time- and temperature-dependent change in
put terminals. Compare OUTPUT RESISTANCE.
output voltage divided by the IC™s open-loop volt-
input resonator In a velocity/modulated tube, the
age gain.
resonator in which electron bunching occurs.
input-voltage offset For a differential amplifier,
input routine A computer program section that
the input signal voltage at the differential input
manages data transferal between an external
that results in zero output voltage.
storage medium and a memory input area.
input-voltage range The range, in volts, over
input section 1. See INPUT ROUTINE. 2. See IN-
which the input voltage can fluctuate in an inte-
grated circuit so that the common-mode rejection
input sensitivity 1. The level of input-signal am-
ratio (CMRR) specifications are not exceeded.
plitude that will result in a certain signal-to-noise
input winding The signal winding of a magnetic
ratio at the output of a device. The specified sig-
nal-to-noise ratio is usually 10 or 20 dB. 2. The
inquiry A programmed request for information
level of input signal in a frequency-modulated de-
from storage in a computer.
vice, required to produce a specified amount of
inquiry display terminal A video display/key-
noise quieting. The specified level of noise quiet-
board terminal used to make an inquiry to a com-
ing is usually 20 dB. Alternatively, 12-dB SINAD
puter system, and display the response.
(ratio of signal to the level of noise and distortion)
inquiry station A terminal from which an inquiry
can be specified. 3. The minimum level of input
can be sent to a central computer.
voltage required to actuate a logic gate.
inrush The initial surge of current that occurs
input signal The signal (current, voltage, and
when voltage is first applied to the primary wind-
power) presented to the input terminals of a cir-
ing of a transformer with no load connected.
cuit or device for processing.
inscribe To convert data to a form on a document
input tank In a double-tuned stage of a transmit-
that is readable by a character-recognition device,
ter or power generator, the tank circuit in which
as through the use of magnetic ink, for example.
the input signal is resonated. This is generally
insect robot A member of a fleet of robots, all of
the base or gate circuit. Compare OUTPUT
which are under the control of a single computer.
insect robot • instantaneous speech power

The term arises because the system functions
like an anthill or beehive, in which the individual

machines are “stupid,” but the system as a whole
is “smart.” Such robots often have six legs, like
insects. Compare AUTONOMOUS ROBOT.
insert A (usually metallic) bushing that can be
molded into a plastic part (or pressed into it after
molding is completed) to provide a bearing sleeve
or threaded hole.
insert core A ferromagnetic core whose position
can be adjusted to vary the inductance of the coil
surrounding it. Time
t1 t2
insert edit 1. In magnetic tape recording, a section
(Instant) (Instant)
of tape on which new audio is recorded over ex-
isting audio. 2. The process of recording new au-
instantaneous amplitude
dio over existing audio in a defined interval on a
magnetic tape.
insertion gain In a circuit or system, the gain re- instantaneous automatic gain control Abbrevia-
sulting from the amplifier inserted into the sys- tion, IAGC. An automatic gain control whose op-
tem; it is usually expressed in decibels. Compare eration almost immediately follows a change in
INSERTION LOSS. signal amplitude.
insertion loss Loss of energy or gain by placing instantaneous automatic volume control Abbre-
certain devices or subcircuits (filters, impedance viation, IAVC. An instantaneous automatic gain
matchers, etc.) in a circuit. It is usually expressed control system for the immediate control of vol-
in decibels. Also see INSERTION RESISTANCE. ume in receivers and audio-frequency amplifiers.
insertion phase shift The difference in phase pro- instantaneous companding A form of compand-
duced by a circuit installed in an electrical trans- ing that operates according to the instantaneous
mission line. amplitude of the input signal.
insertion resistance The resistance of a com- instantaneous contacts Timer contacts that open
ponent or instrument that is introduced into or close almost immediately upon application of
a circuit. Thus, the internal resistance of a the control signal.
microammeter becomes an insertion resistance instantaneous current Symbol, i or Ii. The value of
in the circuit in which the meter is connected for an alternating or fluctuating current at a particu-
current measurement. lar instant in the cycle.
inside antenna See INDOOR ANTENNA. instantaneous disc A phonograph disc that can be
inside diameter Abbreviation, ID. The innermost played back immediately after being recorded.
diameter of a body or figure having two concen- instantaneous frequency The frequency of a sig-
tric diameters. Compare OUTSIDE DIAMETER. nal at a particular moment in time. The instan-
inside lead See START LEAD. taneous frequency changes in frequency-
inside radiation See INDOOR RADIATION. modulated or phase-modulated signals.
inside spider A voice-coil centering device within a instantaneous power 1. In a single-sideband, sup-
loudspeaker. pressed-carrier signal, the power at a specified in-
inst 1. Abbreviation of INSTRUMENT or INSTRU- stant in time. It varies between zero and the peak
MENTATION. 2. Abbreviation of INSTANT. envelope power (PEP). 2. The output power of an
instability Inconsistency in the operation of a cir- audio amplifier at a specified instant in time.
cuit or device, in the parameters of a device, or in instantaneous power output The rate of power
an electrical quantity. It can be attributed to a delivery to a load at a given instant.
number of causes, including temperature, load- instantaneous relay A relay, such as a fully elec-
ing, age, humidity, negative resistance, and ra- tronic type (having no moving parts), that shows
dioactivity. virtually no delay in its operation.
installation tape number An identification num- instantaneous sample A measurement obtained
ber given to a reel of magnetic tape by the pro- by INSTANTANEOUS SAMPLING.
cessing facility. instantaneous sampling The measurement of
instant Abbreviation, inst. The point in time at wave or signal amplitude at a specific moment in
which an event occurs, or at which a quantity time. See, for example, INSTANTANEOUS CUR-
reaches a particular value. RENT and INSTANTANEOUS VOLTAGE.
instantaneous Occurring at a specified moment, instantaneous speech power In the output of an
or instant, of time. audio amplifier, the instantaneous value of power
instantaneous amplitude The amplitude, speci- in a speech wave, as opposed to that in a sine
fied in amperes, volts, or watts, of a signal, spec- wave. Also see INSTANTANEOUS VALUE and
ified at a particular moment in time. SPEECH POWER, 1.
370 instantaneous value • instrument transformer

instantaneous value The magnitude of a fluc- instrumental error See INSTRUMENT ERROR.
tuating value at a selected instant in time. See, instrument amplifier Also called INSTRUMENTA-
for example, INSTANTANEOUS CURRENT, TION AMPLIFIER. A high-gain, wideband ampli-
INSTANTANEOUS POWER, INSTANTANEOUS fier that increases the sensitivity of an
SPEECH POWER, and INSTANTANEOUS VOLT- instrument (such as an oscilloscope, meter, or
AGE. Compare AVERAGE VALUE, and EFFEC- graphic recorder).
TIVE VALUE. instrument-approach system See INSTRUMENT
instantaneous voltage Symbol, e or E i. The value LANDING SYSTEM.
of an alternating or fluctuating voltage at a par- instrumentation Planning and providing instru-
ticular instant in the cycle. ments and instrument systems for the collection
instant loop In electronic security applications, a and, sometimes, storage and analysis of data.
circuit that actuates an alarm without delay instrumentation amplifier 1. A form of inte-
when an intrusion is detected. grated-circuit voltage amplifier designed for high
instruction In digital computer operations, a set of linearity, high input impedance, and high
bits defining an operation. Consists of an opera- common-mode rejection. It is intended for use
tion code specifying the operation to be per- with electronic instruments. 2. See INSTRUMENT
formed, one or more operands or their addresses, AMPLIFIER.
and one or more modifiers or their addresses (to instrument chopper A refined chopper for con-
modify the operand or its address). verting a direct-current (dc) signal to alternating
instruction address In a computer memory, the current (ac) for an ac instrument, such as a volt-
address of a location containing an instruction. meter or recorder.
instruction address register Also called program instrument error Discrepancy in measured quan-
counter. A register that holds instruction ad- tities resulting from inaccuracy of the instrument
dresses so that the retrieval of the instructions used, insertion resistance, environmental factors,
from memory can be controlled during a program operator error, etc.
run. instrument flight Also called blind flight. Aircraft
instruction code Also called INSTRUCTION SET. flight guided by navigational instruments and
The symbols and characters that compose the signals alone. Required when visibility is ex-
syntax of a computer programming language. tremely poor.
instruction format In a computer™s basic machine instrument fuse A fast-acting, low-current fuse
code, the part that specifies how characters or used to protect a sensitive instrument, such as a
digits are used to represent the codes within the galvanometer, milliammeter, and/or microam-
machine™s instruction set. meter.
instruction modification In a computer instruc- instrument lamp A light or lamp that illuminates
tion, a change in the instruction code that makes the face of an instrument to facilitate viewing in
the computer do a different operation when the the dark.
routine containing the code is encountered again. instrument landing Also called blind landing. Air-
instruction register A register in a computer con- craft landing guided entirely by instruments. Re-
taining the address of the current instruction. quired when visibility is poor and when landing is
Also called CONTROL REGISTER (abbreviation, imperative at a given location at a given time.
CR). instrument landing station The radio or radar
instruction set 1. The range of commands that station in a blind-landing system (see INSTRU-
form a programming language. 2. See INSTRUC- MENT LANDING SYSTEM).
TION CODE. instrument landing system Abbreviation, ILS.
instruction storage A memory circuit that stores The complete instrument and signal system (on
computer instructions or programs. the ground or in aircraft) required for an INSTRU-
instruction time The time required for a control MENT LANDING.
unit to analyze and implement a computer pro- instrument multiplier See MULTIPLIER PROBE,
gram instruction. 1.
instruction word In digital computer program- instrument preamplifier An external, sensitive
ming, a word containing the instruction code amplifier for an instrument that has an internal
(type of operation to be performed) and the ad- input amplifier. Also see INSTRUMENT AMPLI-
dress part (location of the associated data in stor- FIER.
age). instrument relay See METER RELAY.
instrument A device for measuring electrical instrument resistance See METER RESISTANCE.
quantities or the performance of electronic equip- instrument shunt A resistance connected in par-
ment. A meter provides a direct indication; other allel with a current-measuring instrument, used
devices, such as a bridge, must be adjusted, the to increase the range of currents that can be mea-
measured quantities being determined from one sured.
or more adjustments (sometimes augmented with instrument transformer A transformer used to
calculations). change the range of an alternating-current meter.
instrument transformer • Integrated Services Digital Network

integral 1. Also called indefinite integral and an-
tiderivative. For given mathematical function f,
function g, whose derivative is equal to f. 2. Also
called definite integral. The area under a curve of
a function, between two vertical lines defined by
two specific points in the domain of the function.
3. The part of a number to the left of the radix
point. 4. Pertaining to integers (positive or nega-
instrument shunt tive whole numbers) or quantities that can be
represented by integers.
integral action In automatic control operations, a
For ammeters, it is called a current transformer; control action delivering a corrective signal pro-
for voltmeters, it is called a potential transformer. portional to the time that the controlled quantity
insulant A nonconducting material, used to pre- has differed from a desired value.
vent the flow of electric current between or among integral contact In a relay or switch, a contact
points. See INSULATOR, 1. that carries current to be switched.
insulated Isolated from conductors by an INSU- integral-horsepower motor A motor rated at one
LANT. horsepower.
insulated-gate field-effect transistor Abbrevia- integral multiple A whole multiple of a number.
tion, IGFET. See METAL-OXIDE SILICON FET. Thus, a harmonic is an integral multiple of fun-
insulated resistor A resistor around which is damental frequency f: 2f, 3f, 4f, etc.
molded a nonconducting material, such as vitre- integral number See INTEGER.
ous enamel or a plastic. integrate 1. To perform the function of mathemat-
insulating tape Electrical insulation in the form of ical or electrical INTEGRATION. 2. To construct a
a thin, usually adhesive, strip of fabric, paper, or circuit on a piece of semiconductor material.
plastic. integrated Constructed on a single piece of mate-
insulation 1. A coating of dielectric material that rial, such as a semiconductor wafer.
prevents a short circuit between a conductor and integrated amplifier An audio-frequency (AF) am-
the surrounding environment. 2. The application plifier having a preamplifier, intermediate ampli-
of a dielectric coating to an electrical conductor. fier, and output amplifier on a single chassis.
3. Electrical separation between or among differ- integrated capacitor In an integrated circuit, a
ent components, circuits, or systems. fixed capacitor in which one plate is a layer of ma-
insulation breakdown Current leakage through, terial diffused into the substrate, the dielectric is
and rupture of, an insulating material because of a thin-oxide film grown on top of the first layer,
high-voltage stress. and the other plate is a metal layer deposited on
insulation ratings Collectively, the dielectric con- top of the oxide film.
stant, dielectric strength, power factor, and resis- integrated circuit Abbreviation, IC. A circuit
tivity of an insulating material. Sometimes in- whose components and connecting “wires” are
cluded are such physical properties as rupture made by processing distinct areas of a chip of
strength, melting point, etc. semiconductor material, such as silicon. Classi-
insulation resistance The very high resistance ex- fied according to construction (e.g., monolithic IC,
hibited by a good insulating material. It is ex- thin-film IC, hybrid IC).
pressed in megohms (or higher units of resistance) integrated data processing Abbreviation, IDP.
for a sample of material of stated volume or area. The detailed electronic classification, sorting,
insulation system Collectively, the materials storage, and mathematical processing of data
needed to insulate a given electronic device. within a coordinated system of equipment, usu-
insulator 1. A material that, ideally, conducts no ally at one location.
electricity; it can, therefore, be used for isolation integrated electronics The branch of electronics
and protection of energized circuits and compo- that is concerned with the design and fabrication
nents (also see DIELECTRIC). Actually, no insu- of integrated circuits.
lator is perfectly nonconductive (see, for example, integrated resistor See DIFFUSED-LAYER RESIS-
INSULATION RESISTANCE). 2. A molded piece of TOR.
solid insulating material, used to electrically iso- Integrated Services Digital Network Abbrevia-
late conductors”especially in antenna systems tion, ISDN. A communications network or con-
and power transmission lines. 3. Any body made nection intended primarily for Internet access
from an insulating material. via telephone lines. Allows significantly higher
insulator arcover A sudden arc, or flow of current, data speed than is possible with a conventional
over the surface of an insulator, because of ex- analog connection. In addition, it is possible to
cessive voltage. use a digital system, such as a computer, online
integer A positive or negative whole number, as simultaneously with an analog voice conversa-
opposed to a fraction or mixed number. tion.
372 integrating circuit • interactive photovoltaic system

integrating circuit See INTEGRATING NETWORK. intelligence bandwidth 1. The bandwidth neces-
integrating galvanometer A device for measuring sary to convey a specified amount of data within
the change in electric flux produced in a coil in an a certain period of time. 2. The total bandwidth of
electric field. Even very slow changes can be mea- one complete signal channel in a communica-
sured. tions or broadcast system.
integrating meter An instrument whose indica- intelligence signal 1. A signal that conveys data
tion is a summation (usually) of an electrical or information. 2. The modulating waveform in a
quantity that is time-dependent (e.g., ampere- communications or broadcast transmission.
hour meter and watt-hour meter). intelligent network Abbreviation, IN. 1. In gen-
integrating motor An electric motor that follows eral, any advanced and sophisticated communi-
the integral of the input signal. The angle of rota- cations network, particularly a broadband digital
tion of the motor shaft is equal to the integral of network. 2. A network designed to readily accom-
the input waveform. modate new technologies and services, such as
integrating network A four-terminal network videoconferencing, interactive television, or re-
whose output voltage is proportional to the time mote control.
integral of the input voltage. It can be a passive intelligent terminal A computer terminal (e.g., an
resistance-capacitance (RC) circuit or it can use input/output video display/keyboard unit) that
an operational amplifier. Compare DIFFERENTI- through its circuitry (i.e., by use of a micropro-
ATING NETWORK. cessor) has some data-processing ability.
intelligibility tests Tests that measure the coher-
ence of electronically reproduced speech.
intensification of image See IMAGE INTENSIFI-
Input Output
intensifying ring In some electrostatic cathode-
ray tubes, an internal metal ring serving as an ex-
tra anode to accelerate the beam and, thus,
brighten the image.
intensity The degree or extent of a phenomenon
(such as amplitude, brightness, loudness, power,
’ force, etc.).
+ intensity control In an oscilloscope circuit, the
Input Output
potentiometer that adjusts the direct-current
voltage on the control electrode of the cathode-
ray tube and, accordingly, the brightness of the
image. Also called BRIGHTNESS CONTROL and
integrating networks
intensity level 1. A measure of sound magnitude,
expressed in decibels, with respect to a value of
one microwatt per square centimeter (10-6
integrating photometer A photometer whose
W/cm2) at sea level in the atmosphere. 2. The set-
reading is the average candlepower at all angles
ting of the brightness control in a cathode-ray-
in one plane.
tube device.
integration 1. The process of determining a
intensity modulation 1. Modulation of electron-
mathematical function when its derivative is
beam intensity in a cathode-ray tube. Also called
given. 2. The processing of a signal by an INTE-
z-axis modulation. 2. Sometimes, the video-signal
GRATOR circuit. 3. Collectively, the processes
modulation in a television image.
by which an INTEGRATED CIRCUIT is manufac-
intensity-modulation amplifier The z-axis ampli-
fier in an oscilloscope. Also see INTENSITY MOD-
integrator 1. See INTEGRATING NETWORK. 2. A
device having an output variable whose value is
interaction The (sometimes mutual) influence of
proportional to the integral of one variable, with
one circuit or device on the behavior of another,
respect to another, or is proportional to the inte-
as in induction.
gral of an input variable, with respect to elapsed
interactive display A computer display device
with which its operator can supply data to the
intelligence 1. Meaningful data that modulates a
computer in response to what is displayed. Ex-
carrier [e.g., the voice or music in a frequency-
ample: touch screen.
modulated (FM) radio signal, or the image in a
interactive graphics A computer graphics system
television signal]. 2. Also called machine intelli-
using a cathode-ray tube to draw or modify three-
gence. The quality of a system or device, espe-
dimensional representations.
cially a computer, that allows it to “learn” (i.e., to
interactive photovoltaic system A solar-power
better its capability by repeatedly operating on a
plant that operates in conjunction with the utility
given problem).
interactive photovoltaic system • interference stub

companies. Energy is sold to the companies dur- surface of a resistor material or semiconductor
ing times of daylight and minimum usage, and is substrate. The fingers of each contact are inter-
bought back from the companies at night or dur- connected at one end, the fingers of one contact
ing times of heavy usage. The principal advantage being interleaved with those of the other.
of this system is that the user can keep using interdigital tube A magnetron having a cathode
electricity (by buying it all from the utilities) if the surrounded by anode segments that are alter-
solar-energy system breaks down. But such a nately interconnected at opposite ends in the
system does not provide the independence from manner of INTERDIGITAL CONTACTS.
utility companies that some users desire. Com- interelectrode capacitance Capacitance between
pare STAND-ALONE PHOTOVOLTAIC SYSTEM. or among electrodes”especially between the
interactive program A computer program in plate and control grid of a vacuum tube.
which the machine and its operator engage in interelement capacitance Internal pn-junction
two-way communication. Most personal comput- capacitance in a semiconductor device, such as a
ing software is of this type, in contrast to pro- diode or transistor.
grams that carry out all their functions without interface 1. The circuitry that interconnects and
operator intervention (other than initialization). provides compatibility between a central proces-
interactive television Television provided to con- sor and peripherals in a computer system. 2. Col-
sumers, in which viewers can transmit data, as lectively, the hardware and software that allows a
well as receive it. For example, a survey might be computer to interact with its operator. 3. To pro-
conducted in which viewers are polled and send vide an efficient pathway for data between two de-
in their responses. Another example: products vices or systems. 4. The meeting of surfaces or
might be ordered while viewing an advertisement. regions in a material. 5. The surface of a body
interactive mode See CONVERSATIONAL MODE. that mates with another body similar or identical
interbase resistance The internal resistance be- to it.
tween the bases of a unijunction transistor. interface resistance See CATHODE INTERFACE.
interblock A part of a computer program or a interface routine A computer program routine
hardware device that will prevent interference be- that links one system to another.
tween parts of a computer system. interfacial connection A connection that runs
interblock space 1. On a magnetic tape, the space through a printed-circuit board and joins circuit
between recordings, caused by starting and stop- joints on opposite faces of the board.
ping the tape. 2. On magnetic tape used as a interference 1. In communications, degradation
computer storage medium, the interval between of reception caused by noise or undesired signals.
recorded blocks. 2. The interaction of acoustic or electromagnetic
intercarrier receiver A television (TV) receiver cir- waves from more than one source, especially
cuit in which video, sound, and sync compo- when they are of the same frequency, producing a
nents of the composite TV signal are amplified characteristic INTERFERENCE PATTERN of high-
together in the radio-frequency (RF), intermedi- amplitude and low-amplitude regions.
ate-frequency (IF), and video IF stages; then they interference attenuator A device or mode of oper-
are separated in the video detector and video am- ation that reduces the amplitude of interference.
plifier stages. Compare SPLIT-SOUND RE- interference eliminator A filter, wavetrap, or sim-
CEIVER. ilar device that removes interfering signals or
intercept receiver In military service, a search re- noise. Also see INTERFERENCE.
ceiver tuned over a wide band of frequencies to lo- interference filter See INTERFERENCE ELIMINA-
cate and evaluate enemy signals. TOR.
interchangeability The ability of one component interference pattern A regular pattern of high-
to substitute directly for another component of amplitude and low-amplitude regions, lobes, or
the same kind. Example: capacitor interchange- bands, produced when waves of identical fre-
ability, transistor interchangeability. Also see RE- quency from two or more sources combine in
PLACEMENT. varying phase. Such patterns can be observed
intercharacter space The three-unit interval be- with sound, radio waves, infrared, visible light,
tween letter symbols in telegraphy. Compare IN- ultraviolet, X rays, and gamma rays. The phe-
TERWORD SPACE. nomenon is of interest in acoustic engineering,
intercom A comparatively simple two-way tele- the design of radio antenna systems, and in
phone or low-power radio system for use on the physics (particularly optics).
premises of a home or business. interference stub A length of twin-lead feeder cut
intercommunicator See INTERCOM. to appropriate length, connected to the antenna-
interconnection 1. A mutual connection of sepa- input terminals of a television receiver, and
rate circuits. 2. The interconnection of two or short-circuited at the opposite end. A stub of the
more separate power-generating systems. correct length resonates at the frequency of an in-
interdigital contacts A pair of contacts with “fin- terfering signal and, acting as a wavetrap, keeps
gers” that are plated, printed, or deposited on the it out of the receiver. Also see STUB.
374 interference trap • intermittent commercial and amateur service

interference trap A wavetrap that suppresses in- Tuned
to IF
terfering signals at the rejection frequency of the
trap. to IF
interferometer 1. A radio telescope having two an-
tennas spaced at a distance of many wave-
lengths, providing much greater resolution than a Output
single antenna. Pioneered by M. Ryle of England
and J.L. Pawsey of Australia. 2. Any device that Input
displays an INTERFERENCE PATTERN for testing
or experimental purposes.
interfix A method used in information-retrieval
systems that eliminates ambiguity in the re-
sponses to inquiries by describing the relation-
intermediate-frequency amplifier
ship between keywords in a record.
Interframe A method of digital IMAGE COMPRES-
SION developed by MPEG (Moving Picture Experts detector, automatic gain control (AGC), and oscil-
Group). It operates by eliminating redundant lator stages.
data from between image frames. Compare IN- intermediate-frequency converter See IF CON-
interharmonic beats Beat notes produced by var- intermediate-frequency interference Interfer-
ious combinations of the harmonics of a signal. ence from signals at the intermediate frequency
interim storage See TEMPORARY STORAGE. of a receiver or instrument.
interior label On a magnetic tape used as a com- intermediate-frequency selectivity The selectiv-
puter-storage medium, a label recorded at the be- ity of an intermediate-frequency (IF) channel
ginning of the tape. Compare EXTERIOR LABEL. alone, usually determined by the characteristics
interior protection 1. In electronic security appli- of the bandpass filter(s) in the IF channel.
cations, a set of sensors contained entirely within intermediate-frequency transformer A coupling
the region to be protected. 2. The installation and transformer designed for use in an intermediate-
operation of a security system whose sensors are frequency amplifier.
all within the region to be protected. intermediate-puck drive In a tape recorder, a
interlace A form of data storage in which portions speed-reducing drive system in which an inter-
of the data are stored in alternate locations in the mediate wheel conveys motion from the motor
tape or disk. shaft to the rim of the flywheel.
interlaced field A video image field produced by intermediate puck wheel See IDLER WHEEL.
INTERLACED SCANNING. intermediate repeater In wire telephony, a re-
interlaced scanning In the display of a video im- peater inserted into a line or trunk at some point
age, the alternate presentation of the even- and other than the end.
odd-line fields. This process increases the obtain- intermediate result Obtained during a program
able image resolution for a given refresh rate, but run or the execution of a subroutine, a result that
can result in “jerkiness” of the image when rapid is used again as an operand in deriving the final
motion is portrayed. result.
interlace factor A number expressing the extent intermediate section Any of the internal sections
to which two fields are interlaced. Also see IN- of a multisection filter. Thus, the middle section
TERLACED SCANNING. of a three-section filter.
interleaving In multiprogramming, the inclusion intermediate storage In a computer system, a
in a program of segments of another program so storage medium for temporarily holding totals or
that both can be effectively executed simultane- working figures. Also called WORK AREA.
ously. intermediate subcarrier A modulated or unmodu-
interlock switch See ELECTRICAL INTERLOCK. lated subcarrier that modulates either a carrier or
intermediate amplifier See BUFFER. another intermediate subcarrier.
intermediate frequency Abbreviation, IF. In a su- intermittent 1. Pertaining to a circuit fault, such
perheterodyne circuit, the frequency of the signal as an open or short circuit, that occurs some of
that results from beating the incoming signal the time, but not all the time. 2. See INTER-
with the signal produced by the local oscillator. MITTENT CONDITION. 3. Pertaining to a phe-
intermediate-frequency amplifier In a super- nomenon that is observed some of the time, but
heterodyne circuit, the fixed-frequency amplifier not all the time; sporadic. 4. Pertaining to a DUTY
that boosts the intermediate-frequency signal. CYCLE greater than zero, but less than 100 per-
Also see INTERMEDIATE FREQUENCY. cent; usually between 25 and 50 percent.
intermediate-frequency channel Usually, the in- intermittent commercial and amateur service
termediate-frequency amplifier in a superhetero- Abbreviation, ICAS. Operation of equipment,
dyne circuit, but sometimes including the second such as radio transmitters, for short, irregular
intermittent commercial and amateur service • international farad

periods, as in amateur (hobbyist) activity or infre- intermodulation noise Electrical noise produced
quent commercial service. ICAS ratings are in one channel by signals in another; it is caused
higher than continuous commercial service (CCS) by INTERMODULATION.
ratings. Compare CONTINUOUS COMMERCIAL internal absorptance The ratio of flux absorbed in
SERVICE. a substance to the flux leaving at the entry sur-
intermittent condition A defect in a circuit or de- face of the substance. It does not include energy
vice that causes erratic and unreliable operation. reflected at the entry surface.
The cause of such a problem is often difficult to internal amplification In a radioactivity counter
determine. tube, current enhancement resulting from cumu-
intermittent dc See INTERMITTENT DIRECT lative ionization initiated by an ionizing particle.
CURRENT. internal arithmetic In a digital computer, arith-
intermittent direct current A regularly pulsed metic operations performed in the computer, as
unidirectional current. Also called PULSATING opposed to those performed by peripherals.
DIRECT CURRENT. internal impedance The impedance in a device, as
intermittent duty A DUTY CYCLE of less than opposed to that added from the outside. Compare
100 percent, but greater than zero. Generally, an INTERNAL RESISTANCE.
operating duty cycle of 25 to 50 percent. internal input impedance The impedance in a cir-
intermittent-duty rating The dissipation or cuit or device, as “seen” from the input terminals.
power rating of a component, circuit, or system, Compare INTERNAL OUTPUT IMPEDANCE.
under conditions of intermittent use, usually a internal input resistance The resistance in a cir-
25-percent to 50-percent DUTY CYCLE. cuit or device, as “seen” from the input terminals.
intermittent operation Operation characterized Compare INTERNAL OUTPUT RESISTANCE.
by often long nonoperating intervals. Intermittent internal noise Electrical noise generated within a
operation is often random, whereas on-off opera- circuit, as opposed to that picked up from out-
tion tends to be regular. side. Such noise comes from transistors, diodes,
intermittent signal An interrupted signal result- integrated circuits, resistors, and any other com-
ing from the intermittent operation of a circuit or ponent through which current flows.
device. internal output impedance The impedance in a
intermodulation Abbreviation, IM. 1. The (usually circuit or device, as “seen” from the output termi-
undesired) modulation of one signal by another, nals. Compare INTERNAL INPUT IMPEDANCE.
caused by nonlinear processing of the signals. 2. internal output resistance The resistance in a cir-
The heterodyning of components in the side- cuit or device, as “seen” from the output termi-
bands produced by an amplitude-modulated (AM) nals. Compare INTERNAL INPUT RESISTANCE.
or single-sideband (SSB) transmitter. internal resistance 1. The resistance of a device,
intermodulation distortion Abbreviation, IMD. 1. as opposed to added resistance. See, for example,
Distortion products in the output of an ampli- METER RESISTANCE. 2. In a cell or battery, the
tude-modulated (AM) or single-sideband (SSB) equivalent resistance, resulting from imperfect
transmitter, caused by heterodyning of compo- conductivity of the electrolyte and electrodes,
nents in the sidebands. 2. Distortion products in which limits the maximum deliverable current.
the output of an audio amplifier, caused by het- internal thermal shutdown In an integrated cir-
erodyning of the fundamental components. 3. cuit, the junction temperature at which thermal
The extent to which distortion as defined in 1 shutdown occurs. It is generally indicated in de-
occurs. See INTERMODULATION-DISTORTION grees Celsius (°C).
PERCENTAGE. internal transmittance The ratio of flux reaching
intermodulation-distortion meter See INTER- the exit surface of a material to the flux leaving
MODULATION METER. the entry surface. Reflection is not taken into ac-
intermodulation-distortion percentage Abbrevi- count. The sum of internal transmittance and IN-
ation, IDP. The degree to which a low-frequency TERNAL ABSORPTANCE is always equal to 1.
test signal modulates a higher-frequency test sig- international broadcast station A shortwave
nal when both are applied simultaneously (in a broadcast station transmitting programs for in-
prescribed amplitude ratio) to a device under test; ternational reception between 6 and 26.6 MHz.
IDP = 100(b “ a)/a, where a is the peak-to-peak international callsign The call letters of a station,
amplitude of the unmodulated high-frequency assigned within a country, according to the
wave and b is the peak-to-peak amplitude of the method of arrangement (identifying letters, or let-
modulated high-frequency wave. ters and numerals) prescribed by the Interna-
intermodulation meter An instrument for mea- tional Telecommunication Union.
suring percentage of intermodulation distortion international candle See CANDLE.
(IMD). The instrument combines a dual-frequency international coulomb A unit of electrical quan-
signal generator, filter circuits, and percent-of- tity, equal to 0.99985 absolute coulomb.
modulation meter. Also see INTERMODULATION- international farad A unit of capacitance, equal to
DISTORTION PERCENTAGE. 0.99952 absolute farad.
376 international henry • interpreter

international henry A unit of inductance, equal to international watt A unit of power, equal to
1.00018 absolute henry. 1.00018 absolute watt.
international joule A unit of energy, equal to Internet A worldwide, interconnected system of
1.00018 absolute joule. computer networks. Originated in the late 1960s
International Morse Code See CONTINENTAL as ARPAnet (Advanced Research Projects Agency
CODE. network). Still used extensively by educators and
international ohm A unit of electrical resistance, scientists, but gaining popularity among
equal to 1.000495 absolute ohm. The other inter- personal-computer users. Sometimes called
national units are derived from this value. the INFORMATION SUPERHIGHWAY.
International Radio Consultative Committee interphone An intercom aboard a mobile vehicle.
Abbreviation, CCIR (Comite Consultatif Inter- interpolation Finding a value that falls between
national Radiodiffusion). An international orga- two values listed in a table, indicated by a dial,
nization reporting to the International plotted on a graph, derived by estimate, or given
Telecommunication Union, and studying techni- by intermediate calculation. For example, if a lin-
cal operations and tariffs of radio and television. ear variable capacitor has a value of 100 pF when
International Steam Table calorie A unit of heat its dial is set to 10, and 140 pF when the dial is
energy equal to 4.1868 joules. set to 20, then the capacitance when the dial
International System of Units Abbreviation, SI reads 15 (midway between 10 and 20) can be as-

(Systeme International d™Unites). The system of sumed to be 120 pF (midway between 100 pF and
units of measurement established in 1960 under 140 pF). When functions are not linear, interpola-

the Treaty of the Meter. The base units are as fol- tion is usually not exact.
“METER (m), length: 1,650,763.73 times the
wavelength of the light emitted in a vacuum of
krypton 86
“KILOGRAM (kg), mass: the mass of the protype F
kilogram kept at Sevres, France

“SECOND (s), time: the duration of C
9,192,631,770 periods of the radiation that cor-
B A”F:
responds to the transition between the two hy-
known points
perfine levels of the ground state of cesium 133 A
“KELVIN (K), thermodynamic temperature: 1„273.16
the thermodynamic temperature of the triple
point of water
“AMPERE (A), electric current: the current that,
flowing through two infinitely long parallel wires interpolation meter See INTERPOLATION-TYPE
in a vacuum and separated by 1 meter, pro- INSTRUMENT.
duces a force of 2 — 10“7 newton per meter of interpolation oscillator A frequency-measuring
length between the wires signal generator with a built-in crystal oscillator,
whose harmonics provide calibration points on
“CANDELA (cd), luminous intensity: the lumi-
the tuning dial. The dial provides a continuous
nous intensity of 1„600,000 square meter of perfectly
indication of generator frequencies between crys-
radiating surface at the temperature of freezing
tal-harmonic points. Also see INTERPOLATION-
International Telecommunication Union Abbre- interpolation-type instrument An instrument,
viation, ITU. An international, nongovernmental such as a meter or signal generator, that is used
organization devoted to standardizing worldwide to transfer an accurate quantity point from a
communications practices and procedures. standard to another instrument and to provide a
International Telegraph and Telephone Consulta- range of values between such points. A secondary
tive Committee See CCITT. standard is sometimes used as an interpolation-
International Telegraph Consultative Committee type instrument (see, for example, INTERPOLA-
international units A system of electrical units, interpole motor A direct-current motor with small
based on the resistance through a specified auxiliary poles (interpoles) between its main field
quantity and configuration of the element mer- poles. The interpoles reduce sparking at the com-
cury. The INTERNATIONAL OHM forms the basis mutator.
for the international system of units. interpreter A computer program that can convert
international volt A unit of electrical potential, instructions given in a high-level language (BA-
equal to 1.00033 absolute volt. SIC, for example) into the machine language that

interpreter • intrinsic conduction

a computer uses; if it is not resident in the com- interstage coupling The transfer of a signal be-
puter™s nonvolatile memory, it must be loaded tween two circuit stages, such as those of an am-
each time the machine is activated. plifier. Common forms of interstage coupling
interrecord gap See INTERBLOCK SPACE. include direct coupling, capacitive coupling, trans-
interrupt A break in a computer program, as when former coupling, diode coupling, and optoisolator
a background job is interrupted so that a fore- coupling.
ground job can be run. Also see BACKGROUND interstage diode A semiconductor coupling diode
JOB and FOREGROUND JOB. used between two circuit stages.
interrupted commercial and amateur service interstage transformer A coupling transformer
See INTERMITTENT COMMERCIAL AND AMA- used between two circuit stages. It provides di-
TEUR SERVICE. rect-current isolation, and also can match purely
interrupted continuous wave Abbreviation, ICW. resistive impedances.
A continuous wave that is interrupted at regular intersymbol interference In a digital communica-
intervals, as in the chopping of a wave at a regu- tions signal, a condition in which a given symbol
lar rate. Compare CONTINUOUS WAVE (CW) and overlaps with one or more other symbols (either
MODULATED CONTINUOUS WAVE (MCW). immediately preceding it or immediately following
interrupted dc A direct current or voltage that is it), upsetting the ability of the receiver to decipher
periodically started and stopped by switching or signals in certain time intervals. The phe-
chopping. nomenon is sometimes a problem in time-division
interrupter contacts Auxiliary contacts operated multiplexing”especially at data speeds near the
directly by the armature of a stepping switch. maximum for the system.
interruption frequency See QUENCHING FRE- intersystem A power-generating network of inter-
QUENCY. connected separate systems.
interruption-frequency oscillator See QUENCH intersystem communications Communications
OSCILLATOR. between computer systems, either through direct
interrupt signal The signal that causes a break linking of central processors, or by mutual use of
(INTERRUPT) in a computer program. peripherals and input/output channels.
intersatellite communication 1. Communica- intertie See INTERCONNECTION, 2.
tion between or among satellites. 2. Communi- interval 1. The amount of separation between suc-
cation between two earth-based stations, using cessive points, events, or quantities. 2. The con-
two or more satellites. 3. Communication be- tinuous range of values between two defined
tween an earth-based station and a satellite- points. 3. A specific period of time, with defined
based station, using at least one intermediate beginning and ending points.
relaying satellite. intervalometer A timing device for operating
equipment over a precisely defined time interval.
interval timer A device that provides power to an
Satellites equipment for a precise interval upon application
of a simple initiating signal or action. See also IN-
interword space The seven-unit interval between
words or code groups in telegraphy. Compare IN-
intoxication tester See DRUNKOMETER.
intracoding The coding of data using only data
that it contains.
Earth Intrafax Western Union™s private facsimile system.
Intraframe A method of digital IMAGE COMPRES-
SION developed by MPEG (Moving Picture Experts
Group) and JPEG (Joint Photographic Experts
Group). It operates by eliminating redundant data
intersatellite communication within image frames. Compare INTERFRAME.
intrinsic-barrier diode See PIN DIODE.
intrinsic-barrier transistor A bipolar transistor
intersecting storage ring A device for producing
with a layer of intrinsic semiconductor between
great amounts of energy. It is similar to a vacuum
one of its pn junctions.
tube. High-speed subatomic particles are fed to a
intrinsic concentration The number of minority
ring-shaped evacuated structure in opposite di-
carriers exceeding the normal equilibrium num-
rections. The two particle beams collide at vari-
ber in a semiconductor.
ous points, yielding high energy.
intrinsic conduction The flow of electron/hole
intersection The logical AND operation.
pairs in an intrinsic semiconductor subjected to
interstage capacitor A coupling capacitor used
an electric field.
between two circuit stages.
378 intrinsic flux • inverse voltage

intrinsic flux A quantity equal to the product of inverse feedback See DEGENERATION.
the intrinsic flux density and the cross-sectional inverse fourth-power law A rule of propagation for
certain complex forms of energy: I = k/d 4, where I
area in a magnet.
intrinsic flux density The increased flux density is the intensity of the field, d is the distance from
of a magnet in its actual environment, as com- the source, and k is a constant.
pared with the flux density resulting from the inverse impedances Impedances (Z1 and Z2) that
same magnetizing force in a perfect vacuum. are the reciprocal of another impedance (Z3), sat-
isfying the relationship Z1Z2 = (Z3)2. Also called
intrinsic mobility Electron mobility in an intrinsic
MOBILITY. inverse leakage The flow of a small static reverse
intrinsic Q The value of the Q, also known as the current in semiconductor devices.
FIGURE OF MERIT, for an unloaded circuit. This inverse-parallel circuit See BACK-TO-BACK CIR-
value is generally higher than the value when a CUIT and BACK-TO-BACK CONNECTION.
load is connected to the circuit. inverse peak voltage See PEAK INVERSE VOLT-
intrinsic semiconductor A semiconductor whose AGE.
characteristics are identical to those of a pure inverse piezoelectric effect Mechanical move-
crystal of the material. In this condition, the ment in a piezoelectric material, caused by appli-
semiconductor is nearly an insulator. Example: cation of voltage.
highly purified germanium or silicon before n- or inverse resistance See REVERSE RESISTANCE.
p-type impurities have been added. Compare EX- inverse resonance See PARALLEL RESONANCE.
TRINSIC SEMICONDUCTOR. inverse-square law The energy or power intensity
intrusion alarm A set of electronic sensors and as- of a phenomenon is inversely proportional to the
sociated circuitry composing a system that de- square of the distance from the source. This is
tects and warns of the presence of unauthorized often applied to quantitative reasoning about
personnel within a specific region. radiant energy, electromagnetic energy, and
intrusion sensor A sensitive pickup (such as a acoustic energy. Thus, if the distance doubles,
the energy or power drops to 1„4 its previous
photocell, ultrasonic detector, or capacitive
transducer) that responds to a nearby body by value.
delivering an actuating signal to an intrusion
INV Abbreviation of INVERTER.
inv Abbreviation of INVERSE.
Invar A nickel-steel alloy (36% nickel) having a low
temperature coefficient of linear expansion (1
ppm/°C). Invar is used in electronic equipment
where mechanical distortion resulting from tem-
perature changes must be negligible, and in mag-
netostrictive circuits (see MAGNETOSTRICTION).
inverse 1. Opposite in nature (e.g., an INVERSE
CHARACTERISTIC). 2. Of opposite sign (e.g., a
negative current or voltage). 3. An operation of
opposite kind; thus, subtraction is the inverse of
addition, and division is the inverse of multiplica-
inverse beta The beta of a transistor operated with
the emitter and collector interchanged.
inverse bias See REVERSE BIAS.
inverse characteristics The characteristics of a
bipolar transistor when operated with the emitter
and collector reversed.
inverse conduction See REVERSE CONDUC-
inverse trigonometric function An angle ex-
inverse cube law A principle relating the intensity
pressed in terms of a given trigonometric func-
of an effect to the reciprocal of the cube of the dis-
tion, followed by the exponent -1 or preceded by
tance from the source. The magnetic field around
“arc” (sin-1 is the equivalent of arcsin).
a solenoidal coil of wire obeys this principle.
inverse voltage 1. The negative voltage at the an-
inverse current See REVERSE CURRENT.
ode of a rectifier during the negative half-cycle of
inverse-distance law The inverse-square law ap-
alternating-current (ac) input. 2. The voltage
plied to the propagation of radio waves, assuming
across a power-supply filter capacitor during the
that the waves do not encounter obstacles.
inverse voltage • invister

negative half-cycle of ac input. 3. Semiconductor-
junction reverse voltage.
inverse Wiedeman effect See DIRECT WIEDE-
inversion 1. A reversal of the normal vertical tem-
perature gradient of the atmosphere, often result-
ing in long-distance tropospheric radio-wave
propagation. 2. Speech scrambling (see SCRAM-
BLER CIRCUIT). 3. Phase inversion (see PHASE
INVERTER). 4. Changing direct current into al-
ternating current, often increasing the voltage
(see INVERTER, 1).
inverted amplifier A push-pull, grounded-gate,
field-effect-transistor (FET) amplifier.

D inverter, 1
S Input Output

In Out
0 1
1 0

inverter, 2
D +
inverting transponder In a communications
satellite, a transponder in which the downlink
inverted amplifier
band is “upside-down” in frequency relative to the
uplink band. That is, the highest downlink fre-
inverted-L antenna An antenna having a horizon- quency corresponds to the lowest uplink fre-
tal radiator and a vertical feeder or lead-in at- quency, and the lowest downlink frequency
tached to one end of the radiator. The entire corresponds to the highest uplink frequency.
arrangement resembles an upside-down L. The Compare NONINVERTING TRANSPONDER. See
overall length is generally 1„4 to 1„2 wavelength. also DOWNLINK, TRANSPONDER, UPLINK.
inverted speech See SCRAMBLED SPEECH.
inverter 1. Also called power inverter. A device that
converts direct current (dc) into alternating cur-
rent (ac), often of a much higher voltage (e.g., 12
Vdc into 117 Vac). 2. A logic circuit that provides
an output pulse that is a negation of the input
pulse. Also called a COMPLEMENTER or a NOT
inverting adder An analog adder circuit that is
provided with an amplifier for a 180° phase
inverting amplifier An amplifier providing a 180°
phase shift between input and output.
inverting connection Connection to the inverting
invisible failure In a computer system, a hardware
input terminals of a differential amplifier or oper-
or software failure whose effect on the system is
ational amplifier. Also see INVERTING INPUT.
unnoticeable in a given application. A failure that
is invisible in one application might be vividly ap-
inverting input In a differential amplifier or opera-
parent in some other application.
tional amplifier, the input circuit that produces a
invister A unipolar semiconductor material, capa-
phase reversal between the input and output.
ble of operation at very high frequencies.
380 involution • ionization time

involution Raising a number to a power: squaring, current that is proportional to the intensity of the
cubing, etc. Compare EVOLUTION. radiation.
inward-outward dialing Also called direct dialing. ionization current 1. Current in an ionized gas
In a telephone system, a method of dialing in (such as air). 2. Current flowing in an electrolyte.
which calls can be made to and from branch ex- 3. Current in an ionization chamber, Geiger-
changes, without operator assistance. Mueller tube, or similar gaseous device. 4. In a
I/O Abbreviation of input/output (see INPUT/ gas tube, current flowing after the ignition poten-
OUTPUT EQUIPMENT). tial has been reached. 5. Negative grid current re-
Io Symbol for OUTPUT CURRENT. sulting from gassiness in a vacuum tube.
iodine Symbol, I. A nonmetallic element of the ionization density The extent to which ionization
halogen family. Atomic number, 53. Atomic exists in an ionized layer of the atmosphere. The
weight, 126.905. Also see HALOGEN. higher the ionization density, the greater the ef-
ion A charged atom [i.e., one that has gained one fect on radio waves”especially at frequencies be-
or more electrons (a negative ion, or anion) or lost low about 150 MHz.
one or more electrons (a positive ion, or cation)]. ionization gauge A form of vacuum tube that can
ion burn A spot burned on the screen of a cathode- be used to measure the hardness of a vacuum. It
ray tube by negative ions from the cathode strik- consists of a cathode, an anode (plate), and a pos-
ing a single point on the faceplate with high itively charged grid. Plate current flows as a re-
intensity for long periods. sult of ionization of the atoms within the tube.
ion concentration 1. The number of ions, ex- The more nearly perfect the vacuum, the lower
pressed as a percentage or as a number per unit the plate current.
volume, in a substance. 2. Ionization density in
the atmosphere.
ion exchange resins Granular resins that contain Anode
acid or base groups, and that trade ions with
salts in solutions. The resins play a part in the
To recorder
purification of water for various industrial pro-
and measuring To vacuum system
circuits Gas ions
ionic binding forces In a crystal, the binding
forces that occur when valence electrons of one Electrons
atom are joined to those of a neighboring atom
whose outer shell they fill.
ionic bond In a solid, a bond between atoms, dc
formed as a result of the attraction between op- Cathode
positely charged atoms (ions).
ionic conduction Conduction, as in a gas or elec-
trolyte, by ion migration (positive to the cathode,
negative to the anode).
ionization gauge
ionic crystal A crystal whose lattice is held to-
gether by the electric forces between ions. Also
ionic current Current caused by ion movement in ionization potential The voltage at which a sub-
a gas or liquid. Also see ION, IONIZATION, and stance (especially a gas) ionizes. Also called (for a
IONIC CONDUCTION. gas) ignition potential (see BREAKDOWN VOLT-
ionic semiconductor A semiconductor in which AGE).
the carrier is an ion, as opposed to an electron or ionization pressure In an ionized gas, the pres-
hole. sure increase resulting from the ionization, as
ionic switch See ELECTROCHEMICAL SWITCH. compared with the same volume and mass of gas
ionization 1. The loss or gain of one or more elec- when not ionized.
trons by an atom. Also see ANION, CATION, and ionization resistance See CORONA RESISTANCE.
ION. 2. The formation or existence of significant ionization smoke detector A device that senses


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