. 37
( 42)


main disadvantage of tantalum capacitors is that
clearing output peripherals for upcoming pro-
they are comparatively expensive. Compare CE-
gram runs.
take-down time The duration of the TAKEDOWN
take-up reel In a reel-to-reel tape recorder/repro-
ducer, the reel on which the tape accumulates
during recording or reproduction.
talk-back circuit See INTERPHONE.
talk-listen switch A transmit-receive switch in an
intercommunication system (see INTERCOM). Electrolyte
talk power See SPEECH POWER.
tally 1. To obtain a sum or total. 2. The rows of
operands, subtotals, and totals that an adding
machine prints.
tally reader A device that, via optical character
recognition (OCR), can read the digits and sym- Tantalum
bols on a tally (see TALLY, 2).
Metal case
tamper switch A device that closes a circuit or ac-
tuates an alarm when a certain set of conditions
is altered.
tan Abbreviation of TANGENT.
tan“1 Arc tan (inverse tangent function).
tandem transistor An assembly of two series- Lead
connected transistors in the same envelope.
tangent 1. Abbreviation, tan. The ratio of the side tantalum capacitor
opposite to the side adjacent to an acute angle in
a right triangle. 2. A line that intersects a curve at
tantalum detector A radio-frequency contact de-
a single point without crossing the curve. 3. A
tector consisting essentially of a fine tantalum
plane that intersects a curved surface at a single
wire whose point lightly touches the surface of a
small pool of mercury.
tangent galvanometer A galvanometer in which
tantalum-nitride resistor A resistor consisting of
the current is proportional to the tangent of the
a thin film of tantalum nitride deposited on a
angle of deflection. Compare SINE GALVANO-
substrate. Also see THIN FILM.
T-antenna See TEE-ANTENNA.
tangential mode In acoustics, the reflection of
tap A connection made to an intermediate point on
sound waves from four surfaces in a room having
a coil, resistor, or other device. See, for example,
six interior surfaces.
tanh Abbreviation of HYPERBOLIC TANGENT.
tap changer A device that facilitates adjustment of
tank 1. A parallel-resonant inductance-capaci-
the turns ratio of a transformer by changing the
tance circuit in the output of a radio-frequency
tap changer • target acquisition

tap on the primary winding, the secondary wind- (see, for example, LOG TAPER). However, a wind-
ing, or both. It also facilitates the adjustment of ing having uniform resistance change is often
the impedance-transfer ratio. It can be used for called LINEAR TAPER.
power supplies or audio- or radio-frequency tape skew A condition in which a magnetic tape
transformers. passes between the recording or playback heads
tape 1. Magnetic tape. 2. Insulating tape. 3. To in an irregular way. The result is that the various
make a magnetic tape recording (audio, video, channels, or tracks, are not always perfectly
and/or digital data). aligned.
tape cable 1. A form of cable in which all of the tape sort The (computer) operation of sorting data
conductor centers lie in the same plane. 2. A flat in a magnetic tape file into a record-key-
cable, commonly used in situations, where re- determined sequence.
peated flexing occurs. tape splicer A mechanism that aligns and secures
tape cartridge A holder and the reel of blank or the overlapping ends of broken magnetic tape so
prerecorded magnetic (1„8-inch audio or wider that they can be cut (often with an integral cutter)
video) tape it contains, which can be inserted into to form butted ends, and taped into a splice.
a recorder/reproducer without having to thread tape station See TAPE DECK.
or otherwise handle the tape for either playing or tape-to-head contact See HEAD-TO-TAPE CON-
rewinding. TACT.
tape comparator In a data-processing or com- tape transmitter A transmitter that receives its
puter system, a machine that compares tapes signal input from a recorded tape.
generated from the same input, for differences in tape transport In a tape deck or reproducer, the
the data thereon; it is a character-by-character device that moves the tape past the heads.
process. tape unit 1. See TAPE DECK. 2. See TAPE GROUP.
tape core A ring-type magnetic core made by tape verifier In computer operations, a device that
tightly winding metal tape in several layers for the checks the integrity of data on paper tape
desired thickness. through comparison with an original document.
tape counter See POSITION INDICATOR. tape width In magnetic tape, the dimension perpen-
tape deck In a tape recorder/reproducer, the com- dicular to tape travel; in general, the greater the
plete tape-transport mechanism (drive, heads, tape width, the more tracks the tape can contain.
equalization circuitry, and preamplifiers). tape-wound core See TAPE CORE.
tape drive 1. See TAPE TRANSPORT. 2. See TAPE tapped coil An inductor to which one or more in-
DECK. 3. A tape recorder/reproducer for com- termediate connections (taps) are made at appro-
puter data, used for backup and/or archiving. priate turns to provide intermediate values of
tape file A data file recorded on magnetic tape. inductance.
tape group An assembly of two or more tape decks. tapped component A coil, transformer, choke, re-
tape label On a reel or cassette of magnetic tape sistor, or other component in which an interme-
containing a data file, a record at the beginning or diate connection is made. See, for example
end that contains information about the file. TAPPED COIL.
tape loop An endless loop of magnetic tape. tapped inductor See TAPPED COIL.
tape magazine See TAPE CARTRIDGE. tapped resistor A resistor in which one or more in-
tape mark 1. A character that subdivides the mag- termediate connections (taps) are made to appro-
netic tape file on which it is recorded. Also called priate parts of the resistance element to provide
CONTROL MARK. 2. A character marking the end steps of resistance.
of a length of magnetic tape on a reel. Also called tapped transformer A transformer having one or
END-OF-TAPE MARK. more tapped windings.
tape plotting system In computer operations, a tapped winding A transformer or choke winding
system for operating a digital incremental plotter with one or more taps. Also see TAP and TAPPED
using the information on magnetic tape. COIL.
taper In a potentiometer or rheostat, the rate of tap switch A multiposition switch used to connect
change in resistance during uniform rotation of an external circuit to various taps on a compo-
the shaft. See, for example, LINEAR TAPER and nent. Also see SELECTOR SWITCH and TAP.
LOG TAPER. target 1. The bombarded electrode in an X-ray
tape recorder A machine for recording audio, tube. 2. The scanned storage element in a televi-
video, or data signals on magnetic tape; it can sion camera tube. 3. In radar operations, the
usually also play back the recorded material. scanned object. 4. An object intended for nu-
tapered potentiometer A potentiometer having a clear-particle bombardment. 5. A goal”espe-
tapered resistance winding (see TAPERED WIND- cially in a production process (deadline, desired
ING). number of units, etc.).
tapered winding A resistance winding (in a rheo- target acquisition 1. The moment at which a target
stat or potentiometer) in which the resistance comes within the range of a radar system.
change per unit length of winding is nonuniform 2. The observation of a new target on a radar screen.
674 target discrimination • tee-equivalent circuit

V TE Abbreviation of transverse electric (see, for ex-
Te Symbol for TELLURIUM.
teach box A robot-control device via which an op-
erator can program the machine to carry out spe-
cific movements. The operator manipulates
controls, and the robot™s computer stores the
data. When the data is accessed, the robot repro-
Primary duces the motions.
tearing In a television picture, the abnormal condi-
tion in which poor synchronization causes the
horizontal lines to be irregularly displaced. The
effect resembles cloth being torn.
115 Vac
technetium Symbol, Tc. A metallic element pro-
duced artificially. Atomic number, 43. Atomic
tapped transformer
weight, 98. Formerly called masurium.
technician 1. A person who repairs faulty
electronic equipment. 2. A person who assists
target discrimination The extent to which a radar
with the design and debugging of a system proto-
system can distinguish between two targets that
type. 3. A person who operates an electronic
are close together. Also called target resolution. It
is specified in linear units (such as meters, kilo-
technocentrism Overdependence on, and/or ob-
meters, or miles).
session with, the products of technology, particu-
target identification Any method by which the
larly computers.
identity of a radar target is determined.
tee Pertaining to a network, connection, or config-
target voltage In a television camera tube, the
uration whose geometric shape or schematic rep-
backplate-to-cathode voltage.
resentation resembles an uppercase letter T.
task environment The characteristics of the space
tee adapter See TEE JUNCTION.
in which an autonomous robot works. It depends
tee antenna An antenna consisting of a horizontal
on such factors as the intended application(s),
radiator with a vertical lead-in or feeder con-
the required speed at which the robot(s) must
nected to its center point.
work, and the human/robotic or computer/
robotic interface.
task-level programming In robotics, the writing of
programs to perform sequences of actions. A Insulator
complex process, it is a primitive level of artificial
intelligence (AI). An example is a program that di-
rects a robot to prepare and serve a meal.
taut-band meter A movable-coil meter in which
the conventional spiral springs of the coil are re- Horizontal
placed by two tightly stretched, thin, straight section
metal ribbons, whose twist provides torque that
returns the pointer to zero after a deflection.
Tb Symbol for TERBIUM.
BS Abbreviation of talk between ships.
Tc Symbol for TECHNETIUM.
T circuit See TEE NETWORK. tee antenna
T circuit parameters See R PARAMETERS.
T circulator See TEE CIRCULATOR.
TCL Abbreviation of TRANSISTOR-COUPLED tee circuit See TEE NETWORK.
LOGIC. tee circulator In microwave systems, a tee-shaped
TCM Abbreviation of thermocouple meter (see junction of three waveguides with a ferrite post at
TDM Abbreviation of TIME-DIVISION MULTIPLEX. tee-equivalent circuit An equivalent circuit in
TDR 1. Abbreviation of TIME-DELAY RELAY (see which the components are arranged in the form
DELAY RELAY). 2. Abbreviation of TIME- of a tee. See, for example, TEE NETWORK and
tee junction • telephone amplifier

tee junction 1. A tee-shaped splice between two telegraphy. In its simplest form, it consists of a
wires. 2. A tee-shaped fixture for splicing one coax- key and a sounder powered by a battery. Also see
ial line perpendicularly to another. 3. A tee-shaped PRINTING TELEGRAPH, 1, 2.
section for joining one waveguide perpendicularly telegraph channel 1. The frequency band as-
to another. Also called WAVE GUIDE TEE. signed to a particular telegraph station. 2. The
frequency band occupied by a telegraph signal.
telegraph code Broadly, Morse code. Wire telegra-
phy often uses a special version, such as the
American Morse code.
telegraph key See KEY, 1.
telegraph sounder See SOUNDER.
telegraph system A complete, integrated, coordi-
nated arrangement of equipment for communica-
tion by means of telegraphy. Included are
telegraph keys or keyers, sounders or printers,
relays, switchboards, wire lines and cables, and
power supplies.
tee junction
telegraphy The branch of electrical communica-
tions that deals with the transmission and recep-
tion of messages by means of prearranged
tee network A three-terminal network resembling
codes”especially over wires. Also see MORSE, 1,
a tee.
tee pad A three-resistor pad in which two series re-
telemeter 1. An indicating instrument that mea-
sistors and a shunt resistor are arranged to form
sures the value of a quantity generated at a dis-
a tee.
tant point or measures and transmits the value.
tee switch A combination of three switches ar-
2. The action afforded by the device in 1.
ranged to form a tee; two switches are in series
telemetering See TELEMETRY.
with a shunt switch in between. If the series
telemeter receiver See TELEMETRIC RECEIVER.
switches are open and the shunt switch is closed,
telemeter transmitter See TELEMETRIC TRANS-
isolation is greatly improved, compared to a sin-
gle series switch.
telemetric receiver A system that selects, ampli-
Teflon FEP A plastic insulating material. Dielectric
fies, and demodulates or rectifies a radio signal,
constant, 2.1. Dielectric strength, 2800 V/mil.
and actuates indicating instruments, recorders,
Teflon TFE A plastic insulating material. Dielectric
or data processors.
constant, 2.2. Dielectric strength, 600 V/mil.
telemetric transmitter A specialized transmitter
tel 1. Abbreviation of TELEPHONE. 2. Abbrevia-
that generates radio-frequency (RF) power, adds
tion of TELEGRAPH. 3. Abbreviation of TELE-
to it signals delivered by data transducers, and
delivers the modulated power to an antenna for
telautograph A device that transmits and receives
transmission to a distant telemetric receiver.
handwriting, drawings, and similar material. At
telemetry The transmission of data signals over a
the receiver, a pen follows the movements of a
distance, either by radio or wire, and the recep-
similar pen at the transmitter.
tion and application of the signals to indicating
teleammeter A TELEMETER for measuring cur-
instruments, recorders, etc.
rent generated at a remote point.
teleoperation The remote control of autonomous
robots. A human operator can control the speed,
telecast A television program for general reception.
direction, and other movements of a robot from
The term a contraction of television broadcast.
some distance away. See also TELEPRESENCE.
telechir A remotely controlled, autonomous robot.
telephone Abbreviation, tel. An instrument for
transmitting and receiving messages by means of
telecommunication Communication, usually be-
telephony. In its simplest form, it consists of a
tween widely separated points, by electrical or
microphone, earphone, switching and ringing de-
electronic means.
vices, wire line or cable, and power supply. Also
telecontrol See REMOTE CONTROL and TELEOP-
telephone accessories Devices (such as answering
telefacsimile See FACSIMILE.
machines, speaker phones, facsimile machines,
telegram Abbreviation, tel. A (usually printed-out)
etc.) used in conjunction with a telephone set.
message transmitted and received via telegraph
telephone amplifier A small audio amplifier, usu-
or teletypewriter. Compare CABLEGRAM and RA-
ally with a self-contained loudspeaker, for in-
creasing the sound volume of a telephone output.
telegraph Abbreviation, tel. An instrument for
Some amplifiers of this kind are connected to the
transmitting and receiving messages by means of
676 telephone amplifier • televise

telephone line, and others receive sound from the Telephoto receiver See FACSIMILE RECEIVER.
telephone receiver. Telephoto transmitter See FACSIMILE TRANS-
telephone-answering machine See ANSWERING MITTER.
MACHINE. telepresence An advanced form of robotic TELE-
telephone bypass capacitors A set of fixed capac- OPERATION, in which a human operator has the
itors installed between each wire in a telephone impression of being at the robot™s location. It in-
line and an electrical ground to bypass radio- cludes vision systems, pressure sensors, sound
frequency energy. It can reduce or prevent radio- sensors, tactile sensors, and electromechanical
frequency interference (RFI) to telephone sets and control devices. The operator uses, or wears,
data terminals. equipment similar to that used for VIRTUAL RE-
telephone data set A device that converts signals ALITY (VR).
from a data terminal for passage over a telephone teleprinter A terminal telegraph printing machine.
circuit to a data-processing center. Also see PRINTING TELEGRAPH, 1, 2.
telephone dialer In a security system, a circuit TelePrompTer A device that presents a running
that automatically dials one or more telephone display on a screen before a television announcer,
numbers, alerting the recipient(s) that an emer- performer, or speaker, of dialogue.
gency exists at a given location. teleran A ground-to-air communications system.
telephone induction coil A small telephone-to- Ground-based radar pictures are transmitted, via

line impedance-matching transformer used in television, to aircraft.
telephone systems. telescoping antenna A vertical antenna consisting

telephone patch See PHONE PATCH. of separate lengths of metal tubing of progres-
telephone pickup A device for receiving conversa- sively smaller diameter so that one can slide into
tions from a telephone to which it isn™t directly another. The antenna can be pulled out to full
connected. length or compressed to the length of the largest-
telephone plug See PHONE PLUG. diameter section.
telephone-radio patch See PHONE PATCH.
telephone receiver The handheld part of a tele-
phone set, containing the microphone and ear-
phone, and, in some cases, the dialing keypad.

telephone repeater An amplifier and associated
telescoping antenna
equipment used to boost the amplitude of a tele-
phone signal at an appropriate point along the
line. teletext A method of communication in which a
telephone service entrance The point at which video image is sent of a page of printed material.
the telephone wiring in a house or building con- telethermoscope A device for measuring the tem-
nects to the outside telephone line. perature of distant objects.
telephone silencer A device for muting a tele- Teletorque See AUTOSYN and SYNCHRO.
phone or its bell. Teletype 1. The transmission and/or reception of
telephone system A complete, integrated, and co- text messages in digital form, displayed or
ordinated arrangement of equipment for commu- printed at a distant location. 2. See TELETYPE-
nication by means of telephony. Included are WRITER.
telephones, switchboards and associated equip- teletype grade A term descriptive of a circuit hav-
ment, wire lines and cables, and power supplies. ing the quality necessary for communication via
PRIVATE AUTOMATIC EXCHANGE (PAX), PRI- Teletypesetter An electronic system for operating
VATE BRANCH EXCHANGE (PBX), and TELE- a distant Linotype.
PHONE. teletypewriter A variety of printing telegraph us-
telephone test set See PHONE TEST SET. ing electric typewriters and associated equip-
telephone transmitter The sound pickup unit ment. The message is typed on the keyboard at
(microphone) of a telephone. Also see TRANSMIT- the transmitting station and is typed out in corre-
TER, 2. sponding letters at the receiving station. The
telephony The branch of electrical communication same typewriter is able to send and receive mes-
dealing with the transmission and reception of sages. Also see RADIOTELETYPEWRITER.
sounds”especially over wires. Also see WIRE teletypewriter exchange Abbreviation, TWX. A
TELEPHONY. center for switching and routing teletypewriter
Telephoto 1. The transmission and/or reception communications. Also see TELETYPEWRITER.
of photographs by means of FACSIMILE. 2. A teleview To observe a scene or program via televi-
photograph transmitted and/or received by sion.
means of FACSIMILE. televise 1. To convert a scene into a television
telephoto lens A camera lens providing a tele- signal. 2. To broadcast a scene or program via
scopic effect. television.

television • temperature derating

television 1. Abbreviation, TV. The transmission the influence of changing temperature. It is gen-
and/or reception, via electromagnetic fields, wire erally expressed in percent per degree (%/°C) or
cable, and/or fiberoptic cable, of images, usually in parts per million per degree (ppm/°C).
with sound. 2. A system for receiving signals, as temperature-compensated crystal oscillation
defined in 1. 3. Video programs or data, with or Oscillation in a crystal oscillator, in which the
without sound, transmitted via electromagnetic crystal and/or circuit is automatically compen-
fields, wire cable, and/or fiberoptic cable. sated against frequency drift caused by tempera-
television band See UHF TELEVISION CHANNELS ture change.
and VHF TELEVISION CHANNELS. temperature-compensating component A circuit
television camera The pickup device that scans a component, such as a capacitor or resistor, whose
scene and delivers a series of electrical signals temperature coefficient is equal in magnitude and
that can be used to reconstruct the image on the opposite in sign to that of a conventional compo-
screen of a picture tube. nent to which it is connected to cancel tempera-
television-camera tube See CAMERA TUBE, ture-induced variation in the latter™s value.
television channel A radio-frequency band allo-
cated exclusively for the transmission of a televi-
sion signal. In conventional broadcasting, this
band is usually 6 MHz wide. See, specifically,
television engineer A trained professional skilled control
in video electronics engineering, as well as in ba-
sic engineering and associated subjects.
television engineering The branch of electronics
engineering devoted to the theory and application
of television.
television interference Abbreviation, TVI. Inter-
ference to the reception of television signals, usu-
ally occasioned by signals from radio services or
computers, or by electrical noise.
televisor 1. A television transmitter or receiver.
2. A person or entity responsible for the broadcast
of television programs or signals.
televoltmeter A TELEMETER for measuring volt- Temperature-
age generated at a remote point. compensating
Tank capacitor
telewriter See TELAUTOGRAPH. capacitor
Telex 1. A teleprinter system that operates via the
telephone lines, and was once commonly used by temperature-compensating component
businesses for sending and receiving short mes-
sages. It has largely been supplanted by computer-
ized data communications systems. 2. A hard-copy temperature compensation The use of a device,
message sent or received by such a system. such as a temperature-compensating compo-
telluric currents Also called terrestrial currents. nent, to correct a temperature-induced deviation
A flow of electrical charge carriers, primarily elec- in the value of a conventional component.
trons, in the earth. temperature control 1. The adjustment of tem-
tellurium Symbol, Te. A rare, metalloidal element perature. 2. The automatic maintenance of tem-
related to selenium. Atomic number, 52. Atomic perature at a desired level, as in a
weight, 127.60. temperature-controlled oven. 3. A device for con-
TE mode See TRANSVERSE ELECTRIC MODE. trolling temperature, as defined in 1 or 2.
temp 1. Abbreviation of temperature. (Also, T.) temperature-controlled crystal oscillator Abbre-
2. Abbreviation of temporary. 3. Abbreviation of viation, TCCO. A high-precision crystal oscillator
TEMPLATE. in which the crystal plate (and sometimes the cir-
temperament The tuning of a keyboard-type mu- cuitry, as well) is held at constant temperature.
sical instrument to produce a nearly perfect dia- temperature degree See DEGREE, 2 and THER-
tonic scale. MOMETER SCALE.
temperature Symbol, T. A quantitative measure of temperature derating Deliberate reduction of op-
the heat exhibited by an object or phenomenon. erating current and/or voltage of a device to a
Also see THERMOMETER SCALE. specific temperature to ensure proper operation.
temperature coefficient A figure that states the Also see DERATING, DERATING CURVE, and
extent to which a quantity drifts or varies under DERATING FACTOR.
678 temperature gradient • terrain echoes

temperature gradient A range of temperature terawatt Abbreviation, TW. A large unit of power;
1 TW = 1012 W.
variation, such as the rate of change of tempera-
ture, with respect to change of power dissipation, terbium Symbol, Tb. A metallic element of the
or the rate of change of temperature with spatial rare-earth group. Atomic number, 65. Atomic
displacement. weight, 158.93.
temperature inversion See INVERSION, 1. terbium metals A group of rare-earth metals, in-
temperature meter An indicator (usually a direct- cluding europium, gadolinium, terbium, and occa-
current voltmeter or millivoltmeter) whose scale sionally dysprosium.
reads directly in degrees. term In an algebraic expression, constants, vari-
temperature scale See THERMOMETER SCALE. ables, or combinations of these, separated by op-
temperature-sensitive resistor See THERMIS- eration signs (e.g., the expression 4xy + z has two
TOR. terms).
temperature shock See THERMAL SHOCK. terminal 1. A connection point at the input, out-
temperature-to-voltage converter A circuit or de- put, or an intermediate point of a device, or a
vice, such as a thermocouple, that delivers an point at which a voltage is to be applied. 2. A
output voltage proportional to an applied temper- metal tab or lug attached to the end of a lead for
ature. connection purposes. 3. Pertaining to the end of a
template 1. A diagram, usually drawn on paper, to series of events, etc. (e.g., terminal tests). 4. In a
show the locations at which components should data-communications system, a point of data in-
be placed or tasks should be performed. It is put or output. Also called data terminal. If it does
taped or cemented temporarily to the work, and not have computing capability of its own, it is of-
the points are transferred to the latter by prick- ten called a dumb terminal.
punching. 2. A stencil-like plate with alphanu- terminal block A group of several terminals, in-
meric and circuit symbols, used as a drafting aid. tended for interconnection of circuits, mounted
Sometimes called “drafting stencil.” on a solid insulating block.
temporary magnet 1. A body that exhibits mag- terminal board An insulating board carrying sev-
netism only briefly after it has been exposed to eral lugs, tabs, or screws as terminals (see TER-
another magnet. Compare PERMANENT MAG- MINAL, 2). Also see TERMINAL STRIP.
NET. 2. See ELECTROMAGNET. terminal guidance The navigation of a missile or
temporary storage 1. In computer and data-pro- aircraft to help it reach its target or destination.
cessing operations, the storage of data or instruc- terminal impedance The internal impedance of a
tions only until they are needed. Also called device measured at the input or output termi-
INTERIM STORAGE. 2. Locations in a computer nals.
memory set aside during a program run for hold- terminal point of degradation The point at which
ing intermediate results of operations. degradation of a circuit or component is com-
NETIC WAVE. terminal repeater A telephone repeater operated
ten code A set of abbreviations used by two-way at the end of a line.
radio operators. Each “ten signal” represents a terminal strip A strip of insulating material, such
specific statement or query. as plastic or ceramic, on which are mounted one
tension 1. A force that tends to stretch, pull tight, or more screws, lugs, or other terminals. Also see
or pull apart. Compare STRAIN. 2. A term refer- TERMINAL, 2.
ring to VOLTAGE”especially in a utility power
transmission line.
ten-turn potentiometer A precision potentiome-
ter whose shaft must be turned through 10 com-
plete revolutions to cover the entire resistance
terminal strip (lug-type)
T-equivalent circuit See TEE-EQUIVALENT CIR-
CUIT. terminal voltage The voltage at the output termi-
tera- Abbreviation, T. 1. A prefix meaning nals of an unloaded battery or generator.
trillion(s), (i.e., 1012). 2. A prefix meaning 240. ternary code See TRINARY NUMBER SYSTEM.
tera-electronvolt Abbreviation, TeV. A large unit ternary fission The splitting of an atomic nucleus
of energy; 1 TeV = 1012 electronvolts. Also see into three nuclear pieces. Also see FISSION.
ELECTRONVOLT. ternary number system See TRINARY NUMBER
terahertz Abbreviation, THz. A unit of extremely SYSTEM.
high frequency equal to 1012 Hz. Also called Fres- terrain echoes Radar images caused by reflections
nel. from hills, mountains, and other natural ter-
teraohm A unit of high resistance, reactance, or restrial surface features. Also see GROUND
impedance equal to 1012 ohms. CLUTTER.
terrestrial magnetism • texture sensing

terrestrial magnetism See EARTH™S MAGNETIC test run In computer operations, using test data to
FIELD. check the operation of a program, by comparing
tertiary coil A third winding (see TERTIARY the results obtained thereby with what should
WINDING). ideally result.
tertiary winding A third winding on a transformer test set A combination of instruments assembled
or magnetic amplifier. on a single panel, and usually enclosed in a car-
tesla Symbol, T. A unit of magnetic flux density; 1 rying case, for convenience in making tests.
T = 1 weber per square meter = 104 gauss. test signal 1. A signal used for conducting a test of
Tesla coil A special type of air-core step-up trans- a component, circuit, or system. 2. In radioteleg-
former for developing high voltage at radio fre- raphy, a special signal signifying that the trans-
quencies. It consists essentially of a low-turn mitting station is testing equipment. Also see
primary coil, through which radio-frequency (RF) VEE SIGNAL.
current flows, and a multiturn secondary coil, test-signal generator A device, such as an oscilla-
across which the high voltage, is developed. tor, for producing a signal for testing equipment
test A procedure consisting of one or several steps, (see TEST SIGNAL, 1).
in which (1) the mode of operation of a circuit or test tape A magnetic tape containing signals for
device is established, (2) the value of a component testing equalization, frequency response, head
is ascertained, or (3) the behavior of a circuit or adjustment, stereo balance, etc. in an audiotape
device is observed. recorder, high-fidelity sound system, computer
test bench An equipment installation intended for tape drive, or videocassette recorder.
the testing, repair, or debugging of electronic de- tetravalent See QUADRIVALENT.
vices by a technician. tetrode An electron tube in which the principal
test data Data used to test a computer program, electrodes are cathode, control grid, screen, and
including samples within limits that might be en- plate.
countered during the program™s implementation. tetrode transistor 1. A bipolar transistor with two
tester 1. See TEST INSTRUMENT. 2. A technician emitters. 2. A dual-gate field-effect transistor.
who primarily makes tests and measurements.
testing window See WINDOW, 2.
test instrument A device for checking the opera-
tion of a circuit or the value of a component. This
class of instrument is usually less accurate than
measurement instruments. Also see TEST SET.
test lead The flexible, insulated wire attached to a
test prod.
test pattern A picture-and-line display on the B
screen of a television picture tube, used to check
such features as aspect ratio, linearity, contrast,
test point A terminal intended for connection of
test equipment in the repair or debugging of a cir-
cuit. Often, test points are labeled by the letters
TP followed by numerals (such as TP1, TP2, etc.). E1 E2
test probe See PROBE, 1.
test prod A stick-type probe (see PROBE, 1) with a tetrode transistor
flexible, insulated lead terminating in a plug or
lug for attachment to an instrument.
TeV Abbreviation of TERA-ELECTRONVOLT.
Te value The temperature at which a centimeter
cube of glass or ceramic exhibits 1 megohm of re-
text editor A computer program for finding and
changing data in a file.
texture map In computer graphics, the topograph-
ical qualities of the surface of a three-dimen-
sional rendition. For example, the image of an
test prods
orange would have a “bumpy” texture map; the
image of a peach would have a “fuzzy” texture
test program In computer operations, a program map.
devised to check the functioning of hardware. texture sensing The ability of a robotic end effec-
Also called utility and test routine. tor to determine the relative smoothness or
680 texture sensing • thermal shock

roughness of a surface. One common scheme WIRE ANEMOMETER, HOT-WIRE FLOW-ME-
uses reflected light or infrared. Scattered reflec- TER, and HOT-WIRE MICROPHONE.
tions indicate a rough or matte surface. thermal-conductivity gasmeter See GAS DETEC-
tgt Abbreviation of TARGET. TOR.
TH Abbreviation of true heading. thermal detector 1. See BOLOMETER. 2. In a se-
Th Symbol for THEORIUM. curity or fire-protection system, a device that
TH Symbol for heater temperature. closes a circuit or actuates an alarm if the tem-
thallium Symbol, Tl. A metallic element. Atomic perature rises to a specific level.
number, 81. Atomic weight, 204.38. thermal emf See SEEBECK EFFECT.
thalofide cell An evacuated photoconductive cell thermal gasmeter See GAS DETECTOR.
using thallium oxysulfide as the light-sensitive thermal imaging See THERMOGRAPHY.
material. thermal instrument See HOT-WIRE METER and
TION. thermally sensitive resistor See THERMISTOR.
theory A reasonable proposition put forth to ac- thermal meter See HOT-WIRE METER and THER-
count for the behavior of, or the relationships be- MOCOUPLE-TYPE METER.
tween, bodies and forces, or to explain concepts thermal neutron A neutron that is essentially in
and their relations. When a theory has stood up thermal equilibrium with the surrounding me-
under exhaustive tests, it might reveal a scientific dium or environment.
law. thermal noise Frequency-independent electrical
therm A gas heating unit. 1 therm = 100,000 noise caused by the agitation of particles (e.g.,
British thermal units (105 Btu). atoms and electrons) in a material by heat. Ther-
thermal agitation Random movement of particles mal noise is proportional to bandwidth, resis-
(such as electrons) in a substance, because of tance, and absolute temperature.
heat. thermal radiation See HEAT.
thermal-agitation noise See THERMAL NOISE. thermal recorder A graphic recorder in which a
thermal ammeter See HOT-WIRE AMMETER. strip of paper coated with a thin layer of opaque
thermal anemometer See HOT-WIRE ANEMO- wax is drawn between a knife-edge platen and a
METER. heated writing stylus that melts the wax beneath
thermal conductivity The heat-conducting ability its point, exposing the underlying black paper as
of a material. Compare electrical conductivity (see a fine line.
CONDUCTIVITY). thermal resistance Symbol, RT. For a semicon-
ductor device, the rate of change of junction tem-
perature, with respect to power dissipation; RT =
thermal conductivity
dT/dP, where RT is in degrees Celsius per milli-
watt, T is the temperature in degrees Celsius, and
Thermal conductivity
P is the power in milliwatts.
Element (mW/m/°C)
thermal resistor A resistor that is sufficiently
Aluminum 22.0 temperature-sensitive to be used as a heat sen-
Carbon 2.4 sor. Examples: thermistor and germanium
Chrominum 6.9 diode.
Cooper 39.0 thermal response time For a power-dissipating
Gold 30.0 component, the elapsed time between the initial
Iron 7.9 change in power dissipation and the moment at
Lead 3.5 which the temperature has changed by a speci-
Magnesium 16.0 fied percentage (usually 90%) of the total value.
Mercury 0.8 thermal runaway A destructive process resulting
Nickel 8.9 from cumulative temperature effects. In bipolar
Platinum 6.9 transistors, this can occur if the collector current
Silicon 8.4 increases as the temperature rises. As the unit
Silver 41.0 gets hotter, the collector-base junction dissipa-
Thorium 4.1 tion increases, generating still more heat. The
Tin 6.4 ultimate result, if the process continues
Tungsten 20.0 unchecked, is destruction of the component. The
Zinc 11.0 process can also occur in certain batteries when
they are charged too rapidly or at excessively high
thermal-conductivity device An instrument or temperatures.
control unit using a heated filament whose tem- thermal shock The effect of applying heat or cold
perature and, accordingly, conductivity is varied to a device so rapidly that abnormal reactions oc-
by some sensed phenomenon. See, for example, cur, such as rapid (often catastrophic) expan-
GAS DETECTOR, HEATED-WIRE SENSOR, HOT- sions and contractions.
thermal switch • thermoelectric junction

thermal switch A switch actuated by a tempera- thermistor bridge A four-arm bridge (see BRIDGE,
ture change. Types vary from the simple thermo- 1) in which one arm is a thermistor and, there-
stat to complex servosystem switches with a fore, is temperature sensitive.
temperature-transducer input. thermistor power meter A radio-frequency
thermal time-delay relay A delay relay utilizing power-measuring instrument based on a ther-
the slow-heating and slow-cooling property of one mistor bridge.
of its components. thermistor probe A temperature probe containing
thermion An ion or electron emitted by a hot body, a thermistor as the sensing element.
such as the heated cathode of a vacuum tube. thermistor thermometer An electronic ther-
thermionic Pertaining to thermions and their ap- mometer in which the temperature-sensitive ele-
plications. ment is a thermistor.
thermionic cathode A heated cathode, in contrast thermoammeter See THERMOCOUPLE-TYPE
to a cold cathode, used as an emitter of electrons METER.
or ions. Also see THERMION. thermocouple A device consisting essentially of a
thermionic current Current caused by therm- bond between two wires or strips of dissimilar
ionic emission”especially in an electron tube. metals (such as antimony and bismuth). When
thermionic detector A vacuum-tube detector. the bond is heated, a direct-current voltage ap-
Also see THERMION and THERMIONIC EMIS- pears across it.
thermionic diode A hot-cathode diode tube.
Glass envelope
thermionic emission The emission of electrons by
a hot body, such as the filament or cathode of a
vacuum tube. Also see THERMION and HOT
thermionics The study of electron emission from Electrodes
objects or materials at high temperature.
thermionic tube An electron tube (i.e., one in
which electrons or ions are emitted by a heated
cathode). Also see THERMION, THERMIONIC
thermionic work function The energy required to thermocouple
force an electron from inside a heated cathode
into the surrounding space (in thermionic emis-
sion). Also see WORK FUNCTION. thermocouple bridge A four-arm bridge (see
thermistor A temperature-sensitive resistor, usu- BRIDGE, 1) in which one arm is a thermocouple;
ally made from specially processed oxides of therefore, it is temperature sensitive, as well as
cobalt, magnesium, manganese, nickel, uranium, being voltage-productive.
or mixtures of such substances. Thermistors are thermocouple meter See THERMOCOUPLE-TYPE
available with either a positive or negative tem- METER.
perature coefficient of resistance. The name is a thermocouple-type meter A radio-frequency (RF)
contraction of thermally sensitive resistor. meter consisting of a thermocouple and direct-
current (dc) ammeter, milliammeter, or micro-
ammeter, connected in series. The thermocouple
Semiconductor is heated, directly or indirectly, by an applied RF
layer current, and the resulting dc output deflects the
meter pointer.
thermodynamics The science dealing with the re-
lationships between heat and mechanical energy
and their interconversion. Also see CARNOT
thermoelectric cooler A cooling device based on
the Peltier effect.
thermoelectric effect The production of thermo-
electricity by certain materials.
thermoelectricity Heat-produced electricity, as in
thermocouple operation.
thermoelectric junction A junction between two
conductors that exhibits variable characteristics
thermistor under conditions of changing temperature.
682 thermoelectric series • thin-film resistor

thermoelectric series A series of conducting met- thermostatic switch See THERMOSTAT.
als, sequenced so that if a thermocouple is made thermoswitch See THERMOSTAT.
from two of the metals, current flows at the hot theta wave A form of brain wave that occurs at
junction from the metal occurring earlier in the extremely low frequencies, and is associated with
series. sleep or mental incoherence.
thermoelectron An electron emitted by a hot cath- Thevenin™s theorem The proposition that, with
ode. Also see THERMION and THERMIONIC reference to a particular set of terminals, a net-
EMISSION. work containing a number of generators and con-
thermoelement A thermocouple, especially a stant impedances can be simplified to a single
miniature one, used in a THERMOCOUPLE-TYPE generator in series with a single impedance.
METER. The equivalent circuit will deliver to a given load,
thermogalvanometer See THERMOCOUPLE the same current, voltage, and power delivered by
TYPE METER. the original network. Compare COMPENSATION
thermography A means of locating or mapping by THEOREM, MAXIMUM POWER TRANSFER THE-
detecting infrared images. It can be in the form of OREM, NORTON™S THEOREM, RECIPROCITY
live video, similar to television, or in the form of THEOREM, and SUPERPOSITION THEOREM.
photographs, using infrared film. Many common thick film A film of selected material (conductive,
cameras can be used with infrared film to make resistive, dielectric, etc.) applied to a substrate by
infrared photographs (thermographs). painting, photography, or similar process. See,
thermojunction The junction of the two metals in for example, PRINTED CIRCUIT. Compare THIN
a thermocouple. A voltage appears when the dis- FILM. Typically, thick films are 1 mil or more in
similar metals are heated. thickness.
thermoluminescence Luminescence resulting thick-film component A unit, such as a capacitor
from the moderate heating of certain materials. or resistor, fabricated by thick-film techniques.
thermomagnetic effect The effects of temperature See, for example, PRINTED COMPONENT. Also
on the magnetism of a body, or vice versa. see THICK FILM. Compare THIN-FILM COMPO-
thermometer A (usually direct reading) device for NENT.
measuring temperature. Also see ELECTRONIC thick-film resistor A resistor fabricated by thick-
THERMOMETER and THERMOMETER SCALE. film techniques. See, for example, PRINTED
thermometer scale The scale on a thermometer, RESISTOR. Also see THICK FILM. Compare
graduated in degrees, from which temperature is THIN-FILM COMPONENT.
read. For a description of different scales, see thick magnetic film See MAGNETIC THICK FILM.
ABSOLUTE SCALE, CENTIGRADE SCALE, thin film An extremely thin layer (less than 1 mil)
FAHRENHEIT SCALE, REAUMUR SCALE, and of a selected material (conductive, resistive, semi-
RANKINE SCALE. The Kelvin scale is the same as conductive, dielectric, etc.) electrodeposited or
the absolute scale, and the Celsius scale is the grown on a substrate. Compare THICK FILM.
same as the centigrade scale. thin-film capacitor A capacitor made by elec-
thermonuclear reaction A nuclear reaction in trodepositing a thin film of metal on each side of
which energy is released when lighter atoms are a grown layer of oxide, as in an integrated circuit.
converted into heavier atoms at temperatures in Also see THIN FILM.
the millions of degrees Celsius. Also see FISSION, thin-film component A unit (such as a capacitor,
FUSION, and NUCLEAR REACTOR. resistor, diode, or transistor), fabricated by thin-
thermopile A device consisting of two or more film techniques. Also see THIN FILM. Compare
thermocouples connected in series for increased THICK-FILM COMPONENT.
voltage output. thin-film integrated circuit An integrated circuit
thermoplastic material A plastic that can be re- in which the components and “wiring” are pro-
softened by applying heat after having been duced by depositing (or growing) and processing
molded into a desired shape. Example: poly- materials on a semiconductor slab or wafer (the
thermosensitivity Sensitivity of a circuit or device thin-film memory In a computer, a storage me-
to heat. ium that is a magnetic thin film (see THIN FILM)
thermosetting material A plastic that cures on a nonmagnetic substrate (often glass) and that
chemically (will not ordinarily soften again when can be magnetized to represent digital data.
heat is applied) after having been heat-molded thin-film microelectronic circuit An integrated
into a desired shape. Example: Bakelite. Com- circuit that occupies (essentially) two dimen-
pare THERMOPLASTIC MATERIAL. sions; that is, a very thin integrated circuit.
thermostat A temperature-sensitive switch. In one thin-film resistor A resistor fabricated by thin-
common form, a movable contact is carried by a film techniques (see THIN FILM) (e.g., TANTA-
strip of bimetal and the stationary contact is LUM-NITRIDE RESISTOR). Compare THICK-
mounted nearby. FILM RESISTOR.
thin-film semiconductor • three-phase rectifier

Tip contact
thin-film semiconductor A very shallow layer of
semiconductor material, such as single-crystal Sleeve
silicon, electrodeposited on a substrate. Also see contact
Ring contact
thin-film transistor A transistor fabricated by
three-conductor jack
thin-film techniques. Also see THIN FILM and
thin magnetic film See MAGNETIC THIN FILM.
third-generation computer A computer in which
the active discrete components are integrated cir-
Third Law of Thermodynamics As the tempera-
ture of absolute zero is approached in an isother- Tip
mal process involving a solid or liquid, the change Sleeve
in entropy approaches zero; and the entropy of a
substance is zero at absolute zero. three-conductor plug
third-octave band See ONE-THIRD-OCTAVE
thirty-channel multiplex A form of pulse-code- three-electrode tube See TRIODE.
modulated (PCM) multiplex using eight digits and three-element tube See TRIODE.
the A-law. There are 30 speech channels and two three-gun picture tube A color-television picture
utility channels. tube having a separate gun for each primary color
Thomson bridge See KELVIN BRIDGE. (red, green, and blue).
Thomson effect The liberation or absorption of three-halves-power law See CHILD™S LAW.
heat (depending on the material of interest) when three-junction transistor A pnpn or npnp tran-
an electric current flows from a warmer to a sistor. Also see NPNP DEVICE.
cooler part of a conductor. three-phase bridge rectifier A bridge-rectifier cir-
Thomson heat The amount of thermal energy cuit for three-phase alternating current. Two
transferred because of Thomson effect. diodes are provided for each phase. The ripple
Thomson voltage The voltage drop between two frequency is six times the line frequency. Also see
points on a conductor that are at different tem- BRIDGE RECTIFIER, POLYPHASE RECTIFIER,
peratures. and THREE-PHASE CIRCUIT.
thoriated-tungsten filament In a vacuum tube, a three-phase circuit The circuit of a three-phase
filament made of tungsten to which thorium ox- system. See THREE-PHASE SYSTEM and, specif-
ide has been added to increase the emission ically, DELTA CONNECTION and WYE CONNEC-
of electrons. Also see THERMION and THER- TION.
MIONIC EMISSION. three-phase current Current in a three-phase cir-
thorium Symbol, Th. A radioactive metallic ele- cuit. The currents in the three legs differ in phase
ment. Atomic number, 90. Atomic weight, by 120°.
232.04. Thorium, when heated, is a copious emit- three-phase four-wire system See FOUR-WIRE
ter of electrons, so the filaments or cathode cylin- WYE SYSTEM.
ders of some electron tubes are coated with one of three-phase generator A (usually dynamo-type)
its compounds. generator of three-phase current or voltage. See
thoron Symbol, Tn. A radioactive isotope of RADON. THREE-PHASE SYSTEM.
three-address instruction A computer program three-phase half-wave rectifier A half-wave recti-
instruction having three addresses, two for fier circuit for three-phase alternating current.
operands and one for the result (of the operation One diode is provided for each phase. The ripple
called for). frequency is three times the line frequency. Also
three-channel stereo A form of stereophonic see HALF-WAVE RECTIFIER, POLYPHASE REC-
sound recording and reproduction in which three TIFIER, and THREE-PHASE CIRCUIT. Compare
distinct channels are used; these are usually des- THREE-PHASE BRIDGE RECTIFIER.
ignated the left, right, and center channels. three-phase motor An alternating-current motor
three-coil meter See ELECTRODYNAMOMETER. operating on three-phase power. Above frac-
three-conductor jack A female connector in which tional-horsepower size, the three-phase motor is
two separate conductors are provided, in addition smoother running and more simply structured
to the ground conductor. than the single-phase counterpart.
three-conductor plug A male connector in which three-phase power The total power dissipated or
two separate conductors are provided, in addition delivered in a three-phase alternating-current
to the ground conductor. circuit.
three-dimensional television See STEREO- three-phase rectifier A rectifier for three-phase al-
SCOPIC TELEVISION. ternating current. At least one diode is included
684 three-phase rectifier • thumbwheel switch

for each phase. Also see POLYPHASE RECTIFIER, smallest amount of forward current that flows
THREE-PHASE BRIDGE RECTIFIER, THREE- through a diode. 3. In a gas, the smallest level of
PHASE CIRCUIT, and THREE-PHASE HALF- current for which a discharge will maintain itself
WAVE RECTIFIER. under variable conditions.
three-phase system An alternating-current elec- threshold detector A device that prevents a signal
trical system in which three currents or voltages from passing until its peak amplitude reaches a
exist simultaneously. They are of equal ampli- certain value.
tude, but are 120° out of phase with each other.
three-phase, three-wire system An electrical sys-
tem having three conductors, with an alternat-
ing-current phase difference of 120° between
conductor pairs. Off
three-phase-to-single-phase transformer An al-
ternating-current transformer with three-phase
input and single-phase output (one terminal is
three-phase-to-two-phase transformer An alter- Input Output
nating-current transformer with three-phase in-
put and two-phase output, the output currents
are 180° out of phase with each other.
three-phase voltage Voltage in a three-phase al-
ternating-current circuit. The voltages across the
threshold detector
three legs differ by 120°.
three-quarter bridge A bridge rectifier having
diodes in three arms and a resistor in the fourth. threshold frequency 1. The cutoff frequency or fre-
three-space A mathematical continuum in which quencies in a band-pass, band-rejection, low-pass,
each point is uniquely defined by three variables or high-pass filter. 2. The lowest frequency for a
in an ordered triple, such as (x,y,z), and each or- metal or semiconductor junction at which incident
dered triple corresponds to exactly one point in radiation gives rise to the photoelectric effect.
the space. A common coordinate system is the threshold of hearing The minimum intensity level
Cartesian system consisting of three axes, x, y, at which sounds are audible in an environment
and z”each mutually perpendicular and inter- containing essentially no background acoustic
secting at the origin (0,0,0). noise.
three-space coordinates Any set of coordinates threshold of pain The intensity level at which
used for locating points or plotting graphs in hearing a sound causes physical discomfort. This
three dimensions. is approximately 120 dB above the THRESHOLD
three-state logic See TRI-STATE LOGIC. OF HEARING for most people.
three-way speaker A set of three individual speak- threshold signal The weakest signal that can be
ers contained in a single cabinet: a woofer (low- detected in a receiving system.
frequency speaker), a midrange speaker, and a throat See HORN THROAT.
tweeter (high-frequency speaker). It is common in throat microphone A small microphone operated
high-fidelity music reproduction systems. Com- in contact with the user™s throat.
pare TRIAXIAL SPEAKER. throttle The feedback control device in a regenera-
three-wire system 1. An electric-power feed sys- tive detector or amplifier.
tem using three wires, the center one (neutral) throughput In computer operations, an overall
being at a potential midway between the potential quantitative indicator of processing power, ex-
across the other (outer) two. 2. See THREE- pressed in terms of the amount of data processed
PHASE and THREE-WIRE SYSTEM. 3. See TWO- in a given period of time.
PHASE and THREE-WIRE CIRCUIT. throw-out spiral On a phonograph disc, a lead-out
threshold 1. The initial (observable) point of an ef- groove.
fect (e.g., threshold of hearing). 2. A predetermined thulium Symbol, Tm. A metallic element of the
point, such as of minimum current or voltage, for rare-earth group. Atomic number, 69. Atomic
the start of operation of a circuit or device. weight, 168.93.
threshold component A value of current, voltage, thumbwheel potentiometer A potentiometer op-
sound intensity, etc., selected as the minimum erated by means of a knurled knob (usually pro-
level at which a circuit or device is to operate in truding perpendicularly through a panel) that is
some prescribed manner, or beyond which a turned with the thumb or with a finger.
certain condition will prevail. Also see THRESH- thumbwheel switch A switch operated by means
OLD, 1, 2. of a knurled knob (usually protruding perpendic-
threshold current 1. The minimum value of cur- ularly through a panel) that is turned with the
rent at which a certain effect takes place. 2. The thumb or with a finger.
thy • time-interval mode

thy Abbreviation of THYRATRON. tie cable 1. A cable that connects two distributing
thyratron A gas triode or gas tetrode used princi- points in a telephone system. 2. Any cable that
pally for switching and control purposes. Thyra- interconnects two circuits.
tron action differs from that of the vacuum tube tie point A lug, screw, or other terminal to which
in the unique behavior of the thyratron control wires are connected at a junction.
electrode (grid): Anode current starts to flow tie-point strip A terminal strip with lugs to which
abruptly when grid voltage reaches a particular conductors can be soldered.
value, at which point the grid provides no further tight coupling See CLOSE COUPLING.
control; anode current continues to flow until the tilt switch A device, such as a mercury switch,
anode voltage is either interrupted or reversed. that is actuated by tilting it to a certain angle.
thyratron inverter An inverter circuit (see IN- timbre The quality that distinguishes the sound of
VERTER, 1) using thyratrons as the switching one voice or instrument from that of another,
devices. Also see THYRATRON. largely because of harmonic content.
Thyrector A silicon diode exhibiting very high re- time Symbol, t. 1. The instant at which an event
sistance (approaching that of an insulator) up to occurs. 2. The instant at which a time-base vari-
a certain voltage, beyond which the unit switches able reaches a given value. 3. The interval be-
to a low-resistance conducting state. tween two instants, commonly called duration or
thyristor 1. A pnpn-type bistable semiconductor length of time. Also see STANDARD TIME, TIME
device having anode, cathode, and gate terminals BASE, TIME ZONE, and ZERO TIME.
that is used as an electronic switch. 2. The time base Time as the independent variable in a
generic term for all thyratronlike solid-state de- physical relation or function. It appears in ex-
vices, such as the silicon-controlled rectifier. pressions such as pulses per second, feet per
Thyrite Ceramic silicon carbide, a nonlinear resis- minute, watts per hour, etc.
tance material, or a resistor made of this mate- time compressor In audio recording and repro-
rial. The resistance of Thyrite decreases sharply duction, a device that speeds up or slows down
as the applied voltage is increased. Thyrite resis- the tempo without changing the audio frequen-
tors are used in voltage regulators, equipment cies. It is used for special effects.
protectors, lightning arresters, curve changers, time constant See ELECTRICAL TIME CONSTANT
and similar devices. and MECHANICAL TIME CONSTANT.
THz Abbreviation of TERAHERTZ. time delay See DELAY, 1, 2.
Ti Symbol for TITANIUM. time-delay relay See DELAY RELAY.
tickler A (usually small) coil, through which en- time-delay spectrometry In acoustics, a method
ergy is inductively fed back from the output to the of simulating an echo-free environment within an
input of a circuit to induce oscillation. enclosure that is actually not echo-free.
tickler coil See TICKLER. time-division multiplexing Abbreviation, TDM. In
tickler-coil regeneration Positive feedback ob- data and computer communications, a time-
tained via inductive coupling between a small coil sharing technique in which several terminals use
(tickler) in the output circuit of an amplifier, and the same channel by transmitting data at regular,
a (usually larger) coil in the input circuit. Also see staggered intervals (i.e., one is active while the
TICKLER. others are idle). This gives the appearance of si-
multaneous real-time operation.
time-division-multiplex switch A switch with mul-
tiple ports”each port corresponding to a certain
+12 V time slot in a time-division-multiplex scheme. The
input and output (send and receive) ports are con-
nected by selecting the same TIME SLOT for each.
time-domain reflectometry Abbreviation, TDR.
Tickler Measuring the reflective characteristics of a de-
In vice or system by superimposing the direct and
reflected components of a step-formed test signal
on a time-calibrated oscilloscope screen.
time duration See TIME, 3.
time-duration modulation See PULSE-DURA-
tickler-coil regeneration TION MODULATION.
time factor The ratio ta/tr, where ta is analog time
(the relativistic duration of an event as simulated
tickler oscillator An oscillator circuit in which
by a computer), and tr is real time (the actual du-
positive feedback is obtained through inductive
ration of the event). Also called TIME SCALE.
coupling between an output (tickler) coil and an
time-interval mode In computer operations, oper-
input coil.
ation that allows a number of events to be
tie A bracket, clamp, clip, ring, or strip for holding
counted between two points on a waveform.
several wires tightly as a cable or bundle.
686 time modulation • tolerance

time modulation Any form of modulation in which tin 1. Symbol, Sn. A metallic element. Atomic
the instantaneous characteristics of a signal are number, 50. Atomic weight, 118.71. Tin is widely
varied. used in electronics as a structural material, a
timeout The expiration of an allotted time period constituent of solder, and (in foil form) as the
for a given operation. plates of some fixed capacitors. 2. To prepare the
timer 1. A device for automatically controlling the tip of a soldering gun or iron, or the stripped end
duration of an operation. See ELECTRONIC of a wire or cable, by applying a coat of solder.
TIMER. 2. A device for measuring the duration of tin-oxide resistor See METAL-OXIDE RESISTOR.
an operation. tinsel Metal film strips interwoven with fabric
time sharing In computer operations, a method threads to provide a flexible cord, particularly for
for interlaced (i.e., nearly simultaneous) use of a headphones.
machine or facility by two or more persons or tint control In a color-television receiver, the con-
agencies. As the cost of computers diminishes, so trol for changing color hue.
does the need for time sharing. Also see TIME- tip jack The mating connector for a tip plug.
DIVISION MULTIPLEXING. tip plug 1. A prod terminating in a phone tip. 2. A
time-sharing dynamic allocator In computer stor- plug-type connector terminating in a phone tip.
age, a program that allocates memory areas and
peripherals to programs being entered into a time-

sharing system; it also controls program execution.
timeshift 1. To receive a message at a significantly

later time than when it was sent. 2. To use a
videocassette or videodisc recorder to view a tele-
vision program at a later time than when it was
time-shifting communications Any form of com-
munications in which the recipient reads or views
the message(s) at a significantly later time than
the message is sent from the source. A common
example is electronic mail (e-mail) using online

computer networks.
time signals Special radio transmissions made tip plug, 2
under the auspices of the National Bureau of
Standards, for indicating Coordinated Universal
Time (UTC). titanium Symbol, Ti. A metallic element. Atomic
time slot A specifically defined time interval in a number, 22. Atomic weight, 47.88. Titanium en-
data signal. It is of importance primarily in digital ters into some dielectric compounds (e.g., tita-
communications, where a given time interval can nium dioxide).
be high or low or at some discrete value. titanium dioxide Formula, TiO2. A ceramic dielec-
time-space-time switch A large switch consisting tric material. Dielectric constant, 90 to 170.
of a space block between two time blocks. Dielectric strength, 100 to 210 V/mil.
time zone One of the 24 zones into which the global T junction See TEE JUNCTION.
map is divided for the purpose of standardizing Tl Symbol for THALLIUM.
time. Within these zones, mean solar time is deter-
mined in terms of distance east or west of the zero LOGIC. (Also, TTL.)
meridian at Greenwich (near London, England). TLA Abbreviation of TABLE LOOK-AT.
Each zone is equal to 15 degrees of longitude, or TLC Abbreviation of thin-layer chromatography.
1 hour. Four zones fall within the continental TLU Abbreviation of TABLE LOOK-UP.
United States: Eastern Standard Time (zone of the TM 1. Abbreviation of TRANSVERSE MAGNETIC.
75th meridian), Central Standard Time (zone of 2. Abbreviation of technical manual.
the 90th meridian), Mountain Standard Time Tm Symbol for THULIUM.
(zone of the 105th meridian), and Pacific Standard TM mode See TRANSVERSE MAGNETIC MODE.
Time (zone of the 120th meridian). Also see TM wave See TRANSVERSE MAGNETIC MODE.
timing extraction The retrieval of a timing signal TNS Abbreviation of TRANSCUTANEOUS NERVE
from incoming data. STIMULATOR.
timing pin current Measured in microamperes. toggle A bistable device.
The current that generates a timing waveform in toggle switch A switch having a mechanism that
an integrated-circuit voltage regulator. snaps into the on or off position at the opposite
timing signal A repeating signal sent along with extremes to which a lever is moved.
data to control the synchronization of transmitter tolerance The amount by which error is allowed in
and receiver. a value, rating, dimension, etc. It is usually

tolerance • torque amplifier

tone modulation 1. The transmission of Morse,
Baudot, or ASCII signals by audio-frequency
modulation of a radio-frequency carrier. 2. Any
rapid variation of the amplitude or frequency of
an audio tone.
top cap A small metal cap on top of some electron
tubes, serving as a direct, low-capacitance con-
nection to one of the internal elements”usually
the control grid, but sometimes the plate.
top loading A method of feeding a vertical antenna
at or near the top.

Feed line

toggle switch

expressed as a percent of nominal value, plus Radiating
and minus so many units of measurement (or
parts per million).
toll call In a telephone system, a call that is
charged on a per-minute or per-second basis.
ton Abbreviation, T, t, or tn. A unit of avoirdupois
weight; in the United States, it is usually taken to
mean short ton, a unit equal to 907.20 kilograms Earth
(2000 lb). Compare METRIC TON.
top loading
tone 1. The pitch (frequency) and timbre (relative
harmonic content) of a sound other than noise.
2. A sound consisting of a periodic waveform
topology 1. A branch of mathematics concerned
having constant frequency; also called note.
with the properties of surfaces and spaces. 2. The
tone arm See PICKUP ARM.
details of layout of an integrated circuit. 3. The
tone burst A test signal consisting of a single-
characteristics of a surface.
frequency sine wave sustained for a brief period
of time, usually having a rectangular envelope
toroidal coil A coil wound on a form that is shaped
(rapid rise and decay).
like a donut. The form is made of powdered-iron
tone-burst entry In repeater systems, a technique
or ferrite. Toroidal coils have certain advantages
whereby a short tone signal is used at the start of
over solenoidal coils: greater inductance for a
a transmission to trigger a particular repeater so
given physical size, better isolation properties,
that all repeaters in the system will not go into
and higher Q factor. A disadvantage is that an air
operation simultaneously.
core is not practical.
tone-burst generator An oscillator and associated
circuitry for producing a tone burst.
tone control An adjustable device or circuit for mod-
ifying the frequency response of an amplifier (i.e.,
for emphasizing bass, treble, or midrange pitches).
tone dialing A method of telephone dialing that
uses standard tone pairs actuated via a keypad
with 12 keys representing digits 0 through 9 and
symbols # and *. Some keypads have four addi-
tional keys: A, B, C, and D.
tone generator An oscillator for producing simple
toroidal coil
audio-frequency signals for communications,
control, or testing.
torque 1. The force that tends to produce a rotat-
tone keying In wire and radio telegraphy, the rep-
ing motion. 2. Rotation of the plane of polariza-
resentation of code characters by audio-
tion of light by some crystals.
frequency tones. Also see MODULATED
torque amplifier A device having rotating input
and output shafts and that delivers greater
tone localizer A localizer that provides lateral
torque at the output shaft than that required to
guidance for an aircraft by comparing the ampli-
turn the input shaft.
tudes of two modulating frequencies.
688 torque sensitivity • tracking

torque sensitivity Symbol, KT. For a torque mo- touchplate relay A capacitance relay in which the
tor, torque output per ampere of input current. pickup element is a small, metal plate that actu-
torr A unit of pressure equal to the pressure re- ates the relay when it is touched.
quired to support a column of mercury 1 millime- tough dog A malfunctioning circuit that seemingly
ter high at 0°C and standard gravity; 1 torr = defies all attempts to diagnose and correct its
133.322 Pa (1333.2 microbars). trouble. Also see DOG.
torsion The effect on an object by torque applied to tourmaline crystal A piezoelectric and pyroelec-
one end while the other is being held fast or tric crystal; a transparent plate of tourmaline has
torqued in the opposite direction. the ability to polarize light passing through it.
torsion delay line A delay line in which the delay Also see POLARIZATION, 3; POLARIZED LIGHT;
is manifested in a material that is torqued by me- and POLARIZER.
chanical vibrations. tower 1. A usually tall and self-supporting open-
torsion waves Waves that travel by means of work structure used to support an antenna, and
torque, instead of displacement or compression. usually having three or four sides. 2. A metal
The velocity of propagation depends on the mod- structure, as defined in 1, used as a vertical an-
ulus of rigidity and the density of the propagating tenna.
medium. Townsend discharge In a glow-discharge tube, the
tot 1. Abbreviation of total. 2. To derive a sum or discharge that begins after the applied voltage
total. reaches a given level. It is a low-current, non-self-
total breakaway torque For a torque motor, the sustaining discharge. Compare ABNORMAL
sum of magnetic retarding torque and brush- GLOW and NORMAL GLOW DISCHARGE.
commutator friction. touch screen A special cathode-ray tube (CRT) or
total harmonic distortion Abbreviation, THD. The video display unit that allows input of data via
distortion caused by the combined action of all physical contact with the screen surface. Items
the harmonics present in a complex waveform. are selected by simply touching the appropriate
An important specification in high-fidelity audio spot (“button” or icon) on the screen.
amplifiers. TP Abbreviation of TRANSACTION PROCESSING.
total distortion See TOTAL HARMONIC DISTOR- T pad See TEE PAD.
TION. TR Abbreviation of transmit-receive.
total internal reflection 1. The reflection of visible tr 1. Symbol for RECOVERY TIME. 2. Symbol for
light from a boundary between two substances RISE TIME.
having different indices of refraction. When the trace 1. A tiny or insignificant quantity. 2. The
angle of incidence, relative to the tangent to the movement of the electron beam across the face of
boundary, is smaller than a certain value, as light a cathode-ray tube. 3. A routine used for testing
travels through the more dense medium total re- of, or for locating a fault in, a circuit or computer
flection occurs at the boundary. 2. Reflection of program. 4. The process of implementing such a
electromagnetic waves from an ionized layer in routine.
the atmosphere. This occurs at angles smaller trace element See MICROELEMENT.
than a certain angle, relative to the tangent of the tracer A suitable substance or object introduced
plane of the ionizing layer. In some cases, total in- into the human body and whose progress
ternal reflection does not occur. Actually, most through the body can be followed (or its state
ionospheric reflection is really refraction; the monitored) by means of electronic equipment.
electromagnetic waves are bent by the ionized Tracers are sometimes used also in nonbiological
layer rather than reflected. systems, such as pipelines.
total reflection Full return of a ray by a reflector, track 1. A discrete information band on a magnetic
none of the energy being transmitted by or ab- disk or tape. 2. To follow, as by a stylus, a phono
sorbed in the reflecting material. disc groove. 3. To follow, as by radar, a target.
trackability An expression of the accuracy with
Lower index which a phonograph stylus follows the irregulari-
of refraction ties in a disc.
trackball A device for guiding the cursor or pointer
in a computer. It is often used in laptop (note-
book) computers. It resembles a ball bearing; the
operator moves the cursor or pointer by pushing
Higher index
of refraction on the bearing with a finger.
track-drive locomotion A method of robotic loco-
motion using two or more wheels that drive a belt
(track). It uses the same principle as a military
Light or
radio beam
tracking Following in step, as when ganged cir-
cuits resonate at the same frequency (or some
total internal reflection
tracking • transfer function

frequency difference) at all settings, or when a mitting and receiving information to and from a
missile closely follows its guiding signal. channel.
tracking force See VERTICAL STYLUS FORCE. transcendental functions Nonalgebraic func-
track label On a magnetic storage medium, a tions. These include logarithmic functions, expo-
record that identifies a track. nential functions, trigonometric functions, and
tracking mode In tracking supplies, the usual inverse trigonometric functions.
manner of operation in which the output of each transconductance 1. Symbol, gm. Unit, mi-
of the separate supplies automatically follows cromho. In an electron tube, the extent to which
that of the one being adjusted. Compare INDE- plate current (IP) changes in response to a change
PENDENT MODE. in grid voltage (EG); gm = dIP/dEG. 2. Symbol,
tracking supplies Adjustable power supplies, gfs. Unit, micromho. In a field-effect transistor,
packaged two or more to the unit, in which the the extent to which drain current (ID) changes in
output of each will automatically follow adjust- response to a change in gate-to-source voltage
ment made to one of them. (VGS); gfs = dID/dVGS.
track pitch The distance between tracks (see transconductance amplifier An amplifier in
TRACK, 2). which the output current is a linear function of
traffic 1. Collectively, messages handled by a com- the input voltage.
munications station. 2. Collectively, data and in- transcribe 1. To record material, such as a radio
structions handled by a computer system in program, for future transmission. 2. In computer
continual use. operations, the intermedia transfer of data, as
trailer label At the end of a magnetic-tape or from tape to disk.
floppy-disk file, a record signaling the end of the transcriber A device used for intermedia data
file and often giving such information as the transfer (e.g., one that can move the data on mag-
number of records in the file. netic tape to magnetic or optical disc).
trailer record At the end of a group of computer transcription A recording of material, such as a
records, a record containing information relevant record or tape of a radio program, for later use in
to the group™s processing. a transmitter. See ELECTRICAL TRANSCRIP-
trailing edge The falling edge of a pulse. Compare TION.
LEADING EDGE. transcutaneous nerve stimulator Abbreviation,
trans Abbreviation of TRANSVERSE. TNS. An electronic device for the temporary relief
transaction The exchange of activity that occurs of pain. In its use, electrodes taped to the skin
between a computer, via a terminal, and the user, over the painful area are connected to a portable
including any processing required (e.g., that in- generator of suitable pulse energy.
volved in adding records to, or deleting them transducer A device that converts one quantity
from, a file). into another quantity, specifically when one of
transaction file In data processing, a group of the quantities is electrical. Thus, a loudspeaker
records used to update a master file. converts electrical impulses into sound, a micro-
transaction processing In computer operations, phone converts sound into electrical impulses, a
the use of a central processor for handling, mod- photocell converts light into electricity, a thermo-
ifying, or otherwise acting on information by couple converts heat into electricity, etc.
transactions. transducer amplifier An amplifier used expressly
transaction tape Magnetic tape on which a trans- to boost the output of a transducer.
action file has been recorded. transducer efficiency For a transducer, the ratio
transadmittance For an active device, the ratio of the output power to the input power.
dI2/dE1, where I2 is the alternating-current (ac) transductor See MAGNETIC AMPLIFIER.
component of the current in a second electrode transfer 1. To move a signal from one point to an-
(such as the drain), and E1 is the ac component other”especially through a modifying circuit or
of voltage on a first electrode (such as the gate), device. 2. To transmit information or data from
with constant direct-current operating voltages. one point or device to another, inside or outside a
transceiver 1. A combination transmitter and re- system.
ceiver, housed in a single enclosure, with fre- transfer characteristic A figure or plot expressing
quency control and some ancillary stages the output-input signal relationship in a circuit
common to both units. This design is economical or device. Also see TRANSFER, 1.
because it eliminates redundancy. Such a system transfer efficiency In a charge-coupled device, the
is more easily tuned than a separate transmitter proportion of charge that is transferred under
and receiver if the operating frequency must be given conditions.
changed often, but it can be difficult to carry out transfer function 1. See TRANSFER CHARAC-
split-frequency or split-band communication on TERISTIC. 2. An expression that mathemati-
two frequencies that differ greatly. Compare cally shows how two entities or events occurring
TRANSMITTER“RECEIVER. 2. In computer prac- in different places or at different times are
tice, a read/write data terminal capable of trans- related.
690 transfer rate • transient response

transfer rate The speed at which data can be transformer input voltage See PRIMARY VOLT-
moved between a computer™s internal memory AGE.
and a peripheral. transformer iron See SILICON STEEL.
transferred charge In a circuit containing a capac- transformer loss The expression (in decibels) 10
itor, the net electric charge that moves around log10 (P1/P2), where P1 is the calculated power
the external circuit from one plate of the capaci- that a given transformer should deliver to a par-
tor to the other. ticular load impedance, and P2 is the actual
transform 1. See LAPLACE TRANSFORM. 2. To power delivered.
change the voltage or nature of an electrical pa- transformer oil A petroleum product in which
rameter (e.g., high to low voltage and alternating high-voltage, high-current transformers are
to direct current). 3. To change the form, but not sometimes immersed. The oil protects the wind-
the content, of data. ings from environmental damage.
transformation constant See DISINTEGRATION transformer output current See SECONDARY
transformer 1. A device using electromagnetic in- transformer output voltage See SECONDARY
duction to transfer electrical energy from one cir- VOLTAGE.
cuit to another (i.e., without direct connection transformer-type voltage regulator See VOLT-
between them). In its simplest form, a trans- AGE-REGULATING TRANSFORMER.
former consists of separate primary and sec- transformer utilization factor See UTILITY FAC-
ondary coils wound on a common core of TOR.
ferromagnetic material, such as iron. When an al- transient 1. A sudden, high-voltage spike in an al-
ternating current flows through the primary coil, ternating-current system, caused by arcing or
the resulting magnetic flux in the core induces an lightning. 2. A spurious signal in a hardcopy-
alternating voltage across the secondary coil; the receiving system. 3. Any short pulse attributable
induced voltage can cause a current to flow in an to external causes. 4. Existing for a short period
external circuit. Also see AIR-CORE TRANS- of time, or intermittently for short periods of time.
TIO. 2. A section of radio-frequency (RF) trans-
mission line used to match impedances. Also see

Iron core

Primary Secondary

Symbol Pictorial
transformer, 1

transformer-coupled amplifier An amplifier using
coupling transformers between its stages or at its
input and output points. Compare RESISTANCE-
transformer coupling The inductive coupling
of circuits through a transformer. Also see
transformer equivalent circuit An equivalent cir- transient absorber See SURGE ARRESTER.
cuit depicting the various parameters of a trans- transient arrester See SURGE ARRESTER.
former (such as primary and secondary transient-based amplifier See CRYSTAL AMPLI-
resistances, primary and secondary reactances, FIER, 2.
core losses, etc.) and their relationship to each transient current A momentary pulse of current.
other. Also see TRANSIENT.
transformer feedback Inductively coupled feed- transient response The response of a circuit to a
back (positive or negative) through a transformer. transient, as opposed to its steady-state re-
transformer input current See PRIMARY CUR- sponse, usually evaluated in terms of its ability to
RENT. reproduce a square wave.
transient suppressor • transistor VOM

transient suppressor See SURGE ARRESTOR. transistor current meter An ammeter, milliam-
transient voltage A momentary pulse of voltage. meter, or microammeter circuit containing an
Also see TRANSIENT. amplifier using only transistors. Also see ELEC-
transient voltmeter An instrument that indicates TRONIC CURRENT METER.
the voltage of momentary signals. Usually, a transistorized voltmeter See TRANSISTOR
peak-reading meter in the instrument displays VOLTMETER.
the highest positive or negative value the tran- transistorized voltohmmeter An electronic volt-
sient attains (sometimes holding the deflection meter-ohmmeter combination using a transistor-
for reading later) and can respond to pulses of ized circuit similar to that of a vacuum-tube
1 microsecond in duration. voltohmmeter.
transistor An active (commonly three-terminal) transistor keyer A power transistor acting as a
semiconductor device capable of amplification, keying device.
oscillation, and switching action. The name is a transistor oscillator An oscillator using only tran-
contraction of transfer resistor. Also see ALLOY- sistors as the active components. Also called tran-
BIPOLAR TRANSISTOR, DIFFUSED-BASE TRAN- transistor power supply A high-current, well-
SISTOR, DIFFUSED EMITTER-AND-BASE TRAN- filtered, direct-current power supply for operating
DIFFUSED MESA TRANSISTOR, DIFFUSED PLA- transistor radio Any small, portable, battery-pow-
NAR TRANSISTOR, DIFFUSED TRANSISTOR, ered radio receiver whose active components are
DIFFUSION TRANSISTOR, DOUBLE-BASE transistors and/or other semiconductor devices.
TOR, GROWN-DIFFUSED TRANSISTOR, transistor tester An instrument for checking the
GROWN-JUNCTION TRANSISTOR, JUNC- condition of transistors (i.e., whether good or


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