18WuD2x

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