18WuD2x

390 Kelvin absolute electrometer • keyboard keyer
between which voltage is applied. The movable
plate(s) is displaced over a distance that is proportional
to the potential, against the torque of a
return spring.
Kelvin balance An apparatus for measuring current
in terms of magnetic pull. A coil is attached
to each end of the beam of a balance, and coils
ride directly above two stationary coils. Current
flows through all coils, making one pair attractive
and the other repellent, thus unbalancing the
beam. Balance is restored by sliding a weight
whose position along a graduated scale indicates
the current strength.
Kelvin contacts Electrical contacts designed to
eliminate the effect of lead resistance on the accuracy
of measurement. Two leads run to each test
point, one lead carrying the test signal and the
other leading directly to the measuring instrument.
Kelvin double bridge A special bridge for measuring
very low resistance (0.1 ohm or less). The arrangement
of the bridge reduces the effects of
contact resistance that causes significant error
when such low resistances are connected to conventional
resistance bridges.
R x
R 1 R 2
M
R 3 R 4
R s
Kelvin double bridge
When R 1 /R 2 = R 3 /R 4 ,
R x = (R 1 /R 2 )R s
Kelvin replenisher A static generator consisting of
two pairs of concentric, rotating semicircular
conductors connected to brushes. The machine
can be regarded as a rotating electric doubler.
Kelvin scale See ABSOLUTE SCALE.
Kelvin temperature scale See ABSOLUTE SCALE.
Kelvin voltmeter An electrostatic voltmeter in
which an assembly of figure-8-shaped metal
plates rotates between the plates of a stationary
assembly when a voltage is applied between the
assemblies. The length of the arc of rotation is
proportional to the electrostatic attraction and,
thus, to the applied voltage.
Kendall effect Distortion in a facsimile record
caused by unwanted modulation produced by a
carrier signal.
Kennelly-Heaviside layer (A.E. Kennelly, 1861–
1939; Oliver Heaviside, 1850–1925) An early
name for ionized regions in the upper atmosphere.
These regions reflect and refract radio
waves at certain frequencies. There are several
layers at various altitudes. Also see IONO-
SPHERE and IONOSPHERIC LAYERS.
keraunograph A meteorological instrument for detecting
distant electrical storms. In its simplest
form, it consists of a galvanometer connected in
series with an antenna and ground.
keraunophone A radio-receiving KERAUNO-
GRAPH.
kernel Inside an electrical conductor, a line along
which the magnetic field strength is zero. Generally,
this line is near the center of the conductor.
Kerr cell A nitrobenzene-filled cell that makes use
of the KERR ELECTRO-OPTICAL EFFECT. It can
function as an electric light shutter or control.
Kerr electro-optical effect The tendency of certain
dielectric materials to become doublerefracting
in an electric field.
Kerr magneto-optical effect The tendency of
glass and some other solids and liquids to become
double-refracting in a magnetic field.
Kerst induction accelerator See BETATRON.
keV Abbreviation of KILOELECTRONVOLT.
Kew magnetometer A special magnetometer used
to measure the intensity of the earth’s magnetic
field, and also the magnetic declination at a given
point on the earth’s surface. The device is designed
for very high accuracy, using magnifying
lenses.
key
1. See DECRYPTION KEY. 2. A projection or
pin that guides the insertion of a plug-in component
into a holder or socket. 3. A digit or digits
used to locate or identify a computer record (but
not necessarily part of the record). 4. A specialized
hand-operated switch, used to make and
break a circuit repetitively to form the dot and
dash signals of Morse code telegraphy. Primarily
of historical interest. Used by some amateur radio
operators for hobby purposes. 5. Slang for
principal or main.
keyboard
An array of lettered or numbered, lowtorque
push buttons, used to enter information
into a computer, telegraph, teletypewriter, or automatic
control system.
keyboard computer A digital computer in which
the input device is an electrical keyboard of the
typewriter or calculator type.
keyboard entry The operation of a keyboard to enter
information into a computer for processing.
keyboard keyer A device for automatically sending
Morse code using a typewriter-like keyboard,
rather than a paddle or straight key. Each key on
the keyboard, when pressed, produces the complete
character and a space following it. Most keyboard
keyers have buffers to allow typing well
ahead of the code being sent, with insertion of all
the correct spaces. The speed range is usually