18WuD2x

peripheral equipment • persistor 523
peripheral equipment See PERIPHERAL, 1, 2.
peripheral interface adapter Abbreviation, PIA.
An integrated circuit that acts as an input/output
port to interface a microprocessor with peripheral
devices.
peripheral transfer In a computer system, the
transfer of a unit of data between peripherals, or
between a peripheral and the central processing
unit.
Permalloy A high-permeability alloy of iron and
nickel.
permamagnetic speaker See PERMANENT-
MAGNET SPEAKER.
permanent magnet A body that is always magnetized
(i.e., without the application of electricity
and without requiring the presence of another
magnet). Compare TEMPORARY MAGNET.
permanent-magnet erase Erasure of magnetic
tape by the field of a permanent magnet. Typically,
it is a two-step process: a magnet erases
what it can of the signal, leaving any residual
magnetization for erasure by a second magnet.
permanent-magnet focusing In a cathode-ray
tube, the focusing of the electron beam by means
of permanent magnets.
permanent-magnet generator An electromechanical
generator in which the field (either stationary
or rotating) is provided by a multipole permanent
magnet. Also called magneto.
permanent-magnet loudspeaker See PERMA-
NENT-MAGNET SPEAKER.
permanent-magnet magnetizer A magnetizer using
a permanent magnet as the magnetic-field
source.
permanent-magnet meter An indicating meter in
which a movable coil rotates between the poles of
a permanent magnet. Compare ELECTRODY-
NAMOMETER and IRON-VANE METER.
permanent-magnet motor A motor having a permanent-magnet
field.
permanent-magnet relay A polarized relay using
a permanent magnet.
permanent-magnet speaker An acoustic loudspeaker
in which the core is a strong permanent
magnet (as opposed to a direct-current electromagnet).
Also see MAGNETIC SPEAKER.
permanent storage See NONVOLATILE MEMORY.
permeability Unit, H/m. A quantitative indicator
of the extent to which a material concentrates
magnetic flux: for a given constant magnetic-field
intensity, the ratio of magnetic flux density in the
material to the magnetic flux density in air.
permeability curve See B-H CURVE.
permeability-tuned oscillator A radio-frequency
oscillator in which the frequency is varied or adjusted
by moving a ferromagnetic core in and out
of the coil of an inductance-capacitance (LC)
tuned circuit.
permeability tuning Variation of the resonant frequency
of an inductance-capacitance LC circuit
by changing the position of a magnetic core
Ferromagnetic
core
Coil
permeability tuning
Coil
form
within the inductor. This type of tuning is used in
amplifiers, oscillators, filters, and wavetraps.
permeameter An instrument for measuring permeability.
permeance Unit, Wb/A. In a magnetic circuit, the
ease with which a magnetic field is established.
The reciprocal of RELUCTANCE.
Permendur A high-permeability magnetic alloy
containing equal parts of iron and cobalt. At saturation,
the flux density of this material can be 2
teslas (20,000 gauss).
Perminvar A high-permeability magnetic alloy of
cobalt, iron, and nickel. At saturation, the flux
density of this material can approach 1.2 teslas
(12,000 gauss).
permittivity See DIELECTRIC CONSTANT.
permutation A selection of several factors or objects
from a group, in a specific ordered sequence.
For example, one of the permutations of the elements
of the set (1, 2, 3, 4, and 5) is the ordered
sequence 4, 1, 3, 5, 2.
permutation modulation A method of modulation
accomplished by varying the sequence of digital
bits.
peroxide of lead In a lead-acid cell or battery, a
compound of lead and oxygen that composes the
positive electrode or electrodes.
persistence 1. The effect whereby the retina of the
eye continues to register a projected scene for approximately
0.05 second after the scene disappears.
This allows perception of a sequence of
video frames as a continuous moving image.
2. The tendency of certain phosphors to glow after
the excitation has been removed. Thus, after the
electron beam in a cathode-ray tube has passed
over the screen, the phosphor might continue to
glow for a certain time along the path traced by
the beam. Some phosphors, such as those used
in high-speed oscilloscopes, have virtually no
persistence, whereas others have long persistence.
persistent oscillations Successive oscillations of
constant amplitude. Also called CONTINUOUS
WAVE.
persistor A device used at low temperatures for
temporary memory storage that operates between
superconducting and normal conditions.