PRIMARY WINDING --The winding of a
PICKOFF --In gyros, a sensing device that
transformer connected to the electrical source.
measures the angle of the spin axis with respect
to its reference and provides an error signal that
PRIME MOVER --The source of the turning
indicates the direction and (in most cases) the
force applied to the rotor of a generator, This may
magnitude of the displacement,
be an electric motor, a gasoline engine, a steam
POLARITY --The character of having mag-
turbine, and so forth.
netic poles, or electric charges.
PROTON --A positively charged particle in
POLYPHASE --A circuit that uses more than
the nucleus of an atom.
one phase of alternating current.
RADAR --An acronym for radio detecting
POSITIVE CHARGE --The electrical charge
and ranging.
carried by a body that has become deficient in
electrons.
RADAR ALTIMETER --Airborne radar that
measures the distance of the aircraft above the
POSITIVE FEEDBACK --Feedback in which
ground.
the feedback signal is in phase with the input
signal.
RADIAN --In a circle, the angle included
within an arc equal to the radius of the circle. A
POSITIVE TEMPERATURE COEFFI-
complete circle contains 2 radians. One radian
CIENT --The characteristic of a conductor in
equals 57.3 degrees, and 1 degree equals 0.01745
which the resistance increases as temperature
radian.
increases.
RATE GYRO --A gyro with one degree of
POTENTIAL --The amount of charge held by
freedom that has an elastic restraint, with or
a body as compared to another point or body.
without a damper, and whose output will be
Usually measured in volts.
proportional to the rate of the applied torque.
POTENTIOMETER --A variable voltage
RATIO --The value obtained by dividing one
divider; a resistor that has a variable contact arm
number by another, indicating their relative
so that any portion of the potential applied
between its ends may be selected.
REACTANCE --The opposition offered to
POWER --The rate of doing work or the rate
the flow of an alternating current by the
of expending energy. The unit of electrical power
inductance, capacitance, or both, in any circuit.
is the watt.
RECTIFIERS --Devices used to change
POWER FACTOR --The ratio of the actual
alternating current to unidirectional current.
power of an alternating or pulsating current, as
These may be vacuum tubes, semiconductors,
measured by a wattmeter, to the apparent power,
such as germanium and silicon, and dry-disk
rectifiers, such as selenium and copper oxide.
The power factor of an inductor, capacitor, or
insulator is an expression of their losses.
RELUCTANCE --A measure of the opposi-
tion that a material offers to magnetic lines of
POWER SUPPLY --A unit that supplies
force.
electrical power to another unit. It changes ac to
dc and maintains a constant voltage output within
RESISTANCE --The opposition to the flow
limits.
of current caused by the nature and physical
PRECESSION --The reaction of a gyro to an
dimensions of a conductor.
RETENTIVITY --The measure of the ability
at right angles to the direction of the applied
of a material to hold its magnetism.
torque in such a manner that the direction of spin
of the gyro rotor will be in the same direction as
RHEOSTAT --A variable resistor.
the applied torque.
AI-8