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POTENTIAL ENERGY—Energy caused by the position of one body with respect to another body or to
the relative parts of the same body [1].
POTENTIOMETER—A variable resistor, used as a position sensor in servosystems, having a terminal
connected to each end of a resistive element and a third terminal connected to a wiper contact. The
output is a voltage that is variable depending upon the position of the wiper contact. The potentiometer
is commonly referred to as a variable voltage divider. It, in effect, converts mechanical information into
an electrical signal [1] [15].
POWER—The rate of doing work or the rate of expending energy. The unit of electrical power is the watt
[1].
POWER AMPLIFIER—An amplifier in which the output-signal power is greater than the input-signal
power [8].
POWER-AMPLIFIER (CHAIN) TRANSMITTER—Transmitter that uses a series of power amplifiers to
create a high level of power [18].
POWER FACTOR—The ratio of the actual power of an alternating or pulsating current, as measured by a
wattmeter, to the apparent power, as indicated by ammeter and voltmeter readings. The power factor of
an inductor, capacitor, or insulator is an expression of their losses [2] [16].
POWER GAIN—In an antenna, the ratio of its radiated power to that of a reference [11] [18].
POWER LOSS—(1) The electrical power, supplied to a circuit, that does no work and is usually dissipated
as heat [2] [4]. (2) The heat loss in a conductor as current flows through it [10].
POWER PENTODE—A special purpose tube used to provide high-current gain or power amplification.
Each grid wire is directly in line with the one before and after it, a fact which allows more electrons to
reach the plate [6].
POWER RATIO—See POWER GAIN [11].
POWER STANDING-WAVE RATIO (PSWR)—The ratio of the square of the maximum and minimum
voltages of a transmission line [10].
POWER SUPPLY—A unit that supplies electrical power to another unit. It changes ac to dc and maintains
a constant voltage output within limits [6] [7].
PREAMPLIFIER (PREAMP)—An amplifier that raises the output of a low-level source for further
processing without appreciable degradation of the signal-to-noise ratio [18].
PRECESSION—The rotation of the spin axis of a gyro in response to an applied force. The direction of
precession is always perpendicular to the direction of applied force [15].
PRECESSION VECTOR—In a gyro, a vector representing the angular change of the spin axis when
torque is applied. The precession vector represents the axis about which precession occurs [15].
PRESTANDARD NAVY SYNCHROS—Synchros that are designed to meet Navy, rather than
servicewide, specifications [15].
PREVENTIVE MAINTENANCE—Visual, mechanical, electrical, and electronic checks that are made to
determine whether or not equipment is functioning properly [16].
