POTENTIAL ENERGYEnergy caused by the position of one body with respect to another body or to
the relative parts of the same body .
POTENTIOMETERA 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  .
POWERThe rate of doing work or the rate of expending energy. The unit of electrical power is the watt
POWER AMPLIFIERAn amplifier in which the output-signal power is greater than the input-signal
POWER-AMPLIFIER (CHAIN) TRANSMITTERTransmitter that uses a series of power amplifiers to
create a high level of power .
POWER FACTORThe 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  .
POWER GAINIn an antenna, the ratio of its radiated power to that of a reference  .
POWER LOSS(1) The electrical power, supplied to a circuit, that does no work and is usually dissipated
as heat  . (2) The heat loss in a conductor as current flows through it .
POWER PENTODEA 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 .
POWER RATIOSee POWER GAIN .
POWER STANDING-WAVE RATIO (PSWR)The ratio of the square of the maximum and minimum
voltages of a transmission line .
POWER SUPPLYA unit that supplies electrical power to another unit. It changes ac to dc and maintains
a constant voltage output within limits  .
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 .
PRECESSIONThe 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 .
PRECESSION VECTORIn 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 .
PRESTANDARD NAVY SYNCHROSSynchros that are designed to meet Navy, rather than
servicewide, specifications .
PREVENTIVE MAINTENANCEVisual, mechanical, electrical, and electronic checks that are made to
determine whether or not equipment is functioning properly .