Neets Master Glossary

1-56 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].