"A"
"B"
"C",
"D",
"E",
"F",
"G",
"H",
"I",
"J",
"K",
"L",
"M",
"N",
"O",
"P"
"Q",
"R",
"S",
"T",
"U",
"V",
"W",
"X",
"Y",
"Z"
Previous set of "P" definitions and terms.
PERCENT OF MODULATION. The degree of modulation defined in terms of the maximum permissible
amount of modulation.
PERIGEE. The point in the orbit of a satellite closest to the earth [center].
PERIOD TIME. The time required to complete one cycle of a waveform.
PERIODIC WAVE. A waveform that undergoes a pattern of changes, returns to its original pattern, and
then repeats the same pattern of changes. Examples are square waves, rectangular waves, and sawtooth
waves.
PERIPHERAL DEVICE. In a data processing system, any equipment, distinct from the central processing
unit, that may provide the system with additional capabilities.
PERISCOPE. An optical instrument, housed in a long tube; used to translate the observer's line of
sight in a vertical direction.
PERMANENT MAGNET SPEAKER. A speaker with a permanent magnet mounted on soft iron pole
pieces. [Speaker Manufacturers]
PERMANENT MAGNET MOTOR. A PM motor uses a permanent magnet instead of armature windings. The permanent magnets are mounted [embedded] on the rotor. Permanent Magnet [PM] motors are normally small and produce little horsepower. Manufacturers
PERMEABILITY. The measure of the ability of a material to act as a path for magnetic lines of force.
PERSISTENCE. The length of time a phosphor dot glows on a CRT before disappearing.
PHASE. The angular relationship between two alternating currents or voltages when the voltage or current
is plotted as a function of time. When the two are in phase, the angle is zero; both reach their peak
simultaneously. When out of phase, one will lead or lag the other; that is, at the instant when one is at
its peak, the other will not be at peak value and (depending on the phase angle) may differ in polarity as
well as magnitude.
PHASE ANGLE. The number of electrical degrees of lead or lag between the voltage and current
waveforms in an ac circuit.
PHASE-LOCKED LOOP. An electronic circuit that
controls an oscillator so that it maintains a constant
phase angle relative to a reference signal. (PLL).
PHASE MODULATION (pm). Angle modulation in which the phase of the carrier is controlled by the
modulating waveform. The amplitude of the modulating wave determines the amount of phase shift,
and the frequency of the modulation determines how often the phase shifts.
PHASE SHIFTER. A device used to change the phase relationship between two ac signals. Manufacturers of RF Phase Shifters
PHASE-SHIFT KEYING. Similar to ON-OFF cw keying in AM systems and frequency-shift keying in
FM systems. Each time a mark is received, the phase is reversed. No phase reversal takes place when a
space is received.
PHASE SPLITTER. A device that provides two output signals from a single input signal. The two output
signals differ from each other in phase (usually by 180 degrees).
PHASE VOLTAGE. The greatest root mean square (effective) difference of potential
between any two legs of the circuit.
PHOSPHOR. The material used to convert the energy of electrons into visible light.
Next page of "P" Terms and definitions
