PHASE ANGLE-- The number of electrical degrees of
ONE-LINE SCHEMATIC-- A drawing of a system
using only one line to show the tie-in of various
lead or lag between the voltage and current
components; for example, the three conductors
waveforms in an ac circuit.
needed to transmit three-phase power are
PHASE DIFFERENCE-- The time in electrical
represented by a single line.
degrees by which wave leads or lag another.
ONE-LINE SKETCH-- A drawing using one line to
PHOTOELECTRIC VOLTAGE-- A voltage
outline the general relationship of various
produced by light.
components to each other.
PICO-- A prefix adopted by the National Bureau of
OPEN-CIRCUIT POTENTIAL-- The potential of an
Standards meaning 10-12.
electrode measured with respect to a reference
PIEZOELECTRIC EFFECT-- The effect of
electrode when essentially no current flows to or
producing a voltage by placing a stress, either by
from the electrode.
compression, expansion, or twisting, on a crystal
OPEN LOOP-- A system having no feedback.
and, conversely, producing a stress in a crystal by
OPERATING CHARACTERISTICS-- A combina-
applying a voltage to it.
tion of a parameter and its set point.
PILOT MOTOR-- The small dc motor that drives the
PARALLAX-- The error in meter readings that results
input shaft of an actuator.
when you look at a meter from some position other
POLARITY-- (1) The condition in an electrical circuit
than directly in line with the pointer and the meter
by which the direction of the flow of current can be
face. A mirror mounted on the meter face aids in
determined. Usually applied to batteries and other
eliminating parallax error.
direct voltage sources. (2) Two opposite charges,
PARAMETER-- A variable, such as temperature,
one positive and one negative. (3) A quality of
pressure, flow rate, voltage, current, or frequency
having two opposite magnetic poles, one north and
that may be indicated, monitored, checked, or
the other south.
sensed in any way during operation or testing.
PARALLEL CIRCUIT-- Two or more electrical
ing the anode of a cell that increases the internal
devices connected to the same pair of terminals so
resistance of the cell.
separate currents flow through each; electrons have
POTENTIAL ENERGY-- Energy due to the position
more than one path to travel from the negative to
of one body with respect to another body or to the
the positive terminal.
relative parts of the same body.
PERIPHERAL-- Existing on or near the boundary of
POTENTIOMETER-- A three-terminal resistor with
a surface or area.
one or more sliding contacts, which functions as an
PERMEABILITY-- The measure of the ability of a
adjustable voltage divider.
material to act as a path for magnetic lines of force.
POWER-- The rate of doing work or the rate of
pH-- A logarithmic measure of the acidity or alkalinity
expending energy. The unit of electrical power is
of a solution. A value of 7 is neutral; low numbers
t h e watt.
are acid (1-6); large numbers are alkaline (8- 14).
Each unit represents a tenfold change in
POWER SUPPLY-- The module that converts the
115-volt, 60-hertz incoming power to ac or dc
power at a more suitable voltage level.
PHASE-- The angular relationship between two
alternating currents or voltages when the voltage or
PRIMARY WINDING-- The winding of a trans-
current is plotted as a function of time. When the
former connected to the electrical source.
two are in phase, the angle is zero, and both reach
PRINTED CIRCUIT BOARD-- Devices usually
their peak simultaneously. When out of phase, one
plugged into receptacles that are mounted in
will lead or lag the other; at the instant when one is
at its peak, the other will not be at peak value and
PRIORITY-- The order established by the relative
(depending on the phase angle) may differ in
polarity as well as magnitude.
importance of the function.