18WuD2x

556 private branch exchange • program
premises but having trunk-line connection to the
central office. Compare PRIVATE AUTOMATIC
EXCHANGE.
private line 1. A communication circuit in which
the use is limited, by electronic means, to certain
subscribers. 2. A subaudible-tone system used to
restrict access to a communications system. The
tone frequency is predetermined. For access to
the system, a transmitted signal must contain
the tone of the appropriate subaudible frequency,
in addition to the voice or other information.
probability 1. The branch of mathematics concerned
with the likelihood of an event’s occurrence.
It has many applications in quality control
and physics. 2. The mathematical likelihood that
an event will occur.
probable error Abbreviation, PE. The value of error
above and below which all other error values are
equally likely to occur.
probe 1. A usually slender pencil-like implement
with a pointed metal tip and a flexible, insulated
lead. It is used to contact live points in a circuit
under test (e.g., voltmeter probe and oscilloscope
probe). 2. A device used to sample a radiofrequency
voltage or current at a desired point
(e.g., WAVEGUIDE PROBE). 3. A pickup device
shaped like a probe for insertion into close
quarters (e.g., PROBE THERMISTOR).
probe meter See PROBE-TYPE VOLTMETER.
probe thermistor A thermistor of slender construction
for insertion into an area in which the
temperature is to be monitored or controlled.
probe thermocouple A thermocouple in the form
of a slender probe for insertion into close quarters
for temperature sensing or temperature control.
probe tip See PROD.
probe-type voltmeter A voltmeter installed in a
long probe or wand. Kilovoltmeters are sometimes
constructed in this fashion, with a long
multiplier resistor housed in the probe.
probing A process for locating, or determining the
existence of, external artificial interference (e.g.,
power-line noise) in a radio communications circuit.
problem-oriented language Any high-level computer
programming language that allows the user
to write programs as statements in terms applicable
to the field of interest (e.g., COBOL’s statements
in English for problems relating to
business).
problem reduction In artificial intelligence, a process
in which problems are made easier by breaking
them down into smaller logical parts.
process control The control of a process, such as
one of manufacturing, by means of computers.
processor 1. A circuit or device used to modify
a signal in response to certain requirements
(e.g., clipper and waveshaper). 2. See DATA-
PROCESSING MACHINE. 3. See CENTRAL PRO-
CESSING UNIT. 4. See MICROPROCESSOR.
prod The metal tip of a probe (see PROBE, 1).
product 1. The result of mixing or heterodyning of
two or more signals. 2. The result of modulating
one signal with another. 3. The result of combining
or processing a signal or signals in a specified
manner. 4. The saleable end result of a manufacturing
process. 5. The result obtained when two
or more quantities are multiplied by each other.
product detector A detector circuit whose output
is the product of two signals applied simultaneously
to the circuit. In a single-sideband receiver,
for example, one of the signals is the incoming
signal; the other, the signal from the local beatfrequency
oscillator.
IF
Local osc.
+12 V
product detector
Out
production lot A manufactured set of components,
circuits, or systems, intended for sale. All
of the units in the lot are identical. The finished
product is suitable (presumably) for consumer
use.
production unit One unit in a production lot; a
finished unit, ready for use by a consumer.
product modulator A modulator whose output is
equal or proportional to the product of carrier
voltage and modulating voltage.
product of sine waves The result of multiplying
one sine wave by another with attention being
paid to the power factor. In the case of a resistive
circuit, where the power factor is equal to 1, all
voltage-current (EI) products are positive, and are
equal to the true power. A product wave has negative
half-cycles when the circuit contains reactance.
professional engineer A person licensed by a state
board of examiners to work independently as an
engineering. Also see PE and REGISTERED PRO-
FESSIONAL ENGINEER.
program 1. In computer operations, a detailed sequence
of instructions representing an algorithm