18WuD2x

50 automatic chrominance control • automatic intercept
gain of the chrominance bandpass amplifier by
automatically adjusting its bias.
automatic circuit breaker Any device that opens
a circuit automatically when the flow of current
becomes excessive. The breaker generally resets
automatically after a specified length of time, or
after power has been temporarily removed from
the circuit.
automatic coding The use of a computer to determine
the steps for solving a problem, before the
actual program for the problem is written. This
can help software engineers develop long and/or
complex computer programs.
automatic contrast control A circuit that automatically
adjusts the gain of the video IF and RF
stages of a television (TV) receiver to preserve
good picture contrast.
automatic controller In servo systems, any of several
circuits or devices that samples a variable
signal, compares it with a standard (reference)
signal, and delivers a control or correction signal
to an actuator.
automatic crossover 1. Current limiting in a
power supply. 2. A device that switches a circuit
from one operating mode to another automatically
when conditions change in a predetermined
manner.
automatic current limiter A circuit or device for
holding the output current of a power supply to a
safe value during overload.
automatic current regulator A circuit or device
that holds the output current of a generator or
power supply to a predetermined value, in spite of
wide variations in load resistance.
automatic cutout A device that shuts down a circuit
or system when the safe limits of operation
are exceeded. A circuit breaker is an example of
such a device, as is a thermostat in a power amplifier.
automatic data processing Abbreviation, ADP.
The use of computers and accessories for calculations
and tabulations using data gathered automatically
by the system.
automatic degausser A system for automatically
demagnetizing the picture tube in a color television
(TV) receiver.
automatic dialing unit Abbreviated, ADU. A device
that automatically generates dialing digits.
Many telephone sets have these devices, some of
which can be programmed for several different
telephone numbers, including country codes and
area codes.
automatic dictionary A computer system component
that substitutes codes for words and
phrases in information retrieval systems. In language-translating
systems, it provides wordfor-word
substitutions.
automatic direction finder Abbreviated ADF. A
specialized receiver/antenna combination for automatically
showing the direction from which a
signal arrives.
automatic error correction A technique of correcting
transmission errors using error-detecting
and error-correcting codes and, usually, automatic
retransmission.
automatic exchange A transmission exchange in
which interterminal communications are accomplished
without operators.
automatic focusing A method of focusing a picture
tube automatically, in which a resistor connects
the focusing anode to the cathode; thus, no
external focusing voltage is necessary.
automatic frequency control Abbreviation, AFC.
A system that keeps a circuit automatically tuned
to a desired signal frequency. A detector (such as
a discriminator) operated from the tuned circuit
delivers a dc output voltage only when the circuit
is operating above or below the signal frequency;
otherwise, it has zero dc output. The dc output,
when present, alters the capacitance of a varactor
in the tuned circuit to retune the stage to the desired
frequency.
automatic gain control Abbreviated AGC. A system
that holds the output of a receiver or amplifier
substantially constant despite input-signal
amplitude fluctuations. A rectifier samples the ac
signal output and delivers a dc signal proportional
to that output. The dc signal is filtered, and
the smoothed-out voltage is applied in correct polarity
as bias to one or more preceding stages to
reduce their gain. The stronger the signal entering
the system, the greater the reduction in gain.
As a result, weak signals are amplified much
more than strong ones. Various forms of this
scheme are used in many types of amplifiers and
communications systems.
automatic gate bias A method of obtaining gate
bias in a FET, where a resistor develops a voltage
drop because of the current flowing through
it. The resistor is usually placed in the source
circuit, raising the source above ground potential.
automatic height control In a television (TV) receiver,
a system that automatically maintains the
height of the picture, despite signal-amplitude
fluctuations, power-line voltage changes, and
gain variations.
automatic intercept A telephone answering machine.
It allows messages to be recorded when the
subscriber is not able to answer the telephone.