Page 65 - The Illustrated Dictionary of Electronics

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50 automatic chrominance control • automatic intercept

gain of the chrominance bandpass amplifier by automatic error correction A technique of cor-
automatically adjusting its bias. recting transmission errors using error-detecting
automatic circuit breaker Any device that opens and error-correcting codes and, usually, auto-
a circuit automatically when the flow of current matic retransmission.
becomes excessive. The breaker generally resets automatic exchange A transmission exchange in
automatically after a specified length of time, or which interterminal communications are accom-
after power has been temporarily removed from plished without operators.
the circuit. automatic focusing A method of focusing a pic-
automatic coding The use of a computer to deter- ture tube automatically, in which a resistor con-
mine the steps for solving a problem, before the nects the focusing anode to the cathode; thus, no
actual program for the problem is written. This external focusing voltage is necessary.
can help software engineers develop long and/or automatic frequency control Abbreviation, AFC.
complex computer programs. A system that keeps a circuit automatically tuned
automatic contrast control A circuit that auto- to a desired signal frequency. A detector (such as
matically adjusts the gain of the video IF and RF a discriminator) operated from the tuned circuit
stages of a television (TV) receiver to preserve delivers a dc output voltage only when the circuit
good picture contrast. is operating above or below the signal frequency;
automatic controller In servo systems, any of sev- otherwise, it has zero dc output. The dc output,
eral circuits or devices that samples a variable when present, alters the capacitance of a varactor
signal, compares it with a standard (reference) in the tuned circuit to retune the stage to the de-
signal, and delivers a control or correction signal sired frequency.
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 automati-
cally 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 gain control Abbreviated AGC. A sys-
automatic cutout A device that shuts down a cir- tem that holds the output of a receiver or ampli-
cuit or system when the safe limits of operation fier substantially constant despite input-signal
are exceeded. A circuit breaker is an example of amplitude fluctuations. A rectifier samples the ac
such a device, as is a thermostat in a power am- signal output and delivers a dc signal propor-
plifier. tional to that output. The dc signal is filtered, and
automatic data processing Abbreviation, ADP. the smoothed-out voltage is applied in correct po-
The use of computers and accessories for calcula- larity as bias to one or more preceding stages to
tions and tabulations using data gathered auto- reduce their gain. The stronger the signal enter-
matically by the system. ing the system, the greater the reduction in gain.
automatic degausser A system for automatically As a result, weak signals are amplified much
demagnetizing the picture tube in a color televi- more than strong ones. Various forms of this
sion (TV) receiver. scheme are used in many types of amplifiers and
automatic dialing unit Abbreviated, ADU. A de- communications systems.
vice that automatically generates dialing digits. automatic gate bias A method of obtaining gate
Many telephone sets have these devices, some of bias in a FET, where a resistor develops a volt-
which can be programmed for several different age drop because of the current flowing through
telephone numbers, including country codes and it. The resistor is usually placed in the source
area codes. circuit, raising the source above ground poten-
automatic dictionary A computer system compo- tial.
nent that substitutes codes for words and automatic height control In a television (TV) re-
phrases in information retrieval systems. In lan- ceiver, a system that automatically maintains the
guage-translating systems, it provides word- height of the picture, despite signal-amplitude
for-word substitutions. fluctuations, power-line voltage changes, and
automatic direction finder Abbreviated ADF. A gain variations.
specialized receiver/antenna combination for au- automatic intercept A telephone answering ma-
tomatically showing the direction from which a chine. It allows messages to be recorded when the
signal arrives. subscriber is not able to answer the telephone.