18WuD2x

508 overload relay • oxidation-reduction potential
overload relay A relay actuated when circuit current
exceeds a predetermined value. Compare
UNDERLOAD RELAY.
overload time The maximum length of time that
an equipment can safely be subjected to an overload
level of current.
overmodulation Modulation in excess of a prescribed
level—especially amplitude modulation
greater than 100%. Compare COMPLETE MODU-
LATION and UNDERMODULATION.
Relative amplitude
overshoot
Overshoot
Time
Carrier level
overmodulation
Time
overmodulation alarm See OVERMODULATION
INDICATOR.
overmodulation indicator A device, such as a
neon bulb, incandescent lamp, light-emitting
diode, analog meter, or digital meter, adapted to
give an alarm when the modulation percentage of
a signal exceeds a predetermined value.
overpotential See OVERVOLTAGE.
overpower relay A relay actuated by a rise in
power above a predetermined level. Compare UN-
DERPOWER RELAY.
overpressure For a pressure transducer, pressure
in excess of the maximum rating of the device.
override 1. To intentionally circumvent an automatic
control system. 2. To bridge a functional
stage of a system.
overscanning The deflection of the beam of a cathode-ray
tube beyond the edges of the screen.
overshoot 1. The momentary increase of a quantity
beyond its normal maximum value (e.g., the
spike sometimes seen on a square wave because
of the overswing of a rising voltage). 2. Momentary
overtravel of the pointer of an analog meter.
overswing See OVERSHOOT, 2.
overtemperature protection The use of an automatic
device, such as a thermal relay or thermostat,
to disconnect a device from the power
supply when the device’s temperature becomes
excessive.
overthrow See OVERSHOOT, 2.
overtone See HARMONIC.
overtone crystal A piezoelectric quartz crystal
that oscillates at odd multiples of the frequency
for which it was cut. This allows crystal operation
at frequencies otherwise obtainable only from a
fundamental-frequency crystal ground so thin as
to be prohibitively fragile.
overtone oscillator A crystal oscillator using an
OVERTONE CRYSTAL.
overtravel See OVERSHOOT, 2.
overvoltage A voltage higher than a specified or
rated value. Compare UNDERVOLTAGE.
overvoltage circuit breaker A circuit breaker that
opens when voltage exceeds a predetermined
value.
overvoltage protection The use of a special circuit
or device to protect equipment from excessive
voltage. When voltage increases beyond the overvoltage
limit, the protective circuit causes shutdown.
overvoltage relay A relay actuated when voltage
rises above a predetermined value. Compare UN-
DERVOLTAGE RELAY.
overwrite In computer operations, to record new
data over existing data (e.g., to update the files on
a magnetic disk or tape).
Ovshinsky effect In thin-film solid-state devices,
the tendency for switches to have the same characteristics
for currents in either direction.
O wave One (the ordinary) of the pair of components
into which an ionospheric radio wave is divided by
Earth’s magnetic field. Compare X WAVE.
Owen bridge A wide-range four-arm bridge that
measures inductance in terms of a standard capacitance
and bridge-arm resistances.
own coding Additional program steps added to
vendor-supplied software so that it can be modified
to fit special needs.
ox Abbreviation of OXYGEN.
oxidation 1. The combination of a substance with
oxygen. Generally a slow process, such as the
corrosion of iron or aluminum in the atmosphere.
The process is accelerated by the presence of
moisture and/or high temperatures. 2. The loss
of electrons from a cell or battery during discharge.
oxidation-reduction potential The potential at
which oxidation occurs at the anode of an electrolytic
cell, and at which reduction occurs at the
cathode.