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opposite side (mathematics). The side of a triangle opposite the angle being referenced. In the illustrated
triangle, the solid line shows the side opposite the angle Ø.
optical coupler. An optoelectronic device used to couple electronic circuits by using electromagnetic
radiation, either visible or invisible. The input circuit contains some form of light source, usually a
light-emitting diode (LED). The intensity of the light is determined by the amount of current flowing in the
input circuit.
The output circuit contains a photodiode, phototransistor, or light-dependent resistor. The light
source and light sensor are mounted in a light-tight housing, so the light emitted by the source striking the
sensor controls the output of the coupled circuit.
optical micrometer (precision measuring instrument). A precision instrument, used to measure the
depth of scratches and other surface damage to a piece of material. The lens of the instrument is focused on
the undamaged surface which is used as a reference, and then it is focused at the bottom of the damage. The
amount the lens must be moved to change the focus is converted into a measure of the depth of the damage.
optical pyrometer (temperature measuring instrument). An instrument used to measure the temperature
of molten metal inside a furnace. A piece of resistance wire extends across the optical path of the
instrument, and current through the wire is increased until its heat causes the wire to glow.
The user of the instrument looks at the molten metal in the furnace through the instrument, and
while watching it, increases the current through the resistance wire until it glows with exactly the same
color as the molten metal. The indicator on the instrument converts the amount of current flowing through
the resistance wire into terms of the temperature of the molten metal.
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optional equipment (installed aircraft equipment). Equipment approved for installation in an aircraft,
but not required to be installed. Several types of communications and navigation radio equipment and
different types of instruments are included in the optional equipment list.
option approach (air traffic control). An approach requested and conducted by a pilot which will result in
either a touch-and-go, missed approach, low approach, stop-and-go, or a full-stop landing.
optoelectronic device. An electronic device that produces, modulates, or senses electromagnetic radiation
in the ultraviolet, visible light, or infrared portions of the energy spectrum.
optoelectronics. The branch of electronics that deals with the relationships between electrical current and
light. Optoelectronics makes use of light-emitting and light-sensitive devices.
orange peel (finishing system problem). Roughness caused by the surface of a finishing material drying
before the material below the surface. The rough surface may be caused by using the wrong viscosity
finishing material, the wrong amount of air pressure on the spray gun, or incorrect setting of the spray gun
controls. It can also be caused by holding the spray gun an incorrect distance from the surface being
sprayed.
orbital electron. An electron spinning in an orbit around the nucleus of an atom. The term orbital electron
is used to distinguish these electrons from free electrons moving from one atom to another.
ordinal number. Ordinal numbers indicate position in a series or order such as first, second, and third.
They tell us the order in which something occurs. The first day, the second order, or the third time are
examples of the use of ordinal numbers.
ordinate. The vertical line (vertical coordinate, or Y-axis) drawn on a graph. Variable quantities are
measured by the scale to which the ordinate is drawn. The horizontal coordinate (X-axis) on a graph is
called the abscissa.
organic brake linings. Brake linings for single-disk brakes, made of a high-friction organic material
reinforced with brass or copper wool. Asbestos was used in the past, but because of its harmful effect on
those who work with it, organic materials have been developed by most brake manufacturers to replace
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 419
asbestos.
organic fabric (aircraft fabric). Natural-fiber fabrics used for covering aircraft structures. Long-staple
cotton and linen are the two most widely used organic fabrics.
OR gate (logic gate). A logic gate having two or more inputs and one output. An OR gate has a logic one
on its output when there is a logic one on any one of its inputs. There are two kinds of OR gates:
INCLUSIVE OR, and EXCLUSIVE OR. An INCLUSIVE OR gate has a logic one on its output any time
　
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