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digital readout (instrument indication method). Information shown on an indicating instrument in the
form of digits. A digital readout differs from an analog readout, which displays information by the position
of a pointer over a calibrated dial.
digital voltmeter. A voltage measuring instrument that displays the voltage in discrete numbers, rather
than by the position of a needle over a calibrated dial.
digitize. To change an analog value into a digital value. Mechanical movement can be followed by
allowing the movement to change the amount of resistance in a variable resistor. This is an analog change.
The analog change can be digitized with an analog-to-digital (A-to-D) converter, which changes
the analog values into combinations of voltage and no voltage (one and zero) that can be used in a digital
computer.
digitized image. A modified image picked up by a miniature TV camera in the end of a fiber optic probe.
This image is converted into a digital electronic signal that eliminates unwanted portions of the viewed area
and allows the desired image to be enhanced for clearer viewing.
dihedral (airplane rigging measurement). The positive angle formed between the lateral axis of an
airplane and a line which passes through the center of the wing or the horizontal stabilizer. Dihedral is used
to increase the lateral stability of an airplane.
diluent. A material used to thin, or dilute, a concentrated material without changing its basic characteristics.
A weak solution contains a large amount of diluent.
Paint thinner is a diluent used to make paint less viscous so it can be sprayed or brushed more
easily. The diluent evaporates after the paint is applied.
diluter-demand oxygen system. A popular type of breathing oxygen system in which oxygen is metered
to the mask where it is diluted with cabin air by an airflow-metering aneroid assembly which regulates the
amount of air allowed to dilute the oxygen on the basis of cabin altitude.
As the aircraft goes to higher altitude, the amount of cabin air metered into the oxygen is
automatically decreased until at about 34,000 feet, the cabin air is entirely shut off and the regulator sends
100% oxygen to the mask.
The oxygen and air flow to the mask only when the wearer inhales, but the regulators have an
emergency position which allows the pilot to manually bypass the demand function and sends a continuous
flow of 100% oxygen to the mask.
dimension. A measurement used to describe the size of an object. The basic dimensions of an object are its
L (length), W (width), and H (height).
dimensional inspection. One step in the overhaul of a piece of equipment. In a dimensional inspection, all
the moving parts are measured with precision instruments, such as micrometer calipers, to determine if
their dimensions are within the tolerances allowed by the manufacturer for the part to be serviceable.
dimension line (mechanical drawings). A light solid line on a machine drawing. A dimension line is
drawn between extension lines that indicate the beginning and the end of a dimension.
A dimension line has an arrowhead at each end and a break in its middle where the dimension and
the tolerance are written.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 191
dimmer (electric lights). A circuit or device used to decrease the intensity of an electric light.
A dimmer may decrease the voltage supplied to the light by adding resistance, as is done with a
rheostat. Or it may shorten the time electrons flow in each cycle of alternating current as is done with an
SCR, a silicon controlled rectifier.
dimpling (sheet-metalworking procedure). The treatment of a hole in a piece of sheet metal for the
installation of a countersunk rivet or screw.
The metal is placed over a female dimpling die, and a male die is driven into it. The dies press the
edges of the hole down so the head of the countersunk rivet or screw will be flush with surface of the metal.
diode (electrical component). A two-element electrical device. A diode contains an anode and a cathode
and acts as an electron check valve. Electrons can pass from the cathode to the anode, but they cannot pass
from the anode to the cathode.
A diode may be either a vacuum tube or a semiconductor device.
dioxide. A chemical compound which contains two atoms of oxygen. Carbon dioxide contains one atom of
carbon and two atoms of oxygen (CO2).
DIP (integrated circuit packaging). The abbreviation for dual in-line package. Different types of
integrated circuits and switches are mounted in DIPs, which are standardized with regard to size, pin
spacing, and the distance between the two rows of pins.
dip (magnetic compass characteristic). The angle formed between a compass magnet aligned with the
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航空术语词典Dictionary of Aeronautical Terms 上(129)
