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air pressure regulator, two pressure gages with a calibrated restrictor orifice between them, and a shutoff
valve.
A regulated pressure of 80 psi is directed into the cylinder being tested, and the pressure drop
across the orifice indicates the amount of air leaking past the piston rings or valves. A cylinder in good
condition should hold at least 75% of the air supplied through the tester. With 80 psi on the input pressure
gage, the cylinder pressure gage should indicate at least 60 psi.
differentially compounded electric motor. An electric motor having both series and shunt field windings.
The two windings are connected in such a way that the magnetic field produced by the shunt winding
opposes the field produced by the series winding.
differential pressure. A single pressure which is the difference between two opposing pressures. The
resultant of a 12 psi pressure opposing a 32 psi pressure, is a 20 psi differential pressure. This is expressed
as 20 psid.
differential-pressure range of aircraft cabin pressurization. The range of cabin pressurization in which
the controller maintains a constant difference between the pressure of the air inside the structure and the
pressure of the air outside the structure.
The amount of differential pressure allowed is determined by the strength of the aircraft structure.
differential screw. A compound screw arrangement. A differential screw changes the separation between
two parts by the amount of difference in the pitch of the two screw threads.
If the coarse screw increases the space 0.050 inch for each revolution, and the fine screw decreases
the space 0.0357 inch for each revolution, one revolution of the differential screw will increase the space by
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Page 189
0.0143 inch.
differential-voltage reverse-current relay (aircraft electrical system component). A reverse-current
relay installed with a high-current aircraft generator. The reverse-current relay closes to connect the
generator to the battery when the generator voltage is a specified amount higher than the voltage of the
battery.
Reverse-current relays used with smaller generators connect the generator to the battery when the
generator produces a specific voltage, regardless of the voltage of the battery.
differentiating circuit (electronic circuit). An electronic circuit whose output is proportional to the rate of
change of the signal in the input circuit.
diffuser (gas turbine engine component). A duct installed in the compressor outlet in a turbine engine to
reduce the velocity of the air leaving the compressor and increase its pressure.
diffusion (light). The scattering of light rays as they pass through a translucent material or as they bounce
off a rough surface. These light rays are disturbed from their straight path, and they travel out in all
directions. Diffused, or scattered, light forms very weak shadows or no shadows at all.
diffusion welding. A form of welding in which the surfaces to be joined are melted and pressed together.
The edge of one surface diffuses into the edge of the other.
digital circuits. Electronic circuits which operate as switches or gates. There are only two digital
conditions, and these represent logic one and logic zero. These two values may be represented by high and
low voltage levels, or on and off conditions.
Digital circuits containing the appropriate gates can be made to perform arithmetic and logic
operations.
digital computer. A digital electronic device that contains a central processing unit (CPU), an input, an
output, and some memory units. Digital computers are used to process numbers or words and to control
many different types of electrical and mechanical devices.
digital data (digital information). Data in one of only two conditions: zero or one, off or on, false or true,
low or high. Digital data differs from analog data in that it does not have any in-between conditions.
digital display. A series of alphanumeric characters that may be formed by segments made visible, usually
by light-emitting diodes (LED) or liquid crystal displays (LCD). The segments are selected by a dedicated
digital computer to form the appropriate character.
The most widely used numerical display is made of seven segments arranged to form the numeral
eight (8). By selectively energizing two or more segments, any numeral between zero (0) and nine (9) may
be formed.
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digital multimeter. An electrical test instrument that can be used to measure voltage, current, and
resistance. The indication is in the form of a liquid crystal display in discrete numbers.
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航空术语词典Dictionary of Aeronautical Terms 上(128)
