时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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ultrasonic inspection. A type of nondestructive inspection in which a piece of material is examined for hidden flaws. Pulses of mechanical vibration at an ultrasonic frequency are passed through the part being tested. This vibration produces an electrical signal which is displayed on the screen of a cathode-ray oscilloscope. The display produced by the vibrations passing through the material being tested is compared with the display produced by a vibration of the same frequency passing through a similar material known to have no faults. Any difference in the displays is an indication of an internal fault. ultrasonics. The branch of science and technology that deals with mechanical vibrations having a frequency higher than the human ear can normally hear. Ultrasonic energy has a frequency greater than 20,000 hertz. ultrasonic soldering. A method of soldering aluminum with soft solder. Aluminum is difficult to solder because, when it is heated, oxides form on its surface and prevent the solder wetting the metal. The tip of a special soldering iron is vibrated at an ultrasonic frequency as it heats the metal and melts the flux in the solder. This vibration breaks the oxide film away from the surface of the metal, and it floats on top of the flux. The flux covers the hot metal and prevents new oxides forming. Soft solder will stick to aluminum when there are no oxides on it. ultraviolet-blocking dope. Dope that contains tiny aluminum flakes or some other pigment that blocks the passage of ultraviolet rays from the sun. This coat of dope protects the organic fabrics and the clear dope from deterioration by these rays. ultraviolet lamp. A form of vapor lamp that produces electromagnetic radiation whose wavelength is slightly shorter than that of visible light. Ultraviolet light is often called “black light.” ultraviolet radiation. Radiation of electromagnetic energy whose wavelengths are between about 100 and 4,000 angstroms. See angstrom. The wavelengths of ultraviolet rays are just shorter than those of rays visible to the human eye. umbilical cord (rocket component). A cable used to carry power from a launch pad to a rocket or spacecraft being readied for flight. The umbilical cord is disconnected before the vehicle leaves the pad. An umbilical cord is also used to tether and to supply oxygen to an astronaut when operating outside a spacecraft in space. unbalanced cell (nickel-cadmium battery condition). A cell in a nickel-cadmium battery that has become discharged to a lower level than the other cells in the battery. An unbalanced cell will take more charging current than the other cells, and this can lead to overheating and thermal runaway of the battery. Unbalanced cells can be corrected by deep-cycling the battery. unbalanced transmission line (radio transmission line). A form of two-conductor cable used to carry an electromagnetic signal from a transmitter to its antenna. An unbalanced line does not have the same voltage between each of the two conductors and ground. A coaxial cable is a form of unbalanced transmission line. |
