时间:2011-03-11 23:18来源:蓝天飞行翻译 作者:航空 点击:次
self-centering chuck (machine tool component). A type of chuck used on a drill motor or lathe that has all its jaws connected in such a way that they move together. When a drill or piece of work is placed in the chuck and the jaws tightened, all of the jaws move inward together and hold the drill or the work centered in the chuck. self-demagnetization. The process in which the magnetic fields surrounding a piece of magnetized material try to demagnetize it. If a permanent magnet sits for a long period of time, it will partially self-demagnetize. But if a keeper, a piece of soft iron, is placed across its poles, the lines of magnetic flux will not spread out from the poles, and the magnet will self-demagnetize far less than if no keeper were used. self-excited generator. An electrical generator whose field coils are supplied with current produced in the armature. The voltage regulator for a self-excited generator is a variable resistor in the field circuit between the armature and the field coils or between the field coils and ground. When the resistance in the field circuit decreases, the field current increases, and the generator output voltage increases. Most aircraft generators are self-excited, but DC alternators are not. self-extinguishing. A combustible material is said to be self-extinguishing if it burns when it is exposed to a flame or to a high temperature, but the burning process automatically stops as soon as the flame or source of high temperature is removed. self-locking nut. A type of nut with a built-in locking device that makes the nut tightly grip the threads of the bolt. This locking device may be a fiber collar, with a hole slightly smaller than the major diameter of the bolt threads, or it may be a portion of the threads in the nut that is slightly out of phase with its main threads. Selsyn system. The registered trade name for a DC synchro system. Mechanical movement of the transmitter shaft moves a two-arm wiper across a tapped, circular, variable resistor. Direct current enters the transmitter through the arms of the wiper and flows through the resistor out to the indicator. Here, the current flows into three sections of a coil wound around a ring-shaped core. A small permanent magnet on the pointer shaft is free to rotate inside the indicator coil. |