masking board meaning in English

遮光板

The shadow mask is the critical component of the colour picture tube and the important component for the choice of colour , its function concentrates on the limitation of electronics bound diameter and the screening direction , the electronics bound which is sent by the electronics gun goes scanning , during the scanning process , we should guarantee every bound gathering into the small holes situated on the screen , then these bounds will point to the regularized position through the small holes on the flat mask , and then three basic colours will be produced , at the same time , those useless electronics will be blocked by the mask board
平板荫罩是彩色显像管的关键部件之一，是一个重要选色元件，其作用是限制电子束直径和上屏方向，由电子枪发射的电子束在偏转磁场的作用下进行扫描，扫描过程中必须使每个电子束只能射中荧光屏上的为该束指定的那些小孔上会聚，并通过荫罩上诸多的小孔分别打到各自对应的荧光质点上，发出三种基色（红，绿，蓝），而无用的电子则被荫罩板截获。